CHAPTER I: INTRODUCTION

DEFINITION OF AGRICULTURE

Agriculture is the systematic raising of useful plants and livestock under the
management of man.

Agriculture is a purposeful work through which the elements of nature are harnessed to
produce plants and animals to meet human needs. Although it does not by itself create
civilization, civilization cannot develop without agriculture.

The broad industry engaged in the production of plants and animals for food and fiber,
the provision for agricultural supplies and services, and the processing, marketing and
distribution of agricultural products (Herren and Donahue, 1991).

DEVELOPMENT OF AGRICULTURE

Pastoral stage (Hunting/gathering)

Primitive man satisfied his daily needs directly from nature by hunting wild animals,
gathering wild plants and fishing. The hunters-gatherers moved from one location to
another in search of food to sustain them. The fishing tribes were more likely settled
in one place as a permanent home usually near bodies of water.

When did agriculture start?

The geologic event, the Ice Age, further explains the recent beginnings of agriculture.
Agriculture was not practiced until the climatically stable Holocene warming. During
the most recent glaciations, there was a warm period sandwiched between the
Oldest Dryas (18 000–14 600 BP) and Younger Dryas (12 900–11 500 BP) cold
periods. This warm period allowed hunting-gathering which delayed the emergence
of agriculture.

Beginnings of agriculture

The time scale shown in Figure 1 provides an indication of how recent agriculture.
The gradual transition from hunting-gathering to agriculture began at about the 10 –
15 T years ago.

Where did agriculture start?

Agriculture started simultaneously in various parts of the world. Figure 2 shows the
areas where agriculture started; they lie between 20º and 45º latitude North and
South of the equator.
Figure 1. Timeline showing the recent beginning of agriculture.
Figure 2. Centers of agricultural origin.
Based on evidences (archaeological, botanical, linguistics, history, literature), agriculture
had been practiced in the following areas (Figure 2):

Near East. Archeological evidence showed that agricultural villages existed about
8,000 to 9,000 B.C. in an area known as the Fertile Crescent (Figure 3), an area
extending from Mesopotamia (now Iraq) across Syria and down the eastern of the
Mediterranean sea to the Nile Valley of Egypt, most of what is now called the Middle
East; this area is often recognized as “the cradle of civilization”. Wheat and barley
farming pattern was established and spread overland through Iran. Other crops
include grapes, peaches, apricots and melons.

Ethiopia. Archeological, botanical and linguistic evidences suggested that

agriculture has been established by 9000 years before present.

Southern Asia. First crops spreaded overland from Iraq and Iran in South Asia
about 5,000 years before present In Southern India and Ceylon, irrigation reservoirs
were constructed as early as 3,500 – 3,300 before present.

East Asia. There was diffusion of SW Asian wheat complex by mainland diffusion.
Crops like yams, bamboo, soybeans and rice are native to tropical Far East region.
Agriculture flowed from China and Thailand to Malaysia, Indonesia and Philippines.

Southeast Asia. Agriculture consisted of growing various crops including rice,

banana, coconut, and yam.

Pacific and Oceania. Agriculture in New Guinea and Pacific Islands remained
somewhat primitive until modern times. Crops are taro, yams, coconut, bananas,
sugarcane and breadfruit.

South America. Agriculture stemmed from the domestication of indigenous crops

like beans, potato, tomato, eggplant, vegetables, peanut, pineapple and squash.

Central America. Plant remains of corn and other crops were found dated 10600-
7600 years before present.
Figure 3. Map showing Fertile Crescent.
Why did agriculture start?

Many theories on the origin of agriculture presented by Harlan (1992) include the
following:
1. Agriculture as a divine gift
2. Agriculture as a discovery
3. Agriculture as a result of stress
4. Agriculture as an extension of gathering

What types of plants were used?

Earlier the diet of man consisted mostly of the animals that he hunted with
occasional supplements from plant sources. Subsequently, his diet began to change.
Apparently, at a number of different sites, e.g. Near East, the Far East, Asia, Mexico
and Peru, quite independently, man began to turn towards plants as a food source.
The reason for this change is obscure, but is probably associated with population
pressures in environments which were initially favorable for man and for the game he
hunted. As the availability of game animals decreased, alternative food sources
became imperative; so man looked towards the vegetation that was earlier
considered as feedstuff for many of the animals and birds he hunted.

Many of the earlier plants used have the following characteristics:

 Thrive in disturbed areas

 Short life cycle
 High competitive ability

Early man intuitively realized that in a vegetative diet, he needed three major
components i.e. carbohydrates for energy, protein for muscle development, and
vitamins to augment different types of proteins and minerals. It is of interest that from
the multitude of plants from which the early domesticators have to choose, two plant
families achieved absolute dominance with regards to carbohydrates and protein
sources, namely Graminae (Poaceae) and the Leguminosae (Fabaceae),
respectively. In fact, all subsequent civilizations have since been established around
a diet originating largely from these basic plant sources. For example:

 The Americas - maize and peanuts

 Africa - sorghum and beans
 The Middle East - wheat, barley and beans
 Asia - rice and soybeans

In areas where this combination of cereal and legumes was less adapted, community
development has tended to be slower and remained more scattered, with
dependence on food being on a wide range of diverse plant families for example,
bananas, sweet potatoes, taro, yam and coconuts.
ORIGIN AND DOMESTICATION OF MAJOR CROPS OF THE WORLD

Origin of Major Crops

The center of origin of crops means a geographical area where a plant species,
either domesticated or wild, first developed its distinctive properties. The center of
origin of the major crops of the world is presented in Fig. 4.

The Philippines is also home to many plant species. According to International Union
for the Conservation of Nature (IUCN), the Philippines ranks fifth in the world in
terms of species diversity and endemism, A total of 39,100 species of flora and fauna
have been identified in the country, of which a high 67% are endemic. Some plant
species endemic to the Philippines include the following:

Plants found only in the Philippines

Some of the plants that are endemic in the Philippines are the following (Figure
Figure 5):

1. Abaca (Musa textilis)

2. Pili (Canarium ovatum)
3. Kapa-kapa (Medinilla magnifica)
4. Lubi-lubi/Niyug-niyugan (Ficus pseudopalma)
5. Duhat (Syzygium cumini)
6. Jade vine (Strongylodon macrobotrys)
7. Kahoy-dalaga (Mussaenda philippica var ‘aurorae’)
8. Waling-waling (Vanda sanderiana)

Domestication of Major Crops

Crop plant domestication began approximately 10,000 years ago at the dawn of
agriculture (Harlan1992). During the domestication process, early agriculturalists
consciously or unconsciously selected among wild germplasm for material that was
better adapted to human use and cultivation (Frary and Douanlar, 2003). Since the
transition from wild species to domesticate, crop plants have continued to change
due to selection exerted by ancient and modern plant breeding and cultivation
practices. Figure 6 presents the center of domestication of major crops (Gepts,
2003). Domestication is an ongoing process and selection is driven by changing
human needs and agricultural conditions.
Figure 4. Origin major crops of importance to the Philippines.
Figure 5. Endemic plants in the Philippines.

Figure 6. Map showing the centers of domestication of crops (Gepts, 2003).

WORLD AND DOMESTIC FOOD SITUATION AND PRODUCTION CENTERS

The world population is expected to increase by 2.6 B over the next 45 years from 6.5 B
today to 9.1B in 2050. Much of the increases will be from developing countries. The
population in developing countries will increase from 5.3 B to 7.8 B in 2050.

As the world population continues to increase geometrically, great pressure is being

placed on agricultural lands. It is imperative to increase current levels of food production
to provide an adequate supply of food to increasing population.

‘Of the world's total land area of 150 million km2 much is not suitable for
agriculture. Arable land comprises 10% of the total. Permanent crops are 1%;
meadows and pastures, 24%; forest and woodland, 31%. The remaining 34% is
land surface that supports little or no vegetation: Antarctica, deserts, mine sites,
urban areas. Nearly all of the world's productive land is already exploited. Most of
the unexploited land is too steep, too wet, too dry or too cold for agriculture. In
Asia, nearly 80% of potentially arable land is now under cultivation.’
(http://www.globalchange.umich.edu/globalchange2/current/lectures/food_supply/food.htm)

Globally, countries may be categorized either as a developed or a developing country.

Table 1 shows the population growth and poverty level are high, while technology
(including those in agriculture) generation and dessimination are low in developing
countries compared to developed countries.

Table 1. Population growth, poverty level, technology generation and dissemation

in developed and developing countries.

Parameters Developed Developing

Poverty Level low high
Population growth low high
Technology generation high low
Managing technology high low
Knowledge gap low high

The rapid population growth in most developing countries had greatly reduced the arable
land per capita (Figure 7). It is estimated that by 2050, the amount of arable land will be
just over one-tenth of a hectare per person, from 0.50 ha in 1961 (http//info.4health.org).
Figure 7. Population and arable lands in developing countries. (Source:UNFPA/FAO)

Philippine Population, Food Supply and Agriculture

In the Philippines in 2008, the population was 88.57 M (BAS, 2008). The annual
population growth from 2000-2007 is 2.04%. It is projected, however, that with the
population growth rate of 1.96%, the population is estimated to be 97.97 M in 2010
(www.index.mundi.com/philippines/population.html).

Table 2. Population, Employment and Area for Agriculture: Philippines (BAS, 2008).

Population (M persons) 88.57

Employment (agricultural sector) (M persons) 12.03
Total area devoted to agriculture (M ha) 9.671
Arable land (M ha) 51%
Permanent croplands (%) 44%
 About 32% of the country's total land area constitutes the agricultural land. The
amount of arable land is 4,936 M ha, of which 4,226 M ha are permanent croplands.
There were 12.04 M persons (34% of total employment) employed in the agriculture
sector and about three-fourths were male workers (BAS, 2009).

At constant prices, the agriculture and fishery sector had 3.23% growth in 2008. The
average annual rate of increase was 3.98% for the period 2006 to 2008. The share
of agriculture in the gross domestic product (GDP) in 2008 is 18%.

Presently, the increase in food supply is about 2% per year which is just enough to
keep up with population increase. About 20% of this increase is the result of
expansion of new production areas. The remaining 80% is due to technological
advances in production like improved irrigation, crop protection, better cultivars,
improved crop nutrition, postharvest handling, etc.

If population increases exponentially and the population growth outpaces the rate of
food production, then starvation results. There is a limit to what a given area can
produce and we cannot utilize all areas for food production. Therefore, other sources
of food must be considered such as the use of synthetic foods, use of lower plant
forms and further increasing their production efficiencies.

Production Performance

Table 3 presents the volume and value of production of the major crops in the
country, respectively. Palay production was 3.27% lower than the 2008 level. Corn
output was up by 1.53%. Production of coconut grew by 2.27% while that of
sugarcane decreased by 13.79%. Output gains were recorded by other major crops
such as banana, peanut, tobacco and cassava (BAS, 2009). The percentage
distribution of production of the 9 major crops by region in 2009 is presented in Table
4.

Agricultural Trade
The country’s total export earnings amounted to US$ 3,135.75 M in 2009. Coconut oil
and fresh banana remained as top earners among agricultural exports
Table 3. Volume and value of production major crops in the Philippines (BAS, 2009).

Crops Value (Million pesos) Volume (Metric Tons)

Palay 53,491.35 16,266,417
Coconut 23,798.53 15,667,565
Corn 20,961.41 7,034,033
Banana 16,133.22 9,013,186
Sugarcane 7,595.39 22,932,819
Mango 5,536.86 771,441
Pineapple 4,032.06 2,198,497
Cassava 2,861.21 2,043,719
Coffee 2,235.48 96,443
Rubber 1,850.69 390,962
Camote 1,064.99 560,516
Calamansi 980.17 192,187
Eggplant 960.54 200,942
Onion 789.04 127,055
Tomato 706.24 198,948
Cabbage 586.18 124,712
Tobacco 549.70 36,383
Garlic 483.73 10,451
Abaca 424.54 65,825
Mongo 325.75 27,694
Peanut 263.95 30,978
Table 4. Major agricultural crops in the Philippines.

Percentage Distribution of Production by Region, Philippines, 2009 ('000mt)

REGION PALAY CORN COCONUT SUGARCANE PINEAPPLE BANANA MANGO COFFEE
PHILIPPINES 16,266.40 7,034.00 15,667.60 22,932.80 2,198.50 9,013.20 771.4 96.4
LUZON 55.48 38.69 23.4 14.41 10.62 10.34 57.84 18.91
CAR 2.65 2.87 0.01 0.04 0.03 0.3 0.48 5.91
Ilocos Region 8.31 4.99 0.24 0.09 0.01 0.48 38.11 0.11
Cagayan Valley 12.77 22.72 0.46 0.88 1.48 4.65 4.91 1.14
Central Luzon 17.25 3.09 1.27 4.51 0.06 0.61 7.58 1.77
CALABARZON 2.35 0.74 9.13 7.81 4.02 1.21 5.49 9.42
MIMAROPA 5.72 1.48 4.27 0 0.01 2.27 1.08 0.21
Bicol Region 6.43 2.8 8.02 1.07 5 0.82 0.18 0.35
VISAYAS 21.11 7.88 17.17 65.03 1.26 8.85 14.35 6.62
Western Visayas 13.56 3.88 3.05 54.37 0.7 3.71 5.77 6.12
Central Visayas 1.7 2.65 2.77 8.88 0.22 2.08 8.46 0.26
Eastern Visayas 5.85 1.35 11.34 1.77 0.34 3.06 0.12 0.24
MINDANAO 23.41 53.43 59.43 20.56 88.12 80.81 27.81 74.48
Zamboanga Peninsula 3.48 2.52 11.14 0 0.1 2.9 7.49 1.31
Northern Mindanao 3.59 16.64 11.13 15.23 46.71 18.39 4.65 6.24
Davao Region 2.61 3.2 17.18 2.29 1.02 41.6 4.8 24.51
SOCCSKSARGEN 7.56 16.3 5.71 2.85 40.02 11.36 6.96 28.57
Caraga 2.62 1.26 6.29 0 0.21 2.32 2 2.72
ARMM 3.56 13.51 7.98 0.19 0.05 4.24 1.91 11.13
STAGES OF DEVELOPMENT OF PHILIPPINE AGRICULTURE

Pre-colonial period

Indo-Malayan migrants brought with them wet-rice agriculture, with carabao as a

source of animal power for cultivation. This type of agriculture predominated near
bodies of water like rivers and lakes. Slash-and-burn or kaingin culture or non-plow
farming predominated in other areas. This indicated shifting agriculture rather than
sedentary type of rice culture and the tribes were mainly nomadic.

Main crops consisted of rice, gabi, yams, bananas, corn millet, coconuts, citrus,
ginger, clove, cinnamon and nutmeg. No agricultural specialization existed. Pattern
of agriculture was chiefly subsistence. Farms were small, and chiefly backyard in
coastal and riverbank settlements. Most barangays were self-sufficient. Land was
abundant and population was estimated to about 500,000 by the mid-16 th century.
Private land ownership did not exist.

Absence of food surpluses was attributed to the absence of full-blown ruling class
who could exploit producers for surplus, limited foreign trade and food scarcity in
some settlements.

Colonial Period

This period introduced a non-producing class for which Filipinos produced surpluses,
leading to an increase in agricultural production.

Mulberry, cocoa, wheat, cucumber, cantaloupe, watermelon, coffee and new

varieties of cereals, peas and other vegetables were introduced to the country. The
development of haciendas allowed for the introduction of technological innovations in
production and processing like steam or hydraulic-powered sugar mills.

In March 6, 1909, the College of Agriculture was founded in Los Baños as a unit of
the University of the Philippines. Consequently, science-based methods of crop and
animal production were introduced.

Post-war period

 Introduction of technological improvements

 50’s campaign for use of modern farm inputs and farm mechanization.
 60’s building up of market for tractors and power tillers.
 Establishment of the International Rice Research Institute (IRRI).
 Introduction of high yielding rice varieties which was also termed the green
revolution.
 Further development and expansion of international agricultural trading
especially coconut and its by-products, tobacco, sugar, pineapple, etc.

State of Philippine Agriculture

The Philippines is rich in agricultural potential. However agricultural commodities

reveal a poor state of agriculture competitiveness.
 The modernization of the country’s agriculture sector has been mandated with the
signing into law Republic Act 8435 or the Agriculture and Fisheries Modernization
Act (AFMA). But the AFMA was signed into law in 1997 and the country remains the
biggest rice importer in the world.

An analysis of the strengths, weaknesses, opportunities of and threats to Philippine

agriculture (Table 5) is given below:

Table 5. Strengths, weaknesses, opportunities of and threats to Philippine agriculture

Strengths Weaknesses

 Availability of expertise in agricultural  Physical

research and development  Climate – typhoons, drought
 Basic institutions in research are in  Soil – loss of top soil due to
place erosion particularly in sloppy
 Endowed with natural resources areas
 Availability of agricultural technologies  Biological
to boost production  Insect pests
 Weeds
 Pathogens
 Nutrient deficiencies and toxicities
 Suitable varieties
 Socio-economic
 Low farm income
 Small landholdings
 Decreasing interest in agriculture
 Inadequate support and extension
services for optimum production
 Inadequate incentives and support
for more efficient production, e,g,
irrigation facilities as well as
postharvest infrastructures
 Inadequate farm-to-market roads
 Marketing problems

Opportunities Threats

 Diverse agro-environment for a  Population growth

diverse cropping system  Globalization
 Wide range of soils and climate to  Weak governance
grow different crops  Deteriorating natural resource
 Whole year round growing period endowmnts
 Sunlight: 11-13 hrs
 Temperature: 24-32 °C
 Rainfall: 2400-4000mm/yr
MEANING AND SCOPE OF CROP SCIENCE

Definitions:

Science. Systematically accumulated and tested knowledge. It refers to the ordered

knowledge of natural phenomena and the rational study of the relationship between
the concepts in which these phenomena are expressed.

It is not a set of facts but a way of giving unity and intelligibility to the facts of nature
so that nature may be controlled and new facts predicted

Plant. Any organism belonging to the kingdom Plantae, typically lacking of active
locomotion or obvious nervous system or sensory organs and has photosynthetic
ability.

Crop. Domesticated/cultivated plants grown for profit. It usually connotes a group or

population of cultivated plants.

Two groups of science practitioners may be identified: the theoretical, academic or

basic scientist and the applied scientist. The basic scientist brings the saturated
solution of knowledge to the point of crystallization while the applied scientist brings the
idea to a practical achievement.

The major applied sciences in crop production are the following:

Crop science. It is concerned with the observation and classification of knowledge

concerning economically cultivated crops and the establishment of verifiable
principles regarding their growth and development for the purpose of deriving the
optimum benefit from them. It is divided into areas as follows.

Agronomy. It came from the Greek word “agros” meaning field and “nomos”
meaning to manage. Thus agronomy deals with the principles and practices of
managing field crops and soils.

Horticulture. It came from the Latin words “hortus”, which means a “garden”, (a term
derived from the Anglo-saxon word “gyrdan”, which means “to enclose”) and “colere”,
which means ‘to cultivate”. The concept of gardens and plants within an enclosure is
distinct from the culture of field crops, a medieval concept. It also implies more
intensive crop cultivation, as contrasted from the extensive cultivation of field crops.
CLASSIFICATION OF CROPS

The most important and commonly used method of classifying plants is the botanical
method, which is based on descent or the phylogenetic relationship of plants.
Approximately more than 300,000 plant species have already been identified.
Taxonomy, or the study of plant classification, is dynamic and it changes as new
knowledge becomes available. The four divisions of phyla of the plant kingdom identified
by Eichler in 1833 have since been expanded by modern taxonomists to 28 divisions.
However, the orginal four divisions are still in use because of their simplicity, adaptability
and practicality to practical crop science. The four divisions of the plant kingdom are:

1. Thallophyta – algae, bacteria and fungi

2. Bryophyta – small green plants without true roots or flowers such as the
mosses.

3. Pteridophyta – green plants with vascular tissue, true roots, and usually distinct
leaves. This group includes the psilophytes, club mosses, horsetails and ferns.

4. Spermatophyta – all seed-bearing plants that bear true flowers. Majority of the
economically important plants are included in this division. The division is
subdivided into 2 groups, namely:

a. gymnosperms – all plants with naked seeds like the pine trees.

b. angiosperms – plants with seed enclosed in a vessel; further divided into 2

classes;

1) monocotyledon – with one cotyledon

2) dicotyledon – with two cotyledons

Divisions of Kingdom Plantae

The kingdom Plantae is divided into five main divisions and they are as follows:

 Thallophyta
 Bryophyta
 Pteridophyta
 Gymnosperms
 Angiosperms
These divisions are based on the following criteria:
• Differentiated/Undifferentiated plant body
• Presence/absence of vascular tissues
• With/ without seeds
• Naked seeds/seeds inside fruits
Thallophyta
Thallophyta is the first division of the plant kingdom. Algae and fungi are the two main sub-
divisions. It also includes bacteria, molds, lichens, and slime.
Features of Thallophyta:

 They have a simple body design with no differentiation into root, stem and leaves.
 They have unicellular reproductive organs.

Bryophyta
Bryophyta are known as the amphibians of the plant kingdom. Mosses, hornworts, and liverworts
are the three main sub-divisions.
Features of Bryophyta:

 They do not have roots but have crude stems and leaves.
 The roots are replaced by the rhizoids which acts as an anchor.

Pteridophyta
Pteridophyta are the vascular plants that use spores for reproducing. They are also known as
cryptogams as they do not produce flowers and seeds. Ferns, lycophytes, and horsetails are the
three main divisions of Pteridophyta.
Features of Pteridophyta:

 They are multicellular. The male sex organ is known as antheridia and the female sex
organ is known as archegonia.
 They contain vascular tissues.

Gymnosperms
Gymnosperms are the flowerless plants which produce cones and seeds. The term gymnosperm
means “naked seeds”. Coniferophyta, cycadophyta, ginkgophyta, and gnetophyta are the four
divisions of gymnosperms.
Features of Gymnosperms:

 They are pollinated by the wind.

 They produce needle-like leaves.

Angiosperms
Angiosperms are the flowering plants. Approximately 80 percent of the known green plants are
covered by the angiosperms. Monocotyledonous and dicotyledonous plants are the two divisions
of angiosperms.
Features of Angiosperms:

 They have vascular bundle with xylem and phloem tissues.

 The root system of this division of plant kingdom is fully developed.

An example of a botanical classification of a dent corn is as follows:

Classification unit

Kingdom Plantae
Division Spermatophyta
Subdivision Angiospermae
Class Monocotyledonae
Order Graminales
Family Gramineae
Genus Zea
Species mays
Type `Indentata’

Scientific name Zea mays L.

Carl von Linne, better known as Carolus Linnaeus, was the originator of this binomial
system of plant nomenclature. The publication of his book entitled Genera Plantarum led
to the modern taxonomy or classification of plants.

The first letter of family names is always capitalized and more often written entirely in
capital letters. Most families names end with –aceae attached to a genus name; e.g.
Rosaceae, Magnoliaceae, Liliaceae, etc. Eight families, however, do not follow this
standard rule. So for the sake of uniformity and consistency, new names have been
proposed for these families. The new names appear in parenthesis following the old
names. Either the old or the new names can be used.

COMPOSITAE (ASTERACEAE)

CRUCIFERAE (BRASSICACEAE)

GRAMINEAE (POACEAE)

GUTTIFERAE (CLUSIACEAE)

LABIATAE (LAMIACEAE)

LEGUMINOSAE (FABACEAE)

PALMAE (ARECACEAE)
 UMBELLIFERAE (APIACEAE)

In writing scientific names, the first letter of the genus name is capitalized, while the
species name is in small letter. Scientific names are italized or underlined.

In Crop Science, plants are classified in many ways; either based on the manner of
culture (agronomic or horticultural), on their use (food, fiber, beverage, oil, medicinal)
on their climatic requirement (temperate, sub-temperate, tropical), on the length of
their life cycle (annuals, biennials, perennials), on their habitat (aquatic, terrestrial,
aerial, arctic.), on their photoperiodic response (long-day, short-day, day-neutral)
among others.

Table 6 presents the comparison between agronomic and horticultural crops. Examples
of agronomic and horticultural crops based on use are given in Table 7.
 Table 6. Comparison between agronomic and horticultural crops.

CRITERIA AGRONOMIC CROPS HORTICULTURAL CROPS

Cereals, grain legumes, peanut, forages, Vegetable, fruits, ornamentals, plantation
Commodities
sugarcane, etc. crops, etc.
Diversity/unit growing area less more

extensive intensive
Management
lower higher
Income/unit area
limited wide
Adaptation
eaten as staples consumed with staples
Utilization
usually processed and eaten in the mature usually consumed in fresh form and can be
Consumption
stage eaten at any stage depending on purpose

Aesthetic value lower higher

provides important vitamins and minerals
carbohydrates, proteins, lipids, vitamins
Nutritive value and some carbohydrates, proteins and
and minerals
lipids

Life cycle semi-annual, annual, few perennials semi-annual, annual, biennial and perennial
Compatibility to cropping
less compatible higly compatible
system

Moisture content of harvested low high

product

Note: The difference between agronomic and horticultural crops may also depend on the purpose for which the crop is grown,
type of culture, the traditions and customs of the country.
Table 7. Examples of horticultural and agronomic crops based on use.

Leafy pechay, kangkong, mustard

Cole/crucifers cabbage, cauliflower, broccoli
sweet potato, Irish or white potato, bulb onions, garlic,
Root and bulb
ginger
Vegetable
Legumes/pulses pole and bush sitao, mungbean
Solanaceous eggplant, bell pepper, tomato
cucumber, muskmelon, watermelon, squash,
Cucurbits
ampalaya
mango, durian, lanzones, santol, citrus, mangosteen,
Tree
guava, jackfruit
Fruits Nut pili, cashew
Small strawberry, grapes, pineapple
Herbaceous banana, papaya
Oil coconut, African oil palm, castor bean
Beverage coffee, cacao, tea
Herbs and spices basil, coriander, rosemary, tarragon, black pepper
Fiber abaca, sisal, maguey, salago
Plantation sambong, lagundi, tsaang-gubat, garlic, pansit-
Medicinal pansitan, ampalaya, yerba-buena, guava, banaba,
akapulko, niyug-niyogan
Essences/flavoring vanilla, anise, bay leaf, cinnamon
Latex and resin rubber, pili, sawoe
rose, chrysanthemum, anthurium, dendrobium,
Cutflower gladiolus, carnations, lilies, gerbera, heliconia,
curcuma, bird-of-paradise
Flowering pot miniature roses, dwarf chrysanthemums,
plants bougainvillea, poinsettia, mussaenda, African violet
Aglaonema, asplenium, caladium, dieffenbachia,
Foliage
philodendron, anthurium, croton
Ornamentals
ferns, palmera, anthurium, asparagus, selom, fortune
Cutfoliage
plant, dracaena
celosia, salvia, begonia, cosmos, impatiens, petunia,
Bedding plant
marigold, zinnia, periwinkle, ground orchid
Landscape plants yucca, palms, flowering and evergreen trees
Bermuda grass, bluegrass, manila grass, carabao
Turf grass
grass
Cereals rice, corn, sorghum, wheat, millet
Field legumes mungbean, ricebean, cowpea
Fiber cotton, ramie, jute, kenaf
Drug tobacco
Oil soybeans, sunflower, safflower (kasubha)
Sweeteners sugarcane, sugar beet
Forage and pasture Stylosanthes sp., Centrosema sp., guinea grass, paragrass, napier grass
Biofuel jatropha, coconut, sweet sorghum, sugarcane, cassava
Special Purpose Classification
 1. Green manure – crop usually leguminous crops grown for a specific period of
time and then plowed under into the soil to improve soil fertility

2. Silage – forage crops harvested, processed and stored for animal feeds

3. Soilage – forage crops which are cut when green and succulent and are directly
fed to livestock

4. Catch crop – fast-growing crop grown simultaneously with or between

successive plantings of a main crop

5. Cover crop - grown primarily to provide ground cover to improve soil properties,
control erosion and minimize weeds

6. Companion crop –planting one plant in proximity to another due the benefits it
bestows on the other crop like insect-repelling qualities

7. Trap crop – a crop grown to protect the main crop from biotic and abiotic factors

CROP PRODUCTION AS A SCIENCE, ART AND BUSINESS AND ITS DEVELOPMENT

As a science. Modern crop production is not based on guess-work or trial and error
method. Its science is derived from the adoption or application of the basic sciences of
chemistry, mathematics, physics and from various applied sciences like physiology,
meteorology, anatomy, plant breeding, etc.

As an art. It is an art because it requires skills to produce crops even with little or no
scientific training. The art of crop science reaches its greatest expression in horticulture,
specifically in ornamental horticulture where plants are raised for their aesthetic qualities,
e.g., in floral arts as well as in landscaping.

As a business. Plants are not grown simply to satisfy the needs of man but to realize
some profit in the process of producing it. Thus, maximization of output relative to
production input is one of the guiding principles of production. Scientific knowledge
utilized to produce plants at the time when there is demand and when the best prices
could be obtained when sold, e.g., production of off-season tomatoes and flowers and
raising disease-resistant field crops to reduce the cost of crop protectant chemicals.

Man’s needs for raw materials required to meet his basic needs for food, clothing and
shelter and the increasing requirements of the processing and food industry have served
as incentives to further improve crop production practices.

Early recognition of the importance of agricultural research was made by the British
Empire by the establishment of agricultural research stations. Similarly, in the U.S.
 experiment stations were also established in the land-grant state colleges. It may
therefore be presumed that the formal start of scientific agriculture dates back to the time
when these agricultural experiment research stations were established.

Agricultural research in the Philippines has been established through schools and
experiment stations, both private and public. These are:

1. State Colleges and Universities offering degrees in Agriculture.

2. Department of Agriculture Research Networks

3. National Commodity Research Centers

 FIDA – Fiber Industry Development Authority
 NTA – National Tobacco Administration
 PhilRice– Philippine Rice Research Institute
 PCA – Philippine Coconut Authority
 SRA – Sugar Regulatory Administration
 PRCRTC – Philippine Rootcrops Research and Training Center
 NPRCRTC- Northern Philippines Rootcrops Research and Training Center
 NARC –National Abaca Research Center

4. Specialized Discipline Oriented Research Centers

 IPB – Institute of Plant Breeding
 NCPC – National Crop Protection Center
 NPGRL – National Plant Genetic Resources Laboratory
 PHTRC – Postharvest Horticulture Training and Research Center
 BIOTECH – National Institutes of Molecular Biology and Biotechnology

5. Major International Research Organizations

 IRRI – International Rice Research Institute (Philippines)
 CIMMYT – Centro International de Mejoramiente de Maize y Trigo (Mexico)
 CIP – Centro International de Patatas (Peru)
 ICRISAT – International Center for Semi-Arid Tropics (India)
 CIAT – Centro de International de Agricultural Tropical (Colombia)
 ICARDA – International Center for Agricultural Research for Dry Areas (Syria)
 IITA – International Institute for Tropical Agriculture (Nigeria)
 ICRAF – International Center for Research on Agroforestry (Kenya)
 AVRDC – Asian Vegetable Research and Development Center (Taiwan)
 Bioversity – formerly International Plant Genetic Resources Institute (Italy)

6. Private Seed Companies

 East west
 Syngenta
 Pioneer
 Monsanto
 Allied Botanicals
CONTRIBUTION OF RELATED SCIENCES TO CROP PRODUCTION
Some of the scientific fields and areas of knowledge related to crop production (Figure 8)
are the following:

1. Crop breeding and genetics – concerned with the improvement of the inherent
or heritable properties of crops.

2. Botany (plant morpho-anatomy, plant physiology, plant systematics and plant

ecology) – concerned with plant structures, processes and relationships among
plants as well as plant relationship with their environment.

