Principles of AGR 1st Semester BB Sir Final 063
Principles of AGR 1st Semester BB Sir Final 063
Principles of AGR 1st Semester BB Sir Final 063
(A class note)
Prepared by:
Mr. B. B. Adhikari
Asst. Professor
Department of Agronomy
IAAS, Lamjung Campus, Sundarbazaar
Lamjung
2063
B . B Adhikari
Lamjung Campus-063
1.1 Definition of Agriculture, hunting and gathering system, shifting cultivation, subsistence 1
agriculture, traditional agriculture, commercial agriculture, green revolution
1.2 Definition of ecological agriculture, sustainable agriculture, soil less agriculture, precision 1
farming, contract farming, cooperative farming, periurban agriculture.
1.3 Definition of agronomy, relation of agronomy to other science, definition of food security, major 1
problems of Nepalese agriculture, role of agronomist in solving food problems
1.4 Classification of Crops based on phylogenic similarities, life cycle, growing season, agronomic 1
classification and special purpose classification.
2.3 Precipitation and its effect on crop production, arable land classification based on precipitation 1
(arid, semi arid, sub humid and humid), relative humidity and wind and their effect on crop
growth.
3. Tillage
3.1 Definition, brief history and objectives of tillage, soil tilth, types/methods of tillage (conventional 1
and conservation tillage), adventage and disadvantage of conventional tillage.
3.2. Definition of primary and secondary and inter tillage, conservation tillage (minimum, zero and 1
mulch tillage), adventage and disadvantage of conservation tillage.
4. Seed and seed quality
4.1 Definition of seed, seed technology, characteristics of quality seed (genetic, physiological, 1
physical, entomological, and pathological), importance of quality seed.
4.2 Different classes of seed (Breeder, foundation, certified seed I, certified seed II, improved seed), 1
seed germination, external and internal condition for seed germination, seed dormancy, causes of
seed dormancy, seed certification.
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6.1 Definition of soil fertility and soil productivity, criteria of essentiality of elements, classification 1
of essential elements (structural, mineral, macro and micro nutrients), forms of elements
absorbed by plants, dynamics of nutrients in soil plant environments.
6.2 Manures and fertilizers: Importance of organic manures, classification of manures (bulky and 1
concentrated organic manures), brief description of FYM, compost, vermicompost, animal
manures, night soil, sewage and sludge, biogas slurry, oil seed cakes, green manures.
6.4 Factors affecting fertilizer use, time of fertilizer application, methods of fertilizer application, use 1
and limitation of organic manures, green manures, bio-fertilizer and chemical fertilizer.
6.5 Integrated nutrient management, agronomical practices to be adopted for soil fertility and soil 1
productivity maintenance.
7. Weed Management
7. 2 Classification of weeds based on life cycle, cotyledons and morphological characters, modes of 1
weed seed dispersal (wind, water, animals and humans)
7.3 Concept of weed management, prevention, eradication, control, physical, chemical, biological 1
and chemical control methods, relative merit and demerit of different biological and chemical
control methods.
8.1 Role of water, water requirement of crops, water use efficiency, definition, objective and 1
principles, requirement and frequency of irrigation
8.2 Methods of irrigation: surface irrigation (flooding, check basin, basin/ring, border strip, furrow), 1
subsurface method, sprinkler irrigation, drip irrigation, advantage and disadvantage of sprinkler
and drip irrigation.
8.3 Scheduling irrigation: soil moisture depletion approach, IW/CPE approach, can evaporimeter, 1
critical stage approach.
8.4 Drainage: adverse effect of water logging, types of drainage: surface drainage (open ditch 1
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drainage, random field ditch drainage, land smoothing, bedding/dead furrow), subsurface
drainage
8.5 Rainfed farming: difference between dry land farming and rainfed farming, importance of rainfed 1
farming in Nepal, management of rained farming.
9. Soil erosion
9.1 Definition of soil erosion, types of water erosion (sheet, rill, gully, ravines, stream bank and 1
landslides), factors affecting water erosion, losses due to water erosion.
9.2 Water erosion control practices, wind erosion (saltation, surface creep, suspension), factors 1
affecting wind erosion, losses due to wind erosion, wind erosion control
10.1 Ideotype concept, traits for ideotype, characteristics ideotype of rice, wheat and maize, concept 1
of economic yield and biological yield, harvest index
10.2 Crop density, optimum plant population, factors affecting optimum plant population 1
Total 30
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Agriculture: Agriculture may be defined as the science, art and business of producing crops
and animals under human supervision. The term “agriculture”is derived from the Latin words
“ager” meaning soil and “cultura” meaning cultivation. It is very broad term, which includes
crop production, livestock farming, fisheries, forestry etc.
Subsistence agriculture
This is a type of agriculture system in which, producer consumes a large part of the final
produce. Most subsistence agriculture also produces some of crops or animals very little for sale.
Many farmers of Nepal practiced the subsistence agriculture system.