3. Soil sciences – study the nature and properties of soils; fundamental principles
upon which proper soil management is based.

4. Plant Pathology and Entomology – concerned with pathogens, insect pests

and weeds; their nature, as well as their control.

5. Agricultural engineering – concerned with farm structures, farm machinery,

farm power, water management as well as waste disposal.

6. Agricultural economics – concerned with the economics of production and

marketing of agricultural products.

7. Agricultural meteorology – concerned with the study of weather and climate.

The study of meteorology enables one to do weather forecasting and thus help
farmers minimize losses due to bad weather.

The basic knowledge and understanding of the various related disciplines are essential
to implement appropriate crop management packages for increasing crop productivity.
Figure 8. Related sciences applied to crop production.
 CHAPTER II: PHYSIOLOGICAL PROCESSES AFFECTING CROP PRODUCTION

PHOTOSYNTHESIS

Photosynthesis is the manufacture of sugars and its precursors by green plants in the
presence of light and chlorophyll. The process is represented by the following chemical
equation:

LIGHT
6CO2 + 12 H2O C6H12O6 + 6O2 + 6H2O
CHLOROPHYLL

From the above chemical equation of photosynthesis, two important conclusions have
been shown and supported with experimental evidence. (1) CO2 is fixed as glucose and
must be reduced by a reductant, which may either be H 2O (for higher plants) and H2S in
the case of the sulfur bacteria. (2) O 2 gas formed in photosynthesis must arise from the
H20 molecule not from CO2 as shown by the Ruben and Kamen’s experiment:

CO18
2 + H20
16
C6H12O6 + O16 2
CO2 + H20 18
C6H12O6 + O18

Carbon dioxide is16taken from the air through the stomata while water is absorbed from
2
the soil by the roots and transported in the xylem to sites of photosynthesis. Outdoors,
light comes from the sun, but it may be supplied by artificial lamps under experimental
and greenhouse conditions.

About 90% of the total world’s photosynthetic output occurs in the oceans, while the
remaining 10% by land plants (Bonner and Galston, 1952). Among the land plants,
about 7-8% is accounted for by forest and grasslands, while the remaining 2-3% by
cultivated crops.

The photosynthetic organ, tissues and organelles

Although photosynthesis can occur in any organ containing chlorophyll, the main
organ for photosynthesis is the leaf, while the main organelle involved is the
chloroplastid. The features which make the leaf an ideal organ for photosynthesis
are: (1) its typically expanded form, (2) its usually perpendicular angle to incident
light, (3) its extensive internal surface with an efficient vascular system for
channeling the various reactants and end-products of photosynthesis, and (4) its
pigments for light absorption. The anatomy of a leaf is shown in Figure 7.
Cuticle
Upper epidermis

Palisade
mesophyll
cell
Chloroplast

Spongy
mesophyll
cell
100 µm

Lower epidermis

Stomatal pore Guard cell

Figure 7. Schematic transverse section through a leaf (Heldt, 2005).

A mature mesophyll cell contains about 50 chloroplasts. The chloroplasts of higher

plants are usually lens-shaped bounded by a double membrane. The inner
membrane invaginates parallel to the surface and becomes organized into a
specialized cytoplasmic body consisting of a stack of thylakoids or frets, called the
granum (plural: grana) embedded in a proteinaceous matrix called the stroma
(Figures 8 and 9).
 Figure 8. The chloroplast ultrastructure (adopted from Nobel, 2009).

grana thylakoid

stroma thylakoid

Figure 9. Three-dimensional model of the spatial relationship between grana

and stroma thylakoids (adopted from Staehelin and van der Staay, 2004).

The drawing in Figure 9 shows two grana stacks interconnected by parallel sets of
unstacked stroma thylakoids that spiral up and around the stacks in a right-handed
helical conformation. Where the stroma thylakoids intersect with grana thylakoids,
they are interconnected through neck-like membrane bridges.

Chlorophyll, the principal pigment in photosynthesis, is located in the partition

between two adjacent thylakoids. Chlorophyll a occurs in all higher plants, but other
isomers like chlorophyll b, c, d, etc. are also found. In higher plants, the two main
isomers are a and b in a ratio of 3:1. While chlorophyll a is always found in all plants,
chlorophyll b may be replaced by some other isomers in some plant species.

Figure 10 shows the chemical structure of the chlorophyll molecule. Its basic unit is
the porphyrin ring system, a structure made up of four simpler pyrrole nuclei joined
by carbon linkages. The center of the porphyrin is occupied by a single magnesium
atom. The phytol side chain gives chlorophyll a lipid character. In ring b, chlorophyll a
contains a methyl residue instead of the formyl residue in chlorophyll b (Heldt, 2005).

Figure 10. Chemical structure of chlorophyll (adapted from Heldt, 2005).

The accessory pigments closely associated with chlorophyll are the carotenoids,
chiefly xanthophyll (lutein and zeaxanthin) and carotene, (chiefly ß-carotene).

The similarity of the absorption spectrum of intact chloroplast to its action spectrum
in terms of oxygen evolution shows that light absorption by chlorophyll mediates
oxygen evolution in plants, and this supports chlorophyll as the principal pigment in
photosynthesis (Figures 11). Before light can be utilized in photosynthesis, it must
first be absorbed by the plants. Light wavelengths readily absorbed by the pigment
are also the wavelengths where the intensity of photosynthesis is relatively higher.
Figure 12 shows the absorption spectrum of chlorophyll and other plant pigments.
Absorption of wavelength in the green region of the spectrum is low as green is
typically reflected, and consequently photosynthesis is also relatively low.
Figure 11. The absorption spectrum and action spectrum (in terms of oxygen
evolution) of intact chloroplasts (adopted from Taiz and Zeiger, 2002).

Figure 12. The absorption spectrum of chlorophyll and photosynthetic

accessory pigments.
Component reactions of photosynthesis

Photosynthesis is consisting of two component reactions which occur in sequence,

namely, the light reaction and the dark reaction (Blackman reaction). Light reaction
is a photochemical process with an absolute requirement for light, while dark reaction
is a thermochemical process that can take place in both light and dark.

Light reaction

Light reaction takes place in two reaction centers that are embedded in the thylakoid
membrane: Photosystem I (PS I) and Photosystem II (PS II). The numbering of the
photosystems corresponds only to the sequence of their discovery. Localized in
granal thylakoids, PS II has maximum absorption at 680 nm, with P 680 as the main
pigment. It produces a very strong oxidant which can split water into hydrogen and
oxygen. On the other hand, PS I, found in stromal thylakoids, can utilize light with
wavelengths up to 700 nm with P 700 as the main pigment. It produces a strong
reductant capable of reducing NADP+ to NADPH.

The non-cyclic flow of electrons during the light reaction is represented by the Z-
scheme (Figure 13). In summary, the electron flow in PS II and PS I results in the
production of ATP and NADPH which are subsequently used to fix CO2.

Figure 13. The Z-scheme of light reaction (adopted from Taiz and Zeiger, 2002).
 Dark reaction

The end-products of light reaction, namely ATP and NADPH, are subsequently used
in CO2 fixation. The fixation or reduction of CO2 into carbohydrates can occur via
three pathways: (1) Calvin-Benson or C3 pathway, (2) Hatch-Slack or C4 pathway
and the (3) Crassulacean acid metabolism or CAM pathway.

a. C3 or Calvin-Benson pathway

In the Calvin-Benson cycle, ribulose-1,5-bisphosphate (RuBP) is the CO 2

acceptor and the enzyme ribulose-1,5-bisphosphate carboxylase/oxygenase
(RubisCO) catalyzes the carboxylation reaction. The first stable product, 3-
phosphoglycerate (3-PGA), is a 3-carbon compound, hence the name C3
photosynthesis. The Calvin cycle proceeds in three stages: (1) carboxylation,
during which CO2 reacts with ribulose-1,5-bisphosphate (RuBP), in the presence
of RubisCO; (2) reduction, during which 3-PGA and eventually large
carbohydrate units are produced at the expense of ATP and NADPH; and (3)
regeneration, during which RuBP re-forms for further CO 2 fixation (Figures 14
and 15).

Figure 14. The light and dark (Calvin-Benson cycle) reactions of photosynthesis.
Figure 15. The Calvin-Benson or C3 cycle (adopted from Taiz and Zeiger, 2002).

In the C3 pathway, fixation of one CO2 molecule requires a total of two molecules
of NADPH and three molecules of ATP. Moreover, five-sixths of the triose
phosphate formed by photosynthesis is required for the regeneration of RuBP.
One molecule of triose-phosphate represents the net product and can be utilized
by the chloroplast or exported (check from new version).

Photorespiration and the C2 Pathway

Photosynthetic yield of C3 plants is reduced by the occurrence of

photorespiration, which is a consequence of the properties of RubisCO. RubisCO
is a bifunctional enzyme in the C 3 pathway that can act either as a carboxylase
or as an oxygenase. When RubisCO functions as a carboxylase, the C3 cycle
proceeds to yield two molecules of 3-PGA via carboxylation of RuBP. On the
other hand, photorespiration occurs when RubisCO behaves as an oxygenase,
wherein oxidation of RuBP yields one molecule of 3-PGA and one molecule of
phosphoglycolate, a 2-carbon compound. For C3 plants, a more direct contact
of RubisCO to O2-rich environment favors photorespiration. At present
atmosphere (i.e. 21% O2 and 0.038% CO2), RubisCO catalyzes the oxygenation
of RuBP about 20-60% as rapidly as it catalyzes RuBP carboxylation.
 The C2 photorespiratory carbon oxidation cycle may operate to partially
recover carbon lost from photorespiration. This process involves the cooperative
interaction of three organelles: chloroplast, peroxisomes, and mitochondria
(Figure 16). Photorespiration yields only one 3-PGA molecule in contrast to two
3-PGA molecules in photosynthesis. Another 3-PGA is salvaged from
phosphoglycolate, at the expense of ATP, through a series of reactions in the
peroxisome, mitochondria, and chloroplast via the C2 photorespiratory carbon
oxidation cycle. In broad terms, photorespiration and the C 2 cycle may be viewed
as a wasteful process. With the production of one phosphoglycolate (2-C) and
one 3-PGA (3-C) instead of two 3-PGA, 25% of the carbon is lost during
photorespiration. It is also a metabolically-expensive reaction, requiring five ATP
and three NADPH for every oxygenation of RuBP. This is a significant energetic
cost, which can add up to approximately 50% of the amount of energy expended
on carboxylation. Hence, plants with higher rate of photorespiration (i.e. C 3
plants) have lower rate of dry matter production because of lower photosynthetic
efficiency.

PHOTOSYNTHESIS PHOTORESPIRATION + C2 CYCLE

one molecule
one molecule ofof
3-phosphoglycerate
3-phosphoglycerate
+ (3-C)
(3-C)
two molecules of CO2 O2
3-phosphoglycerate (3-C)
carboxylation
RuBP
oxygenation +
one molecule of
phosphoglycolate (2-C)

series of reactions in the

peroxisome, mitochondria, CO2
and chloroplast

ATP

3-phosphoglycerate (3-C)

C3 cycle

Figure 16. Yield comparison between photorespiration and photosynthesis.

 Other photosynthetic pathways have evolved wherein photorespiration is
avoided. In plants with C4 or CAM physiology, photorespiration is almost entirely
eliminated by concentrating CO2 spatially (C4) or temporally (CAM) before CO 2 is
reduced to triose phosphates. In these ways, the carboxylation function of
RubisCO is favored over oxygenation.

b. C4 pathway or Hatch-Slack

Leaves of C4 plants have a characteristic anatomy, known as Kranz anatomy,

wherein vascular bundles are surrounded by a sheath of chloroplast-rich
parenchyma cells called the vascular bundle sheath, which are surrounded by
the spongy mesophyll. In C4 plants, the bundle sheath cells generally contain
more and/or larger chloroplasts than mesophyll cells (Figure 17 and 18).

Figure 17. Diagram of Kranz anatomy in the C4 grass Panicum capillare (A) and
C4 dicot Atriplex rosea (B) (adopted from Dengler and Nelson, 1999).
 C3 Plants C4 Plants

Tissue pattern (vein spacing)

Cell pattern

Cell differentiation

Leaf anatomy

Figure 18. Features of C3 and C4 leaves (adopted from Dengler and Taylor, 2000).
 The special anatomical feature of C4 leaves favors a more efficient
photosynthesis by assuming the following reaction steps. First, CO 2 (in the form
of HCO3-) is initially fixed by phosphoenolpyruvate (PEP), in the presence of
PEP carboxylase, in the mesophyll cells forming the first stable product,
oxaloacetate (OAA). OAA is a 4-C compound, hence the name C4
photosynthesis. OAA is then converted to C4 acids (malic acid or aspartic acid),
which are subsequently transported to and decarboxylated (CO 2 is released) in
the bundle sheath cell where RubisCO and RuBP are present in large quantities.
Because of this CO2-pumping mechanism, CO2 is generated in the bundle sheath
cells resulting in its significantly higher CO 2 concentration. This largely favors the
carboxylation function of RubisCO such that CO2 in the bundle sheath cells is
refixed by RuBP via the C3 pathway. Apparently, the C3 cycle occurs in the
bundle sheath cells of C4 plants (Figure 19).

Figure 19. The C4 photosynthetic pathway (adopted from Taiz and Zeiger, 2004).
c. Crassulacean Acid Metabolism (CAM) pathway

The CAM pathway is found in succulent plants (e.g. cactus and members of the
pineapple family). While C4 plants eliminate photorespiration through a spatial
CO2-concentrating mechanism, CAM plants do this through temporal regulation
of photosynthetic reaction steps. Like in the C4 pathway, PEP is the initial CO2
acceptor and PEP carboxylase is the initial carboxylating enzyme. Malic acid,
produced in the initial carboxylation of PEP as in the C4 pathway, accumulates in
the vacuole and acidifies the cells. However, these processes occur in the dark
which means that stomates of CAM plants are open at night. During the light
period (i.e. day), the malic acid is decarboxylated, yielding CO 2 which is fixed
through the C3 pathway in the chloroplast. Since the stomates are closed at
daytime, CAM plants maximizes water-use efficiency which allow them to thrive
even in arid environments (Figure 20).

Figure 20. The Crassulacean acid metabolism (CAM) pathway (adopted

from Taiz and Zeiger, 2002).
atmosphere

light reactions
RuBP PCR
CO2 cycle
ATP
NADPH
3-PGA
mesophyll cell

a. C3 photosynthesis

light reactions
NADPH
ATP
RuBP ATP
PEP CO2
CO2 NADPH
PCR
cycle

4-Carbon 3-PGA
organic acids
mesophyll bundle sheath cell
cell
b. C4 photosynthesis

Light

light reactions
PEP starch

CO2
3-PGA PCR ATP
cycle
NADPH
CO2
4-carbon RuBP
organic
acids
(storage)
stomates open stomates
closed
c. CAM photosynthesis

Figure 21. Comparative flow diagram of C3, C4, and CAM photosynthesis.
Table 8. General characteristics of the C3, C4, and CAM plants.

C3 Plants C4 Plants CAM Plants

Typically temperate species, e.g. Typically tropical or semi-tropical Typically xerophytic species, e.g. cacti,
spinach, wheat, potato, tobacco, species e.g. corn, sugarcane, orchids, agave, bromeliads, and other
sugarbeet, soya bean, sunflower amaranthus, sorghum, savannah succulents
grasses; plant adapted to high light,
temperature, and also semi-arid
environments

Moderately productive, 30 tons dry Highly productive. 80 tons ha -1 is Production is usually very poor;
weight ha-1 for sunflower is possible possible for sugarcane pineapple is highly possible

Cells containing chloroplasts do not Kranz-type anatomy and peripheral Lack Kranz-type anatomy and peripheral
show Kranz-type anatomy and generally reticulum are essential features reticulum; only one type of chloroplast
lack peripheral reticulum; only one type
of chloroplast.

Initial CO2 acceptor is ribulose-1,5- Initial CO2 acceptor is phosphoenol CO2 acceptor is PEP in the dark and
bisphosphate (RuBP), a 5-C sugar. pyruvate (PEP), a 3-C acid RuBP in the light

Initial CO2 fixation product is the 3-C Initial CO2 fixation product is the 4-C CO2 fixation products are oxaloacetate in
phosphoglycerate oxaloacetate the dark and phosphoglycerate in the
light

Only one CO2 fixation pathway Two CO2 fixation pathways separated in Two CO2 fixation pathways are
space separated in time

High rates of glycolate synthesis Low rate of glycolate synthesis Low rate of glycolate synthesis

Low water-use efficiency and salinity High water-use efficiency and salinity High water-use efficiency and salinity
tolerance tolerance tolerance
Photosynthesis saturation at 1/5 full Do not readily photosaturate at high light Do not readily photosaturate at high light
sunlight intensity intensity

High CO2 compensation point Low CO2 compensation point High affinity for CO2 at night
Open stomate by day Open stomate by day Open stomate by night
Factors affecting photosynthesis

Operationally, three basic processes are evident during photosynthesis.

1) The diffusion of carbon dioxide from the air to the reaction

sites in the leaves.
2) The light dependent reactions (photochemica);
3) The carbon dioxide fixation reactions (biochemical)

The main environmental factors affecting the above processes may be briefly stated
as follows;

Diffusion. Carbon dioxide concentration in air and in the leaf, and the resistance to
diffusion in the pathway influence the diffusion rates.

Photochemical. Light intensity influences reaction rates. Light absorption is in turn

affected by the concentration of pigments, adequacy of nutrients and leaf
morphology and position.

Biochemical. Temperature is the main factor, as well as the presence of inhibitors.

On a single leaf basis, net photosynthesis per leaf area of C 4 plant species increases
with light intensity up to full sunlight, leaves of C3 plants become light- saturated at
1/4 - 1/3 full sunlight, while shade leaves may be saturated at light intensities 1/10
of full sunlight. The efficiency of photosynthesis in terms of light utilization at high
light intensities is obviously greater in the C4 response.

On carbon dioxide concentration, photosynthesis is dependent on the ambient C0 2

concentration, especially at high light intensities. The differential which exists in
photosynthetic efficiency at high light intensities between the C4 and C3 plants is
greatly reduced at high carbon dioxide. Stomatal aperture also has a significant
influence on the diffusion resistance to carbon dioxide during periods of moisture
stress. Partial or complete stomatal closure during moisture stress to prevent loss of
water during transpiration serves as carbon dioxide diffusion resistance.

Optimum temperatures for net photosynthesis of C 3 species range from 25-30 °C.
Above this temperature range, photorespiration increases more rapidly than
photosynthesis, resulting in net photosynthesis decline. By contrast C 4 plants, which
lack photorespiration, have temperature optima far higher than C3 plants, and can
thus survive in high temperature and high light intensity situations where C 3 plants
are typically photosynthetically inactive.

As regards leaf age, maximum photosynthetic efficiency is reached about full leaf
expansion and thereafter, there may be some decline in efficiency. However, the
capability of the leaf for photosynthesis during its life span depends largely on the
environment to which it is exposed to. Older shaded leaf may lose the ability to
photosynthezise efficiently at high light intensities but remain photosynthetically
 efficient at lower light intensities which occur at the lower canopy. One reason for
reduced photosynthetic efficiency in older leaves may be a relative increase in their
respiration rate with age.

Unlike those for individual leaves, the over-all photosynthetic efficiency of a crop
canopy is quite different because it involves the aggregate response of many leaves
which occupy different positions, and, therefore, environments, in the canopy.

Light interception by the canopy. The percentage of the incident light intercepted
by the canopy is a function largely of the leaf surface area of the crop. In the early
stages of growth, there is sufficient leaf area available to intercept radiation, and
much is wasted by striking the soil. At some stage, however, a closed canopy should
be formed such that almost all the incident radiation is absorbed by the crop. A
convenient measure of the “leafiness” of a crop is the leaf area index (LAI) which is
defined as the ratio between leaf area of a crop, and the area of ground
occupied by the crop. In some crops like the soybean, the percentage light
intercepted is directly proportional to the LAI up to the point when 95% of the light
was intercepted (defined as the critical LAI). The production of LAI above the critical
value represents unnecessary leafiness and a waste of photosynthates. However,
the critical LAI for a crop is not absolute but depends on the intensity of the incident
radiation. Similarly, when comparison are made across canopies formed by different
planting arrangements, crop growth rate depends on the amount of light intercepted
by each canopy arrangement, at least until a closed canopy is formed and all the
incident light is intercepted. For soybeans, the rate of dry matter production remains
constant for LAI greater than the critical LAI (referred to as the critical LAI response).
For some crops like kale and rice, however, crop growth rate decline when LAI
exceeds the critical value, due to the `parasitic’ effects of lower shaded leaves in the
canopy, which are not photosynthesizing sufficiently to make up for respiration. This
is termed an optimum LAI response.

Light distribution through the canopy. Incident light striking a leaf surface is either
reflected by the leaf, transmitted through it, or absorbed. Transmission in the visible
range is greater at wavelengths in the 520-640 nm region (i.e. green). Consequently,
there is a change in the quality of light reaching the leaves in the lower canopy.
Suggestions for improving light distribution through the canopy include more diffuse
spatial arrangement of leaves, more erect leaves and smaller leaf size to increase
the amount of `flecking’ of direct radiation onto lower leaves.

a. Photosynthesis and crop yield.

There are a number of possible approaches to improving the photosynthetic

efficiency of the plant canopy in order to increase total output or yield. Among the
options include: 1) improvement of the photosynthetic efficiency of the individual
leaves, and 2) the manipulation of the canopy structure so as to optimize the light
distribution over the canopy leaf surface. However, there is a considerable
debate whether higher grain yield potential could be achieved by increasing total
canopy photosynthesis. There is no doubt that increasing canopy photosynthesis
may have a direct effect on yield in such crops where the economic yield/product
is in the vegetative growth (e.g. sugarcane, fibers, leafy vegetables and turf
grass). In many grain species, however, total biological dry matter production is
already more than adequate and it is apparent that further increases will not
necessarily increase grain yield. The problem thus becomes a matter of
changing the relative partitioning of the photosynthates by the plant into
vegetative and economic grain components. Consideration of the relative
partitioning of photosynthates between vegetative and reproductive components
by the plant has led to the concept of harvest index, which is defined as the
proportion of the total biological yield which is recovered as economic
yield (Donald, 1962, 1968). Harvest index of important grain crops is given in
Table 9.

Table 9. Harvest index of some grain crops.

Crop Harvest Index

Wheat 0.40-0.55
Corn 0.40-0.55
Sunflower 0.30-0.35
Dry beans 0.45-0.55
Lentils 0.45-0.55
Soybean 0.25-0.35
Sorghum 0.40-0.55

This problem is particularly evident in indeterminate crops such as grain

legumes, in which continued vegetative growth occurs during pod development.
This vegetative dry matter production represents photosynthates which could
have been diverted into grain.
RESPIRATION

Cellular respiration is one of the distinguishing attributes of living organisms. The energy
required to sustain vital biological processes is generated from cellular respiration. In
plants, this energy is consequently used to power synthetic, mechanical, electrical, and
active osmotic processes.

Broadly, respiration is defined as an enzyme-catalyzed reaction involving the

transformation of organic substrates into carbon dioxide and water, accompanied by the
release of energy (chiefly in the form of adenosine triphosphate, ATP). The summary of
this exothermic process is represented by the following chemical equation:

C6H12O6 + 6O2 6O2 + 6H2O + E

The over-all reaction for respiration may be viewed as the opposite of photosynthesis,
although the specific reaction steps vary considerably between the two processes. Table
10 summarizes the salient differences between respiration and photosynthesis.

Table 10. Comparison between respiration and photosynthesis.

  Respiration Photosynthesis
Occurence in all living organisms in green plants
Reactants C6H12O 6 + O2 CO2 + H2O
End Products CO2 + H2O + E C6H12O 6 + O2
Organelle/s involved cytoplasm and mitochondria chloroplast
Light not required required
Chlorophyll not required required
Sensitivity to temperature sensitive only the dark reaction
Energy transformation chemical to heat light to chemical
Reaction type exergonic endergonic
Effect on plant biomass decrease increase

Stages of Respiration

Cellular respiration in plants and other organisms is often termed as “dark

respiration” to distinguish it from photorespiration which is linked to photosynthesis.
The so-called dark respiration, however, proceeds even in the presence of light. In
dark respiration, the complete oxidation of substrates involves three major reaction
sequences, as shown in Figure 22:
 a. Glycolysis
b. Krebs cycle
c. Electron transport system or ETS

In primitive organisms like the anaerobic bacteria, energy is derived chiefly from
glycolysis. In higher plants, glycolysis and mitochondrial respiration (Krebs cycle and
ETS) must proceed in sequence to generate more energy needed for growth and
development.

Cytosol Mitochondria

High-energy electrons High-energy electrons

carried by NADH carried mainly by NADH

Glycolysis
2 Krebs
Electron
glucose pyruvic Cycle
acid
Transport

Figure 22. Stages of dark respiration.

Glycolysis

Glycolysis (syn. glycolytic sequence, anaerobic phase, or Embden Meyerhof

pathway), the first step in dark respiration, occurs in the cytoplasm. Partial
oxidation of a glucose molecule (6-C) yields two molecules of pyruvic acid (3-C).
In the process, substrate phosphorylation of the sugar molecule results to a net
production of 2 ATP.

While glycolysis is considered the anaerobic phase of dark respiration, oxygen

must be sufficiently available in order to proceed to mitochondrial respiration.
When oxygen is limiting, pyruvic acid generated during glycolysis remains in the
cytosol and anaerobic respiration (syn. fermentation) occurs. During
 fermentation, either ethanol or lactic acid is produced, with the process liberating
considerably smaller amount of energy as compared with mitochondrial
respiration. For every pyruvic acid molecule proceeding to anaerobic respiration,
one NADH which would otherwise be a potential source of 3 ATP after its
oxidation through the ETS is instead utilized to reduce pyruvic acid to alcohol or
lactic acid.

Krebs Cycle

When oxygen is not limiting, the pyruvic acids produced in the cytosol during
glycolysis are imported into the mitochondrial matrix where Krebs cycle occurs
(Figures 23 and 24). Pyruvic acid is first oxidized to acetyl co-enzyme A (acetyl
co-A) and then subsequently converted into CO2 through the Krebs cycle (syn.
tricarboxylic acid cycle or citric acid cycle). Krebs cycle involves series of
chemical reactions which form carbon skeletons used for the synthesis of larger
molecules. For every glucose molecule (2 pyruvic acid molecules), the Krebs
cycle also forms 6 NADH and 2 FADH2 and yields 2 ATP via substrate-level
phosphorylation.

Figure 23. The ultrastructure of a mitochondrion.

 Figure 24. The Krebs cycle.

Electron Transport System (ETS)

The final stage of dark respiration occurs in the inner mitochondrial membrane.
In the electron transport system, NADH (from glycolysis and Krebs cycle) and
FADH2 (from Krebs cycle) are oxidized to yield ATP. Unlike in glycolysis and
Krebs cycle, ATP is generated in ETS via oxidative phosphorylation. Finally, the
electrons and protons recombine with O2 to form metabolic water.

Energy Yield

Approximately 30 ATPs are generated for every glucose (or other hexose)
molecule completely oxidized during dark respiration (Table 11 and Figure 25).

Table 11. Total ATP yield for every complete oxidation of one glucose molecule.

Equivalent ATP after ETS

Part reaction Total ATP
(Oxidative Phosphorylation)
Glycolysis    
2 ATP (substrate-level phosphorylation) - 2
2 NADH 2 NADH X 2 ATP = 2 ATP 4

Krebs Cycle
2 ATP (substrate-level phosphorylation) - 2
8 NADH 8 NADH x 3 ATP = 24 ATP 24
2 FADH2 2 FADH2 x 2 ATP = 4 ATP 4
    36
 Cytosol
Mitochondria

Glycolysis
2 2
acetyl
Krebs Electron
glucose pyruvic
acid co-A Cycle Transport

about about 36
32 ATP ATP
direct synthesis direct synthesis by ATP synthase per glucose molecule

Figure 25. Bioenergetics of dark respiration.

Growth and Maintenance Respiration

Respiration of crops can be separated into two components: growth respiration (Rg)
and maintenance respiration (Rm). Growth respiration is proportional to the gross
photosynthesis (P) and maintenance respiration is proportional to dry mass (W). This
gives:

R = Rg + Rm
R = kP + cW

where k is the coefficient for growth respiration and c is the coefficient for
maintenance respiration.

Growth respiration is the cost of converting the immediate products of

photosynthesis into plant material. It is found that the coefficient k varies
considerably between 0.12 and 0.45 with plant species and plant tissues.
Subprocesses of growth requiring Rg as the source of energy (in the form of ATP)
had been enumerated as follows: (1) reduction of nitrate and sulfate taken from the
soil, (2) active uptake of minerals and organic substrates into growing cells, (3)
monomer synthesis from those substrates, (4) polymerization, (5) tool maintenance,
(6) active mineral uptake by roots, and (7) phloem loading in source organs.

On the other hand, maintenance respiration refers to the CO 2 resulting from protein
breakdown, plus the CO2 produced in respiratory processes that provide energy for
maintenance processes. Maintenance includes processes that keep cellular
structures and intracellular gradients of ions and metabolites, and also the process of
 physiological adaptation that maintain cells in response to changing environment. In
simple terms, Rm maintains cellular functionality. The coefficient c varied with many
biotic and environmental factors including temperatures, nitrogen status, and water
stress. Maintenance processes are usually slow in developing storage organs such
as tubers and seeds. This is expected because proteins in those organs are mostly
inactive storage molecules (i.e. slow turnover). Maintenance respiration responds
strongly to temperature and is positively-related to plant N content. In effect, the
factors which affect the rate of maintenance respiration also influence crop growth.

Factors affecting respiration

1. Age and nature of tissues

Different tissues and organs respire at different rates. Greater over-all metabolic
activity of a given tissue requires higher respiration rate. Younger tissues (e.g.
developing buds) have higher respiration rates than older tissues (e.g. mature
leaves) as they need more energy for growth processes. Moreover, respiration
rates of vegetative tissues also decreases from growing tip to more differentiated
regions. In dormant organs (e.g. some seeds), the absence of growth-associated
events may be attributed to very low respiration rates or no respiration at all.

At maturity, respiration rate remains constant or decreases slowly as the tissue

ages and senesces. In the case of climacteric fruits (e.g. banana, mango,
avocado, tomato, jackfruit, etc.), ripening, which leads to senescence, is
associated with a considerable increase in the rate of respiration and ethylene
biosynthesis.

On the other hand, tissues with higher moisture content respire more than drier
tissues. This explains why perishables (e.g. fruits and vegetables), which have
higher moisture content, deteriorate faster than durables (e.g. cereals).

Wounded, damaged, or infected tissues also exhibit higher respiration rates than
healthy tissues.

2. Temperature

The rate of respiration is a function of temperature. In general, respiration rate

increases with increasing temperature, until a temperature threshold, during
which respiration rate decreases as a result of protein denaturation. The
temperature coefficient (Q10) of respiration describes doubling of the respiration
rate for every 10˚C in temperature between 0˚C and 35˚C.This temperature
stimulation of respiration reflects the increased demand for energy to support the
increased rates of biosynthesis, transport, and protein turnover that occur at high
temperatures.
 3. Oxygen

Respiration rate decreases with decreasing availability of oxygen. Under limited

oxygen (hypoxia) or in the absence of oxygen (anoxia), anaerobic respiration or
fermentation occurs. This is apparent in waterlogged conditions wherein plant
roots of paddy rice produce alcohol as a consequence of oxygen limitation
through the process of alcohol fermentation.

4. Carbon dioxide

The decrease in respiration rate due to increase in carbon dioxide concentration

is an example of feedback inhibition. This is a regulatory mechanism wherein
accumulation of considerable amount of the product (i.e. CO 2) inhibits the
forward reaction of respiration. For example, storage of some fruits in a high-CO 2
(e.g.10%) environment inhibits respiration, and prolongs the postharvest life of
these produce.

TRANSPIRATION

Transpiration is the loss of water from plants in the form of water vapor. This evaporative
process is dependent on energy, the heat of vaporization (539 cal g-1), which is required
to convert water from liquid state to gaseous state with no change in temperature:

539 cal g-1

H2O(l) H2O(g)

While it may be considered as a simple evaporative process (a physical process),

transpiration is more complex when viewed as a plant process. Unlike evaporation,
transpiration is modified by plant factors such as leaf structure and stomatal behavior
(the biological component of transpiration), which operates in addition to the
environmental factors that control water loss.

Transpiration is considered a ‘necessary evil’. It is important to plant life because: (1) it

keeps cells hydrated, (2) it maintains favorable turgor pressure for the transport of
nutrients absorbed by the roots from the soil, and (3) it serves as a cooling process, i.e.
considerable heat load is dissipated in the process due to the high heat of vaporization
of water. However, when the rate of transpiration is extremely high, the plants may
undergo dehydration and desiccation, which may possibly lead to plant death.

Total water lost by plants through transpiration may be substantial. The daily water loss
of a large, well-aerated, tropical plant such as palm trees may be up to 500 L. On the
other hand, a corn plant may loose 3-4 L day -1, whereas a tree-size desert cactus loses
less than 25 mL day-1. It is estimated that about 99% of the water absorbed by a corn
plant during its growing season is lost in transpiration.

Types of transpiration

Most of the water lost by plants is through transpiration, although water may be
released by plants in liquid form. The latter process is called guttation, wherein
water droplets are secreted as a consequence of root pressure through the
hydathodes, which are located along the margins of the leaves.

There are three types of transpiration which is categorized based on the avenue of
exit of water vapor:

1. Cuticular transpiration. Loss of water through the epidermis which is

usually covered with a cuticle. In some plants of the temperate zone, about 5-
10% of the water lost from plants maybe lost by this pathway.

2. Lenticular transpiration. Loss of water through numerous pores in the outer

layer of a woody plant stem, called lenticels. In deciduous species (trees
which sheds off leaves) and in some fruits, water loss through lenticels may
be quite substantial.

3. Stomatal transpiration. Loss of water through the stomata which can

account as much as 90% of the water lost from plants.

Stages involved in transpiration

Figure 26 illustrates the path of water movement from leaf surfaces to the
atmosphere, and is described as follow:

1. evaporation of water from cell surfaces (phase change of water)

2. diffusion of water vapor from leaf intracellular spaces to the atmosphere

Diffusion is the movement of substances from a region of higher concentration to a

region of lower concentration. Thus, the gradient of water vapor between the leaf
intercellular spaces and the external atmosphere is the driving force for transpiration.
Diffusion of water during transpiration is greatly influenced by relative humidity and
vapor pressure deficit.

Relative humidity (RH). It is the ratio (in %) of the actual water vapor in the air to
the water vapor pressure at saturation at same temperature and pressure. Air inside
leaves is usually 100% RH while RH of atmosphere rarely exceeds 90% (and in
temperate climates, it is around 30 - 70%). Thus, water diffuses out from the plants
 to the atmosphere since there is higher amount of water/water vapor in the
intracellular spaces (100%RH) relative to the atmosphere.

Vapor pressure deficit (VPD). Expressed in Pa, it is the difference between the
actual water vapor pressure and the water vapor pressure at saturation at the same
temperature. When VPD is 0 Pa (i.e. when RH of the atmosphere is 100%), there is
no net movement of water (no transpiration). The lower the RH of the atmosphere,
the greater the VPD and the faster the rate of transpiration are.

Figure 26. Stages of transpiration (adopted from Heldt, 2005)

Soil-Plant-Air Continuum of Water

To better understand the process of transpiration, we may take a look at the

movement of water from the soil and out of the leaf to the atmosphere (soil-plant-air
continuum of water), frequently termed as the transpiration stream.

1. Movement of water from the soil to the root xylem

Water, together with dissolved nutrients, is absorbed by roothairs due to

difference in water potential between the soil and the root tissues. Once within
the root cells, water is transported radially towards the xylem (the major conduit
for water transport) through one or more of these pathways (Figure 27):
 a. extracellular or apoplastic route

In this pathway, water moves between any non-living parts, e.g. capillary
spaces of the cell walls and intercellular spaces.

b. intracellular route

Intracellular movement of water toward the root xylem may be through the (i)
symplastic pathway, and (ii) transmembrane or transcellular pathway. In the
symplastic route, water moves from one cell to another through the living
parts of the roots (the symplast), which is connected by protoplasmic
connections called plasmodesmata. On the other hand, in the
transmembrane or transcellular pathway, water crosses the vacuolar
membrane (tonoplast) and the plasma membranes, as observed in the
endodermis which is lined with Casparian strip, a water-impermeable layer.

Figure 27. Possible routes of water movement through the root to the xylem:
apoplastic, symplastic, and transcellular pathways (adopted from Öpik
and Rolfe, 2005).

2. Movement of water from root xylem to leaf xylem

Upon reaching the root xylem, water is moved up to the higher plant parts via
long distance transport which usually terminates in the leaves. This ascent of
water is explained by the transpiration-cohesion-adhesion theory which describes
how the xylem sap is pulled up under tension or negative pressure (Figure 28).
The physical properties of water (i.e. capillarity, cohesion, and adhesion), along
with the high tension brought about by the negative pressure, help overcome the
frictional and gravitational resistances along the way.

3. Movement of water from leaf xylem to the air

Movement of water out of the plant system to the atmosphere is highly influenced
by RH and VPD (as explained in the previous section), and follows a path
towards an area with lower water potential (Ψ; expressed in MPa). The
atmospheric Ψ may be as low as -100 MPa as compared to values greater than -
10 MPa in the leaf intercellular spaces (the highest possible Ψ is 0 MPa), and
this results to the outward movement of the water vapor.

Figure 28. The transpiration-cohesion-adhesion theory.

Factors affecting transpiration

Since stomatal transpiration is the chief type of transpiration, any plant or

environmental factors which modify stomal behavior will affect the rate of
transpiration.

1. Plant factors

a. Efficiency of evaporative surface

The evaporative surface is a function of leaf area and stomatal density.

Broader leaves with higher stomatal density exhibit relatively faster rate of
transpiration.

b. Efficiency of water absorption

This is a function of the total root absorbing surface.

c. Other surface/stomatal modifications

The presence of morpho-anatomical modifications in the leaf (e.g. sunken

stomata, trichomes, degree of cuticular depositon, etc.) also alters
transpiration rate. Stomatal transpiration is predominant in plants with thicker
cuticle deposition in the leaves.

d. Phytohormones

Abscisic acid (ABA) induces stomatal closure while cytokinins and

gibberellins (GA) promotes stomatal opening.

e. Canopy structure

Canopies with better light transmission ratio (e.g. pyramidal crowns) exhibit
higher transpiration rate.

7. Environmental factors

a. Edaphic (soil) factors

Mineral nutrients such as nitrogen (N), phosphorus (P), and potassium (K)
stimulates stomatal opening by regulating the turgidity of guard cells.
 b. Atmospheric factors

i. Light

Stomates tend to close at lower light intensity. Except for CAM plants,
stomatal transpiration is not occurring in the dark.

ii. Relative humidity

High air humidity reduces the VPD between the leaf and the atmosphere,
thereby reducing the rate of transpiration. When the atmosphere is
saturated with water vapor (RH = 100%), VPD = 0 MPa, and transpiration
stops.

iii. Temperature

At constant RH, changes in temperature will not affect transpiration rate,

although reduction in transpiration rate is generally observed at
temperatures between 20- 40˚C.
iv. Wind velocity

Gentle breezes enhance transpiration as moderate wind speeds remove

the boundary layer. The boundary layer is a thin film of still air (with high
RH) hugging the surface of the leaf. In contrast, very strong wind may
lead to stomatal closure, a plant mechanism to avoid desiccation.

v. Oxygen and carbon dioxide concentrations

Under low carbon dioxide level, the rate of photosynthesis is adjusted by

increasing the stomatal aperture, inevitably facilitating the lost of water as
well. In contrast, low oxygen level stimulates stomatal closure.

TRANSLOCATION

Plants are considered autotrophic, which means they can synthesize their own food. The
absorption and transport of raw materials used for photosynthesis and the movement of
photosynthetic products to sites of storage and consumption are important in
understanding plant growth and development. The photoassimilates, or products of
photosynthesis, must be transported and distributed not only at short distances (at the
cellular level) but across plant tissues and organs in order to bring about growth. The
long-distance, multidirectional movement of photosynthates through the phloem is
called translocation.
Phloem translocation is a highly significant process that functions to ensure an efficient
distribution of photosynthetic energy and carbon throughout the plant. For example, this
process allows organic compounds to be transported from actively-photosynthesizing
leaves to newly-developing organs (e.g. buds, young leaves, root tips, etc.). From an
agricultural perspective, phloem translocation plays a significant role in determining
productivity, crop yield, and the effectiveness of applied herbicides and other xenobiotic
chemicals.

Unlike transpiration dominated by passive mechanisms, translocation is an active

process. Metabolic energy is required for translocation because substances are often
moved against concentration gradients. It is also sensitive to temperature changes.
While the main vessel for the transport of water and dissolved solutes is the xylem,
phloem serves as the major conduit for the products of photosynthesis.

The main form of photosynthate translocated in the plant is sucrose.

Source and Sink

The direction of long-distance translocation in the phloem is determined largely by

the relationships between sources and sinks. The underlying principle of phloem
translocation is that photoassimilates are transported from a source to a sink.

A source is an organ or tissue that produces more assimilate than it requires for its
own metabolism and growth. It is a net exporter or producer of photoassimilate, that
is, it exports more assimilate than it imports. Mature leaves and other actively
photosynthesizing tissues are the predominant source organs in most plants.

On the other hand, a sink is a net importer or consumer of photoassimilate. Roots,

stem tissues, and developing fruits are examples of organs and tissues that normally
function as sinks. Sink organs may respire the photoassimilate, use it to build
cytoplasm and cellular structure, or place it into storage as starch or other
carbohydrates.

A plant organ may function both as a source or a sink during its ontogeny. For
example, leaves initially act as sink organs. Emerging and young leaves are not yet
photosynthetically-active, importing assimilates from older leaves to support their
rapid metabolism and enlargement. As leaves approach maximum size and growth
rate slows, their metabolic demands diminish and switching gradually over to a net
exporter. Mature leaves then serve as a source of photoassimilates for sinks
elsewhere in the plant.

Another example are the modified storage organs of some plants (e.g. corm of taro
and rhizome of ginger) which are commonly used as asexual planting materials. As
the taro or ginger plants mature, considerable proportion of the assimilates produced
by the leaves are mobilized to the developing corm or rhizome. Development of
these plants parallel the progressive enlargement of these modified structures. In this
 case, the corm or rhizome acts as sink organs. Once the plants die, and the corm or
rhizome are harvested and used as planting materials, the stored organic
compounds in these modified organs are metabolized to support the growth
demands of the new shoots which will emerge from them. In this case, the corm or
rhizome functions as source organs.

The mechanism of translocation

Phloem loading refers to the transfer of materials from the photosynthetic mesophyll
cells into the sieve elements (component of the phloem tissue). On the other hand,
phloem unloading refers to the removal of these materials from the phloem in the
sink. Figure 29 shows the phloeam loading and unloading via different pathways in
plants. The plasmodesmata indicated by the double line allow unhindered diffusion of
sugars and amino acids. The companion cells participating in apoplastic loading are
called transfer cells. Intermediary cells are specialized companion cells involved in
symplastic loading (Nobel, 2009).

APOPLASTIC
LOADING
APOPLASTIC
UNLOADING

SYMPLASTIC
LOADING
SYMPLASTIC
UNLOADING

Plasmodesmata

Figure 29. Phloem loading and unloading via apoplastic and symplastic pathways
(Nobel, 2009).
Figure 30. The Munch pressure flow hypothesis of assimilate transport from
source to sink.

The Münch pressure flow hypothesis, proposed by Ernst Münch in 1926, is widely-
accepted as the most probable mechanism for translocation (Figure 30). The
hypothesis explains that the flow of solution in the sieve elements is driven by an
osmotically-generated pressure gradient between source and sinks tissues:

1. Active loading at the source raises the osmotic pressure in the sieve
elements resulting in an influx of water (coming from the xylem), which
increases turgor pressure in the sieve elements.

2. The process creates pressure difference between the source and sink
organs, and assimilates are transported from high pressure area (source) to
low pressure area (sink) by bulk flow.

3. With increasing concentration of assimilates in the sieve elements at the sink

end, the osmotic pressure increases and this is relieved by phloem
unloading.
 4. Phloem unloading causes a reduction in the osmotic pressure within the
sieve elements at the sink end, causing the movement of water back to the
xylem tissue, and consequently leading to a decrease in turgor pressure
within the sieve elements.

5. As new assimilates from source organs are loaded into the sieve elements,
osmotic pressure rebuilds and the above events are repeated.

Allocation and partitioning of assimilates

Allocation refers to the regulation of the quantities of fixed carbon that are
channeled into various metabolic pathways. In the source organ (e.g. leaf),
assimilates can be used for (1) metabolic utilization within the chloroplast
(metabolism and biomass), (2) synthesis of starch within the chloroplast (storage
compound), and (3) synthesis of sucrose for export to sink (transport compound). In
sink organs such as root, fruit, and young leaves, the fate of assimilates are either
(1) for metabolic utilization and growth processes, or (2) storage.

Partitioning, on the other hand, refers to the differential distribution of assimilates to

competing sinks (Figure 31). In plants at the vegetative stage of growth, the principal
sinks are the meristem and developing leaves at the shoot apex, roots, and
nonphotosynthetic stem tissues. With the onset of reproductive growth, the
development of flowers, fruits, and seeds creates additional sinks. This serves as the
basis for the common practice of pruning fruit trees (e.g. guava) to ensure a smaller
number of sinks (fruits) per tree. Partitioning assimilate among a smaller number of
fruit encourages the development of larger and more marketable fruit.

There are a number of factors which determine assimilate partitioning in a crop:

1. Sink strength

The ability of a sink to accumulate assimilates is called sink strength. It is a

function of sink size and sink activity.

2. Proximity of the sink to the source organ

Assimilates move preferentially toward sin leaves above and in line with the
source leaf. Lower mature leaves feed mainly the roots, the higher mature leaves
feed mainly the young leaves and the shoot apex.

3. Stage of development

Developing flowers and fruits become dominant sinks during the reproductive
stage of a crop. On the other hand, storage roots (e.g. cassava and taro) used as
planting materials export assimilates to developing vegetative tissues.
4. Nature of vascular connections between source and sinks

Each leaf is connected to the main vascular system of the stem by a vascular
trace, which diverts from the vascular tissue of the stem into the petiole. Source
leaves preferentially supply sink organs with which they have direct vascular
connection, often directly above or below them (Figure 32).

Figure 31. Phloem translocation from source to sink (adopted from Öpik and
Rolfe, 2005)
The small curved arrows indicate assimilates moving into the axial sinks.

Figure 32. The pattern of photosynthate transport from the leaf to an axillary
fruit in tomato (adopted from Wardlaw, 1990).
MINERAL NUTRITION

Essential Elements

At least 60 elements have been shown to be present in plant tissues, and if all the 92
naturally-occurring elements are supplied to plants in readily available forms, the
plant may well absorb all of them.

However, nutritional studies have established that an element may always be

present in the plant tissue but not necessarily essential and that the importance of an
element is not in proportion to the amount present.

In 1939, Daniel Arnon and Perry Stout made an important contribution in the study of
mineral nutrition when they introduced the concept of essentiality of elements.
According to them, an element is considered essential if it satisfies all the criteria
below:

1. There is a positive requirement of the element for normal growth or

reproduction, or to complete the plant’s life cycle.

2. The function of the element cannot be replaced by another (i.e. the deficiency
symptom attributed to a particular element cannot be corrected by the
addition of another element).

3. The element has direct or indirect function in plant metabolism.

Essential element is a term often used to identify a plant nutrient. The term
‘nutrient’ implies essentiality, so it is redundant to call these elements essential
nutrients. Based on the criteria, 17 elements have been considered essential (Table
12). This includes nine macronutrients (C, H, O, N, P, K, Ca, Mg, S), which are
taken by plants in relatively large quantities (≥ 0.1% of the plant dry mass), and eight
micronutrients (Fe, Cu, Zn, Mn, Mo, B, Cl, Ni), which are taken in relatively smaller
amounts (≤ 0.01% of the plant dry mass). The first three macronutrients are
incorporated into the plant during photosynthesis. The other macronutrients and
micronutrients are called mineral nutrients since they are absorbed from the soil
except for nitrogen which may be incorporated into the plant during its biological
fixation in the root nodules of legumes.

There are some elements that stimulate growth but do not fulfill Arnon and Stout’s
criteria for essentiality, or which are essential only for certain plant species or group.
These elements are called beneficial nutrients among which include Co, Na, Si, Al,
Se, and V.
 Table 12. Mineral elements and their respective year of acceptance as
essential (adopted from Allen, 2007).

Year of Year of
Element Element
Essentiality Essentiality
Nitrogen 1804 Manganese 1922
Phosphorus 1839 Copper 1925
Potassium 1866 Boron 1926
Calcium 1862 Zinc 1926
Magnesium 1875 Molybdenum 1939
Sulfur 1866 Chlorine 1954
Iron 1843 Nickel 1987

Table 13 summarizes the general functions of essential elements. These functions

can be categorized into three:

a. Structural – as important components of biomolecules (e.g. N, P, Ca, Mg, S)

b.Catalytic – as co-factor of enzymes (e.g. most micronutrients)
c.Osmotic – regulation of cellular hydration (e.g. K)

Table 13. Chemical symbols and common forms of the essential elements
absorbed by plant roots from soil (Foth, 1990).

Forms Commonly Absorbed

Nutrient Chemical Symbol
by Plants
Macronutrients
Nitrogen N NO3-, NH4+
Phosphorus P H2PO4-, HPO42-
Potassium K K+
Calcium Ca Ca2+
Magnesium Mg Mg2+
Sulfur S SO42-
Micronutrients
Manganese Mn Mn2+
Iron Fe Fe2+
Boron B H3BO3
Zinc Zn Zn2+
Copper Cu Cu2+
Molybdenum Mo MoO42-
 Chlorine Cl Cl-

Decline in soil fertility

Soil may be viewed as a reservoir of mineral nutrients needed by plants for growth
and development. Some natural processes and human activities, however, may
cause a reduction in soil fertility:

1. Soil erosion

Soil erosion is the physical loss and displacement of the fertile topsoil which
can be categorized into four types:

a. Geological erosion – a natural erosion process that leads to soil formation

and processes that maintain the soil in a favorable balance suitable
for crop growth

b. Wind erosion – which is caused by extreme wind speeds

c. Water-borne erosion – which is caused by rainfall and run-off (emitted
interflow and overlandflow)

i. Raindrop erosion – the detachment and transport of soil particles

due to the impact of rainfall

ii. Sheet erosion – the removal of thin layers of soil in sloping land
due to sheet or overland flow

iii. Interrill erosion – the combination of splash and sheet erosion and
it occurs in between rills

iv. Rill erosion – the detachment and transport of soil particles due to
the shearing effects of water flowing in rills

v. Gully erosion – erosion that takes place in channels or gullies

which are larger than rills. Gullies are distinguished from rills in
that the former cannot be obliterated by tillage practices.

vi. Stream channel erosion – the scouring of the bed of open

channels and the eventual transport of the detached soil
particles by streamflow

d. Accelerated erosion due to human activity – includes the breakdown and

transport of soil aggregates by human or animal activities such as tillage
and land cover destruction.

2. Crop removal
 3. Conversion of nutrients to unavailable forms
a. Combination with other elements forming insoluble forms
b. Microbial mediated transformations
c. Volatilization (especially nitrogen)
d. Leaching

To sustain the productivity of soils, the rate of fertility decline must be regulated.
Practices that would minimize erosion, leaching, volatilization, nutrient fixation must
be adopted. Soil surfaces prone to wind and water erosion should be covered with
vegetation. Appropriate farming practices should be used in sloping areas such as
contour farming, terracing, hedgerow planting, etc. Moreover, the fertility level of the
soil can be maintained by fertilizer supplementation (i.e. addition of organic and
inorganic fertilizers).

Nutrient Disorder

Figure 33 shows the growth or yield of a crop as a function of nutrient

concentrations.

Maximum
Growth/Yield

critical nutrient concentration

Adequate Zone

Toxic
Deficiency Zone Zone

Nutrient Concentration

Figure 33. Crop growth and yield as a function of nutrient concentrations.

When a nutrient is available in the soil at low concentrations or when the nutrient is
non-limiting but the crop cannot extract it from the soil, nutrient deficiency
symptoms appear. These are specific visible abnormalities which are reflective of
the metabolic disruptions resulting from nutrient deficiencies. Deficiency symptoms
appear when the nutrient level falls below the critical nutrient concentration. The
critical nutrient concentration may also be viewed as the nutrient level beyond which
a crop exhibit optimum growth or yield.

In the leaves, deficiency symptoms may be categorized into five types:

1. Chlorosis – yellowing of the leaves (uniform or interveinal) due to chlorophyll

degradation
2. Necrosis – death of leaf tissue (tip, marginal, or interveinal)
3. Lack of new growth, which may result in death of terminal or axillary buds and
leaves, dieback, or resetting
4. Accumulation of anthocyanin resulting in reddish coloration of leaf tissues
5. Stunted leaf growth with green, off-green, or yellow color

Table 11 shows the key to identification of plant nutrient deficiency symptoms. At the
initial stage of symptom development, symptoms may be readily associated with
specific nutrient deficiencies. However, as symptom development progresses, it may
become difficult to distinguish symptoms of one nutrient deficiency with another.

At the adequate zone, crops assume normal growth and development. But when the
nutrient levels become too high, especially in the case of micronutrients, toxicity
symptoms appear which also cause a corresponding decline in crop growth of yield.

On the basis of nutrient deficiencies, essential elements may be further classified as

mobile or immobile. Mobile nutrients are those elements which are translocated
readily from old to young leaves when deficiency occurs such that symptoms of
deficiency are first manifested in the older leaves. Examples of mobile nutrients are
N, P, K, Mg, and Zn. On the other hand, immobile nutrients are those nutrients
whose deficiency symptoms emerge first on young leaves. This is because immobile
nutrients are not easily metabolized (in the case of metallic elements) or are not
transported in the phloem, thus limiting their movement from one plant part to
another. Examples of immobile nutrients are Ca, B, Cu, Mn, S, and Fe.
 Uniform over leaf,
Nitrogen
small leaves
Chlorosis
Possibly sulfure if
Interveinal or blotchy symtoms are also
on young leaves
Old and mature
leaves Tip or edge scorch,
possibly interveinal Potassium
yellowing or browning
Necrosis
Interveinal or blotchy,
varying shades of Magnesium
color

Uniform over leaf Sulfur, Iron

Leaf edges purple,

Chlorosis interveinall yellowing, Sulfur
cupping

Zinc, Manganese,
Interveinal or blotchy Iron, Copper
Young leaves

Internal blotches and

Calcium
leaf edge scorching
Necrosis
Yellow to brown interveinal
areas, red to brown-purple
leaves, deformed, curled, Boron
torn leaves

Figure 34. Key to identification of nutrient deficiencies.

 Figure 35. Mineral deficiency symptoms in leaves.

Mg N K P

Figure 36. Mineral deficiency symptoms in corn leaves.

GROWTH ANALYSIS

Growth analysis, as a field of research, was developed in the 1900s in an attempt to

evaluate the interdependence of processes occurring within the plant and the
environment. In traditional growth analysis, simple primary data, e.g. plant biomass and
assimilatory area (usually leaf area), are measured to investigate processes within and
involving the whole plant or group of plants. Individual growth analysis is taken when
plants are still widely spaced and later crop growth analysis when canopy closes or
when plants become progressively crowded. Below are the five commonly measured
parameters for traditional growth analysis.

1. Relative Growth Rate

Relative growth rate (RGR) was introduced by Briggs et al. in 1920. RGR, expressed
in g.g-1.d-1, is the fundamental parameter of traditional growth analysis which
describes the relationship between plant weight and time. RGR reflects the
exponential rate of increases in plant biomass and is useful in growth evaluation of
plants of comparable sizes. Since plant growth is exponential only during the early
vegetative stage, RGR is constant only for short periods and is continually changing
(generally decreasing) as plant size increases. The mean value of RGR is expressed
by the following equation:

ln W 2−ln W 1
RGR=¿
t 1−t 2

where W1 is plant dry weight at time 1 and W2 is plant dry weight at time 2.

2. Crop Growth Rate

Crop growth rate (CGR), described by Watson (1958), measures the rate of dry
mater accumulation of a given crop community per unit land area. CGR estimates
the increase in biomass by integrating the gains from photosynthesis and losses
from respiration. Variations in CGR between/among species or cultivars may be
related to the compensatory effects of leaf area and photosynthetic rate, and the
trade-offs between the effects of crop height, leaf shape, and leaf inclination. CGR
generally shows a steady increase at the early stages of growth, reaches a peak
value by the time of canopy closure, then levels off as a consequence of mutual
shading before finally dropping. Mean CGR is expressed as g.m -2.d-1 and is
estimated by the following equation:

(W 2 −W 1)
CGR=¿
G a (t 1−t 2)

where W1 is plant dry weight at time 1,W2 is plant dry weight at time 2, and Ga is the
ground area expressed in m-2.
3. Net Assimilation Rate

Net assimilation rate (NAR), expressed in g.m -2.d-1, was first described by Gregory
(1917) to measure the efficiency of biomass production. NAR describes the increase
in biomass of a plant at any given time with consideration to the leaf area of the plant
at that given time. It measures the excess of dry matter gained over losses from
respiration, hence, it is a crude estimate of average net photosynthetic rate over
time. In general, NAR declines once mutual shading among leaves in a canopy
becomes apparent. Mean NAR is computed using the following equation:

( ln LA 2−ln LA 1 )(W 2−W 1)

NAR=¿
(LA 2− LA 1)( t 1−t 2)

where W1 is plant dry weight at time 1,W2 is plant dry weight at time 2, LA2 is the leaf
area expressed in m-2 at time 2, and LA1 is the leaf area expressed in m-2 at time 1.

4. Leaf Area Ratio

Leaf area ratio (LAR) was first described by Briggs et al. (1920) as the ratio of leaf
area and the total plant dry weight. It is a function of (1) leaf weight ratio (total leaf
dry weight/total plant dry weight) or the difference in partitioning of assimilates
between the leaves and other parts of the plant, and (2) specific leaf area (total leaf
area/total leaf dry weight) or the difference in the utilization of available assimilates
for leaf growth, i.e. leaf expansion vs. leaf thickening. LAR is computed by the
following equation:
LW A A
LAR=¿ . =
W LW W

LW AW
where is the leaf weight ratio, is the specific leaf area, A is the total leaf
W LW
area, and W is the total leaf dry weight.

5. Leaf Area Index

Leaf area index (LAI) was described by Watson in 1947. It is the total functional leaf
area per unit ground area. For example an LAI of 3.0 means that a crop stand
maintains a leaf area three times more than the ground area beneath it. Thus, LAI
has implication on the relative amount of radiation intercepted by leaves at different
depths of the canopy. If the plant in the example above has leaves with horizontal
orientation, only leaves in the first layer will receive full light, whereas leaves in lower
layers will receive light that has penetrated the first layer and that amount is close to
or less than the light compensation point. LAI is computed using the following
equation:
A
LAI =¿
Ga
 where A is the total leaf area and Ga is the total ground area.

GROWTH AND DEVELOPMENT

An organism from the moment of its inception is endowed with the capacity for
development. This is turn depends primarily on growth and morphogenesis. Growth which
is the more readily measurable aspect of development is accomplished fundamentally by
the processes of cell division and cell enlargement.

Development has three interrelated aspects, namely: growth, differentiation, and

organization. Development is the term to denote the attainment of size by virtue of growth
and architectural style by the concomitant process of morphogenesis. Growth is an
irreversible time change generally accompanied by an increase in size, weight or mass.
Differentiation is the outward sign of selective gene action, the reflection of change in the
cell’s biochemical program as a consequence of the release of information encoded in one-
dimensional sequences.

The fact that growth and differentiation act in coordination implies organization.
Organization is the orientation and integration of differentiated cells in space together with
regulated growth with the consequent attainment of form and structure of the complete
organism.

Differentiation and organization are thus aspects of morphogenesis.

Morphogenesis refers to the process concerned with the shaping of three dimensional
structures by folding and aggregation of one-dimensional gene products, or aggregation and
redistribution of cells. The molding of the whole into a definite pattern (morphogenesis)
should be distinguished from differentiation, which is essentially a process of developing
localized differences.

There is no clear demarcation between the two aspects of morphogenesis since

the position of a group of cells may determine the course of differentiation.

1. Correlations

The regulatory effect exerted by one part of the plant on the growth and development
in another part has been called correlation. Among the more common correlation effects
are exemplified by the influence of the shoot on vascular differentiation, apical dominance,
root/shoot interaction, abscission, tropism and stolon development among others.

The basis for this interaction could often be traced to the role played by chemical
growth regulators such as for instance the various phytohormones or it may be a case of
competition for nutrients.

2. Endogenous rhythm
 There are recurring events or oscillations with properties not directly reflecting
environmental fluctuations. While in many instances the rhythm may be started by certain
environmental factors, once started it may persist for several cycles even under constant
condition of the environmental parameter that started.

There are several rhythms known in plants which are classified according to the
duration of each cycle or frequency of recurrence. The three most common rhythms are the
annual rhythm (which reoccur every year), the lunar rhythm (which reoccur every new
moon) and the circadian rhythm (which reoccur every 24 hours).

Among the familiar circadian rhythms in plants are the closing of opening of foliage
and flowers of certain plants even when transferred to continues light or darkness, e.g.
folding of the acacia leaf before sunset, the increase in respiration of certain flowers at
specific time of the day even under constant ambient temperature.