Traditional agriculture
Agriculture system, which are based on indigenous knowledge and practices and have evolved
over many generations. Many farmers of South Asia including Nepal follow traditional
agriculture.
Green revolution
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During 1960’s many countries were facing food deficit. The scientists at International
Agricultural Research Centers (IARC) were working to improve the production of food crops.
Dr. Norman Borlaug (a pathologist) working at CIMMYT, Mexico developed high yielding
wheat varieties, which were semi dwarf, adaptive, resistant to disease, responsive to fertilizer and
irrigation. These varieties were successfully introduced in many countries. Besides that farmers
were encouraged to use fertilizer, irrigation and pesticides. Improved varieties coupled with
production technology drastically increased the food production. Eventually Dr. Borlaug
received Nobel Prize 1970. IRRI also developed high yielding, semi-dwarf, fertilizer responsive
rice varieties, which increased the rice production of Asian farmers (where >90% rice is
produced). This whole process of transformation of agriculture is known as green revolution.
1.2 Definition of ecological agriculture, sustainable agriculture, soil less agriculture, precision farming,
contract farming, cooperative farming, periurban agriculture.
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Ecological agriculture/eco-farming
Ecological agriculture is the farming practices that enhance or at least do not harm the
environment and are aimed at minimizing the use of chemical inputs. The ecological agriculture
is based on the principles of increasing diversity, security of favourable soil condition for plant
growth particularly by managing organic matter and enhancing soil life, minimizing loss due to
flow of solar radiation, air, water and soil through microclimatic management, water
management and erosion control and minimizing loss from pest by means of prevention and safe
treatment.
Sustainable agriculture
Any agricultural practice or philosophy and approach of production system that makes
agriculture economically viable, ecologically sound, socially just and culturally appropriate.
There are different models of sustainable agriculture evolved throughout the world. Some of
these models are Low Input Sustainable Agriculture (LISA), Low External Input Sustainable
Agriculture (LEISA), organic farming, biodynamic farming, regenerative agriculture,
permaculture and natural farming.
a) Hydroponic system: Cultivation of crop in water is called hydroponic. In this system the
roots of plants are continuously or intermittently submerged in nutrient solution and aerial parts
are supported at the base with cardboard, plastic or wires. The continuous submergence limits the
oxygen supply and thus an aeration pumping system has to be provided for the growth of plants.
b) Aeroponic: Cultivation of crop in air is called aeroponic. In this system the plants are grown
in holes in panels of expanded polystyrene or foam plastic with roots suspended in mid air
beneath the panel and enclosed in a spraying box. Plant roots continuously or intermittently
saturated with a mist of nutrient solution.
c) Sand culture: Plants are grown in inorganic media like sand, gravel or in organic media like
coconut coir dust, saw dust etc and nutrient solution is given for plant growth.
Precision farming
In large area of field there is always variation in different aspects. That variation may be yielding
potential, incidence of weeds, insects and diseases etc. This special variability can be detected
with special scientific system like GPS (Global Positioning System), remote sensing etc. After
detecting the variability in the field, site-specific crop management practices can be applied. The
equipment like Variable Rate Technology (VRT) is now available, which can adjust seed,
fertilizer and pesticides according to need of specific site. This system of farming is called
precision or prescription farming.
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Contract farming
This is a farming practice in which land is taken on contract for cultivation of crops. Much big
company, transnational cooperation takes land on lease and grows crops on large scale for profit.
This system is also called cooperate farming. In Nepal, the poor, land less and small landholders
also enter into production relation of share tenancy, as there is no option for them other than to
sit idle and remain semi starved at home. Land reform act of 1964 made sharecropper as the legal
tenant. Thus there are lands, which have dual ownership of landlord and tenant.
Cooperative farming
This is a farming practice in which land, equipment, labour and benefit are shared equally among
the members of community or group involved in agricultural production. Kibutz in Israel is one
of the examples of co-operative farming. There may be some different form of cooperative
farming where only the part of production system or marketing system are shared among the
members of co-operative.
Peri-urban agriculture
In urban and semi urban area (periphery of city areas) vacant space, balcony, rooftop, backyard
space is utilized to grow vegetable, ornamental, herbal and fruit crops. Small animals like swine,
goat, poultry, pigeon, duck, rabbit, etc are raised either for commercial use or for home
consumption.
Hanging pots, baskets, sacs, plastic bottles, containers etc. are kept in sunny areas to utilize
vertical space and to grow crops either for beautification or for home consumption. Growers
generally utilize the garbage, recycled waste, and available local resources for cultivation. Plastic
tunnels, greenhouse, hydroponics and advanced technology are also used for commercial
production. As the consumers are available in nearby market, this type of agriculture is
remunerative and successful in the city. Urban agriculture is also done to utilize extra time after
office and business work, to supply fresh vegetable for home consumption, to protect
environment and beautify home. This type of agriculture is flourishing in many cities of the
world.
1.3 Definition of agronomy, relation of agronomy to other science, definition of food security, major problems
of Nepalese agriculture, role of agronomist in solving food problems
Agronomy
The term agronomy has been derived from two Greek words: Agros: means field and nomos
means management. Thus agronomy has been defined as “the branch of agricultural science that
deals with principles and practices of crop production and field management”.
Or
“Agronomy is the are and science of crop production covering soil, tillage, seed, sowing time,
methods of seeding, manures and fertilizers use with their time of application, irrigation
schedule, pesticide application, post harvest techniques and efficient and economic management
of farm”.
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3) Plant pathology
Different disease pathogens attack the plant from seeding to harvesting and storage.
Understanding the effect of the several fungal, bacterial and viral diseases, factors affecting their
development and control measures are very much essential for successful crop production with
higher crop productivity.
4) Entomology
Understanding the effect of various crop pests such as insects, mites, nematodes, rodents etc,
factors affecting their development and control measures are needed for successful crop
production.
6) Weed science
Weed not only reduce the crop yield as a result of competition but also impair the quality of
produce through contamination. Therefore, understanding of the deleterious effect of weed
competition and contamination and their suitable control measures is also essential for successful
crop production.
7) Seed technology
“Seed technology may be defined as the methods through which the genetic and physical
characteristics of seed could be improved. It involves such activities as variety development,
evaluation and release, seed production, processing, storage and certification. Seed technology is
an interdisciplinary science, which deals from varieties release to all aspect of seed handling.
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Plant breeder, agronomist, botanist, pathologist, entomologist and physiologist can work together
on the various aspects of seed technology.
8) Post harvest technology
All the crops that a farmer harvest from his farm can neither be sold nor consumed immediately
and some of the products are to be stored for long or short period or have to be processed before
use. Hence, the knowledge about storability, processing and processing quality is of great
importance for successful crop husbandry.
9) Agro-meteorology
An understanding of the effects of various components of climate and weather on crops such as
solar radiation, temperature, rainfall, humidity, hailstorm, wind and its velocity, other
atmospheric composition etc. is a prerequisite for successful crop production.
10) Agri-engineering
An understanding of principles and practices of irrigation and drainage management, soil and
water conservation and appropriate implements and machines are very essential for crop
production.
Food security
Food security is the practices of managing the essential food materials to global, regional or
national level. For people to be food secure that is to have access at all times to the food required
for a healthy and productive life. There must be both availability of food and access to food.
Access to food by households (and individuals) is conditioned by poverty. The poor usually lack
adequate means to secure access to food.
Over 1.1 billion people in developing countries were living in poverty in 1990, more than 500
million in conditions of extreme poverty. South Asia is the home of about 50% of the developing
world’s poor (more than 500 million people). Today there are more than 700 million people who
do not have access to sufficient food to meet their needs for a healthy and productivity life. They
often go hungry and do not know when they will have their next meal. Many of these hungry
adults and children also suffer from diseases associated with hunger and poverty. Hunger and
food insecurity have a significant effect on health and nutrition of both adults and children. They
can lead to growth failure in children.
South Asia is the home of about half of the developing world’s hungry and food insecure people,
but this population group is growing rapidly in Sub-Saharan Africa. Much of the poverty and
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food insecurity is in rural areas, mainly in low potential areas such as arid zones, but urban
poverty is also growing rapidly.
Major key factors that influence future food production and consumption
Global and regional food production and consumption during the next 10-20 years will be
influenced by a large number of factors. Changes in the following four sets of factors are likely
to be particularly important:
1. Economic growth and economic policies
2. Population growth and urbanization
3. Rural infrastructure, agricultural production technology, and access to modern inputs.
4. Natural resource management and environmental considerations.
5) Environmental degradation
Decline soil fertility. * Soil erosion * Flood and natural calamities.
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1.4 Classification of Crops based on phylogenic similarities, life cycle, growing season, agronomic
classification and special purpose classification.
Classification of plant is an important thing for scientific studies and is obviously based on well-
demarcated characteristics of the things or concept so classified. Crops are grouped in several
ways namely on the basis of range of cultivation, place of origin and distribution, different
characters, uses, cultivation requirements and other common behaviour. Crop plants are grouped
in three main classes according to the range of cultivation. They are:
a) Garden Crop
Crop plants that is grown on a small scale in gardens such as kitchen garden, flower garden and
backyard garden. Especially vegetable crops grown in little area for domestic use and not grown
for commercial purposes.
b) Plantation Crops
Crop plants that are grown on large scale. They are mostly not seasonal. They are permanent in
nature. Harvesting continues for long period of time from a single planting eg. tea, coffee,
coconut etc.
c) Field Crops
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Crop plants grown on large scale. They are mostly seasonal in nature eg. rice, wheat, maize etc.
They are concerned with solving basic needs of people.