Plant movements

Unlike other organisms, plants do not have any locomotory organs. Nevertheless,
plants may exhibit movement of some organs in response to environmental stimuli. The
three steps in plant movement are: (1) perception, which involves the recognition of the
environmental stimulus by the plant, (2) transduction, which involves the biochemical and
biophysical changes (e.g. electrical signals, action potentials, chemical messengers, etc.)
which occur in response to the perceived stimulus, and (3) response which shows the
changes in the organ affected by the perceived stimulus (e.g. bending, curving, folding, etc.)

Plant movements are divided into two categories:

(1) Tropic movements (tropisms), wherein the direction of the environmental stimulus
determines the direction of the movement. Examples of tropic phenomena include
phototropism (response to light), gravitropism (response to gravity), solar tracking (where
the flat blade of the leaf is always at nearly right angle to the sun throughout the day).

(2) Nastic movements, wherein movement may be triggered by an internal timing

mechanism (biological clock), and the direction of the stimulus does not determine the
direction of movement. Examples of nastic movements are hyponasty and epinasty
(bending up and bending down of leaves, respectively), nyctinasty (folding of some leaves in
response to light which usually assumes a rhythmic pattern because of its interaction with
the biological clock), hydronasty (the folding and rolling of leaves in response to water
stress), thigmonasty (syn. thigmomorphogenesis, response to touch or mechanical stress),
and seismonasty (syn. seismomorphogenesis, response to shaking without contact to the
organism).

Both nastic and tropic movements are often the result of differential growth, and
reversible uptake of water in specific cell types. For example, leaf movements may be
attributed to differential water uptake of special cells called motor cells, which collectively
form the pulvinus.
Crop Adaptation

Because plants are devoid of active locomotion they can not move away from
unfavorable environments. Their capacity to adapt to their environments enables them to
survive under a wide range of changing environmental conditions.

1. Morphological adaptation
This is exemplified by the presence of metamorphosed or specialized organs which
performs non-typical functions such as the pneumatophores or modified roots of certain
trees growing in marshes, which serve as “breathing” organs, the modified petiole of the
water hyacinth which serves as float, the modified roots of radish which serves as organ for
food storage and the modified root of singkamas (yambean) which serves as organ for water
storage, and the shade leaves production which are more adapted to low light intensities,
etc.

2. Physiological adaptation
These are exemplified by the closing of stomates of many bromeliads during the day to
help conserve water as well as the abscission of leaves in deciduous plants to reduce the
evaporative surface area thereby conserving moisture.

3. Biochemical adaptation
These are biochemical changes with some bearing on certain survival mechanisms
such as the increase in praline and abscisic acid in plants during period of moisture stress to
regulate increased water-holding capacity of tissues for moisture as well as stomatal closure
to conserve water. The increase in heat-shock proteins when plants are subjected to sudden
and transient sub - or supra-optimal temperatures, and increase in amides to help plants
detoxify ammonia concentrations in tissues, the increase in calorific respiration in aroids to
help volatilize certain essential oils which serve as attractants to pollinating insects at the
time of flower anthesis.

PLANT GROWTH REGULATION

Plant growth regulators (PGRs) refer to organic substances, other than vitamins and
nutrients, which are active in very minute amounts (often <1 μM), are formed in certain
parts of the plant, and which usually are translocated to other sites where they promote,
inhibit, or otherwise modify physiological, biochemical, and/or morphological processes.
Depending on concentration, a PGR may be promotive or inhibitory to plant biological
processes. In general, PGRs are promotive at relatively low concentrations but become
inhibitory at relatively higher concentrations.

Endogenous (produced within the plant) PGRs are called plant hormones or
phytohormones. Phytohormones are differentiated from synthetic PGRs in that the
latter are applied in plants exogenously (originating outside the plant). For example,
indole-acetic auxin (IAA) is a plant hormone, a naturally-occurring auxin, while 2,4-
dichlorophenoxyacetic acid (2,4-D) is a synthetic auxin.

Currently, there are five phytohormones that occur universally in nature: (1) indole-
auxins, (2) gibberellins, (3) cytokinins, (4) ethylene, and (5) abscisic acid (Figure 37).
Other substances which need further evidences of their universal occurrence as
phytohormones include brassinosteroids, jasmonates, polyamines, salicylates, among
others (Table 14).

Table 14. Phytohormones and the year of first unequivocal identification and
demonstration of their existence in plant tissues.

Year of Identification and Demonstration of

Phytohormone
Existence
Major phytohormones
Ethylene 1930 Gane
Indole-auxin 1942 Haagin-Smit et al.
Gibberellin 1958 MacMillan and Sutter
Cytokinin (zeatin) 1963 Letham
Abscisic acid 1965 Comforth et al.

Other phytohormones*
Brassinosteroids (brassinolide) 1979 Grove et al.
Jasmonates (jasmonic acid) 1980 Veda and Kato
Polyamines 1985 Smith
Salicylates (salicylic acid) 1991 Pearce et al.

* needs further evidences to show their universal occurrence in the Plant Kingdom

Indole-Auxin

Chemical nature

Auxin is a generic term applied to growth regulators with the special capacity to
promote cell elongation. The naturally-occurring auxins are the indole-auxins
represented by indole-3-acetic acid (IAA) and some of its natural analogs. First to be
identified and isolated, IAA is the most dominant natural auxin in plants.

Compounds which serve as IAA precursors may also have auxin activity (e.g.
indoleacetaldehyde and indoleacetonitrile). Some plants contain other compounds
that display weak auxin activity (e.g. phenylacetic acid). IAA may be present as a
free acid or as a conjugate such as indoleacetyl aspartate. 4-chloro-IAA have also
 been reported in several plant species, though it is not clear to what extent the
endogenous auxin activity in plants can be accounted for by 4-chloro-IAA.

Sites of biosynthesis

IAA is synthesized from the amino acid tryptophan primarily in actively-growing

tissues (e.g. shoot apical meristem, leaf primordial, young leaves, and developing
fruits). It is also produced in mature leaves and root tips, although at much lower
concentrations.

Transport

IAA transport is cell to cell and is polar in nature. The basipetal transport to the root
and acropetal transport to the upper organs involves vascular (xylem and phloem)
and non-vascular tissues (parenchyma cells associated with vascular tissues).

Effects

1. Promotes cell enlargement and cell division in the cambium (synergetically with
cytokinin) in tissue culture
2. Stimulates differentiation of phloem and xylem
3. Stimulates root initiation in cuttings
4. Induces ethylene biosynthesis at supra-optimal concentration
5. Mediates the tropistic bending responses of shoots and roots to gravity
(gravitropism), light (phototropism), and touch (thigmotropism)
6. Promotes apical dominance
7. Delays leaf senescence and leaf and fruit abscission (auxin may also promote
(via ethylene) leaf and fruit abscission depending on the timing and position)
8. Promotes fruit setting and fruit development in some plants
9. Can also delay fruit ripening but may promote flowering in some plants (e.g.
bromeliads)
10. Induces femaleness in dioecious flowers (via ethylene).
11. Induction of parthenocarpic (seedless) fruit development (e.g. tomato)
12. Popularly used as herbicides (e.g. 2,4-D, Agent Orange, dicamba etc.)

Gibberellic acid

Chemical nature

The gibberellic acid or gibberellins (GAs) belong to a family of compounds based on

the ent-gibberellane structure. The most widely available compound is GA3, which is
a fungal product. On the other hand, the most biologically-active GA in higher plants
is probably GA1, which is the form primarily responsible for stem elongation. Most of
the 125 GAs characterized today are inactive or are just precursors of the active GAs
(e.g. GA1, GA3, GA4, and GA20).

Sites of synthesis
 GAs are synthesized from mevalonic acid in (1) elongating shoots, (2) young leaves
of developing apical buds, (3) developing seeds and fruits, and (4) apical regions of
the roots.

Transport

The major conduit for the non-polar transport of GAs is the phloem.

Effects

1. Stimulates stem elongation (may reverse physiological and genetic dwarfism in

plants)
2. Promotes bolting (rapid elongation of floral stem) in long-day plants
3. Induces germination of seeds that normally require a cold treatment
(stratification) or light (positively photoblastic seeds).
4. Stimulates the de novo synthesis of α-amylase in germinating cereal grains.
5. Promotes fruit set and fruit growth in some fruits (e.g. grapes)
6. Induces maleness in dioecious flowers of some species

Cytokinins

Chemical nature

Cytokinins (CKs) are adenine derivatives which have the capacity to induce cell
division in tissue culture (in the presence of optimal concentrations of auxin). The
most common CK base in plants is zeatin, the first natural CK which was isolated
from corn endosperm. CKs also occur as rebosides and rebotids.

Site of biosynthesis

CK is synthesized through the biochemical modification of adenine. The major site of

CK biosynthesis is at the root apical meristem although seeds (embryo) and
developing leaves have been shown to produce significant amounts of CK as well.

Transport

CK produced in the roots is transported to the upper organs via the xylem.

Effects

1. Regulates morphogenesis in cultured tissues (synergetically with auxin)

2. Releases lateral buds from apical dominance.
3. Delays leaf senescence
4. Promotes cotyledon and leaf expansion
5. Promotes nutrient mobilization (e.g. in expanding leaves)
6. Enhances stomatal opening in some species
 7. Enhances the accumulation of chlorophyll as it promotes the conversion of
etioplasts into chloroplast.

Ethylene

Chemical nature

Ethylene is the only phytohormone occurring in gas state. It is an unsaturated

hydrocarbon (an alkene) synthesized from the amino acid methionine (primary
precursor) in many tissues in response to stress. Later on, it was discovered that 1-
aminocyclopropane-1-carboxylic acid (ACC) is the immediate precursor for ethylene
biosynthesis. Ethylene does not seem to be essential for normal vegetative growth
but it is the only hydrocarbon with a pronounced effect on plants.

Sites of synthesis

Ethylene is synthesized in most tissues in response to senescence (e.g. ripening

fruits) and stresses.

Transport

Being a gas, ethylene moves by diffusion from the site of synthesis. This may
account for the effects of ethylene at sites quite distant from its sites of synthesis.
ACC can be transported via the xylem pathway.

Effects

1. Promotes ripening of climacteric fruits

2. Induces epinasty (downward curvature of leaves)
3. Induces lateral cell expansion
4. Formation of adventitious roots
5. Induces flowering in pineapple and other bromeliads
6. Enhances flower, fruit and leaf senescence
7. Induces femaleness in dioecious flowers of some species
8. Promotes shoot and root growth differentiation
9. Releases tissues/organs from dormancy
10. Promotes leaf and fruit abscission
11. Enhances flower opening in some species

Abscisic acid

Chemical nature
The name of this growth regulator is rather unfortunate. It was first called “Abscisin ll”
because it was thought to control the abscission of cotton bolls. At almost the same
time, another group named it “dormin” for a purported role in bud dormancy. By a
compromise, the name abscisic acid (ABA) was coined. It now appears to have little
role in either function. As a result of the original association with abscission and
dormancy, ABA is often recognized more as an inhibitor, although it can act as much
a promoter (e.g. storage protein synthesis in seeds). In fact, it is considered the most
ideal natural inhibitor because of its following features: (a) non-specific as to
physiological process inhibited; (b) effects are reversible; and (3) no unfavorable
after-effects of supra-optimal concentrations.

Site of synthesis

ABA is synthesized from mevalonic acid in mature leaves particularly in response to

water stress. Seeds are also rich in ABA which may be imported from the leaves or
synthesized in situ.

Transport

ABA is exported from leaves in the phloem. There are some evidences that ABA
may circulate to the roots in the phloem and then return to the shoots in the xylem.

Effects

1. Counteracts the effect of gibberellins on α-amylase synthesis in germinating

cereal grains
2. Enhances stomatal closure (e.g. during water stress)
3. Promotes leaf senescence
4. Promotes storage protein synthesis in seeds
5. Induces transport of photosynthates towards developing seeds, and its
subsequent uptake by growing embryos
6. Induces and/or maintains dormancy in seeds and buds.
Table 15. Some effects of exogenous plant growth substances on plants. Effects in capitals are of significance as
characteristic of particular substances. The symbol * indicates that there is evidence for the role of the relevant
endogenous substance in the control of the process referred to. (Hill, 1973)

Effect produced
by exogenous
Auxins Gibberellins Cytokinins Abscissic Acid Ethylene
application of
growth substance
1 Stimulates root Yes* No. Often inhibits Variable response Has been reported Yes
initiation in in some cases
cuttings

2 Stimulates Yes* Yes Yes, in some May inhibit* No, but causes
cambial cases, but little radial expansion of
division studied stem cells in some
legume seedlings

3 Promotes fruit Yes* Yes* Yes, in some cases No No

growth

4 Promotes Yes, in pineapple To some extent; No Inhibits flowering in YES, IN

flowering in due to ethylene inhibits flower some Long day PINEAPPLE
other types of production initiation in some plants under
plant woody plants, e.g. inductive
apple daylengths. Effects
on Short Day plants
variable*

5 Reverses No YES* No No No
some types of
genetic
dwarfism
6 Releases No Yes, mimics factors Some cases* NO. INDUCES Yes, in some cases
vegetative of light and reported; may be DORMANCY IN
buds from temperature associated with bud SOME WOODY
dormancy growth in some SHOOTS*
other cases, e.g.
effect on lateral
buds

7 Accelerates No Yes* No NO. TENDS TO Yes, in some

seed INHIBIT* cases*
germination in
general

8 Has an effect YES. APICAL Yes, normally Yes; often breaks Not studied Not studied
in maintaining APPLICATION increases apical dominance if
or breaking MAINTAINS dominance* applied to lateral
apical APICAL bud*
dominance DOMINANCE*

9 Inhibits protein Some cases Yes, in some cases YES, IN SOME No. Accelerates No, tends to
and chlorophyll reported CASES this , notably in leaf accelerate
breakdown in discs senescence*
senescence

1 Sex Favors maleness Favors maleness No action YES, for Favors femaleness
0 expression gynoecious plants

1 Induces No No No Yes No
1 stomatal
closure
1 Affect tropic Yes* Yes* No Yes; endogenous Yes. Associated
2 responses inhibitors may be with auxin relations
involved in some of the tissue*
aspects*

1 Controls YES, WITH No YES, WITH No No

3 differentiation CYTOKININS AUXINS
in tissue
cultures

1 Inhibits root Yes* No. Occasionally Little studied Yes Yes

4 growth promotes

1 Affects xylem Yes* Yes Yes, in some cases Yes, in some cases Not studied
5 differentiation but little studied but little studied

1 Affects Yes, largely Not directly Probably, through Yes. Accelerates* YES. EFFECT DUE
6 abscission of through effect on effect on delay of this in some plants TO SPEEDING UP
leaves or fruits ethylene senescence (e.g. cotton, lupin) OF
production* SENESCENCE*

1 Affects stem No YES, PROMOTES* No May inhibit with Inhibits

7 growth in intact repeated
plants in the application
light
1 Promotes stem No YES* Yes, but only No No
8 elongation and known in one plant
flowering in
rosette
biennials
1 Causes No Yes Yes, in some cases No. Inhibits Yes
9 germination in
light-requiring
seeds

2 Causes No Yes* Has been reported No. Inhibits this. No, but may
0 synthesis of α- (Effect reversed by increase the
amylase in kinetin) release of enzyme
cereal grains already present

2 Promotes Not studied, but No No No YES*

1 climacteric probably due to
respiratory rise ethylene
in ripening fruit production
 CHAPTER III: FACTORS AFFECTING CROP PRODUCTION

INTRODUCTION

The development and performance of crops is governed mainly by the genotype

(internal factors) and the environment (external factors). The genotype sets the ultimate
limits within which the plant/crop may vary, such as growth duration, size, tolerance to
environmental stresses and others. The environment, on the other hand, determines
developmental pattern of a plant within the limits set by the genome.

Crop productivity, whether in terms of dry matter production or yield (economically

important partitioned dry matter), is a function of the crop genotype, the environment
where the crop is growing, and the interaction between genotype and environment, such
as: YIELD = Genotype (G) + Environment (E) + (G x E). Thus, attainment of maximum
productivity of a crop genotype is influenced by its growing environment. Even under the
most ideal environmental condition, crop growth cannot exceed its genetic potential.

Crop environment is an array of interacting factors with varying degree but has
cumulative influence on crop growth and development. This is composed of climatic,
edaphic and biotic factors other than the crop. In this chapter, factors affecting crop
growth and development or in general the crop production will be discussed. Some crop
production aspects or considerations on genetic factors will be introduced.

COMPOSITION OF THE ATMOSPHERE

The lower atmosphere (up to 80 km) is well-mixed and has a different composition with
reference to air at sea level. The composition of an unpolluted air is shown in Table 16.
Although existing in trace amounts, the total mass of a gas can still be quite large
because the total mass of the atmosphere is very large. Man-made pollution is
distributed throughout the atmosphere, but it is highly concentrated in the bottom 10 m of
the air column.
 Table 16. Composition of unpolluted atmosphere (Hodges, 1977).

Molecule Formula Fraction of the Atmosphere

Nitrogen N2 78.09%
Oxygen O2 20.94%
Argon Ar 0.93%
Carbon dioxide CO2 0.03%
Neon Ne 18.000 ppm
Helium He 5.200 ppm
Methane CH4 1.300 ppm
Nitrous oxide N2O 0.250 ppm
Carbon monoxide CO 0.100 ppm
Ozone O3 0.020 ppm
Sulfur dioxide SO2 0.001 ppm
Nitrogen dioxide NO2 0.001 ppm

The air enclosing the earth serves as the source of CO2 and oxygen O2. It also mediates
the balance of water through: precipitation, condensation, and evapotranspiration. Air
composition is maintained at fairly constant levels (e. g. 79% N, 21% O2, 0.03% CO2 by
volume) at the vegetation-atmosphere interface through continuous air movement. Very
high concentrations of pollutants may come in contact with plants, in the presence of
temperature inversions and still air.

The atmosphere is consists of several gases with CO 2, O2, and N2 comprising the more
important gases in plant growth and development. Carbon dioxide is hardly limiting in
crop production, except in places with dense plant population exposed to high light
intensities coupled with no or little air circulation. Once CO 2 becomes deficient, the rate
of photosynthesis is affected which is subsequently reflected in yield reduction. On the
other hand, O2 is required during respiration. After assimilation by plants, both CO 2 and
O2 become the major structural components of plant organic materials (e. g. primary and
secondary metabolites). Nitrogen gas has to be converted to available forms, such
nitrate (NO3-) ammonium (NH4+), first before it is assimilated into organic materials.

Carbon Monoxide and Carbon Dioxide

While the carbon monoxide (CO) is toxic to animals and is produced in large
amounts by inefficient combustion, it is not generally toxic to plants. Both CO and
CO2 can be taken up by the plant and are subsequently incorporated into plant
organic structures. Increase in CO 2 in the atmosphere may contribute to the global
warming.
Dust Particles

Dust and soot come from incomplete combustion and any process that releases fine
particulate matter. More than 80% of particulate matter in the air comes from coal-
fired electric power generation plants, coking operations of steel mills, and other
industrial processes. Particles fall to earth near the pollution source with the larger
particles settling out first. However, once small particles reach high altitudes they are
dispersed by prevailing winds over the globe and considered as air pollutants. Small
particles including fungal spores have worldwide distribution. Heavy metals such as
lead (Pb), cadmium (Cd), and manganese (Mn) are usually distributed on particles.
Since small particles have diverse chemical composition and a very large surface
area, they are biologically active. Most of the particle-borne substances are taken up
by the plant via soil-root continuum.

Sulfur Dioxide

Sulfur (S) is released into the atmosphere from volcanoes, anaerobic decay
processes hydrogen sulfide (H2S), and by the aquatic and terrestrial plants dimethyl
sulfoxide (DMSO) [(CH3)2SO]. Large amount of sulfur dioxide (SO2) is also released
from human activity. Ores of copper (Cu), zinc (Zn), lead (Pb), nickel (Ni) and iron
(Fe) often form as sulfides in minerals, which may contain as much as 10% sulfur.
During smelting, S02 released in smelters is recovered by scrubbers and sold as
sulfuric acid ((H2SO4-). Petroleum and coal also contain an appreciable amount of S
that is liberated upon combustion. Oxides of S and N combined with water leads to
the formation of acid rain that may precipitate at great distances from the pollution
source.

Fluoride

Industrial processes such as phosphate fertilizer production, aluminum reduction,

steel making, ceramic firing, brick kilns, etc. release hydrogen fluoride (HF) or
fluoride (F-) into the atmosphere both as gases or attached to particles. Fluorides are
extremely phytotoxic often showing effects on plants at concentrations of < 1 ppb,
and have great impact on the areas close to the pollution source.

Phytochemical Smog

In the 1930s, automobiles were a major source of air pollution. However, direct
exposure to automobile exhaust was less toxic to plants than due to exposure to
smog. The interaction of vehicular exhaust, O2 and sunlight results in the formation of
phytochemical oxidants. Those of greatest importance are ozone (O3), peroxyacetyl
nitrate (PAN) (C2H3NO5), and nitrous oxide (N2O). The impact of air pollution on
plants may involve visible effects like necrosis, bronzing, chlorosis and stunting.
Herbaceous plants exposed to PAN typically show bronze, silver or glaze on the
undersurface of the leaf. The young and actively growing tissues are most sensitive
to PAN. Chloroplasts are particularly sensitive to PAN, which may act to oxidize
sulfhydryl groups on proteins. PAN is a strong oxidant and may either act directly or
 induce free radical formation to oxidize fatty acids in the membranes, resulting in
damage and death. Ozone has probably received more detailed attention than any
other gaseous air pollutants. Reductions in yield at varying ozone levels are shown in
Table 18. Since 03 is easy to detect, it is often used as an index for air quality.
Moreover, it is a gaseous pollutant and can be carried to great distances from the
point of origin.

Table 18. Percentage yield loss based on seasonal average at 12-h ozone
concentration (Treshow and Anderson, 1989).

Percentage Yield Loss based on

Crop 3-Month and 12-Hour Average Ozone Concentration
40 ppb 50 ppb 60 ppb Ambient Zone
Lemon 12.7 20.8 22.9 28.3
Dry bean 0.5 16.9 22.7 27.2
Onion 14.2 20.8 22.9 23.2
Grape 9.4 15.2 19.5 20.8
Cotton 6.6 11.1 15.3 19.6
Orange 8.9 14.7 18.2 19.3
Rice 6.8 9.2 10.2 10.4
Alfalfa 4.3 7.4 7.5 7.6
Sweet corn 3.8 5.4 6.1 6.1
Tomato 0.6 1.6 2.6 4.5
Wheat 0.8 1.4 1.7 1.7

CLIMATIC ELEMENTS

Climate varies with latitude, altitude or elevation from the sea level, topography and
geography. It ranges from near uniformity in the tropics to wide seasonal variations in
high latitudes (temperate areas). The climate of a place may adversely affect the crop
growth and development processes such as germination, vegetative growth,
reproduction, or seed development. Under extreme climatic conditions plant species
may not survive. Thus, climate is a major determinant of the geographic distribution of
both natural vegetation and cultivated crops. The effect of the weather on plant growth
and development is reflected on the plant diversity, considering the varying plants’
responses to weather fluctuations within a climatic type. Monteith and Ingram (1998)
identified the spatial distribution of climate, seasonal changes and global climatic
changes as the three major aspects of climatic variations affecting crop production.

Climate from the context of crop production is classified into: macroclimate and
microclimate. Macroclimate is at large or geographical scale that encompasses
thousands of square kilometers having a unified picture of the climatic components that
when placed together are not affected by the most of disturbances near the ground. The
determinants of the macroclimate are: solar radiation; wind; precipitation; Coriolis force
(changes in air movements due to deflection in earth’s rotation); effects of latitude, land
and water; maritime climate, topography, rainshadow effect (rains in the leeward side of
mountains --- opposite of orographic effect), etc.

Microclimate on the other hand, is a small scale climate that differs from the surrounding
area. It has no exact limits, but can vary in height with reference to the biological object
of interest (Shaw, 1988). It may cover areas as small as a few square meters (a garden
bed) to as large as many square kilometers (a valley). Microclimate within a crop canopy
may influence the crop physiological and growth processes such as, photosynthesis,
respiration, translocation, evapotranspiration, and nutrient uptake and assimilation. It is
at this level that a crop could also influence microclimate through changes in light
quantity and quality down the crop canopy, alteration of humidity and temperature at
particular layers of the crop canopy, etc. Microclimate can be modified with management
practices, such as: i) plowing, changing planting patterns or changing crop covers that
may alter the radiation properties of the surface; ii) drainage, irrigation or shaping the
surface that may change the water balance; and iii) addition or removal of windbreaks
that may change wind flow pattern.

Climate in general is an interaction of solar radiation, temperature, precipitation (rainfall),

atmospheric humidity and air movement (wind). These factors are aerial in nature and
influence the soil that compounds the effect on the plant. The distinction between climate
and soil as separate components of the environment of plants is not an absolute one.
Climate is defined as long-term averages of various observed parameters, such as
temperature, precipitation, and radiation, while weather refers to short-term events and
fluctuations such as precipitation or maximum temperature on a daily or weekly scale
(McKeown et al. 2006). The dependence of crop productivity or yield on climatic factors
involves: the dependence of yield in different places on climate, and the dependence of
yield in any one place on weather.

Solar Radiation

The amount of solar radiation that reaches the outer limits of the atmosphere, as
measured on a surface held perpendicular to the sun's rays, is 2 cal cm -2 min-1. This
value is called the solar constant, which fluctuates by about 15%, throughout the
year. Only part of the solar energy reaching the outer limits of the earth’s atmosphere
reaches the surface of the earth. The remainder is partly absorbed and partly
reflected by the various components, such as water droplets, clouds, dusts and
various gases present in the earth’s atmosphere. About 46% of the sun’s energy
reaches the earth’s surface (Figure 38). Only about 1% of solar radiation reaching
the crop canopy is utilized for photosynthesis and other metabolic processes in
plants.
Figure 38. Distribution of solar radiation within the atmosphere and earth interface.
(Source: physicalgeography.net)

There are three aspects of irradiance (rate at which a surface absorbs radiation,
expressed in Watt/m2) that are important to plants, namely: intensity (usually
expressed in foot candles or lux); duration or daylength (expressed in hours/day);
and wavelength (measured in Angstroms or nanometers or identified by its color).

The atmosphere acts as a regulator of solar radiation, wherein it filters the cosmic,
gamma, and X rays to reach the earth (Evans, 1973). The ultraviolet radiation that
reaches the earth’s surface is likewise toned down by the atmosphere at tolerable
levels by the plants. Infrared radiation (higher-than-visible wavelength) has thermal
effects on plants. In the presence of water vapors, this radiation does not harm
plants, although it provides the thermal energy to the plant environment. The third
spectrum, lying between the ultraviolet and infrared, is the visible part of solar
radiation and is referred as light.

Light denotes a range of electromagnetic radiation perceivable by the human eye.

With reference to plants or crop, light can also refer to a wider range of
electromagnetic radiation (Figure 39). The wavelength of visible light approximately
ranges 380-800 nm. This segment of solar radiation plays an important part in plant
growth and development through the processes of chlorophyll synthesis and
photosynthesis and through photosensitive regulatory mechanisms such as
phototropism and photoperiodic activity. Visible light is fundamental to plants
because it corresponds roughly to the photosynthetic active radiation (PAR), which is
in the range of 400-700 nm. Light wavelength other than PAR is also important to
plants. For instance, far red light (700-800 nm) is associated with morphogenesis
 (e.g. germination and flowering), while ultraviolet (UV) light can contribute to the
additional plant heat load or may have damaging effect on the plant, particularly in
hotter environments. It is considered that electromagnetic radiation between 300 and
1000 nm has some biological implications. This range of wavelengths is called the
biological window of light.

Figure 39. The solar radiation emitted by the sun, the amount incident to the earth
surface, and the composition of solar radiation based on wavelength.
(Source: learner.org)

Light has a direct effect on leaf and canopy photosynthesis (photo-energetic effect).
The total dry matter produced by a crop is closely related to intercepted light. The
amount of light received should be above light compensation point (wherein
photosynthesis is equal to respiration) before plants can grow. Light also affects the
development of plants (photo-cybernetic effect). Unlike in photoenergetic effect
however, light levels needed to cause a response are not high but more of a function
of light quality (wavelength).

While extremely low light is detrimental to plants in general, some crops do not
require high light intensity and they can grow well under shade (sciophytes).
Sciophytes have low light saturation point, which is a certain level of light absorbed
by plants above which photosynthesis or dry matter production is not increased. For
instance, many ornamental plants require subdued light to survive. On the other
hand, some crops would require high light intensities to reach their saturation points
(heliophytes). Generally, C3 plants have higher light saturation points (at full
sunlight), while C4 plants have lower light saturation points (at 1/3 full sunlight).
However, C3 plants have lower productivity than C4 plants in terms of growth rate,
photosynthesis and dry matter production under non-limiting light conditions.
 Not all wavelengths of light are equally effective in some plant physiological
processes. Plant response as conditioned by daylength is termed as photoperiodism
or photoperiodic response. In photosynthesis the red and blue wavelengths are the
most effective, but in photoperiodism the far red (dominant under dark condition) and
the red (dominant under lighted condition) wavelengths are the most effective.
Daylength or the duration of the light period determines flowering of photoperiodic
plants. Majority of plants show photoperiodic sensitivity for flowering.. Based on the
flowering response to daylength, plants are classified as short-day, long-day, and
day-neutral plants. When other environmental factors are not limiting, photosynthesis
increases with longer duration of the light period (Salisbury, 1981).

Plants can adapt to light intensities (at varying thresholds) from molecular to
morphological levels. Under changing light conditions, extermely high or low light
intensities coupled by other stress (water, temperature, etc.) may stimulate the
adaptive response in some plants for their survival. While light intensity and quality
(wavelength) can be altered under sheltered or covered growing structures to suit the
light requirement of particular crops, this is not economical in field-grown crops.
Manipulation of light quantity and quality in field-grown crops could be done through
modification of plant spacing or population density, planting orientation, cropping
pattern or changing crop covers that may alter the radiation properties of a surface.

Temperature

Temperature is a reflection of the heat energy intensity. Physical and chemical

processes that control biological reactions within plants are governed by temperature
(Mavi and Tupper, 2004). Plants cannot maintain their cells and tissues at constant
optimum temperature. Metabolism, growth and development are affected by changes
in environmental temperature. The complexity of the thermal environment is matched
by the complexity of plant responses to temperature.

Temperature of the environment is primarily dependent upon solar radiation. Vertical

rays are more energy efficient/unit area irradiated than oblique rays such as those in
the polar regions. Temperature is also dependent upon: i) surrounding land masses
or bodies of water; and ii) altitude. For every 100 m rise in elevation, there is an
about 0.6°C decrease in temperature.

The temperature of a plant or plant community is determined by the following: i) time

of day due to regular diurnal variation of solar elevation; ii) month of the year due to
regular seasonal variation; iii) cloudiness, wind velocity, and origin of the air mass
which cause irregular short-term variations; iv) position in the canopy which is
apparent in sun and shade leaves; v) height above the soil surface; vi) canopy
characteristics such as leaf shape dimension; and vii) soil surface characteristics
which are associated with energy exchanges between the soil, plant and the
microenvironment of the plant.