Among these three classes, agronomy deals with field crops only. These are classified as under:
1. According to the place of origin
2. Botanical classification
3. Commercial classification
4. Economic classification
5. Seasonal classification
6. Classification according to ontogeny
7. Agronomic classification
8. Classification based on leaf morphology
9. Classification based on serving special purpose
2) Botanical Classification
This classification is based upon the similarity of plants parts. Field crops belong to the
spermatophyte division of the plant kingdom in which reproduction is carried out by seeds.
Common plants belong to angiosperm sub division characterized by having their ovules enclosed
in an ovary wall. Angiosperm is further sub divided in to two classes' i.e monocotyledons and
dicotyledons. These are shown diagrammatically as below.
Kingdom (Plant)
Division (Spermatophyta)
Sub division (Angiosperm)
Classes a) Monocotyledon and b) Dicotyledon
Orders
Families
Genus
Species
Sub species
Varieties
The binomial system of nomenclature was first time started by Swedish botanist Carl Linneaus in
1753. The name of the man who first gave the accepted scientific name is affixed by a letter or
abbreviation. eg. maize (Zea mays L.) Both genus and species are underlined separately or
written in italic letter. Genus first letter is written in capital letter and that of species in small
letter. Important families of different crops are given below:
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3) Classification according to Ontogeny: Crop plants are grouped according to their life
cycle.
a) Annual crops: Crop plants that complete their life cycles within a season or year eg.
Rice, wheat.
b) Biennial crops: Crop plants that complete their lifecycle within two years. First takes
vegetative growth and second year completes its life cycle. eg. Cabbage, radish,
turnip, carrot etc.
c) Perennial crops: Crop plants that live for three or more years. eg. Sugarcane, napier,
ginger, sweet potato etc.
4) Seasonal classification
Crops are grouped under the seasons based on their major growing field duration. These are:
a) Kharif crops: Grown during June-July to Sept-Oct eg. Rice, maize, groundnut.
b) Rabi crops: Grown during Oct-Nov to Jan-Feb eg. Wheat, mustard, barley, oats.
c) Zaid or summer crops: Grown during Feb-March to May-June eg. Blackgram, green
gram, cowpea, sesame etc.
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6) Rainfed plus flooded crops: eg. deep water rice, sugarcane, dhaincha, jute (C.
capsularis).
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a) Catch crops: Catch crops are cultivated to catch the forthing season. They replace as main
crop that has failed due to biotic or climatic or management hazards and utilize the remaining
period of the season. They are generally of very short duration, quick growing or usable at any
time. eg. green gram, blackgram. cowpea, coriander, onion etc.
b) Restorative crops: Crops which provide a good harvest along with enrichment of the soil. eg.
legumes. They fix atmospheric N in root nodules, shed their leaves during ripening and restore
soil condition.
c) Paira crops or relay crops: Crops which are grown a few days or weeks before the
harvesting of the standing mature crop. These crops are grown on residual moisture without
preparatory tillage. eg. lentil or khesari broadcasted in paddy field, fingermillet transplanted in
maize field.
d) Smother crops: Those crops which are able to suppress the population and growth of weeds
by providing suffocation (curtailing movement of air) and obscuration (of the incidental
radiation) by their dense foliage due to quick growing ability with heavy tillering and branching.
eg. barley, mustard, cowpea etc.
e) Cover crops: Those crop plants which are able to protect the soil surface from erosion (wind,
water or both) through their ground covering foliage or root mats eg. groundnut, marvel grass,
black gram, rice bean, sweet potato etc.
f) Nurse crops: Crops plants which help in the nourishment of other crops by providing shade
and acting as climbing sticks eg. rai crop in peas, crotolaria in tea.
g) Trap Crops: Crops plants, which are grown to trap soil borne harmful biotic agents such as
parasitic weeds, orobanche and striga that are trapped by solanaceous and sorghum crops
respectively. These weed seeds germinate when they came in contact with roots of these crops.
h) Mulch crops: Crops plants which are grown to conserve soil moisture from bare ground by
their thick and multilayered foliage eg. cowpea.
i) Sod crops: These plants are grown to conserve soil from erosion particularly in non-arable
areas. eg. Cynodon doctylon (Dubo grass), marvel grass.
j) Cash crops: These crops plants are grown for sale to earn hard cash eg. Jute, cotton and
sugarcane etc.
k) Silage crops: These crops plants are grown to preserve in silo pit in a succulent condition by a
process of natural fermentation for feeding livestock during lean months.
l) Green manuring crops: These crops plants are grown to be incorporated it into the soil fresh
to increase the fertility of the soil eg. Dhaincha, sunnhemp etc.
m) Mixed crops: these crops consist of two or more crops that are grown simultaneously in the
same field without preserving their identity with respect to field area. Seed of these crops may be
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mixed together before sowing and broadcasted irregularly or may be sown at the same time and
grown with the same management practices eg. maize + cowpea, wheat + mustard.
n) Intercrops: These consist of two or more crops that are grown simultaneously in alternate
rows in the same field. The crops are not necessarily sown at exactly the same time and their
harvest times may be quite different but they are usually simultaneous for a significant part of
their growing periods eg. sugarcane + wheat, maize + soybean.
o) Mono or sole crop: Crops, which are grown as pure or solid stands are called mono crops. eg.
transplanted rice, jute, tobacco etc.
p) Ratoon crop: This refers to the subsequent harvests taken from the regrowth of the root
stocks, stubbles and stumps after the first harvest eg. sugarcane, napier, berseem, oats etc.
q) Alley crops: When arable crops are grown in alleys formed by trees or shrubs, established
mainly to hasten soil fertility restoration, enhance soil productivity and reduce soil erosion they
are known as alley crops eg. Eucalyptus, Cassia, Subabool etc.
2.1 Definition of weather, climate, micro-climate, meteorology, agro-meteorology, major elements of climate,
solar radiation and its photosynthetic, photoperiodic, thermal and other effects on growth.
Weather
Weather is defined as the state of the atmosphere at a place (within local area like village, city or
even a district) and time (short term i.e. hourly, daily or weekly) as regards heat, cloudiness,
dryness, sunshine, wind, rain etc.
In other words the physical state of the atmosphere at a given place and time is referred to as
“weather”. The study of the effect of weather elements on crop production may help the farmer
to effectively plan for all his agricultural activities. Weather is presented daily by radio or TV as
sunny days, amount of rainfall,, maximum and minimum temperatures, humidity etc.
Climate
The dictionary meaning of climate is “the prevailing weather conditions of an area”. Climate is
defined as the aggregation of atmospheric phenomena as intensity and duration of light, the
temperature, the humidity, direction and velocity of wind, the quantity and pattern of
precipitation etc. over a relatively long period of time (month, season or year) and large territory
(zone, state, country or part of continent) constitute the climate of any place e.g. tropical,
subtropical, temperate climate etc. Climate can be studied as two categories for agricultural
purposes as:
A) Macro-climate
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It refers to the climate of relatively large part of the earth surface, which is observed and
recorded by a network of meteorological stations and forms the basis for the characterization of
zonal and regional climates.
B) Micro-climate
It refers to the weather condition of plant stand or around plant canopy or from the ground
surface of the plant stand to the deepest root zone in the soil. The climate of extremely small area
is called microclimate. It is characteristics of climate determined by the type and height of the
plant cover. It is also influenced by the climatic elements.
Meteorology
It is a branch of physical science that deals with the study of physical processes in the
atmosphere and is influenced by radiation, temperature, humidity and wind movement which are
responsible for changing the state of atmosphere.
Agro-meteorology
It is defined as a branch of applied meteorology that investigates the response of living
organisms to the change in the physical environment. The physical environment involves one or
more properties of the physical surroundings in which the living organisms grow such as air,
water, plants, microbes and foreign matters. The living organisms studied in agro-meteorology
are restricted to cultivated plants, livestock, insects, pests and organism of agricultural
importance.
The field of interest of agro-meteorology extends from the soil surface layer to the depth upto
root penetrates. In the atmosphere it is interested in the air layer near the ground in which crop
and higher organisms grow and animals live, to the highest levels in the atmosphere through
which the transport of seeds, spores, pollen and insects may take place.
Solar radiation
Solar radiation is the source of energy for all the physical processes taking place in the
atmosphere. Sun emits energy in the form of electro-megnetic radiation. Sun is a hot gaseous
body with a surface temperature of about 6000oC and emits huge quantities of energy. Solar
radiations have direct and indirect effect on climate. The modification of the nature of any place,
which is due to varying climatic conditions formed by the amount of solar radiation intercepted,
is called indirect effect of solar radiation. Direct effect of solar radiation on crop production is
expressed in term of the effect of light and temperature.
This solar energy also drives the process of photosynthesis, evaporation, heating the soil and air.
Almost the constant amount of solar radiation (1.94 cal/cm2/min) is emitted by sun continuously,
which is called solar constant. Solar radiation comes through the space without any change or
loss. When it enters the atmosphere, it undergoes changes and losses occur before reaching the
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earth due to absorption by atmosphere, reflection by clouds and scattering by dust particles. It
consists of stream or flow of particles. These particles are called photons. Earth intercepts only a
very minute part (1 in 2 x 109) of the total energy. Solar radiation performs two essential
functions.
1. Provide light for direct growth and development functions in the plants.
2. Provides heat that governs and indirectly affects various physiological processes in the
plant.
The instrument that is used to measure total incoming radiation is called pyranometer. Intensity,
duration and quality of solar radiation, which control growth and development in the plants. The
duration of radiation controls photoperiodism and the intensity and quality control the
physiological processes in the plants.
Short day plants are those whose reproductive phase is initiated when period of shorter light
duration (maximum of about 12 hours) is provided e.g. rice, soybean, sesame, cowpea etc.