Absorbed energy by the plant is usually utilized for metabolic processes and heating
or warming of the plant. Excess heat if not dissipated by leaf or plant will result to rise
in leaf or plant temperature. Considering the energy balance, leaf or crop canopy
temperature is not changed if the energy absorbed by the leaf (Q abs) is equal to the
energy is equal all to the sum of energy lost by re-radiation/emission (Q rad),
convection (Q conv) and transpiration (Q trans). When Q abs < Q rad + Q conv + Q
trans, the leaf will be cooled down. When Q abs > Q rad + Q conv + Q trans
however, the leaf temperature will rise. Environmental variables affecting leaf or
canopy temperature are: radiant flux densities, air temperature, humidity and wind
velocity. Plant characteristics affecting leaf or canopy temperature are: leaf radiative
properties (e.g. reflection coefficient, emissivity), leaf dimension, leaf shape and
angle, stomatal responses, and height above the soil surface.

Plants vary widely in their adaptability to temperature but within species, they are
restricted to narrow limits. Biological activities, in general are limited at the lower
temperature by the freezing point of water, and at the upper range by the thermal
denaturation of proteins. The three cardinal temperatures affecting plant processes
are: i) minimum temperature (that temperature below which the velocity of the
reaction becomes zero); ii) optimum temperature (temperature where the velocity of
the reaction is at maximum); and iii) maximum temperature (that temperature above
which the velocity of the reaction becomes zero) (Fig.40).

Figure 40. Generalized diagram of the response of plant growth rate to the ,
three cardinal temperatures.

Crops may be classified according to temperature requirement, such as, cool-season

crops, and warm-season crops. Other classification such as, tropical and sub-tropical
are also used. Temperature affects crops growth and development or productivity in
general via its effect on: photosynthesis, respiration, nutrient uptake and
translocation, transpiration and other metabolic processes in crops. The net
photosynthesis for instance, follows a response curve based on the three cardinal
temperatures. Differential optimum air temperatures in crops with contrasting thermal
environments has been observed, such as: 20-30oC in temperate wheat (C3), and
30-40oC in tropical maize (C4)(Wardlaw, 1979; Fitter and Hay, 1999)
Photosynthesis and respiration do not respond to temperature in the same way.
Gross photosynthesis in temperate species ceases at temperature just below 0°C
(minimum) and above 40°C (maximum), with the highest rates achieved within 20-
35°C (Figure 41). Respiration rates on the other hand, tend to be low at below 20°C
due to thermal disruption of metabolic control and compartmentation at higher
temperatures causes respiration to rise sharply up to the compensation temperature
(Figure 42).

Figure 41. The temperature relations of net photosynthesis in three species of

the Gramineae from contrasting environments: a) Chionochloa spp.
Tussock grass (alpine C3 photosynthesis), b) wheat (temperate crop,
C3) and c) maize (subtropical crop, C4). The horizontal bars indicate the
optimum ranges (adapted from Wardlaw, 1979).
Figure 42. Schematic representations of plant responses to temperature
(Franzluebbers, 2006 --- from encyclopedia of soils).

Thermoperiodism is the response of plants to diurnal or seasonal changes in

temperature. Its effect on the growth and development of plants is apparent at
species-specific levels. Crops such as soybean, maize, tomato, potato, and mango
 are classified as thermoperiodic, while wheat, peas, and cucumber are classified as
non-thermoperiodic.

Growing degree-days (GDD), sometimes termed as heat units, effective heat units,
or growth units, highlights the association of plant growth, development, and maturity
to air temperature. Degree-day units are used in agronomy to estimate or predict the
length of the different phasic of development in crop plants (Bonhomme, 2000). The
GDD concept assumes a direct between plant growth and air temperature which
starts with the assumption that the growth of a plant is dependent on the total
amount of heat to which it is subjected during its lifetime. A degree-day, or a heat
unit, is the departure from the mean daily temperature above the minimum threshold
(base) temperature. This minimum threshold is the temperature below which no
growth occurs. The threshold temperature ranges 4.5-12.5°C in majority of tropical
plants, and generally lower in temperate crops. (Source)

In general, GDD concept can be applied on the different aspects of crop production:
i) as a predictive tool in determining suitability of certain crops to a particular
environment; ii) prediction risk associated with crops in specific locals; iii) research
such as, determination of sowing date and crop growth and productivity.

Plant growth and crop yields depend on mean temperature and temperature
extremes (Rotter and Geijn, 1999). Under current field conditions, higher
temperatures are associated with higher radiation levels and higher water use. A rise
in temperature may have various implications under varying climatic environments.
At higher latitudes (with reference to equator), a rise in temperature may prolong the
growing season. Higher temperature in mountainous areas will allow for more plant
growth. Plant growth is inhibited at temperatures above the optimum. Day air
temperatures within 15-25oC, and night temperatures of about 10oC or lower, are
considered optimal for plant growth in general (Schulze et al., 2002). Psychrophiles
are organisms that are adapted to cold temperatures, while thermophiles are
organisms requiring high temperature, but most organisms are mesophiles (Hopkins,
2006).

Precipitation

Precipitation or rainfall occurs either as a liquid (rain, drizzle, fog or mist) or solid
(snow, hail and sleet). It is a source of almost all available fresh water, and is very
important in crop production. In the tropics, rainfall is the more important and rarely
occurs in solid form.

Rain formation requires: i) high relative humidity (RH), ii) sufficiently low temperature
(below condensation point), iii) condensation nuclei, and iv) sufficiently low
atmospheric pressure. The process of precipitation consists of the cooling of the air
below its condensation point. Water vapor in the presence of condensation nuclei,
forms water droplets or ice crystals. These increase in size until they become too
heavy to be suspended in air. They then fall as rain or snow. The dominant factor in
the type and distribution of precipitation is the uplift of moist air masses in which
water condenses and falls as precipitation. This uplift is aided by the following
factors: i) convection currents: heated moist air rises and the process of rising
causes cooling (adiabatic cooling) – condensation and precipitation follow; ii) the
 meeting of air masses of different temperature and humidities: when warm moist air
is lifted above cool dense air, the moist air cools and precipitation occurs. This is
known as the frontal effect; iii) the moist air comes across a relief barrier, e.g. a
mountain range: the air mass rises and cools bringing precipitation on the windward
side as relief or orographic rain.

Cloud seeding is a practice done to force the occurrence of precipitation in an area

whether for agriculture or other uses (Figure 43). Cloud seeding is the process of
spreading dry ice (cardice or solid form of CO2) or silver iodide (AgI) aerosols into the
upper part of clouds to stimulate the precipitation process. Since most rainfall starts
through the growth of ice crystals from super-cooled cloud droplets (droplets colder
than the freezing point) in the upper parts of clouds, the AgI particles initialize the
growth of new ice particles
(http://www.weatherquestions.com/What_is_cloud_seeding.htm).

In 1946, Dr. Vincent J. Schaefer observed that ice crystals are formed when cold
water contacts particles of dust, salt, or sand in a warm chamber.  The ice crystals
provide a nucleus around which water droplets can attach. When the droplet
becomes large enough, it falls as rain.  This is the "cold rain" process or "static
method".  Another process is the "warm rain" process that usually involves clouds in
tropical regions that never reach the freezing point.  In these clouds, raindrops form
around a "hygroscopic nuclei", a particle that attracts water such as salt or dust. 
Small droplets collide and coalesce until they form a drop large enough to fall.  To
stimulate the "warm rain" process, calcium chloride (CaCl 2) is usually used to provide
the nucleus for raindrop formation.  On the other hand, the "cold rain" process uses
CaCl2 as a nucleus because its structure is very similar to ice crystals.
(http://www.edwardsaquifer.net/images/cloud_seeding.gif).

Figure 43. The process of cloud seeding using static method. (Source:
http://www.edwardsaquifer.net/images/cloud_seeding.gif)
Topography influences the amount and distribution of rainfall, while air circulation
patterns affect the seasonal distribution of precipitation. Mountain ranges present
barriers to cloud movement, causing them to rise to higher elevations with generally
colder temperatures. This cause the vapors to condense and water to fall on the
windward side as clouds pass over, leaving the leeward side relatively dry.

Moisture influences the growth and development of plants. Water has many roles in
plants, namely: i) it serves as a reactant in many biological reactions; ii) it enters into
the structure of many biological molecules; iii) it serves as a medium for transport of
nutrients and other substances in the plant; and iv) it helps regulate favorable plant
temperature.

Based on moisture requirement, plants are divided into three categories, namely: i)
xerophytes (desert plants), ii) hydrophytes (aquatic plants), and iii) mesophytes (land
plants) that include most of the economically important plants. Moisture also
influences the phytogeographic distribution of plants. Water deficiency in crops
influences the level of productivity and yield of crops. Major plant processes affected
are: i) photosynthesis, ii) respiration, iii) carbohydrate metabolism, iv) assimilate
translocation, iv) dry matter partitioning, and v) nutrient uptake and assimilation.

The effect of drought on photosynthesis for instance is via reduction of leaf area,
stomatal closure, decrease in chlorophyll in mesophyll cells and bundle sheath cell
chloroplast to photosynthesis. Initially, respiration increases as a result of water
deficit due to increased starch hydrolysis to sugar that provide more substrates for
respiration. Respiration rate decreases with increasing degree of water deficit in
plants. Carbohydrate metabolism is greatly reduced in water-stressed leaves due to
reduction in α-amylase. In cotton, reduction in carbohydrate synthesis and starch
synthesis were observed to be about 50% and 66%, respectively.

Translocation of photoassimilate from the leaves is reduced by water deficiency in

the leaf during daytime, although it is increased during night time (corn & soybean).
The reduction in translocation is due reduced source or sink activity rather than direct
effects on the capacity of conducting system. The partitioning of photosynthates can
be changed by drought. This is shown by the reduction in quantity of economic yield
in relation to total biological yield (harvest index). This is exemplified by the abortion
of flowers, fruits, seeds and reduction in number and size of seeds due to drought
stress.

Ion uptake is not seriously affected under moderate water deficit conditions,
although under severe drought conditions ion absorption and movement is reduced
due to restricted movement of minerals in drying soils and from cell to cell upon
uptake. Under water stress condition, nutrient assimilation such as to amino acids
and proteins is adversely affected by drought stress.

In general, drought stress reduces crop productivity due to sequential disruption of

metabolic processes, i. e. from the sequestration of inputs from the the air and soil
for photosynthesis and other related physiological processes up to dry matter
partitioning and is apparently reflected in the level of economic yield produced.
Humidity

Humidity refers to the amount of moisture in the air. Water in the atmosphere exists
in three main states: i) water vapor; ii) cloud droplets or sometimes frozen crystals;
and iii) liquid or sometimes frozen raindrops
(http://www.wildwildweather.com/humidity.htm). Relative humidity on the other hand,
is the measure of the amount of water or moisture in the air as compared to the
amount of water the air can absorbed. When air cannot absorb anymore moisture or
fully saturated the relative humidity is 100%
(http://www.businessdictionary.com/definition/relative-humidity.html ).

The effect of humidity on crop productivity could be viewed through its effect on
photosynthesis. As reviewed by Zhang et al. (1996), the humidity of the air
surrounding a leaf affects photosynthesis by altering stomatal conductance. In many
species, stomata close in response to increased leaf-to-air vapor pressure difference
(VPD), whereby CO2 diffusion from the ambient air to intercellular space of the leaf
decreases. Photosynthesis may be less affected than stomatal opening by low
humidity if mesophyll conductance is not altered. Mesophyll conductance is the
reciprocal of another resistance encountered by CO2 diffusion from intracellular
space to the carboxylation site. The magnitude of humidity response of
photosynthesis is dependent on species, growing conditions such as plant water
status and light intensity. Many researches have been conducted on humidity effect
on photosynthesis and other physiological processes.

Transpiration rate decreases proportionally with the amount of humidity in the air,
considering that water diffuses from areas of higher concentration to areas of lower
concentration. When the air spaces between the mesophyll cells in a leaf are
saturated with water vapor, and the air outside the leaf is likewise saturated (e.g.
during rainy season), there is a narrow gradient that results in a slower transpiration
rate. Conversely, when the air outside the leaf is relatively dry, the gradient becomes
steep (e.g. during dry season), the rate of transpiration would be relatively high.
(http://wiki.answers.com/Q/How_does_humidity_affect_transpiration).

Table 19 shows that change in RH is just as critical as change in temperature. At

100% RH, the vapor pressure deficit (VPD - the difference between the amount of
moisture in the air and how much moisture the air can hold when it is saturated)
remains zero at all temperatures. At higher VPD between the air and the leaf, there
is greater rate of water loss from plants due to transpiration.
 Table 19. Relationship between temperature and relative humidity to the
vapor pressure deficit (Source?).

Temperature (oC) Relative Humidity (%) Vapor Pressure Deficit (Pa)

100 0
90 61
0
70 182
50 304
100 0
90 122
10
70 367
50 613
100 0
90 232
29
70 700
50 1,166

The importance of humidity in crop production, aside from its direct effects on plant
growth, is its effect on disease and pest incidence. Diseases like powdery mildew
require certain humidity conditions for growth. Humidity is also important as regards
the postharvest behavior of commodities. For instance, very dry atmosphere is
conducive to transpirational loss of water from harvested horticultural products,
hence wilting may occur. For agronomic crops, high humidity is not conducive to
grain drying, such that mold buildup and aflatoxin production in certain commodities
may be enhanced.

Wind

Air circulation in the atmosphere results from the sun's radiation falling more directly
on the earth's tropical regions than on the polar regions. The warmer air at the
equatorial regions rises and flows towards the poles, cools and sinks as cold polar
air, and then returns towards the equator as ground flow. The direction of the ground
flow is affected by several factors, namely: i) the earth's rotation or spin from west to
east; ii) the effects of seasons caused by the earth's inclination on its axis; iii)
difference in heating and cooling between land and water masses; iv) difference in
earth elevation; v) effects of mountain ranges; vi) local storms resulting from
interactions between warm and cold air masses. The final result of these interactions
is the establishment of regions, some large and small, each with a different climate.
Sometimes areas with varying climatic patterns are at very short distances apart.

There are annual and diurnal (daily) patterns of wind velocity. On the annual scale,
fluctuations are related to the movement of pressure systems within a year.
Variations on the diurnal scale on the other hand are closely related to radiation input
within a day, wherein greater radiation input results in greater convective influence
and higher wind speed. While radiation can modify wind movement, wind in turn can
modify the temperature of the plant or crop canopy. Wind influences crop production
via its physiological and mechanical impacts on crop growth and development. The
 major physiological processes affected are: transpiration and photosynthesis.
Transpiration increases with wind speed (disruption of boundary layer). Hot wind
accelerates the drying of the plants by replacing humid air by dry air in the
intercellular spaces. Wind also increases turbulence in the atmosphere and
availability of CO2, and thereby increased photosynthesis. Beyond a certain wind
speed, the rate of photosynthesis becomes constant.
(http://agritech.tnau.ac.in/agriculture/agri_agrometeorology_wind.html). Moreover,
wind can affect spore dispersal of disease causal agents. The effect of wind may
vary at different speeds such as shown in the matrix below (Table 20).

Table 20. Effects of wind on plants at varying speed.

Wind Speed (km/hr) Affected Part / Process

  Pollination – sterility due to loss of pollen
Inflorescence – flower drop
> 30 Fruit – fruit drop
Leaf – effect on functional on leaf area
  Crop lodging and grain shattering
40 – 56 Severe damage on crown
> 65 Severe damage on whole plant / uprooted

PHILIPPINE CLIMATE

Philippines is a tropical country which is characterized having a relatively high

temperature, high humidity and abundant rainfall. Temperature, humidity and rainfall are
the most important elements of weather and climate that mainly affect crop production in
the whole archipelago. Philippine Atmospheric Geophysical and Astronomical Services
Administration (PAGASA) is responsible for monitoring these climatic and weather
elements in the Philippines.

Temperature

The mean annual temperature is 26.6 °C based on the average temperature

readings among the weather stations in the country except for the province of
Baguio. The coolest months occurs in January with a mean temperature of 25.5 °C
while the warmest month falls in May with a mean temperature of 28.3 °C. There is
essentially no difference in the mean annual temperature of places in Luzon, Visayas
or Mindanao measured near sea level (PAGASA).

Humidity

Humidity refers to the amount of moisture content of the atmosphere. Having a

relatively high temperature and being surrounded by large bodies of water, the
Philippines has a high relative humidity. The average monthly relative humidty in the
country varies between 71% in March and 85% in September (PAGASA).
Rainfall
 Rainfall is the most important climatic element in the Philippines, especially in crop
production. Rainfall distribution all over the country varies, depending upon the
direction of the moisture-bearing winds and the location of mountain systems that
highly affects rainfall. The mean annual rainfall of the Philippines varies from 965 to
4,064 millimeters annually (PAG-ASA).

Climate Types

Corona’s type of climate classification was proposed by Fr. Corona using rainfall
data from 1951 to 1980. This type of classification of climate is based on seasonal
distribution of rainfall, considering the most important rain periods in the country. It
also considers a dry month as a month with less than 50 mm of rainfall. Using
average monthly distributions of rainfall at different locations, four general types of
rainfall in the Philippines were defined. Based on the distribution of rainfall, four
climate types are recognized, which are described in Figure 44.

Figure 44. Climate Map of the Philippines based on the Modified Corona’s
Classification (Source: PAG-ASA)

SOIL FACTORS
Soil Components

The soil is composed of three phases, namely: i) solid phase – consist of all the
organic and inorganic materials. This phase normally comprise about 50% of the
total soil volume (about 45% mineral, 5% organic matter); ii) liquid phase – is made
up of the soil moisture or soil solution. The liquid phase is about 20-30% of the total
volume; and iii) gaseous phase – soil air comprise the remaining 20-30% of the soil
volume. This phase contains all the gases, particularly CO 2, O2 and N2 (Cosico,
2005). Figure 45 shows the composition of soil.

Air
25% Mineral
45%
Water
25%
OM
5%

Figure 45. Soil composition by volume.

Soil Physical Properties

The soil physical properties that affect crop production via nutrition and water
relations in plants are: i) soil texture, ii) soil structure; iii) soil depth or horizon; and iv)
soil topography or slope.

Soil texture - refers to the size and relative proportion of the various size groups in a
given soil. Based on the International Soil Science Society (ISSS), the classes of
texture from the largest to the smallest size are: sand (2-0.02 mm), silt (0.02-0.002
mm), and clay (< 0.002 mm). There are variations in each class from course to fine
as per USDA, namely: very course sand (2.0-1.0 mm), coarse sand (1.0-0.5 mm),
medium sand (0.5-0.25 mm), fine sand (0.25-0.10 mm) and very fine sand (0.1-0.05
mm). Most soils are mixtures of the various classes of particles. The guide in
determining the textural classification of soils is shown in Figure 46. If a soil consists
of at least two classes of particles it is called a loam. The name of the loam depends
on the dominant particle, e.g. sandy loam, clay loam, gravel loam, silty loam, etc.
Table 21 shows samples of soils of varying texture. The textural properties relevant
to crop production, particularly cation exchange capacity (CEC), nutrient holding
capacity and tillage, are presented in Table 22.
Figure 46. Textural triangle showing the percentage of sand, silt and clay at varying
textural classes (Foth, 1990).

Table 21. Textural classification of different types of soil materials.

Grade Type of Material

Fine Texture Clay, silty clay, clay sand or sandy clay
Medium Texture Loam, silt loam, and clay loam
Course Texture Gravelly sand, course sand, sandy loam, course sandy loam etc.

Table 22. Some soil textural properties relevant to crop production (Source).
Textural Class
Soil Property
Sand Silt Clay
Aeration excellent good poor
Cation exchange low medium high
Drainage excellent good poor
Erodilibility by water easy moderate difficult
Permeability by water fast moderate slow
Tillage easy moderate difficult
Water-holding capacity low moderate high
Nutrient-holding capacity low moderate high
 Soil structure - refers to the arrangement of the soil particles into groups or
aggregates. There are four main groups of structural shapes found in soils. These
shapes are described as plate-like, prism-like, block-like, and spheroidal (round)
(Figure 47). The distribution of these structures is distinct across the soil horizon
(Figure 48).

Figure 47. Different soil structures.

(Source: www.soils.umn.edu/.../soil2125/doc/s3chap1.htm)
Figure 48. Structure of the horizons of a forest soil with an argillic horizon (Miami
loam, an Alfisol), scale in centimeters (Foth, 1990).

Crop growth requires a good soil structure as it affects: i) the water penetration and
drainage, ii) the supply and ease of water uptake, iii) the uptake of nutrient elements,
iv) aeration, v) the way in which the plant root grow, vi) tillability of the land, and vii)
ease of emergence of germinating seeds sown in the field.

Topsoil depth - based on Figure 49, majority of the soil nutrients are obtained in the
topsoil (A horizon, a certain depth that occupies the plowed layer) and the E horizon
 (sometimes considered as A horizon based on the accumulation of humified organic
matter) of a soil. The subsoil (B horizon) is the storage zone for rainwater with
leached material from the upper horizons. This layer also contains the materials that
may have weathered at this layer. (source)

The depth, type, composition, and quality of the topsoil are very crucial in the
selection of crops to be planted in an area based on considerations such as: crop
rooting behavior (volume/depth), water table requirement and nutritional needs. Crop
productivity and topsoil depth interaction are crucial within the context of crop
nutrition and water management.

Figure 49. Characteristics of a soil profile.

(Source: www.soils.wisc.edu/courses/SS325/profile3D_3.gif)

Topography - is the physical configuration of the soil surface. Topography

influences drainage and runoff. Steep slopes cause erosion as water flows faster
downhill, leaving less to percolate into the soil. Erosion in turn affects the speed of
soil-forming processes. Leaching is either speeded up or retarded by topography.
Soils developed in humid regions of high rainfall and flat topography are often highly
leached and waterlogged, depending upon the internal drainage. Gentle slopes
covered with vegetation slow the water flow and allow more time for water to
percolate into the soil creating a well-defined profile. Rapid surface runoff causes
more erosion, and if vegetation is removed, even deeper gullies are cut into the
sloping land. Topography also affects air and soil temperature. On the average,
temperature decreases by 1°C for every 100 m of elevation for the first 10-15 km of
altitude. Thus, an increase in elevation may influence the kind of vegetation growing
in the soil as well as crop growth.
 Topography is a major determinant of the following: i) type of crops that will be
grown, ii) cropping patterns in a cropping system, iii) cultural/conservation
interventions to be imposed in a particular production system. (Source: Gomez,
multiple cropping book)

Chemical Properties

Cation and anion exchange capacity - the sum of the exchangeable cations in a
given weight of soil is called the cation exchange capacity (CEC), and is expressed
in me/100 g soil. In typical soils, CEC value may range from a low value of 10
me/100 g soil to a high value of 30 me/100 g soil (Cosico, 2005. Primer on Soil
Science. Agricultural Systems Cluster, UPLB. College, Laguna. 182 pp.). As soil
solids contain a net negative charge, the greater bulk of the adsorbed ions are
cations (whether from the soil or applied fertilizers). Soil CEC is important in crop
production through crop nutrition, particularly in the soil-holding capacity of nutrients
such as NH4+, and K+ from N and K fertilizers, respectively. Thus, nutrient losses due
to application fertilizers could be reduced by high soil CEC, while these are not yet
taken up by the crop.

Soil colloids also contain positive charges and consequently have the capacity to
adsorb anions, referred to as the anion exchange capacity (AEC). Although it
occupies a lot smaller volume than CEC (≈ 10%), soil AEC is also important in crop
production, particularly in the nutrient-holding capacity of soils for HPO 4-, and SO4-
from P and S fertilizers.

Soil pH - Technically, the term pH is the negative logarithm of the hydrogen ion
activity and a measure of the degree of acidity and alkalinity of the soil. On the pH
scale, 7.0 is neutral (number of H+ is equal to the number of OH-). Acidity is
associated with low pH while alkalinity is associated with high pH. Since the pH
values are based on a logarithmic scale, the acidity increases or decreases by a
factor of l0 for every unit change in the pH scale. Unlike cation exchange capacity,
pH is not a fixed characteristic of a soil. It varies over a period of time, depending on
circumstances or conditions. Values for pH vary considerably among soils ranging
from about 4.0 for an acid soil to l0.00 for alkaline soils.

Hydrogen ion activity (pH) has a direct effect on plant growth. It is important mainly
because of its effect on the availability of plant nutrients. The soil pH is also used as
indicators for the likelihood of occurrence of several soil associated problems: i) pH
below 5.0 - Al, Fe and Mn become more soluble and can become phytotoxic, while
Ca and Mo deficiency are likely to occur; ii) pH below 5.5 - Mo, Zn, K and S
deficiency are likely to occur; iii) pH above 7.5 - Al toxicity, salinity, Zn and Fe toxicity
are likely to occur; iv) pH above 8.0 - calcium phosphates, which are unavailable to
plants, are formed; v) pH above 8.5 - sodium level above normal, salinity problems,
Zn and Fe deficiency likely to occur.
Figure 50. Availability of minerals at different pH in a mineral soil (Taiz and
Zeiger, 2003).

Figure 50 shows the availability of minerals at different pH in a mineral soil. The

optimum soil pH considered for crop production is 6.5. Below 5, soil pH should be
increased by liming. Beyond 7.5, soil pH should be reduced by acidification through
the addition of sulfur or fertilizers with residual acidity like ammonium sulfate.

Soil organic matter – Soil organic matter consists of: i) raw plant residues and
microorganisms (1-10%); ii) active organic fraction (10-40%); and iii) resistant or
stable organic matter or humus (40-60%) (source). After complete decomposition of
the plant residues and active organic fractions, a complex amorphous, colloidal
substance called humus remains. Resistant to further decomposition, humus is the
material that helps improve soil structure, imparts the dark color to the soil mineral
fraction, and increases the soil's water-holding capacity and cation exchange
capabilities. In crop production, soil organic matter is important because of two major
reasons, namely: i) as a "revolving nutrient bank account", it serves as as storage of
nutrients; and ii) it improve soil structures.

As a storage of nutrients, organic matter serves as: i) a storehouse of plant nutrients

derived from recycled crop residues and manures that are released upon
decomposition; and ii) the stable organic fraction (humus) that adsorbs and holds
nutrients in forms available to plants. The rate of addition from crop residues and
manure in a production system must equal the rate of decomposition to maintain this
nutrient cycling in a system.
(Source: http://www1.agric.gov.ab.ca/$department/deptdocs.nsf/all/agdex890).

Philippine soils contain about 2-4% organic matter mainly on the surface and
decreases with soil depth. Organic matter contains about 5% N of which only 2% or
less is actually available for plant use. A reservoir of P, B, Zn and S exist in organic
forms.

Biological Component - the soil contain many living macroscopic and microscopic
organisms which could either be harmful or beneficial to plants. The macroscopic
organisms include earthworms, insects, mites, millipedes, moles, nematodes, slugs,
snails etc. Other organisms like Actinomycetes, algae, bacteria and fungi are also
present. Certain beneficial fungi live in symbiotic associations with plant roots: the
fungus/root association is called mycorrhiza. Soil organisms act both chemically and
physically. They digest crop residues and other organic matter enzymatically by
chemical action. Physically, they move the residues from one place to another,
mixing it with the soil, e.g. earthworms and other burrowing animals.

Soil microorganisms play an active role in soil fertility as a result of their involvement
in the cycle of nutrients like C and N. For instance, they are responsible for the
decomposition of the organic matter entering the soil. Soil microorganisms such as
mycorrhizal fungi can increase the availability of mineral nutrients such as P for plant
uptake. Other soil microorganisms may increase the amount of nutrients in the soil.
Nitrogen-fixing bacteria can transform N2 gas present in the soil atmosphere into
soluble nitrogenous compounds utilizable by plants. The microorganisms that
contribute to the improvement of soil fertility are sometimes called biofertilizers.
Nitrogen fixation, sulfur oxidation, and nitrification are processes carried on by soil
bacteria essential to higher plants. For instance, Rhizobium, a symbiotic nitrogen-
fixing bacterium found in the root nodules of legumes helps in increasing the N
content of the soil upon death and decomposition of the legume plant. Elemental
Sulfur is not available to plants; it must first be oxidized to the sulfate form.
Autotrophic Thiobacillus bacteria bring about this transformation. Under certain
conditions, some autotrophic organisms may oxidize Fe and Mn to less available
form, thus preventing these ions from being taken up by plants at toxic levels.
Azospirillum, on the other hand, induces root growth leading to improvement of water
and nutrient uptake. These are currently used as microbial inoculants in crop
production. Other soil microorganisms produce compounds such as vitamins and
plant hormones that can improve crop productivity, and these are termed as
phytostimulators. On the other hand, some soil microorganisms are plant
pathogenic (disease-causing) in nature. However, some microorganisms present in
the soil are antagonistic to these pathogens, such that they may prevent crop
infection through competition for nutrients and/or production of inhibitory compounds
 such as secondary metabolites (antimicrobial metabolites and antibiotics) and
extracellular enzymes. Other soil microorganisms produce compounds that stimulate
the natural defence mechanisms of the plant and improve its resistance to
pathogens. These soil microorganisms are called biopesticides (e.g. biological
control). (Source: http://www.ucc.ie/impact/agri2f.html)

CLIMATIC AND EDAPHIC STRESSES

Drought

Drought is the insufficiency of rainfall/moisture which seriously affects plant growth

and development. The degree of drought occurrence is classified as: i) absolute
drought - 29 consecutive days without rainfall with at least 0.25 mm; and ii) partial
drought - 15 consecutive days without rainfall of at least 0.25 mm. The intensity and
duration of a drought determines its effects on crop. The occurrence of a short-period
of drought reduces crop yield. Long-term drought has more severe effects.

Drought is attributed to the depletion of water in aquifers (an underground bed or

layer of permeable rock, sediment, or soil that yields water) and lowering of the water
table (level at which the groundwater pressure is equal to atmospheric pressure).
Prolonged droughts may adversely affect crop production. Mitigating measures to
reduce the impact of drought include: irrigation, reclamation, hybridization,
reforestation and development of rangeland for grazing.

Salinization

Soil salinization is the enrichment of salts, mainly sodium chloride (NaCl) or sodium
sulfate (Na2SO4), at or near the soil surface which results in the formation of salt-
affected soil. Salinization causes: i) an increase in osmotic pressure which makes
water mobilization more difficult for plants; ii) toxicity of certain ions to plants (Cl -,
Na+, etc.); and iii) degradation of the soil (changes in structural state, reduction of
hydraulic conductivity, etc.) (http://www.ciseau.org/servlet/salinization).This can be a
natural process in salt marshes or in arid environments.

Primary salinization refers to salts formed by weathering of rocks or natural external

inputs. About 80% is accounted due to this process. If the salt accumulation results
from human activity linked to agricultural practices such as irrigation, it is termed
secondary salinization (Thomas and Middleton, 1993). In regions with insufficient
rainfall, crops need irrigation. Whenever this is done without proper management,
particularly without sufficient drainage, salts from the irrigation water accumulate in
soils.