Similarly, the long day plants require longer light duration (minimum of 13 hours) for the
initiation of reproductive phase e.g. wheat, barley, oat, lentil, chickpea etc. Day neutral plants on
the other hand do not have any specific requirements of duration of light period for the initiation
of the reproductive phase e.g. buckwheat, sunflower, cotton, tobacco, majority of maize varieties
and some varieties of cowpea.
2. Photosynthetic effect
Solar radiation intensity has its influence on photosynthesis of the plants. It is affected by
quantity and quality of light. In general higher is the solar radiation higher is the photosynthetic
rate. Normally, higher solar radiation intensity is suitable for most of the crop plants but the
requirement varies with plant to plant, with their varieties and with their stages of growth. The
radiation that utilized in the photosynthesis process includes the wave lengths ranging from 0.36-
0.76 micron known as photosynthetic active radiation.
Not all the waves in solar radiation spectrum are equally important in plant growth and
development processes. For example the radiation below 0.25 micron is harmful to the plants and
that above 0.76 micron has almost heat or thermal effects only. In the colour spectrum of solar
radiation wave of different colour bands have different effects on the plants. Yellow, orange and
red bands are important in photoperiodism. Similarly, blue, orange and red rays are important in
photosynthesis.
3. Photothermic effect
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Another important influence of solar radiation intensity is in terms of increase in the plant
temperature with the increase in the level of solar radiation intensity. Higher heat builds up in the
plants result in increased transpiration demand. Plants increase their transpiration demand in
order to dissipate the heat to maintain required plant temperature. Light also influenced on
stomata and their opening and closing also. Usually leaves developing under full sunlight
condition have reduced size and closer arrangement of stomata than the plants grown in shade.
Temperature
The measure of intensity of heat energy or hotness or coldness of a substance is called as
temperature. It is measured in metric system i.e. in Celsius scale in which 0 is the freezing point
and 100 is the boiling point. Radiation from the earth is the primary source of heat energy.
Temperature is the most important climatic variable, which affects plant life. The growth of
higher plants is restricted to temperature between 0-60oC and crop plants are further restricted to
a narrower range of 10-40oC. However each species and variety of plants and each age group of
plants has its own upper and lower temperature limits. Beyond three limits a plant gets
considerable damaged and gets even killed. Temperature affects the physical and chemical
processes within the plants. The diffusion rate of gases and liquids change with temperature.
Solubility of different substances depends upon the temperature. The stability of the enzyme
system is affected by the temperature.
Cardinal temperature
Every plant community has its own minimum, optimum and maximum temperature known as
their cardinal temperature. These critical low and high temperatures are required for better
growth and development of crops. They differ with the crop, variety, physical stages of the crop
plants etc. The three types of temperature ranges are:
1. Optimum temperature
The temperature at which a plant functions best is called as the optimum temperature. The ideal
temperature conditions for crop production are in the range of 31-37 oC for hot season and 25-
31oC for cool season crops.
2. Maximum temperature
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Maximum temperature is the one that can be tolerate without injury to crop plants. The
maximum temperature tolerance varies greatly with the crop species. Above which plant growth
stops. The tolerable maximum temperature for hot season is 44-50 oC and cool season crop is
31-35oC.
3. Minimum temperature
Minimum temperature is the temperature at which any plant can continue its activity and below
which no growth occurs. It is approximately the freezing point of water. The growth of many of
the tropical plants is retarded at 20oC and are frequently killed at 10 oC. The tolerance range of
minimum temperature for cool season crops ranges between 0-5oC and hot season crop 15-18oC.
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Effect of temperature on plant processes
1. Biochemical reactions
Temperature affects different types of biochemical processes in plant system. These are
photosynthesis, respiration, transpiration etc. Biochemical reactions are conducted by the
presence of different types of enzymes. Any chemical reaction increases with increase in
temperature. These reactions increase with increase in temperature up to a limit beyond which
the rate of reaction decreases.
a) Photosynthesis
Rate of photosynthesis is reduced due to reduction in temperature. If the light is not a limiting
factor in photosynthesis, the biochemical processes associated with photosynthesis may be
limited by the temperature. When maize plants are subjected to treatment of 10 oC for 10 days,
the rate of photosynthesis is also reduced by 33% of the untreated plants. Temperature also
enhances the production of chloroplast due to which the chlorophyll synthesis will be influenced.
At low temperature, leaves become yellow due to degradation of chlorophyll. Temperature also
governs the rate of leaf emergence and expansion. Leaves emerge at shorter interval with
increase in temperature.
b) Respiration
Photosynthesis is independent to soil temperature but respiration is affected. Higher is the soil
temperature, higher is the respiration, lower is the soil temperature lower is the respiration.
Temperature strongly affects respiration within the range of 0-35 oC. The rate of respiration
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increases about 2-4 times for each 10oC rise in temperature. With further increment in
temperature upto 40oC the rate of respiration decreases. Enzymes begin to denature rapidly at
higher temperature beyond 40oC.
c) Transpiration
Transpiration increases when the magnitude of the differences in temperatures between the leaf
surface and adjacent air. Temperature also affects cuticular transpiration also. A rise in
temperature brings about increase in the rate of transpiration.
d) Activities of growth substances
At optimum temperature the activity of auxin, gibberellins and cytokinins (growth promoters)
are high and activity of abscisic acid (growth regulator) is low with the result that growth rate is
increased. At high and low temperature, the balance of growth substances change and affect
growth.
Where Tmax is maximum temperature and Tmin is minimum temperature of the day and Tb is the
lowest temperature at which there is no growth which is also called base temperature. Base
temperature of rice, wheat and maize is 10, 4.5 and 10oC, respectively.
Thus, a day of 15oC would count as 10 degree days. The concept of degree days can be used to
estimate the suitability of a crop for a given climatic region assuming water is available. This can
also provide an index for comparing the thermal needs of plants as well as for indicating the
suitability of a location for a particular crop. Calculation of GDD is useful for predicting
harvesting dates and secondly, they are useful to select optimum date of planting.
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2.3 Precipitation and its effect on crop production, arable land classification based on precipitation (arid,
semi arid, sub humid and humid), relative humidity and wind and their effect on crop growth.
Land classification
Based on precipitation or amount of rain that falls on the earth’s surface in a year earth has been
divided into the following regions:
a) Arid region: That region where annual rainfall is less than 250 mm. Crop production is
dependent on supplemental water supply through irrigation in these areas.
b) Semi-arid region: Those areas where annual rainfall is about 250-500mm and crop
production of these areas requires either farming practices that conserve water or needs
additional irrigation when there is uneven and erratic rainfall.
c) Semi-humid region: Those areas where annual rainfall is about 750-1000mm and these
areas are allow the cultivation of different types of crops.
d) High humid region: Areas that have annual rainfall of more than 1000 mm and these
areas are suitable for cultivation of water requiring crops like rice, jute etc.
Wind
Air in motion is called wind. It is an important climatic element and has direct and indirect
influence in crop production. Wind is indirectly responsible for causing rainfall and changing the
humidity of a certain places. Directly, the gentle wind is responsible for promoting
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photosynthesis by supplying CO2 in the deeper leaf layer of plant canopy. Gentle wind helps to
pollinate the crop plants, water uptake, conduct proper metabolism, and regulates the
temperature of plant canopy. Hot dry wind is harmful for crop plants because such wind
accelerates the transpiration and evaporation from the soil causing desiccation of plants. It also
affects the photosynthesis by the closing of stomata. High wind velocity causes lodging of
crops, breakage of plant parts, shattering of grains, flower drops and uprooting of whole plant. In
desert and light soil containing field the high wind velocity causes more soil erosion also.
3. Tillage
3.1 Definition, brief history and objectives of tillage, soil tilth, types/methods of tillage (conventional and
conservation tillage), advantage and disadvantage of conventional tillage.
Introduction
Dictionary meaning of tillage is “the preparation of land for crop bearing”. Tillage refers to the
physical manipulation of soil by using different tools and implements in good tilth for better
germination of seed and subsequent growth of crops. Tillage includes all operations and practices
which are used for getting change in physical characters of soil. Tillage includes activities such
as ploughing, harrowing, discing, planking, leveling, and other various intercultural operations.
It is most important and time consuming operation in the field crop production and about 30% of
the total cost of cultivation is for tillage operations. Jethro Tull, called a father of tillage purposed
a theory in 1731 AD that plants absorb minute or fine particles of soils directly from the field.
Therefore he suggested that a number of ploughing and other operations is very essential for
making fine particles of soils. His theory was given in famous book “Horse-hoeing husbandry”.
From the scientific research and evidences it is proved that plant cannot take direct fine soil
particles from the field and the tillage operations are carried out only to prepare seed bed for
sowing crops.
Tillage was considered as an ‘art’ and in recent years research evidences has focused tillage as
‘science’. After harvest of crop, soil becomes hard and compact. This may be due to beating
action of rain drops, irrigation and subsequent drying, movement of intercultural implements,
and labour cause soil compaction. Weeds and crop stubbles are also present in the field, which
may disturb for the sowing of seeds. Seed require loose, friable soil with sufficient air and water
for good germination. Therefore a lot of cultural operations are needed to prepare the virgin soils
into a good seed bed. Tillage operations and methods of land preparation vary from place to
place and even in the same place, depending upon the climate and crops cultivated.
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Most of the present forms of tillage implements made out of wood or iron or combinations of
iron and wood have been designed, developed and manufactured in the 20 th century. After 1950
efforts made to improve the tillage operations aimed of reducing the cost of cultivation,
timeliness of operation achieving desired quality of work. It is normally considered that around
30% of the total cost of cultivation is involved in tillage operations.
Objectives of Tillage
There are several objectives of tillage operation among them the most important objectives of
tillage are listed as below.