Lahar

Lahar is a mudflow of volcanic material. Lahars may carry all sizes of material from
ash to large boulders and produce deposits of volcanic conglomerate. Lahars may
be the result of heavy rain pouring on loose ash material deposited in higher
 elevation and carried down in avalanche effect; or they may result from the mixing of
debris with river water, the flooding of ash by snow or ice melted by an eruption, or
the emptying of crater lakes onto loose material.
(http://www.britannica.com/EBchecked/topic/327929/lahar)

Lahar may affect crops through direct crop inundation or through alteration of soil
characteristic that are crucial to crop nutrition and water management.

Tsunami

Tsunami results from earthquakes and massive landslides, which cause seafloor
movement. Tsunami is also called seismic sea waves. It is sometimes incorrectly
termed as tidal waves, but tsunami is not caused by movement of the tides. Tsunami
can occur in any oceanic region around the world, but it is more common in the
region called Pacific Ring of Fire because of high frequency of earthquakes in that
area of the Pacific Ocean. (www.ussartf.org/tsunamis.htm). Tsunamis can have big
damages on coastal communities they hit.

El Niño and La Niña

El Niño is defined as a spectacular oceanographic/meteorological phenomenon that

develops in the Pacific, mostly off Peru. This is associated with extreme climatic
variability. It is characterized by weather disturbances or unexpected climatic
changes such as absence of rain during the rainy season, or the occurrence of
typhoons during the dry season. The term was first heard in 1892 by a scientist
named Camilo Carillo from fishermen in Port Paita of Peru with reference to the
warming of the ocean water that occurred around Christmas which they call
Corriente del Niño or Current of the (Christ) Child. La Niña refers to the cold phase
during which the equatorial central eastern Pacific sea surface temperatures are
generally below normal. La niña (which means a girl) is also sometimes referred to
as El viejo (the old man). The El niño-La niña pendulum-like swings from one
extreme to the other care called the El Niño Southern Ocillation (ENSO). This
phenomenon is a disturbance of global magnitude affecting both atmosphere and
ocean. (http://www7.nationalacademies.org/opus/elnino.html)

This phenomenon has the following characteristics: i) it occurs in the Pacific basin
every 2-9 years; ii) it usually starts during the Northern winter (December to
February); iii) once established, it lasts until the first half of the ensuing year,
although at times it stays longer; iv) it exhibits phase-locking to annual cycles,
meaning El Niño and rainfall fluctuations associated with it tend to recur at the same
time of the year; and v) it usually has a biennial cycle with El Niño events often
preceded or followed by La Niña. The destructive effect of this phenomenon on
agriculture could be due to prolonged drought, typhoons, and flooding in various
parts agricultural lands.

Greenhouse Effect, Ozone and Global Warming

 One of the most important factors in both short- and long-term climate changes is the
composition of the atmosphere, and how it affects the energy balance of our planet.
The solar radiation reaching the atmosphere is primarily visible light. About 30% of
this is reflected back into space by clouds, ground surface and atmospheric particles.
The rest of the radiation is absorbed by solids, liquid and gases
(http://www.uwsp.edu/geo/faculty/ritter/geog101/textbook/energy/radiation_balance.h
tml). The energy absorbed must eventually leave the earth in the form of infrared
radiation.

The emission of this radiation is hampered by certain traces of gas in the

atmosphere, CO2 being one of the most important. Other gases that function as so-
called greenhouse gases in the atmosphere include methane, N20,
chlorofluorocarbons (CFC-11 and CFC-12) and others such as halons, tropospheric
ozone (O3) and stratospheric water vapor. These gases transmit incoming solar
radiation, but absorb the outgoing terrestrial long-wave radiation, thus trapping heat.
With the rise in the concentration of these gases, more radiation will be absorbed,
resulting ion the warming of the globe.
(http://www.uwsp.edu/geo/faculty/ritter/geog101/textbook/energy/radiation_balance.h
tml)

Atmospheric CO2 concentration is one of the global factors heavily influenced by

human activity, with possible far-reaching consequences for the earth’s climate and
climate-related changes. The biogeochemical cycle of carbon which is the
fundamental element of living matter and all organic molecules, is tightly coupled
with the cycles of other elements, biomass production, and energy flow through
biosphere, all the constituents of this system being in dynamic equilibrium. One of
humanity’s greatest challenges for the future is to manage the global carbon
reservoirs and fluxes in such as way as to maintain this delicate balance, established
during hundred million years of earth’s evolution (Smith and Lytle, 1996).

BIOTIC FACTORS

Beneficial Organisms

Pollinators - Like gymnosperms, many angiosperms depend on wind to carry pollen

from one plant to another. Flowers of these plants usually have small sepals and
petals. Wind is a random pollinator. There is no way to predict the direction or
distance pollens will travel. To ensure that pollen grains reach another plant, wind-
pollinated plants produce enormous amounts of pollen.

Animals are also efficient carriers of pollen. Plants pollinated by this group of
organisms often provide food for some of these animals, such as, beetles, bees,
wasps, butterflies, moths, flies, birds and bats. Plants pollinated by this group do not
produce as much pollen and they have large brightly colored petals, may produce
nectar, and produce certain scents that advertise their pollen and nectar or evolved
structures that allow only certain pollinators to pollinate them. Honeybees, for
example, cannot see the red color so they are commonly found in yellow and blue
flowers. Unlike bees, hummingbirds can see red quite well so they are often attracted
to bright red flowers. While some insects are attracted to sweet-smelling scents, flies
 are attracted to flowers that smell like decaying meat. Moths are common pollinators
which are usually drawn to white flowers that open at dusk when moths are most
active. Moth-pollinated flowers have heavy scents and have petals that form a tube
with nectar at the base. Moths feed on nectar by inserting their long feeding tubes
into flowers.

Decomposers. The decomposers consist mostly of heterotrophic bacteria and fungi

that obtain energy by breaking down organic remains or products of other organisms.
The activities cycle simple compounds back to autotrophs. In a food chain, the
decomposers represent the end of the chain.

Eventhough grazing food webs are the most obvious pathways of energy flow, they
are not the most important ones except in some aquatic ecosystems. For instance,
even when cattles graze heavily on plants of short-grass prairies, they consume only
about 3% of the net primary production available. Far more important are the detrital
food webs, in which decomposers consume organic waste products and dead and
partly decomposed tissues. In land ecosystems, the participants include bacteria and
fungi as well as an assortment of invertebrate detritus feeders like earthworms,
millipedes and larvae of flies and beetles. These decomposers play a major role in
the cycling of nutrients in the soil.

Natural pest enemies. These consist of organisms that are non-destructive to crops
but helpful in keeping down the population of destructive insects and arachnid pests,
as well as pathogens. Examples of natural pest enemies are ladybird beetles that
feed on aphids, wasps that feed on the larval stage of some insects, and Bacillus
thuringiensis that attack the larval stage of Lepidopteran insects. Some carnivorous
mites, which do not feed on crops, feed on more destructive mites like the red spider
mite. Some fungi have been shown to control the nematode population in the soil.
The use of these natural pest enemies has already become an important part of
integrated pest management systems, with the goal of reducing the reliance on
chemical pesticides and maintaining the balance in the agroecosystem.

Pests

There are four categories of pests affecting crops, namely: insect pests, pathogens,
weeds, and vertebrate/invertebrate pests.

Insect pests. Insects, belonging to the largest group of organisms on earth, are
creatures whose bodies are divided into 3 segments, namely the head, thorax and
the abdomen. All insects have one pair of antennae in the head and six-legs
attached to the thorax. Insects may have one or two pairs of wings (Raven and
Johnson, 2006). Both the adult and the larval stage may infest plants as defoliators,
sapfeeders, ovipositors or rootfeeders. Defoliators, sometimes called leaffeeders,
feed on plant leaves. Any reduction in leaf area at different stage of the crop may
reduce photoassimilation, resulting in reduction in dry matter production or economic
yield. Sapfeeders generally consume the photoassimilates, thus reduction of
materials to be used by the plant sinks or growing areas. Sapfeeding may occur from
seedling to grain or fruit development in crops. Ovipositors generally lay their eggs at
various parts of the crop. The eggs hatch into larvae which subsequently feed on
plant parts and use various plant parts as shelter (e. g. bark, leaf. etc.) during pupal
stage to complete their development stage. Rootfeeders basically feed on the roots,
which results in reduction in water and nutrient uptake that eventually reduces dry
matter accumulation in crops.

Pathogens. These are organisms that incite diseases in plants. Pathogens can be
living (i.e., bacteria, fungi, nematodes, and oomycetes) and non-living (i.e., viruses
and viroids). Development of a disease caused by a pathogen generally follows
disease cycle. It decribes the different stages in the development of a disease. It
usually starts with the dissemination of the inoculum, followed by inoculation,
penetration of the pathogen into the host cells, infection, colonization, pathogen
reproduction and development of symptoms in the plants. There will be the
subsequent production of more inocula that could either immediately proceed to
another cycle of disease development or undergo a dormant period. The mode of
transmission of disease or dissemination of inocula could be via wind, rain splashes,
irrigation, insect vectors, animals, contaminated seeds, infected vegetative
propagules and infested planting tools. Bacterial-infected plants usually exhibit
water-soaked appearance, bad smell and presence of bacterial ooze. On the other
hand, fungal spores and mycelia are characteristic of fungal infections (Agrios,
2005).

Weeds. These are plants that grow where they are not wanted. They could be
classified as grasses, sedges and broadleaves. Crop species or varieties can also be
considered as weeds when they grow in areas where they are not supposed to
grow/not part of crop production system. Weeds compete for light, water and
nutrients. Yield reduction due to weeds could even exceed the destruction caused by
insect pests and pathogens, particularly when they dominate in the crop-weed
competition.

Vertebrate and invertebrate pests. Belonging to the vertebrate group are rodents,
birds, bats and monkeys (location-specific), while the invertebrates include the slugs
and snails.

Biotic factors – in the process of evolution, higher plants have acquired a number of
biosynthetic pathways through which a variety of secondary metabolites are
synthesized and accumulated. A wide array of these compounds is released into the
environment in appreciable quantities via root exudation and as leachates during
litter decomposition and is known to play a major role in allelopathy as
allelochemicals.

The term allelopathy, generally refers to the direct or indirect detrimental effect of
one plant (including microorganisms) on the germination, growth, or development of
other plants through the production of chemicals that escape into the environment.
Allelopathic interactions between plants have been implicated vegetation and weed
growth patterns in agricultural systems, and inhibition of growth of several crops.
Allelochemicals have been shown to decrease agricultural and selvicultural yields but
some allelochemicals can be beneficial as natural pesticides.

The indiscriminate application of synthetic pesticides has resulted to the build-up of

resistance of the target insects and pathogens, and causing severe environmental
pollution and health hazards. The use of allelochemicals from plants for this purpose
offers a more environmental-friendly alternative due to the fact that natural chemicals
are renewable and easily degradable. For instance, legume leaf mulches (Flemingia
 macrophylla, Gliricidia sepium and Leucaena leucocephala) are being used to
control weeds. Inula sp. exhibited anti-fungal activity against Helminthosporium
sativum and Fusarium oxysporum. Amaratnhus retroflexus, Chenopodium murale,
and Lepidium draba had allelopathic effects on vegetable crops and wheat. Mendoza
and Ilag (l980), for instance, suggested the possibility of using mimosine (a
prominent constituent of Leucaena leucocephala) as a biocide against fungal
pathogens.

Anthropogenic/Human Factors

The implementation of the various production activities are performed by humans

which unlike other animals has the ability to think and make management decisions.
As a social being he is also influenced by his physical as well as human environment
in which he interacts coupled with the influences of the traditions and customs of his
tribe, community or family.

On farm productivity, the study of Sumayao (l994) showed that while researchers
generally measure productivity in terms of biomass yield, yield of certain
components, economic yield or profitability, farmers and farm families have their own
ways of assessing productivity. They do not measure it solely in terms of market
values, but according to a wide range of indicators.

On crop integration a low-external input agriculture may be more appropriate. From

a development workers’ point of view, increasing productivity will increase farmers’
incomes by producing more for exchange or for the market. Some farmers may grow
other crops than rice not for market but for home consumption and for other reasons
like better use of free time. It is the use value, which is the orientation of PCP (petty
commodity production), rather than the exchange value, which determines how
farmers are likely to react to the technology. It has been shown that generally, when
farmers grow crops for home consumption, their cultural management practices do
not give impressive results, since they use a minimum of agricultural inputs. This
low-external-input-agriculture (LEIA) does not threaten to degrade the ecosystem,
and hence enables farmers to survive much longer with the resources that they
have.

On prospects of adoption, integration of crops after rice seems to have greater

prospects of adoption in households with labor surplus, e.g. farmers with several
children (Sumayao, 1994).

GENETIC FACTORS

Variety

Variety is used loosely in crop science to refer to a named group of plants within a
particular cultivated species which can be distinguished by a character or group of
characters. It does not conform to the usage in taxonomic botany and to avoid the
confusion that may arise, the term cultivar (short for cultivated variety) is often used.
If propagated by vegetative means they are often referred to as clones; if by seeds
 (under certain specified conditions) are called lines. A cultivar is often a distinct
variant selected by someone who believed it was uniquely different from any plant
already in cultivation. It is always capitalized but never underlined or italicized.
Sometimes it may be preceded by the abbreviation cv. or enclosed in single
quotation.

Selection Indices for the Major Crops

Selection is often a natural process of survival of the fittest, but deliberate selection
has led to many improvements in present-day crops. Crop improvement for higher
yields requires some knowledge on production physiology. Identification of
physiological components of yield and their genetic control will help in planning
crosses to maximizing segregation of genotypes possessing the physiological
complementation and balance required for high yield, thereby leading to a more rapid
and predictable yield improvement. A wide genetic variation exists in many of the
yield determining physiological characters. Without genetic variability. there is no
opportunity for genotype improvement by differential selection. The fundamentals of
cultivar improvement are collection of germplasm, generation of genetic variability
(recombination, mutation, migration), genotype evaluation and selection, field testing
and varietal release.

Depending on the crop, there are indices used for selecting superior cultivars, In
most crops, indices generally include features related to: yield quantity and quality,
resistance to diseases, and postharvest characteristics. Some of the indices used for
specific crops in selecting superior cultivars are listed in Table 23.
Table 23. Some of the selection indices for selecting superior cultivars.

Crop C
Selection Indices
Classification rop
R Yield, growth duration, disease resistance (rice tungro disease, rice blast), pest resistance (brown
ice leafhopper)
C Yield, disease resistance (downy mildew, stalk rot), pest resistance (corn borer)
orn
S Root yield, starch content, disease resistance (feathery mottle virus, scab)
weet
Potato
Field Crops
W Yield, disease resistance (potato blight)
hite
Potato
S Yield, determinate growth, shattering characteristics
oybean
P Yield, kernel size, disease resistance
eanut
B Yield, fruit size, bunch size, plant height, uniformity in ripening, disease resistance (bunchy top,
anana sigatoka)
P Yield, fruit size, flesh color, seediness, fruit-bearing regularity, disease resistance (ringspot virus, crown
apaya rot)
D Yield, fruit size, flesh color, flesh taste and consistency, disease resistance (Phytophthora)
urian
Fruit/Plantation P Yield, fruit quality (size, shape and total solids), disease resistance
Crops ineapple
C Yield, nut size, rate of leaf production, crown (spherical)
oconut
C Yield (quantity and quality), size of fruit cluster, internode length (short), disease resistance (coffee
offee rust)
C Yield (quantity and quality), disease resistance (vascular streak, dieback), pest resistance (pod borer)
acao
Vegetable T Yield, disease resistance (bacterial wilt), tolerance to rain, fruit size and color, dry matter content (for
Crops omato processing of tomato paste), puffiness
E Yield, fruit quality (size, shape and color), disease resistance (bacterial wilt), pest resistance (fruit
ggplant borer)
G Yield, bulb size, pungency, total dry matter (for processing), disease resistance
arlic
 O Yield, bulb size, pungency, total dry matter (for processing), disease resistance, growth duration
nion
B Yield, fruit quality (flavor and fibrousness), disease resistance, postharvest handling characteristics
eans
S Yield, fruit quality (size, shape, color, mealiness), disease resistance
quash
C Yield, head quality (size and shape), disease resistance
abbage
C Yield, curd quality (size and color), disease resistance
auliflowe
r

Crop
Crop Selection Indices
Classification
Ornamental
Chrysanthemum (cutflower)color, long, straight ,and strong stem, floral display, disease resistance (white rust), pest resistance (leaf
Crops miner), long postharvest life
Clear color, long, strong and straight stem, resistant to blackspot and powdery mildew diseases, long
postharvest life (slow opener), not prone to bluing, long bud and urn-shaped flowers when
partially open, few thorns, dark green foliage
Anthurium Yield at least 6 flowers per plant per year, color uniform and clear, spathe with high gloss, not too ridged or
too smooth, heart-shaped, spadix slightly reclined and not extending beyond tip of spathe,
should sucker freely but not too much, size of inflorescence proportional to stalk, resistance
to bacterial blight and long postharvest life
Baby Aster Compact inflorescence, disease resistant, long postharvest life
Gladiolus Floret of clear color, good texture and placement, strong straight spikes, at least 1 marketable spike per
corm, rachis with at least 16 florets, good opening characteristics, good floral display, good
corm yield and resistant to Fusarium wilt
Dendrobium Orchid (cutflower)
Long flower sprays (at least 20”), adopted to a wide range of growing conditions, resistant of pests and
diseases (mites, thrips and soft rot), blooming period peaking at period of peak demands,
long vase life (at least 2 weeks), available in a variety of colors, large flowers (21/2 – 3”
flower spread), high yield (at least 12 sprays per year) bloom several times during the year,
and not prone to bud drop
Flowering Pot Plant Short propagation time, possible year-round production, flowering regulation by environmental manipulation,
dimensions relative to container (ideal dimension, height of plant relative to container no
more than 1.6 times the plant diameter as measured at the plant top), responsive to growth
regulators (e.g. dwarfing compounds), relatively resistant to pests and diseases, floral
qualities ad foliage qualities
 CHAPTER IV: SUSTAINABLE CROP PRODUCTION

MAN AND CROPS IN AN ECOSYSTEM

Definition of terms

Ecology – the study of the relationship between organisms and their environment
Ecosystem – a unit of the biosphere in which the community of organisms interacts with
the environment
Agroecosystem – a model for the functioning of an agricultural system with all its inputs
and outputs
Agroecology – the application of ecological concepts and principles to the study, design
and management of agricultural systems. By integrating cultural and
environmental factors into its examination of food productions systems, agro-
ecology seeks to evaluate the full effect of system inputs and outputs and to use
this knowledge to improve these systems, taking into account the needs of both the
ecosystem as a whole and the people within it
Agroforestry – a land use system in which woody perennials are deliberately used in the
same land management unit as annual agricultural crops or animal, either
sequentially or simultaneously, with the aim of obtaining greater outputs on a
sustained basis
Consumers - organisms that obtain nutrients from other organisms; also known as
heterotrophs or organisms that cannot synthesize their own food
Detritus feeders – a diverse assemblage of organisms ranging from worms to viruses
which live off the wastes and dead remains of other organisms
Decomposers – a group of decay organisms, mainly fungi and bacteria. These digest
organic materials by secreting digestive enzymes into the environment. In the
process, they liberate nutrients into the environment
Ecological pyramid – a graphical representation of the energy contained in succeeding
trophic levels, with maximum energy at the base (producers) and steadily
diminishing amounts at higher levels
Producers - are organisms, like green plants, that produce organic compounds from
inorganic compounds; also known as autotrophs

Man whether viewed as an individual or as a group of community is surrounded by

his environment and must invariably interact with it for the following: a) energy
supply, b) supply of materials and c) removal of waste products.

The term ecology is derived from the Greek word oikos, meaning house and -ology
to study. As used today, it is the science which investigates organisms in relation to
their environment.

The ecosystem concept is the basic functional unit of nature which includes both
organism and non-living environment, each interacting with the other and influencing
each other’s properties, and both necessary for maintenance and development of the
system.
 The fundamental steps in the operation of the ecosystem are: 1) reception of energy,
2) production of organic materials by producers, 3) consumption of these materials
by consumers and its further elaboration, 4) decomposition of organic compounds,
and 5) transformation to forms suitable for the nutrition of the producers.

The three fundamental concepts of productivity of an ecosystem are:

1) Standing crop – abundance of organism in the area expressed as number of

individuals, as biomass or energy content

2) Material removal – includes yields to man, organism removed from the

ecosystem by migration and material withdrawn as organic deposits

3) Production rate – is the speed at which growth processes is progressing

Each organism in an ecosystem has a habitat and a niche. The habitat of an

organism is its place of residence, that is, the location where it may be found, such
as “under a fallen log” or “at the bottom of a pond”. The niche of an organism is its
profession or the total role of the organism in the community. A description of an
organism’s niche includes its interactions with the physical environment and with the
other organisms in the community. One important aspect of niche is the manner in
which the organism acquires energy and chemicals. In fact, the entire ecosystem
has two important aspects: energy flow and chemical/nutrient cycling. These begin
when photosynthesizing organisms use the energy of the sun to make their own
food. Thereafter the chemicals and energy are used, some of it is lost as heat while
the solar energy are passed from one population to another as the populations form
food chains and food webs.

All the activity of life is powered by the energy of the sun, from the leaping of the
grasshopper to the active transport of molecules through membranes. Each time
this energy is used, some of it is lost as heat. But while solar energy is continuously
bombarding the earth and is continuously lost as heat, nutrients remain. They may
change in form and distribution, but they do not leave the world ecosystem and must
be recycled continuously.

THE FLOW OF ENERGY

Energy enters the biotic portion of the ecosystem when it is harnessed by the autotrophs
during photosynthesis. Primary productivity is the amount of energy that autotrophs
store in organic materials over a given period. It is extremely high in ecosystems such
as tropical; rainforests and estuaries.

Trophic levels describe the feeding relationships in ecosystems. Autotrophs are the
producers, the lowest trophic level. Herbivores which feed only on the producers occupy
the second level as primary consumers. Carnivores which feed on herbivores act as
secondary consumers or tertiary consumers or higher level consumers when they feed
on other carnivores. Omnivores are consumers that feed on both the producers and
consumers.
In general, only about 10% of the energy captured by organisms at one trophic level is
converted into the bodies of the organisms in the next higher level. The higher the
trophic level, the less is the energy available to sustain it. As a result, plants are more
abundant than herbivores, and the herbivores are more numerous than carnivores. The
storage of energy at each trophic level is illustrated graphically as an ecological pyramid,
Figure 51.

Figure 51. Ecology of practical energy transfer through a living system.

Feeding relationships in which each trophic level is represented by one organism are
called food chains (Figure 52). In natural ecosystems, feeding relationships are far more
complex and are described as food webs (Figure 53). Detritus feeders and
decomposers, which digest dead bodies and wastes, free the nutrients for recycling.
SUN PRODUCERS PRIMARY SECONDARY DECOMPOSERS
(Plants) CONSUMERS CONSUMERS

Figure 52. A simple terrestrial food chain.

Figure 53. Food web.

THE CYCLING OF NUTRIENTS

Figure 54 shows the cycling of nutrients. Energy enters the cycle through the producers
during photosynthesis. The primary consumers then feed on plants, the secondary
consumers feeding on the primary consumers and so on forming a food chain. As the
consumers at each trophic level respire, some of the energy is released to the
environment as heat.

Figure 54. Cycling of nutrients.

1) The carbon cycle

Figure 55 shows the carbon cycle. The reservoir of carbon is C0₂ gas, found in
the atmosphere and dissolved in the oceans. Carbon enters the producers
through photosynthesis. From the autotrophs, it is passed through the food web
and released to the atmosphere as C0₂ during cellular respiration.
 Figure 55. Carbon cycle (Encylopedia Britannica 2008).

2) The nitrogen cycle

Figure 56 shows the nitrogen cycle. Although the atmosphere is mainly nitrogen
gas (78%), producers are unable to use nitrogen in this form. It must be first
converted to ammonia (NH3) or nitrate (NO3-). Nitrogen is converted to ammonia
by nitrogen-fixing bacteria in the soil or in the root nodules of legumes. Other soil
bacteria convert ammonia to nitrates. Humans synthesize ammonia and nitrates
from nitrogen gas to manufacture fertilizers. Lightning, cosmic radiation and
meteor trails also provide high energy needed for nitrogen to react with oxygen
forming nitrites (NO2-) and nitrates. Nitrogen passes from producers to
consumers and is returned to the environment through excretion and the
activities of detritus feeders and decomposers. Some release nitrates, some
ammonia, and others convert nitrate back to nitrogen gas (N2).
 Figure 56. Nitrogen cycle (Encylopedia Britannica 2008).

3) The hydrologic (water) cycle

Figure 57 shows the hydrologic cycle. The hydrologic cycle involves the loss of
moisture from surfaces through the process of evaporation and from plants
through the process of transpiration. As water floats as vapour in the
atmosphere some of it is transported laterally to far distances. Under certain
conditions, the water vapour in the atmosphere returns back to earth during
precipitation either as liquid (rain) or as solid (hail, sleet or snow).

In general, these are the processes involved in the hydrologic cycle: evaporation,
transpiration, condensation, precipitation, run-off, infiltration, sublimation,
percolation and seepage.
 Figure 57. Hydrologic cycle.

4) Polluting, flooding and poisoning the environment

Pollution occurs when human activities produce more nutrients than the natural
cycles or local ecosystems could absorb. It also occurs when humans release
into the environment chemicals and other items injurious to life forms.

Overproduction of substances natural to ecosystems can disrupt their normal

function. One example is the release of large quantities of human and livestock
waste into bodies of water, causing eutrophication. Another is the excessive
release of carbon dioxide into the atmosphere through combustion of fossil fuels
and deforestation, which threatens a dramatic change in climate through the
greenhouse effect. A third is the production of large quantities of oxides of sulfur
and nitrogen through burning of fossil fuels and when these react with water lead
to the production of acid rain.

Mining and industrial processes have exposed natural ecosystems to substances

such as lead, asbestos, mercury and a wide array of synthetic compounds such
as pesticides and dioxin. These pose a threat to human health, as well as
disruption of natural ecosystems.
PRODUCTION SYSTEMS AND CROP MANAGEMENT

a) Lowland

Intensive cropping systems are usually concentrated on lands with adequate water,
naturally fertile soils, low to modest slope, and other environmental characteristics
conductive to high agricultural productivity. The best agricultural lands in most of the
humid tropics including the Philippines have been cleared and converted to high
productivity agriculture. High-productive technologies, if improperly applied can lead
to resource degradation through, for instance, nutrient loading from fertilizers, water
contamination from pesticides and herbicides and water logging and soil salinization.
Food needs require that these systems remain productive and possibly expanded in
area, but they must be stabilized through biological pest management, nutrient
containment and improved water management.

The dynamics of nitrogen transformation in flooded soil should also be understood

which could aid in better fertility management. Figure 58 shows the fate of nitrogen in
flooded soils.

Figure 58. Fate of nitrogen in flooded soils.

In the Philippines, approximately 50% of lowland rice fields are rainfed and the other
50% with adequate irrigation facilities. For the latter, it is often solely devoted to rice
culture while those that are rainfed areas, other crops like mungbean, corn,
vegetables, tobacco and sweet potato may be planted especially during periods of
extended drought.
 Among the practices geared to sustaining the productivity of lowland soils are proper
choice of plants, crop rotation, organic matter augmentation to improve water
movement through soil, aeration, water-holding capacity, soil aggregation and
hydraulic conductivity, and to decrease soil crusting and bulk density and hydraulic
conductivity. When using NH₄ form of N₂, deep fertilizer placement at the reducing
zone will minimize losses through volatilization. When organic matter in form of
residues is added to supplement nutrient sources, their value is increased if nutrient
release through decomposition and mineralization coincides with the crop nutrient
demand. Efficient use of plant nutrients and nutrient cycling can reduce the use of
fertilizers.

For rainfed lowlands planted to other crops other than rice, efficient water
management practices should be followed. When water deficit occurs during a
particular period of the growing period of a crop, the yield response to water deficit
can greatly vary depending on how sensitive the crop is at that particular growth
period.

In general, crops are more sensitive to water deficit during emergence, flowering and
early yield formation than they are during the early vegetative stages (vegetative
stage after establishment) or late growth period (ripening).

Among the recommended supplemental irrigation schedules for the following crops
are as follows:

Bean – water requirement should be satisfied during establishment period and

early part of the flowering period.
Corn – root zone should be wetted at or soon after sowing. Where rainfall is low
and irrigation water is restricted, irrigation scheduling should be based on the
need to avoid deficits during the flowering period, and also during yield formation.
If there is severe water deficit during flowering is unavoidable, water may be
saved during the vegetative period as wll as during yield formation.
Peanut – depending on the level of crop transpiration and water-holding capacity
of the soil, irrigation interval should vary from 8-14 days for sandy soils and up to
21 days for loamy soils, with shorter intervals during flowering when depletion of
available soil water should not exceed 40%.
Potato – when rainfall is low and supply of irrigation water is restricted, water
deficit stress could be avoided by providing irrigation especially during the
stolonization and tuber initiation growth period.
Soybean – supplementary irrigation is best applied during the flowering period.

b) Upland

In the Philippines, the uplands are the zone where both agriculture and forestry are
practiced on rolling to steep land, where slopes ranging upward from 18% (Ramos,
1991). Uplands comprise approximately 17.6 million hectares and cover more than
half (59%) of the country total land area, indicating that the Philippines is relatively
mountainous.

These sloping lands are under increasing population pressures as more people
move into these areas. An estimated population of 17.8 million now live in the
uplands. Some 8.5 million reside on public forest lands, including 5.95 million
members of the indigenous cultural communities and 2.55 million migrants from
lowland groups.

The uplands are important due to the following: (a) serve as vital support systems for
the downstream lowlands and aquatic areas (b) upland forest watershed provide
water to rivers and lakes for irrigation, hydropower and household use (c) water
carries decomposing organic matter to provide lowlands with nutrients through
surface run-off and leaching – replenishing soil nutrients and maintaining the soil’s
productivity (d) serve as abode of indigenous populations and displaced lowland
people (e) provide many plants and animals considered today as principal crops and
livestock for consumption and utilization of human (f) large gene pools still remain
unidentified which can be potential sources of genetic materials that can boost
productivity and sustainability in agriculture, forestry and medicine.

As the population of the Philippines surged, deforestation became a problem.

Statistics show that in 1969, out of the country’s total land area of 30 million ha, 16
million ha was covered with forests. By 1988, the forested area had dwindled to only
6.4 million ha or 20% of the country’s total land area. Each year between 1970 and
1980, about 300,000 ha of forests were converted to other uses, particularly
agriculture.

Many of the upland farmers are among the poorest members of the agricultural
sector. For those dependent on one-crop farming system, they experience
abundance after harvest but there are times when they neither have money nor food.
There is also declining farm incomes. In one area, corm production had dropped
from 3.5 MT/ha to about 0.5 MT/ha in just ten years. Yields of other crops had also
diminished to unprofitable levels in the same period.

Upon analysis of the problem, it became apparent that the main problem of the
upland farmers was not so much improved technology for growing corn and other
crops, but soil erosion. They needed a way of farming slopelands in such a way as
to conserve the topsoil and if possible, improve fertility and productivity.

Sloping Agriculture Land Technology (SALT -1) is a technology package of soil

conservation and food production that integrates several soil conservation measures
(Figure 58).
 Figure 58. SALT -1 www.fao.org

Basically, SALT 1 involves planting field crops and perennial crops in bands 3-5 m
wide between double rows of nitrogen-fixing shrubs and trees planted along the
contour. These minimize soil erosion and maintain the fertility of the soil. Field crops
include legumes, cereals, and vegetables, while the main perennial crops are cacao,
coffee, banana, citrus and fruit trees.

SALT 1 helps considerably in the establishment of a stable ecosystem. The double

hedgerows of leguminous shrubs or trees prevent soil erosion. Their branches are
cut every 30-45 days and incorporated back into the soil to improve its fertility.

The annual crop provides permanent vegetative cover which aids the conservation of
both water and soil. The legumes and the perennial crops maintain soil and air
temperatures at levels favorable for enhanced growth of the different agricultural
crops.

In the Philippines, the recommended hedgerow species used in SALT 1 are

Flemingia macrophylla, Desmodium rensonii, Gliiricidia sepium, Leucaena
diversifolia and Calliandra calothyrsus.
The 10 steps in the establishment of SALT system are as follows:

1. Making the A-frame

2. Determining the contour lines
3. Cultivating the contour lines
4. Planting seeds of different nitrogen-fixing trees and shrubs
5. Cultivating alternate strips
6. Planting permanent crops
7. Planting short-term crops
8. Trimming of nitrogen-fixing trees
9. Practicing crop rotation
10. Building green terraces

Simple Agro-livestock Technology (SALT-2) was developed for small-scale low-

income farmers in the sloping lands of tropical Asia, combines crop production with
the raising of small livestock, in this case dairy goats. A farm of only half hectare is
divided into two parts, one for forage crops, and the other for food and cash crops.
Livestock are fed with forage crops, mainly leguminous shrubs, which are planted
hedgerows along the contours and around the boundary of the farm. Twelve goats
raised under this system for dairy provided an annual net income of more than
$1,000 (Figure 59).

Figure 59. SALT-2. nhttp://www.agnet.org/library/eb/400b/

As in SALT –1, an A frame is used to define the contours, which are planted in
double hedgerows of leguminous shrubs and trees. The farm is divided into two
parts, one quarter of a hectare for forage crops and the remainder for agricultural
crops. The forage crops are planted in hedgerows between the strips. Of the forage
crops, 50% is planted with Desmodium rensonii, 25% with Flemingia congesta and
25% Gliricidia sepium. Flemingia is important in the sytem because it can withstand
drought better than most other forage species.

The 0.25 ha used for crops is planted in a combination of perennial cash crops, and
annual crops used for human food. Permanent crops are planted in 85% of the total
area of this component, using coffee, citrus and black pepper. The remaining 15% is
allotted to annual crops such as corn, mungo, peanut, etc. The crops which are
fertilized with goat manure and/or foliage from the hedgerows, serve as immediate
source of food and income for the farmer.

The boundaries of SALT-2 farm are planted with Gliricidia sepium both for forage
and as boundary fence as well as source of trellis for the black pepper. Fruit trees
such as rambutan can be interspersed with the Gliricidia on two sides, but the fruit
trees should not shade the crops too much.

The goat shed, occupying a space about 58 m², is located right in the center of the
farm, to minimize labor in carrying the forage to the animals. The ideal number of
goats for a shed of this size is about 12 does. The buck house is built separately,
and does are brought to the buck house only when in heat.

The goats should not be kept in the farm until the forage are established.
Recommended breeds of goats are Anglo-Nubians for milk, and crossbreeds of
Nubian and native goats for meat.

Hedgerows are cut regularly and the foliage spread on the alley strips as green
manure, or fed to the goats on a cut-and-carry basis. Cutting the hedgerows starts
when they reach a height of about 1.5-2.0 m, and a stump of 1.0 m high is left to
coppice. During the rainy season, a farmer may have more forage than his animals’
needs, but he still needs to continue cutting so that the hedgerows do not shade out
the agricultural crops. If there is too much green growth, the leguminous shrubs can
be used as green manure for the agricultural crops.

As in SALT -1, crop rotation is practiced in the SALT-2 system. After every second
crop of corn, the strip is planted to legumes such as peanut and mungbean. The
corn and legumes are not utilized as feed but are sold in the market. The cash may
be used to buy concentrates for the goats, while the remaining money as income for
the farmer.

Other livestock may be raised but goat was used because there was a greater
demand for goat meat in the area. Cost and return analysis conducted at the
Mindanao Baptist Rural Life Center (MBRLC), showed that SALT-2 can generate a
monthly net profit of $113 per half hectare, with a return investment of 37.17%.

Sustainable Agroforest Land Technology (SALT -3) is a cropping system in which

a farmer can incorporate food production, fruit production, and forest trees that can
be marketed (Figure 60). The farmer first develops a conventional SALT project to
produce food for his family and possibly food for livestock. On another area of land
he can plant fruit trees such as rambutan, durian, and lanzones between the contour
 lines. Hedgerows will be cut and piled around the fruit trees for fertilizer and soil
conservation purposes. A small forest of about one hectare will be developed in
which trees of different species may be grown for firewood and charcoal for short-
range production. Other species that would produce wood and building materials
may be grown for medium and long-range production. Other species that would
produce wood and building materials may be grown for medium and long-range
production. In some areas where the soil is too steep for row crops, contour lines
may be established two or three meters apart and planted with flemingia or some
other hedgerow species, and in between the hedgerows coffee, cacao, calamansi or
other permanent crops could be planted.

Figure 60. SALT -3 www.nzdl.org/ 

Small Agrofruit Livelihood Technology (SALT -4) is based on a half-hectare of

sloping land with 2/3 devoted to fruit trees and 1/3 intended for food crops.
Hedgerows of different nitrogen-fixing trees and shrubs, such as Flemingia
macrophylla, Desmodium rensonii, and Gliricidia sepium are planted along the
contours of the farm.
FEATURES OF SUSTAINABLE CROP PRODUCTION

Sustainable Agriculture (SA) Concept

Agriculture has changed dramatically, especially since the end of World War II.
Agricultural productivity soared due to new technologies, mechanization, increased
chemical use, specialization and government policies that favored maximizing
production. Although these changes have had many positive effects and reduced
many risks in farming, secondary problems were generated. Prominent among these
are topsoil depletion, groundwater contamination, the decline of family farms,
continued neglect of the living and working conditions for farm laborers, increasing
costs of production, and the disintegration of economic and social conditions in rural
communities.

To address these environmental and social concerns, an alternative system that

promotes productivity at the same time maintaining the resource base should be
implemented, that is Sustainable Agriculture. Its objectives then should be to restore
and improve indigenous natural systems as well as to support the harmony that
existed in nature before chemical agriculture was introduced.

Some Definitions of Sustainable Agriculture

a. An integrated system of plant and animal production practices having site-specific

application that will over the long term that will satisfy human food and fiber
needs, enhance environmental quality and the natural resource base, make the
most efficient use of non-renewable resources and on farm resources and
integrate, where appropriate, natural biological cycles and control, enhances the
quality of life of farmers and the society as a whole.
b. A method, practice, technique/technology or philosophy that is economically
viable, ecologically sound, socially just and humane, culturally acceptable, and
based on holistic or integrative science.
c. A production system which avoids or largely excludes the use of synthetically
compounded fertilizers, pesticides, growth regulators and livestock feed additives.
To the maximum extent feasible organic farming systems rely upon crop rotations,
crop residues, animal manures, legumes, green manures, off-farm organic
wastes, mechanical cultivation, mineral bearing rocks and aspects of biological
pest control to maintain soil productivity and tilth, to supply plant nutrients and to
control insects, weeds and other pests.
d. One that is ecologically sound, economically viable, socially just and humane.
Sustainable agriculture is concerned with improving the soil’s natural capability to
nurture plant life through the constant recycling of nutrients and the maintenance
of soil fertility, moisture and microbial conditions. It is also concerned with building
up and then maintaining the nutrient content of the soil instead of depleting it after
each cropping season.
e. A philosophy and system of farming. It has its roots in a set of values that reflect
a state of empowerment, of awareness of ecological and social realities, and of
one’s ability to take effective action. It involves design and management
 procedures that work with natural processes to conserve all resources, promote
agroecosystem resilience and self-regulation, and minimize waste and
environmental impact, while maintaining or improving farm profitability.
f. One that over the long-term enhances environmental quality and the resource
base on which agriculture depends; provides for basic human food and fiber
needs; is economically viable; and enhance the quality of life for farmers and
society as a whole.
g. Management of resources for agriculture to satisfy the changing human needs,
while maintaining or enhancing the quality of the environment and conserving the
natural resources.
h. An agriculture that can evolve indefinitely toward greater human utility, greater
efficiency of resource use and a balance with the environment that is favorable
both to human and to most other species.
Sustainable agriculture integrates three main goals- environmental health,
economic profitability and social and economic equity. Sustainability rests on
the principle that we must satisfy the needs of the present generation without
compromising the ability of the future generations to meet their own needs. This
implies the importance of responsible stewardship of both natural and human
resources. Human resources stewardship includes consideration of social
responsibilities such as working conditions of laborers, the needs of rural
communities and consumer health and safety both in the present and in the future.
Stewardship of the land and natural resources involves maintaining or enhancing this
vital resource base for a long term.

To understand sustainability requires a system perspective. A system’s approach

gives us the tool to explore the interconnections between farming and other aspects
of the environment. It also implies an interdisciplinary approach. We should also
recognize that making the transition to sustainable agriculture involves a process and
that attainment of the final goal is the responsibility of all participants like farmers,
laborers, policy makers, researchers and educators, retailers and consumers.

Elements/Dimensions of Sustainable Agriculture (based on Philippine Agenda 21)

a. Ecologically Sound

 Dynamic relationship between human beings and environment

 Follow agro-ecological principles:
1. Biodiversity (i.e., ecosystem, species, genetic, and functional diversity
levels)
2. Integrated nutrient management, recycling, balanced fertilization, soil
health, natural resource conservation/management; multi-purpose trees and shrubs,
low external inputs.
3. Appropriate pest management (natural resistance, cultural
management/practices; community ecology; ecological pest management)
4. Agro-community
5. Natural conversion/improvement of genetic materials (plants, animals, etc.)
 Improves standard of living of farmers without negative effect on environment;
human/farmer fulfillment regarding his/her environment
 Uses indigenous farm resources and practices
 Has no adverse effect on resource base
 Has no adverse effect on health

b. Economically Viable

 Promotes village-level enterprise

 Aims to be, if not already is, free from subsidy and credit; is integrated, internally-
or self-organized, and not funder-driven
 Promotes food security (stability, accessibility, availability of quality and safe food
for all sectors) regardless of societal standing
 Results in net positive income
 Has no cost of externalities (or at least such is given value) (Examples of
externalities – destruction of resource base, human and soil health, loss of farm
animals and plant varieties and species, over-mechanization, input subsidy,
interest on loan)
 Is asset preserving, enhancing, and if possible, has excess (Example of assets –
draft animals, manure)
 Presence of local market support systems (with significant role of consumers;
good small-scale home-based product promotion and/or market matching
mechanisms; good post-production system; establishment of organization-based
marketing channel

c. Socially Just, Humane and Equitable

 Enhances community participation/involvement and harmony

 Adopts socially acceptable methods & practices
 Respects dignity and rights of individuals and groups
 Farmer and community have access to land, credit, information, education, and
other resources
 Enhances human and social capital
 Enhances family ties and other positive cultural values; inculcates values system
 Promotes gender sensitivity/responsiveness
 Is food secure
 Availability of appropriate education at all levels and units/sectors
 Politically developed; promotes participatory governance and cooperative
partnerships and devolution

d. Culturally Appropriate and Sensitive

 Promotes and uses (including documentation and validation of indigenous

knowledge systems (IKS)
 Is site- and culture-specific
 Incorporates cultural values, religion, beliefs; articulates farming ethics of respect
to life and natural environment
 Enhances creativity, self-reliance
 Builds-up existing social organization
 Adopts holistic and nationalistic approaches which draw upon inherent Filipino
values, traditions and practices
  Enhances spirituality of farmers and community

e. Grounded on Holistic/Integrative Science

 Leads to being (or is) diversified, location-specific, no-leak system

 Views development as a system (relationship of all elements and sectors)
 Practices diversified and integrated farming

f. Appropriate Technology

 Location and culture specific

 Adopts principles of transparency, accountability and fairness

g. Full Development of Human Potential

 Includes political development and sense of accountability

Goals of Sustainable Agriculture

Sustainable agriculture is any production system that systematically pursues the

following goals:

 A thorough incorporation of natural processes such as nutrient cycling, nitrogen

fixation and pest-predator relationship in pest management. Included in nutrient
management are recycling of nutrients, composting, green manuring and
utilization of various types of organic fertilizers;
 A minimization of the use of external and non renewable inputs that damage the
environment or harm the health of farmers and consumers;
 Utilization of alternative systems of crop improvement, breeding and selection,
and locally-adapted varieties of crops;
 The full participation of farmers and rural people in all processes of problem
analysis, technology development, adaptation and extension;
 A more equitable access to productive resources and opportunities;
 A greater productive use of local knowledge, practices and resources;
 The incorporation of a diversity of natural resources and enterprises within the
farms by raising various crops and livestock and integrating them; and
 An increase in self-reliance among farmers and rural communities

Attributes of Sustainable Agriculture

The SA approach is proactive, experiential, participatory and flexible.

SA is proactive.

Farmers should be transformed from mere farm workers to researchers and their farms
should be converted into research stations. Farmers should be provided with tools on
“learning how to learn” rather than “what to learn”.
SA is flexible.
Flexible means not prescriptive of a defined set of practices, methods,
techniques/technologies or policies that would restrict the options of the farmers. As
conditions and knowledge change, farmers and local communities must be able to, and
be allowed to change.
SA is experiential.

SA is learning process and experiential and not the imposition of a simple model or
package. It relies heavily on the continuous innovation by farmers and local
communities. SA recognizes that these formal innovations are not haphazard
unscientific processes but are results of systematic observation, experimentation and
adaptation. Hence, it does not represent a return to some form of low technology,
“backward” or “traditional” agriculture. Instead, it implies incorporating recent
innovations that may originate from scientists, farmers, or both.
SA is participatory.

For SA to be successful, the proper mix between the intuitive wisdom of the experienced
practitioner (the farmers) with the analysis of those formally trained in the sciences
(scientists/researchers) must be found.

Time-tested Models of Sustainable Agriculture

1. Low External Input sustainable Agriculture (LEISA) - the form of agriculture that
seeks to optimize the use of locally available resources by combining the
different components of the farm system so that they complement each other and
have the greatest possible synergistic effect. It also seeks ways of using external
inputs only to the extent that they are needed to provide elements that are
deficient in the ecosystem and to enhance available biological, physical and
human resources.

2. Organic Farming – a system of agriculture that encourages healthy soils and

crops through such practices as nutrient recycling, crop rotations, proper tillage
and the avoidance of synthetic fertilizers and pesticides.

3. Permaculture – the conscious design and maintenance of agriculturally

productive ecosystems which have diversity, stability and resilience of natural
ecosystems. It is the harmonious integration of landscape and people providing
food, energy, shelter and other material and non-material needs in a sustainable
way.

4. Biodynamic Farming – the holistic system of agriculture devised by Rudolf

Steiner that seeks to connect nature with cosmic forces.

5. Kyusei Nature Farming – a system of agriculture devised by Mokichi Okada in

1935 which advocates a production system which does not disrupt the natural
ecosystem and seeks to achieve the production of healthy agricultural products
without the use of chemical fertilizers and pesticides. It adopts the technique of
using effective microorganisms (EM).
 6. Korean Natural Farming – also known as ‘vital agriculture’ because it maximizes
the use of natural resources in harmony with the environment wherein self-
manufactured farming materials such as Indigenous Microorganisms (IMO),
Fermented Plant Juice (FPJ), Fermented Fruit Juice (FFJ), Fish Amino Acid
(FAA) are applied.

7. Natural Farming or Do Nothing Farming – a system of agriculture devised by

Masanobu Fukuoka that seeks to follow nature by minimizing human
interference: no mechanical cultivation, no synthetic fertilizers or prepared
compost, no weeding by tillage or herbicides, no dependence on chemicals.

Diversification

One important principle to achieve sustainability in crop production is biological

diversity or biodiversity. Biodiversity is defined as the total variability within all living
organisms and the ecological complexes they inhabit. In agriculture, this variability is
termed as agricultural biodiversity or agrobiodiversity or the genetic resources for
food and agriculture. Agrobiodiversity is an important subset of biodiversity and is
considered as the basis of food security. It may be defined as the intraspecies
variation in diversity or the variation of diversity enclosed in one species.

Agrobiodiversity can be divided into three categories:

a. Genetic diversity – this refers to the variation of genes within species.

Example: different traditional varieties of rice (Table 24)

Table 24. Traditional varieties of rice (Oryza sativa) grown in the Philippines.

No. of
Days to Crop stand/ Grain Photoperiodic
Variety productive
mature uniformity characteristics response
tillers
Abrigo 120 11 Good, uniform Medium, slender insensitive

Black tip,
Azucena 125 7 Good, uniform Insensitive
medium slender

Bengawan 125 12 Good, uniform No data Insensitive

Borong 120 8 Good, uniform Medium, oblong Insensitive

Very good,
Borong Red 125 9 Long, slender Insensitive
uniform

Elon-elon 130 8 Good, uniform Short, slender Insensitive

Improved Very good,

120 8 Medium, oblong Insensitive
Milagrosa uniform

Intan 123 10 Good, uniform Medium, slender Insensitive

Milagrosa 130 6 Good, uniform Short, oblong Sensitive

Moguama Very good,

120 11 Long, slender Insensitive
Africa uniform

Pinili 120 10 Good, uniform Medium, oblong Insensitive

Black tip,
Pinitumpo 114 11 Good, uniform Insensitive
medium slender

Puro-puro 120 10 Good, uniform Medium oblong Insensitive

Red Elon-elon 130 8 Good, uniform Short, slender Insensitive

Sinandomeng 125 10 Good, uniform Medium, slender Insensitive

b. Species diversity – this refers to variety of species within a given area or

region. Examples: different species of vegetables raised in backyard gardens
in the Philippine countryside (Table 25)

Table 25. Biodiversity in the Philippine countryside (based on the Philippine

folk song, Bahay Kubo).

Local Name English Name Scientific Name

Singkamas Yam bean Pachyrrhizus erosus L.
Talong Eggplant Solanum melongena
Sigarilyas Winged bean Psophocarpus tetragonolobus
Mani Peanut Arachis hypogaea
Sitaw String bean Vigna unguiculata
Bataw Hyacinth bean Dolichos lablab
Patani Lima bean Phaseolus lunatus
Kundol Wax gourd Benincasa hispida
Patola Sponge gourd Luffa cylindrical L.
Upo Bottle gourd Lagenaria siceraria
Kalabasa Squash Cucurbita moschata
Labanos Radish Raphanus sativus
Mustasa Mustard Brassica juncea
Sibuyas Onion Allium cepa
Kamatis Tomato Lycopersicon esculentum
Bawang Garlic Allium sativum
Luya Ginger Zingiber officinale
Linga Sesame Sesamum indicum

c. Ecosystem biodiversity – this refers to the boundaries of communities in

association with species and ecological system. Examples: coastal
ecosystem, forest ecosystem, rice ecosystem

Importance of biodiversity
 a. Source of food, medicine, fuel, construction materials and other aesthetic,
recreational, cultural and research values
b. Climate and water regulation
c. Creation and protection of the soil
d. Reduction of floods and soil erosion
e. Natural control of agricultural pests
f. Nutrient cycling and organic fertilizer source

Ways to achieve biodiversity

1. Crop Diversification

There are several ways to achieve biodiversity in agriculture, one of which is through
crop diversification through the practice of multiple cropping. Multiple cropping is the
planting of diverse species of crops on the same land (spatial) or in rotation
(temporal) or both as opposed to monocropping or the practice of repeatedly growing
only one crop in the same piece of land. Examples of spatial patterns of multiple
cropping are intercropping or the growing of two or more crops simultaneously on the
same field (example: rice + pole sitao wherein rice is grown in the paddy while pole
sitao is grown along the dikes or bunds), alley cropping or the planting of shrubs or
trees at close in-row spacing, with wide spacing between rows to leave room for
annual or herbaceous plants (example: leguminous trees and shrubs + corn), relay
cropping and multistorey cropping or mixed or row intercropping with the structure of
the tree-crop mixture is made up of different canopy layers or plant heights, thus
giving a multi-storey effect (examples: coconut + coffee + pineapple in Silang,
Cavite; coconut + passion fruit in Lucban, Quezon). Temporal patterns of multiple
cropping system, on the other hand is exemplified by crop rotation or sequential
cropping or the successive planting of different crops in the same field over a period
of time (examples: rice – garlic and rice –tomato in the Ilocos region, rice – onion in
Cental Luzon, rice – watermelon in Pampanga). Combination of spatial and temporal
patterns is exemplified by relay cropping or growing two or more crops
simultaneously on the same field with the succeding crop planted after the preceding
crop has flowered. (corn/peanut/sweet potato). Note the following symbols and their
representations: (+) means mixed with or intercropped with, (-) means followed by or
rotated with, and (/) means relayed with.

Multiple cropping offers numerous benefits. It helps in maintaining soil fertility

especially if legumes are incorporated in the cropping system. Because different
crops have different nutrient requirements, nutrients are utilized more efficiently.
Multiple cropping is also an effective approach in managing pests. Some crops in
spatial multiple cropping systems may attract or repel certain pests. In the case of
crop rotations, pest cycles are broken especially if crops belonging to different
families are grown one after the other. Multiple cropping also narrows the space for
weeds to grow and hamper their growth which may be due to allelopathic effects of
some crops.
 2. Integrated Farming Systems (IFS)

Livestock such as cattle, carabao, swine and small ruminants, poultry, fish or even
bees may also be integrated into crop production systems to achieve sustainability.
Some examples of IFS as practiced in various parts of the Philippines are as follows:
rice-fish-duck system, rice-fish-pig system, rice-fish culture, corn-cattle system, to
name some.

Integration of animals in cropping systems has many advantages. Apart from being
source of food (meat, eggs, milk and honey), animals may be used during land
preparation as draft power or for transporting produce to the market. They can also
serve as capital reserve especially in times of crisis. Animals are also good source of
organic fertilizers which can be used to fertilize crops, thus reducing fertilizer cost. In
rice producing areas, ducks are used to control golden apple snail (golden kuhol) just
after harvest and 25 days after transplanting. They also feed on weeds and some
insects.

Resource Conservation and Regeneration

Sustainable crop production works more on the conservation rather than wasteful
use of valuable farm resources such as soil, water and seeds. Its aim is to ensure
that soil, water and genetic resources are available for use by present generation
while maintaining its potential to meet the needs of future generations to come.

Sustainable crop production also aims to regenerate, restore and renew agricultural
systems especially after a decline to a low condition through the use of resource
efficient and ecologically-sound farming practices.

Soil conservation /regeneration

Soil being an important resource in most crop production venture, needs to be

conserved rather than exploited. Crop production practices should heed the following
principles of soil conservation:

a. Always keep the soil covered to preserve soil moisture, suppress weed growth,
regulate soil temperature, reduce run-off and soil erosion. This may be done be
providing protective soil cover at all times through the practice of mulching or
covering the soil with protective materials such as crop residues or plastic and
cover cropping.
b. Prevent soil erosion through conservation tillage, use of cover crops, contour
farming, terracing, use of windbreaks or shelterbelts, deep tillage.
c. Prevent the soil from being chemically altered by excessive use, acidification and
salinization. Fallowing or leaving the land idle for some time, incorporation of
organic matter, reduction if not elimination of chemical fertilizer use, non-pumping
of ground water are some of the practices to attain this principle.
d. Encourage health of beneficial organisms. This may be done by adding of
organic matter, discontinuing some agricultural practices such as slash and burn
cultivation and use of chemical fertilizers and pesticides that may harm
organisms in the soil.
 e. Grow leguminous crops either as green manure, cover crop, rotational or
intercrop to encourage nitrogen fixation and increase biomass production.

Water conservation

Water is a resource which has helped the development of agriculture and society
and although it seems to be an inexhaustible resource, inadequate supply of quality
water is being felt with increasing frequency both for agriculture uses as well as for
industry and household requirements. Water quality must be maintained by
minimizing contamination of ground water by pesticides, nitrates and heavy metals.

Below are the principles of water conservation:

a. Minimize use of ground water
b. Maximize/optimize the use of soil and subsoil water
c. Optimize the use of rain water
d. Maximize rain water infiltration
e. Decrease evapotranspiration, percolation, seepage and run-off

These principles may be achieved with the following practices:

1. Improve soil structure and storage capacity

a. maintain ground cover

b. less or no tillage
c. fallowing
d. early land preparation

2. Decrease evaporation/evapotranspiration

a. mulching
b. pruning leaves – reduce leaf area
c. maintain ground cover
d. minimum/zero tillage

3. Improve infiltration

a. matter application
b. contour cultivation
c. deep cultivation
d. terracing
e. mulching
f. fallowing
g. early land preparation

Genetic resources conservation

In order to prevent the loss of genetic resources, efforts on conserving genetic

resources should be made. Several approaches are being offered which include the
following:
 a. In situ conservation – the conservation of plant genetic resources in the form of
seeds or live plants under its natural setting. Plant species in consideration are
allowed to interact with wild races in the vicinity through natural selection.

a.1. On-farm management - It sometimes used interchangeably with in situ

conservation, is the maintenance of local crop varieties at the community level,
similar in farmers’ fields and gardens. Plant species in consideration are allowed to
interact with wild races, as well as through farmers’ selection processes (natural and
artificial selection).

b. Ex situ conservation – conservation of plant genetic resources outside its natural

setting.

The three major forms of ex situ conservation are namely:

Seed genebanks. It provides a controlled environment where seeds can be dried to

low moisture content and stored at low temperature without losing their viability.
Examples: rice, corn, legumes, most vegetables

Field genebanks. Such as arboreta, plantations, and botanical gardens, field

genebanks are useful for species that are difficult and impossible to store as seeds
due it their recalcitrant behavior, including vegetative propagated crops and tree
species. Examples: most fruit crops such as mango, durian, lanzones; sweet potato,
cassava

In vitro methods. It conserves plant parts, tissue or cells in nutrient medium. This
method is used to maintain species that do not readily produce seeds, or where the
seeds cannot be dried without damaging them. Examples: banana, yam, bamboo

Other resources

Energy

Modern agriculture is heavily dependent on non-renewable energy sources,

especially petroleum. This cannot be sustained indefinitely nor is it possible to
abruptly abandon our reliance on it. Thus a gradual substitution of petroleum-based
energy sources should be worked at; e.g. hydroelectric and geothermal electric
power generation, use of wind and solar power to store electric energy and dendro-
thermal electric generation plants.

Air

Many agricultural activities affect air quality. These include smoke from
combustion, dust from tillage, traffic and harvest; pesticide drift from spraying; and
nitrous oxide emissions from the use of nitrogenous fertilizers. Option to improve air
quality include incorporating crop residues into soil instead of burning, using
appropriate level of tillage and planting wind breaks, cover crops of strips of native
perennial grasses to reduce dust.
 CHAPTER V: BIOTECHNOLOGY

INTRODUCTION

Biotechnology, broadly defined, includes any technique that uses living organisms, or parts
of such organisms, to make or modify products, to improve plants or animals, or to develop
microorganisms for specific use. It ranges from traditional biotechnology to the most
advanced modern biotechnology. Biotechnology is not a separate science but rather a mix
of disciplines (genetics, molecular biology, biochemistry, embryology and cell biology)
converted into productive processes by linking them with such practical disciplines as
chemical engineering, information technology, and robotics. Modern biotechnology should
be seen as integrations of new techniques with the well-established approaches of
traditional biotechnology such as plant and animal breeding, food production, fermentation
products and processes, and production of pharmaceuticals and fertilizers (Doyle and
Persley 1996).

Definition of terms:

Biotechnology – Any technique that makes use of living organisms or parts thereof
to make or modify products, to improve plants and animals, or to develop
microorganisms for specific purposes. Developed countries define biotechnology as
the application of DNA manipulation techniques such as recombinant DNA and novel
methods of using and manipulating cells to produce novel crops, animals and
microorganisms generally referred to as genetically modified organisms (GMOs).

Agricultural biotechnology is modifications of any living organisms in ways that

improve the efficiency, competitiveness and sustainability of food production.

DNA – A molecule found in cells of organisms where genetic information is stored.

Gene – A biological unit that determines an organism’s characteristics.

Genetic engineering – involves transferring specific genes from one species to

another whether related or unrelated. The selective, deliberate alteration of genes by
man.

Genome – The entire hereditary material in a cell

Modern biotechnology – Application of in vitro nucleic acid techniques, including

recombinant DNA and direct injection of nucleic acid into cells of fusion of cells
beyond the taxonomic family.
 Traits – Characteristics such as size, shape, taste, color, increased yield, disease
resistance, improved postharvest behavior.

Transgene – a gene that has been artificially inserted into an organism.

GM or Transgenic Crop – is a plant that has a novel combination of genetic

material obtained through the use of modern biotechnology.

The key components of modern biotechnology are listed below.

(i) Genomics: The molecular characterization of all genes in a species.
(ii) Bioinformatics: The assembly of data from genomic analysis into accessible
forms, involving the application of information technology to analyze and manage
large data sets resulting from gene sequencing or related techniques.
(iii) Transformation: The introduction of one or more genes conferring potentially
useful traits into plants, livestock, fish and tree species.
(iv) Genetically improved organism.
(v) Genetically modified organism (GMO).
(vi) Living modified organism (LMO).
(vii) Molecular breeding: Identification and evaluation of useful traits in breeding
programs by the use of marker-assisted selection (MAS);
(viii) Diagnostics: The use of molecular characterization to provide more accurate
and quicker identification of pathogens; and
(ix) Vaccine technology: The use of modern immunology to develop recombinant
deoxyribonucleic acid (rDNA) vaccines for improved control of livestock and fish
diseases (Doyleand Persley 1999).

Table 26.The Evolution of the Science of Genetics Leading to Modern Biotechnology

 1866 - Mendel postulates a set of rules to explain the inheritance of biological

characteristics in living organisms.
 1900 - Mendelian law rediscovered after independent experimental evidence
confirms Mendel’s basic principles.
 1903 - Sutton postulates that genes are located on chromosomes.
 1910 - Morgan’s experiments prove genes are located on chromosomes.
 1911- Johannsen devises the term “gene”, and distinguishes genotypes (determined
by genetic composition) and phenotypes (influenced by environment).
 1922 - Morgan and colleagues develop gene mapping techniques and prepare gene
map of fruit fly chromosomes, ultimately containing over 2000 genes.
 1944 - Avery, MacLeod and McCarty demonstrated that genes are composed of
DNA rather than protein.
 1952 - Hershey and Chase confirm role of DNA as the basic genetic material.
 1953 - Watson and Crick discover the double-helix structure of DNA.
 1960 - Genetic code deciphered.
 1971 - Cohen and Boyer develop initial techniques for rDNA technology, to allow
transfer of genetic material from one organism to another.
 1973 - First gene (for insulin production) cloned, using rDNA technology.
 1974 - First expression in bacteria of a gene cloned from a different species.
 1976 - First new biotechnology firm established to exploit rDNA technology
(Genentech in USA).
  1980 - USA Supreme Court rules that microorganisms can be patented under
existing law (Diamond v. Chakrabarty).
 1982 - First rDNA animal vaccine approved for sale in Europe (colibacillosis). First
rDNA pharmaceutical (insulin) approved for sale in USA and UK. First successful
transfer of a gene from one animal species to another (a transgenic mouse carrying
the gene for rat growth hormone). First transgenic plant produced, using an
agrobacterium transformation system.
 1983 - First successful transfer of a plant gene from one species to another.
 1985 - US Patent Office extends patent protection to genetically engineered plants.
 1986 - Transgenic pigs produced carrying the gene for human growth hormone.
 1987- First field trials in USA of transgenic plants (tomatoes with a gene for insect
resistance). First field trials in USA of genetically engineered microorganism.
 1988 - US Patent Office extends patent protection to genetically engineered animals.
First GMO approved. Human genome mapping project initiated.
 1989 - Plant genome mapping projects (for cereals and Arabidopsis) initiated.
 2000 - Plant genome mapping projects for rice and Arabidopsis completed, and
about 44 million hectares of land planted to GMO crops.

DNA = deoxyribonucleic acid, GMO = genetically modified organism, rDNA =

recombinant
DNA, UK = United Kingdom, USA = United States of America.

APPLICATIONS OF BIOTECHNOLOGY

The applications developed from the new methods in biotechnology place them within
the continuum of techniques used throughout human history in industry, agriculture, and
food processing. Thus, while modern biotechnology provides powerful new tools, they
are used togenerate products that fill similar roles to those produced with more
traditional methods.

There is now increasing use of modern molecular genetics for genetic mapping and
MAS as aids to more precise and rapid development of new strains of improved crops,
livestock, fish, and trees. Other biotechnology applications such as tissue culture and
micropropagation are being used for the rapid multiplication of horticultural crops and
trees. New diagnostics and vaccines are being widely adopted for the diagnosis,
prevention, and control of fish and livestock diseases (see the summary in Table 27)

The science of genomics (the molecular characterization of all the genes in a species)
has dramatically increased knowledge of plant genes and their functions. The new
technologies enable greatly increased efficiency of selection for useful genes, based on
knowledge of the biology of the organism and the role of specific genes in regulating
particular traits.

This will enable more precise selection of improved strains. These techniques may be
used for more efficient selection in conventional breeding programs. They may also be
used for the identification of genes suitable for use in the development of transgenic
crops. Thus far, scientists have completed genomic study on rice through the
cooperative efforts of severalinternational and private sector institutions led by Japan.
 Modem biotechnology permits increased precision in the use of new techniques and a
shorter time to produce results. For example, plant breeders and molecular biologists
can collaborate to transfer to a highly developed crop variety one or two specific genes
to impart a new character such as a specific kind of pest resistance.

Table 27. Summary of Applications of Modern Biotechnology to Agriculture

Crop Production Diagnostics. To diagnose plant pests

and pathogens,contaminants, and
quality traits.
Micropropagation or tissue culture.
To multiply disease-free planting
materials on a large-scale.
Development of transgenic crops. To
develop commercially new genetically
modified crop varieties.
Modern plant breeding. To develop
superior plant varieties rapidly and more
precisely.
Marker-assisted selection. To use
genetic markers, maps,and genomic
information in breeding for high yielding,
disease- and pest-resistant varieties.
Biodiversity Characterizing,
conserving, and using biodiversity.
Forestry Gene-mapping. To accelerate
tree breeding.
Macropropagation. Rapid vegetative
propagation by means of cuttings from
large plantation of pines and other trees.
DNA finger printing. To differentiate
species, strains, and cultivars
accurately.
Wood security. The selection of
genetically superior trees for breeding
purpose.

Livestock Production Livestock improvement. To speed up

the reproduction process in animals,
allowing more generations to be
produced.
Transgenic livestock. Development of
transgenic lines of virus-resistant poultry
and other animals.
Livestock health. Application of
diagnostics for the control of major
diseases of livestock.
 Vaccine development. Development of
vaccines for the control of epidemic viral
diseases of livestock.
Fisheries Transgenic fish. Still being
explored. Use of molecular markers in
biodiversity. Research, genomic
mapping, and trait selection in fish and
other aquatic organisms.

1. Molecular Markers

Molecular markers are DNA variations in plant and animal genomes. These are used
in tagging agronomic traits and in selection in breeding populations (MAS or marker-
assisted selection). Use of DNA markers associated with desirable traits reduces the
time and guesswork used in the selection process. Selection is often the rate limiting
step in plant breeding as it requires that the plants be sustained through out their
growth cycle, allow them to express their genes at the right time and have them
exposed to the conditions such as insect attack, drought, etc. that limit growth and
yield in the field. Hence, selection is traditionally a long and laborious process. DNA
markers are detected as early at the seedling stage without exposing the plants to
their selective environments. Detection is highly reliable and rapid, one technical
personnel can process at least a hundred samples per day. Molecular markers are
also used to construct genetic maps, measure the genetic diversity of breeding
materials and identify individuals, breeds, isolates or species. These include RAPD
(random amplified polymorphic DNA), RFLP (restriction fragment length
polymorphisms), EST (expressed sequence tags), microsatellites such as SSR
(simple sequence repeat) and STR (short tandem repeat), SNP (single nucleotide
polymorphism) and known genes. Genomics is an emerging research field of
molecularly characterizing whole genomes or the total genetic material of a species.
Applications of genomics such as information about the structure of economically
important genes, their locations relative to each other, their products and the effect of
other DNA sequences on the production and function of these products are
considered the next revolution in biotechnology. These applications could offer
technical solutions to the biosafety issues currently being raised against transgenic
crops. Or, novel crops not yet imagined today could be developed.

2. Genetically modified organisms

GM crops contain gene(s) that has been artificially inserted instead of the plant
acquiring it through pollination. The resulting plant is said to be “genetically
modified” although in reality all crops have been “genetically modified” from their
original wild state by domestication, selection, and controlled breeding over long
periods of time (James, 2006).

There are three methods of genetic engineering agrobacterium mediated,

microinjection and the biolistic (gene gun) method. Among the three methods earlier
mentioned, Agrobacterium-mediated transformation is the most popular.
Microinjection uses small needles to insert the gene into the plant cell. The third
method makes use of a gene gun which is part of a method called the biolistic (also
known as the bioballistic) method. Under certain conditions, DNA (or RNA) becomes
“sticky”, adhering to biologically inert particles such as metal atoms (usually tungsten
or gold). By accelerating this DNA-particle complex in a partial vacuum and placing
the target tissue within the acceleration path, the DNA is effectively introduced (Gan,
1989). Uncoated metal particles could also be shot through a solution containing
DNA surrounding the cell thus picking up the genetic material before proceeding into
the living cell. The cells that take up the desired DNA, identified through the use of a
marker gene (in plants the use of GUS is most common) are then cell or tissue
cultured to replicate the gene and possibly cloned. The cell or tissue carrying the
transgene(s) are then further cultures to regenerate the whole plant.

DNA delivery with the gene gun also offers advantages for research in such areas as
DNA vaccination/genetic immunization, gene therapy, tumor biology/wound healing,
plant virology and many others.

Figure 61. Methods in genetic engineering. Agrobacterium-mediated

transformation method (A), particle bombardment (gene gun) (B)
and microinjection (C).
Table 28. Traits of some selected transgenic crops field tested and commercialized

Crops Traits in Field Trials/commercialized

Canola 1. Herbicide tolerance

2. Improved disease resistance
3. Hybrid technology
4. Hybrid technology and herbicide tolerance
5. High lauric acid
6. Other oil modifications

Corn 1. Control of Asian-Borer

2. Herbicide tolerance
3. Control of Corn Rootworm
4. Hybrid Insect protected/herbicide
5. Disease tolerance
6. Higher starch content
7. High lysine
8. Improved protein
9. Resistance to storage grain pest
10. Apomixis

Cotton 1. Bollworm Control

2.Control of Boll Weevil
3. Insect protected/herbicide
4. Herbicide resistance
5. Improved fiber/staple quality
6. Disease resistance

Potato 1. Resistance to Colorado Beetle

2. Resistance to Colorado Beetle+Virus resistance
3. Multiple Virus resistance (PVX, PVY, PLRV)
4. Fungal Disease resistance
5. Higher starch/solids
6. Resistance to potato weevil/storage pests

Rice 1. Resistance to bacterial blight

2. Resistance to rice-borers
3. Fungal disease resistance
4. Improved hybrid technology
5. Resistance to storage pests
6. Herbicide tolerance

Soybean 1.Herbicide tolerance

2. Modified oil-High oleic acid
3. Insect resistance
4. Virus resistance
Tomato 1. Delayed/improved ripening
2. Virus resistance
3. Insect resistance
4. Disease resistance
5. Quality/high solids

Vegetables and Fruits. 1.Virus resistance

2.Insect resistance
3.Delayed ripening

BIOTECHNOLOGY THROUGH TIME

Biotechnology requires different levels of sophistication in facilities, basic science

foundation and technical skills. The first level also referred to as traditional biotechnology
involves the manipulation of microorganisms and includes centuries-old fermentation
technologies such as beer brewing, wine making mediated by microorganisms,
production of organic chemicals like antibiotics and mushroom production. The second
level or the classical biotechnology involves the manipulation of tissues and cells from
multicellular organisms such as plant tissue culture and mammalian cell cultures. The
third level or the modern biotechnology involves the manipulation and analysis of the
genetic material, DNA, such as recombinant DNA (rDNA) technology, genetic
engineering and applications of genomics, the study of whole genomes or the totality of
the genetic material of a species at the molecular level.

According to Dr. Benigno Pecson, the accent of modern biotechnology progressed along
several disciplines. From the invention of the microscope to the description of cells and
bacteria, medical science progressed from the splicing of genes into bacteria to the
commercial production of human insulin in bacteria in 1982. Among the earliest
biotechnology successes was in the area of food processing specifically in cheese
manufacture. The rennet enzyme used to come from the lining of claves’ stomachs.
Isolation of the genes that produce rennet and reproducing it in bacteria allows the
production of rennet through fermentation to yield (chymosin) thus, eliminating the need
to extract it from calves’ stomachs. Similarly through biotechnology, yeasts used in
bread making have also been improved, thus speeding up the process of leavening in
breads. Subsequently, biotechnology has been used not only in the pharmaceutical
industry, in medicine, in the animal industry, in the aquaculture industry, in the
production of non-food items like in the pulp and paper and fiber industry and certainly
an expansion of its varius applications in crop production including the more recent
application of biotechnology in the production of biofuels.

In terms of institution and capability building in the country with respect to biotechnology
utilization, several steps have been taken. Establishment of the Institute of
Biotechnology and Applied Microbiology in 1979, creation of the National Committee on
Biosafety of the Philippines (NCBP) in 1990 to review and monitor research and
development activities involving genetically modified organisms. The first policy
issuance of this committee is the Executive Order 430, Biosafety Guidelines (Series # 1
and # 3) in 1992 tasking the Department of Science and Technology as the implementor.
It was through this order that the first contained experiment and field trials of Asian corn
 borer-resistant corn, popularly known as Bt corn, were conducted. Despite the fact that
GM crops have already been produced abroad and used in commercial planting,
acquiring it for domestic use is another story. Since the existing rule concerns only
greenhouse and field studies under the domain of DOST, access to the technology by
farmers have to wait until 2002 when DA issued Administrative Order No. 8 Series of
2002. Governing Rules and Regulations on the importation and release into the
environment of plants and plant products derived from the use of modern biotechnology.
This opened the gate to the first commercial planting of genetically modified corn in the
Philippines. In March 2006, the Philippine Government issued Executive Order 514,
which established the National Biosafety Framework. Subsequently, the Philippine
Senate ratified the Cartagena Protocol on Biosafety to the United Nations Convention of
Biological Diversity.

RATIONALE FOR THE USE OF BIOTECHNOLOGY IN AGRICULTURE

According to Tomeldan (2008) a global far greater than the current financial crisis now
confronting both developed and developing countries is the problem of hunger. It
threatens about 40% of the entire world population and the younger generation that
comprise 25% of the entire humankind. In the Philippines, about 40% Filipinos have
experienced hunger and more are about to suffer the same unless a concerted effort by
the government, private sector, the religious, professional, the academic community and
the workers and common peasants do something about it.

The Philippines had a land area of about 300,439 sq. km. With the current climate
change some experts predict that some lands will be submerged when polar ice will melt
down and unless extensive land reclamation from the sea similar to what the Dutch did
will be done the area of arable land will not increase. Moreover, not all the land area
available will be all devoted to food production, as there is a limit to the expansion of
arable lands. A substantial part of the land is also used for human habitation, for
transportation (road networks, airports and other industrial uses), forest cover to serve
as water shed and for park and recreation areas.

As the population grows, which was about 76.5 million in 2000 and now more than 94
million, feeding the ever increasing number of mouths becomes a continuing problem.
Time is of the essence, and since we can not substantially increase the area for
production the yield per unit area must be achieved and so on. Conventional plant
breeding techniques is slow, require greater land area for field testing because
backcrossing is often done to eliminate some of the bad genes that have been
transferred with the good ones.

Also, traditional cross breeding is limited to exchanges between the same or very closely
related species. It can also take a long time to achieve the desired results and
frequently the characteristics of interest may not exist in any related species. GM
technology enables plant breeders to bring together in one plant useful genes from a
wide range of living sources, not only between species but between genera within a
family.

To confront the hunger problem, Agriculture Undersecretary Segfredo R. Serrano, who

also chairs the Department of Agriculture Biotech Program Steering Committee, believes
that modern farm technologies, particularly biotechnology, are the key to solving the
country’s food security program.

Status of biotechnology in agriculture world-wide and in the Philippines

Transgenic crops were first grown in commercial scale in China (virus protected
tobacco) in 1992 followed by Calgene’s (Flavr-Savr), the first genetically modified
food crop to be produced and consumed in the U.S. in 1994. The US remains the
biggest biotech crop producer with 57.7 million ha, mostly planted to soybean, corn,
cotton, canola, squash, papaya and alfalfa. Transgenic crops are being designed to
possess traits not only addressing various impediments to crop production but also
to avoiding post harvest losses, to improving product quality and to endowing novel
capabilities. Other traits that are currently being incorporated into crop plants are
tolerance to abiotic stress such as drought, increased photosynthetic ability and
improved nutritional qualities.

Transgenic crops are adopted by farmers at a rate greater than any other technology
in the history of agriculture. Multiple benefits reported by growers for selected
transgenic crops include more flexibility in terms of crop management (particularly
important for herbicide tolerant crops), decreased dependency on conventional
insecticides and herbicides, higher yields and cleaner and higher grade of grain/end
product( no worms, no mycotoxin-producing fungi in Bt corn), increased yields for
pest protected crops due to avoidance of damage usually inflicted by the pest,
decreased use of pesticide which redounds not only to savings in pesticide cost but
also to reduction in environmental pollutant, reduced risk for farm workers as well as
consumers, zero or minimal disturbance in the population of beneficial species and
soil conservation, hence, over-all an increased profitability for the farmers and less
disruptive environmental impact.

Currently, large producers include the USA, Argentina, Canada and most likely
China. Some plantings are also reported in Mexico, Spain, France and South Africa.
Commercial planting of certain GM crops have been approved in the EU, Japan,
Netherlands, New Zealand, Australia and recently in Brazil. GM crops have been
grown in several field trials in Malaysia, Thailand and Indonesia. There is high
acceptance of GM crop farming and foods in the USA, Canada and Australia as
consumers believe that risks could outweigh benefits provided that appropriate
regulatory framework in place. The accumulated hectarage of biotech crops for the
period 1996 to 2009 reached almost 1 billion hectares. Notably, almost half (46%) of
the global hectarage was planted by developing countries, expected to take the lead
from industrial countries before 2015.

The Philippines ranks 10th of the 14 “mega countries” whose commitment to biotech
crops is more than 50,000 ha. Based on the hectarage, the mega countries include
USA, Argentina, Brazil, Canada, India, China, Paraguay, South Africa, Uruguay,
Philippines, Australia, Romania, Mexico and Spain (James, 2006).

According to ISAAA, there are now about 125,000 Filipino farmers planting
biotechnology related crops such as rice, corn, coconut, papaya, among others.
BENEFITS OBTAINED FROM GROWING GM CROPS

 High crop yield

 Reduced farm costs
 Increased farm profit
 Improvement in health and the environment

For the second generation GM crops

 Increased nutritional or industrial traits

 Edible vaccines
 Crops that can grow better under stressful conditions e.g. saline, submerged
condition and drought among others.

POTENTIAL RISKS OF GM CROPS

 The dangers of unintentionally introducing allergens and other anti nutrition factors in
food
 The likelihood of transgenes escaping from cultivated crops into wild relatives
 The potential for pests to evolve resistance to the toxins produced by GM crops
 The risk of these toxins affecting non-target organism

According to James, (2006), where legislation and regulatory institutions are in place,
there are elaborate steps to precisely avoid or mitigate these risks. It is the obligation of
the technology innovators (i.e. scientists), producers, and the government to assure the
public of the safety of the novel foods that they offer as well as their benign effect on the
environment.

There are also those risks that are neither caused nor preventable by the technology
itself. An example of this type of risk is the further widening of the economic gap
between developed countries (technology users) versus developing countries
(nonusers). These risks, however, can be managed by developing technologies tailor
made for the needs of the poor and by instituting measures so that the poor will have
access to the new technologies.
PERCEIVED IMPACT TO FILIPINOS FOR GROWING GM CROPS.

As part of the agricultural modernization plan of the government, in addition to boosting

food security, the DA’s Biotechnology Program Office (BPO) is also bent on transforming
agriculture from a resource-based to a technology-based sector. Biotechnologies that
can ensure increased yields, low production cost and high value products are constantly
being developed and promoted in order to maximize the use of limited resources
available for agriculture.

A significant achievement in this regard is the successful introduction and

commercialization of Bacillus thuringensis (Bt) corn which has made possible an
increase a unit yield increase of 37% which translates to an additional profit of P 10,000
per ha. Pesticide expenses are also slashed by up to 60%.

The utilization of both traditional and modern biotechnologies for extracting high-value
byproducts from traditional agricultural commodities is also being achieved. For
instance, coconut is now being used as source of sugar, honey, vinegar, biofuel, virgin
coconut oil (VCO), industrial feedstock and health drink. Abaca is now better known for
non-fiber byproducts like surfboards, car accessories and insulation materials. Rice
hulls, bran and other milling byproducts are now utilized as energy source, medicines
and health supplement. Seaweeds are also being tapped for high-value products such
as health supplements, medicines and cosmetics. In the pipeline are the application of
traditional and modern biotechnology in extracting some useful constituents like
essential oils and useful phytochemicals from such plants like malunggay, banaba,
papaya, mango, pineapple, duhat, guayabano, seaweeds and marine bioactives.

For instance, the development of biotech abaca varieties could help strengthen
Philippine economy since the country provides 85% of the world demand for abaca
products, and there are around 68,000 abaca farmers in the country and 1.5 million
Filipinos sustained by the industry.

Another example is the development and use of open pollinated vegetable varieties, like
eggplant by small farmers which could further boost their income since eggplant enjoys
a high demand 365 days a year.

The Ring Spot virus resistant papaya is enhanced further, to address post-harvest
losses of up to 30-40%. The delayed ripening trait that was incorporated into the GM
papaya would allow farmers to harvest fully matured papaya which will subsequently
ripen with better quality which is maintained up to 14 days longer than its conventional
counterpart.

In rice, the development of varieties resistant to tungro and bacterial blight which is
blamed for 20% and 50% yield loss in rice respectively will further reduce the economic
risk in rice production. Using anther technology, wagwag rice has now intermediate
resistance to tungro, tolerance to salinity and excellent kernel quality in addition to being
early-maturing, semi-dwarf and high yielding. Other rice varieties produced through
marker-aided selections include, NSIC Rc 141 (Tubigan 7) and NSIC Rc 154 (Tubigan
11) which are resistant to the dreaded bacterial leaf blight, which is a serious threat
during the wet season. The PR33395-27-1-B-B-B is a new variety which may be used to
answer the unfavorable effects of climate change, such as greater rainfall variability,
 resulting in increased frequency of flash floods. The Philippines already suffers from
frequent typhoons from July to December. During this period, 10 to 40% of the rice area
is damaged by flash floods in such rice producing areas like Nueva Ecija, Isabela,
Cagayan, Pangasinan, Bulacan, Pampanga, Camarines Sur, Mindoro Occidental, Tarlac
and Nueva Viscaya. Almost all the present varieties cannot survived prolonged
submergence of more than three days, resulting in huge losses. Nationwide, production
losses due to flash floods are valued at 2 million pesos every year. PhilRice’s
submergence tolerant line named Raeline 10, which stands for rain-fed advance elite
line in addition to being tungro resistant, has intermediate resistance to bacterial leaf
blight, early maturing, moderate shatter ability and with eating quality comparable to
IR64, had 100% survival in 21 days of submergence. Field adaptation trial in
Pigcawayan, North Cotobato , a large percentage of the Raeline 10 plants survived 28
days of continues submergence under water, while IR64-Sub 1 was almost wiped out.

In Laoac, Pangasinan, the use of chemical fertilizers has been reduced by 45 % through
the application of biofertilizers.

The Philippine Coconut Authority has developed a scientific management system to curb
brontispa I coconut and synthetic varieties to replace ageing and unproductive trees in
the country. These products and services are crucial for at least 3.5 million farmers who
depend on coconut production as well as to salvage 20-100% of yields at peril.

OTHER BIOTECHNOLOGY ISSUES OF PUBLIC CONCERN

A number of biotechnology issues of public concern include the following: 1) public

health, 2) religious issues, 3) labeling , 4) environment protection, 5) economic
impact of the technology and 6) international trade and competitiveness.

1) Public health concern

Many consumers expressed wariness of new “supercrops” and novelty foods, fearing
that introduced genes could prove allergenic or harmful to humans. For example, if a
few genes inadvertently caused a plant to produce toxins at higher levels than that
found naturally in the non GM counterparts, there could be long-term health
consequences for humans. Some consumers are also worried that a gene
introduced into plants to protect against pests could also cause plants to alter their
pollen, thereby affecting the health of humans prone to some sensitivities such as
asthmatic individuals allergic to pollen.

2) Religious concern

Certain religious groups are concerned that food might contain genes from animals,
such as swine which is prohibited by some religious groups (e.g. muslims) in their
diet, and they have the right to know or be informed if these genes are present in the
food.

3) Labeling
 Some have suggested that the labels indicate the biotechnology used, so that
consumers could decide whether to purchase the product or not. For instance, some
people like the Japanese are quite sensitive about irradiated food due to their
traumatic experience with radiations as a result of the atomic bomb dropped in their
area during World War II.

4) Built-in resistance to pests and tolerance to herbicides of GM crops

There is the concern of the likelihood of transgenes escaping from the transgene
crops to their wild relatives. This can be addressed by the effective implementation
of biosafety regulations and testing.

5) Economic concern

Critics are concerned with the growing presence of large agricultural conglomerate
companies controlling the supply of seeds containing bioengineered traits. Adoption
of the bioengineered plants by farmers is dependent on need and world commodity
prices. Supporters of biotechnology cite convenience and lower rates as main
reason for high adoption by farmers but critics complain about the consolidation of
patent ownership of this new technology which they believe constitutes monopolistic
power in the market place. Their distrust is based in part on conceren about
dependency such concentration brings to the agricultural sector and the possible
abuse of such control.

The concern on private monopolistic power seems in order. Seed companies have
long sought to control their product by limiting farmers from saving seeds for future
planting which is traditional among many farmers especially in developing countries.
Also on March 3, 1998, a U.S. patent was granted to Delta and Pine Land Co. and
the Agricultural Research Service of USDA for a method of genetically engineering
plants to produce sterile seeds. This technology, called “technology protection
system” was subsequently dubbed the “terminator gene technology” by opponents.
The terminator gene is likely to breed in many GMO seeds by the year 2005. Some
question whether the future availability of seeds of genetically modified to contain
“terminator genes” could interfere with agricultural practices of farmers in many
developing countries to save seeds for the next planting season. Thus critics see
these new products as a means by which developing country farmers will become
dependent on multinational corporations and be driven further into poverty without
resources to purchase new seeds each year.

There also appears some concern about how much control companies wield over
research in food and agricultural biotechnology. Companies hold patents and
specific germplasm and research techniques needed for plant research.

6) International trade issues

At present the U.S. is leading the world in biotechnological research development of

GMOs and sale of technology worldwide and the playing field will continue to be
uneven unless other countries will aggressively pursue capability building in all
aspects of biotechnology such as products, techniques and marketing.

7) Biosafety
 On June 4, 1993, President Clinton signed the Convention on Biological Diversity, an
International agreement negotiated at the 1992 Earth Summit in Rio de Janeiro. This
diversity agreement is ratified so far by 174 countries, but not by the U.S. The
agreement calls for protecting a variety of plants and animals found in the wild. A
second meeting was held in Indonesia in November 1995. At the conference, the
parties to the convention on Biological Diversity (COP-2), countries agreed to fund
negotiations for a “biosafety protocol”.

In February 1999, at the sixth and final meeting of the negotiating group in
Cartegena, Columbia, representatives of the participating countries failed to reach a
consensus on the protocol that had the objective of “furthering the safe transfer,
handling and use, especially in trans-boundery instances of living modified
organisms (LMO) resulting from modern biotechnology that may have adverse effect
on human health, animal health, environment, biological diversity, conservation and
sustainable use of biological diversity and the socio-economic welfare of societies.

U.S. business dominate the food technology industry worldwide. Such domination
has contributed to problems with certain trading partners. For instance, the EU lacks
a transparent and predictable regulatory system for the genetically engineered
products. Without such a system in place, policy issues resulting to modified food
have become contentious between the trading partners. (Vogt and M. Parish, 1999.
CRS Report to Congress on Food Biotechnology in the U.S Science Regulation and
Issues).

APPLYING BIOTECHNOLOGY IN RESOURCE POOR AREAS

Modern biotechnology (genetic engineering) is not a silver bullet for achieving food
security, but used in conjunction with other techniques it may be a powerful tool in the
fight against poverty and food insecurity (Persley and Lantin 2000). Other approaches
are available and should be used. Narrowing the yield gap between those obtained from
farmers’ fields and those from experiment stations using the current technologies is just
one example. However, there is concern that some conventional alternatives will not be
able to produce the desired results within a limited time. The advantage of modern
biotechnology rests on the speed at which desired crop varieties are produced. In some
cases, the desirable genetic combination of traits is simply not possible through common
breeding methods, and can be done only through genetic engineering.

To increase food production by at least 40 percent within the next 25 years, Asian
countries not only have to move toward the best technological frontier (to push farmers’
yields to the optimum level), but keep moving the technological frontier itself. As long as
product safety, environmental and ethical concerns, and IP issues are adequately
addressed, modern agricultural biotechnology has the potential to significantly increase
the quantity and quality of the food supply for developing countries.

The resource-poor, rainfed areas in Asia are home to many poor people, and their
population is growing rapidly. Although migration may sometimes be the only viable
livelihood strategy, in many such areas, sustainable intensification of agriculture may be
the best way to achieve poverty reduction and food security. These areas characterized
 by poor soils, shorter growing seasons, lower and uncertain rainfall, and little
infrastructure or access to markets. Yield increases usually lag behind population
growth. Efforts by poor farmers to expand cultivation onto new lands to eke out survival
often lead to deforestation and erosion of fragile highland soils. That in turn threatens
hydropower, road, and irrigation infrastructure in the lowlands.

Policies and investments are required that can achieve food security in ways that protect
natural resources, thereby breaking the vicious cycle of poverty, low productivity, and
environmental degradation. Creation of nonfarm, rural jobs will also be important (ADB
2000b). Sizeable investments in biotechnology in Asia have been made in rainfed areas,
although DMCs continue to give high priority to irrigated agriculture. Irrigated areas
produce 75 percent of total cereal production in Asia. Many IARCs such as the Asian
Vegetable Research and Development

Center, CIMMYT, CIP, ICRISAT, ILRI, and IRRI; and most DMCs have invested heavily
in R&D on orphan crops such as rice, tropical maize, sorghum, potato, banana,
groundnut, and sweetpotato.

APPLICATION OF BIOTECHNOLOGY TO SPECIFIC AGRICULTURAL OBJECTIVES

In Asia, biotechnology has been applied mainly to develop improved varieties adapted to
specific environments. Specific areas where new applications of biotechnology could
address poverty reduction and food security are summarized as follows:

(i) Increasing Productivity and Stability of Crops in Rainfed and Marginal

Environments.

Producing more food on the same area of cultivated land would reduce pressure to
expand cultivated areas to forests and marginal areas. Broadening tolerance of
existing HYV cereals for drought, flooding, salinity, heavy metals, and other abiotic
and biotic stresses would increase yields in rainfed areas. CIMMYT and IRRI, in
cooperation with NARSs in different countries, are focusing their efforts to develop
HYVs of rice and maize for rainfed areas.

(ii) Improving Water Use Efficiency in Crops.

Future availability of water for agriculture is a major issue. By 2020, there may be a
water crisis in Asian agriculture (ADB 2000c). Crops with higher water use efficiency
and tolerance for drought would be an advantage. With the completion of the rice
genome, scientists will be able to identify genes responsible for drought tolerance.

(iii) Integrated Pest Management (IPM) Strategies to Reduce Pesticide Use.

The insecticides now used in many developing countries are often older, broad
spectrum, acutely toxic compounds. Many are now banned in industrial countries
except for export. They are a significant health hazard to farmers and farm workers
throughout Asia. Over 80 percent of total pesticide use in Asia is on cotton, rice, and
vegetables. In the past, governments encouraged the use of chemical pesticides as
part of a yield-increasing package of farm inputs, and some governments still
 subsidize pesticides. The need is now recognized for more sustainable approaches
to IPM to reduce losses to pests without harmful side effects on human health and
the environment. New pest- and disease resistant crops, produced with the aid of
modern biotechnology, may be important components of IPM strategies (Persley
1996). Early applications are being seen in the use of novel sources of resistance (Bt
genes) to control insect pests on maize and cotton. New pest-resistant cotton
varieties are being grown widely in the PRC by 3 million farmers covering 500,000 ha
(Pray 2000). Similar cotton varieties are undergoing field tests in India, Indonesia,
and Thailand. Genetically modified maize and cotton resistant to insect pests is
being tested in the Philippines.

(iv) Increasing Disease Resistance in Crops.

Biotechnology applied to disease resistance in crops would be especially valuable for

combating diseases in tropical environments that have not been controlled by
conventional means. These include important diseases such as downy mildew of
maize; bacterial blight and blast of rice, papaya ringspot virus; banana bunchy top
virus; and bacterial wilt of tomato, eggplant, and potato.

(v) Increasing Nutritional Quality.

Enhancing the protein, vitamin, and micronutrient contents of food grains would
greatly benefit poor consumers who cannot afford supplementary vitamins and
micronutrients. Under the Golden Rice Project, IRRI scientists are undertaking
biotechnology research to enhance the vitamin A content of rice by introducing
genes from daffodil (IRRI 2001).