1. To improve the structure of soil by breaking up the soil mass into loose particles which is
essential for suitable seed bed preparation? Good seed bed is necessary for early seed
germination and initial stand of the crop.
2. To conserve soil moisture through mulching and brings water to root zone from ground water
table.
2. To remove crop stubbles, weeds and their parts like bulb, stolons etc. which is essential for
clean cultivation.
3. To conserve soil moisture through higher infiltration, reduce runoff and increase depth of soil
for moisture storage due to which the rain water could be absorbed easily and soil erosion
can be minimized.
4. To increase oxidation decomposition or mineralization of soil organic matter and increase the
organic carbon content and nutrient availability of the soil.
5. To increase soil aeration which helps in multiplication of beneficial soil microorganisms,
earthworms and degradation of herbicide and pesticide residues and harmful allelopathic
chemicals exuded by roots of previous crop or weeds.
6. To break the hard pans and compacted layers increase the depth of root penetration. Roots
proliferate profusely in loose soil which helps in better nodulation in legumes, better
anchoring of plants for better mechanical support, inducing drought resistance etc.
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7. To incorporate the applied manures and fertilizers and soil reclaiming materials into the soil
by soil inversion action of tillage. Incorporation of manures and fertilizers reduce
volatilization loss.
8. To destroy insect- pest eggs, dormant pupae and fungal spores and their breeding places,
which are present on top layers of soil. They are exposed to sun’s heat or to birds resulting in
reduced pest attack on the succeeding crop.
Soil tilth
Tilth is the term used to express the physical condition of soil i.e. distribution of soil aggregates
and friability of soil resulting from tillage. Soil tilth is the physical condition of soil. A soil is
said to in good tilth when it is soft, friable and properly aerated. Such soil permits easily
infiltration of water and are retentive of moisture for satisfactory growth of plant. A soil with
good tilth is quite porous, friable or mellow and has capacity of free drainage of water upto water
table. When the soil is good tilth soil would be roughly equal capillary and non capillary pores.
Good tilth soil has high water retentive capacity, good aeration and adequate infiltration
capacity. This facilitates free movement of air and moisture in the soil and increase infiltration.
With the increase in non capillary pores in good tilth soil, the soil aeration, the activity of soil
microorganisms and chemical reactions will be increased. For the availability of oxygen in the
rooting zone and to improve the moisture retention capacity of soil, the total porosity and
distribution of pore sizes are very important. Soil tilth is not static but changes with time. When
the land is continuously cropped by using heavy implements, continue heavy rainfall and erosion
by water and wind may destroy the soil tilth. Soils with larger aggregates (more than 5 mm
diameter) are necessary for irrigated agriculture while higher percent of smaller aggregates (1-2
mm in diameter) are desirable for dry land agriculture. The activities of wetting and drying of
soil, or freezing and thawing of soil often regenerates desirable soil tilth.
Concept of Tillage
The ultimate aim of tillage is to manipulate the soil from a known condition into different desired
conditions by mechanical means. Broadly speaking tillage includes all those operations before
and after seed placement, which is concerned with bringing about desired changes in soil
structures, condition for seed germination and growth of the crops such as pulverization, cutting,
inversion, movement of soil etc. The performance of tillage tolls is largely dependent on the soil
condition, tool shape and mode of operation. The force applied by tillage tool brings a fixed
change in the soil condition. The desirable change of soil condition should be evaluated
quantitatively. Considerable advancement has been made in last 50 years in tillage tolls design.
However very little efforts have been made with regards to measurements of the reaction of
tillage tool on soil and its effect on plant growth and yield. An appropriate and adequate
procedure however is essential to measure and specify the tillage tolls. This would not only
optimize the tillage operation but also save the energy input apart from improving the quality of
works. The tillage of the soil consists of two types of operations, which are:
A) First part: Very elaborative and difficult operation of preparing the soil suitable for sowing.
This part comprises of series of operations like ploughing, harrowing, planking etc (to open, to
break up the clods and soil to pulverized condition). This part can be accomplished by:
i) Manual labour: Digging and preparing the ground with hand tools.
ii) Use of bullock pairs or any other draft animals and driven implements.
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iii) Use of mechanical power and power driven implements (Tractor and tractor driven
implements). All these implements come under preparatory of primary tillage.
B) Second part: These are the light type of operations and are known as inter cultivations done
after the crop is sown/ planted, germinated and is about 3-4 weeks old. This operation has to be
least once or may be repeated depending upon the weed infestation, crops grown and physical
condition of the soil. This part can also be accomplished by manual labour, bullock driven
implements, power driven implements. These operations come under the secondary tillage.
Types of Tillage:
There are two types of tillage system which are applied for tillage operation. These are:
A) Conventional tillage or Traditional tillage
Conventional tillage refers to different types of tillage operations performed before, during and
after field preparation for seeding, transplanting and cultivating the crops. The soil is opened
with MB plough for primary tillage. Conventionally it is though that land should be prepared
thoroughly with repeated ploughings. After ploughing, the fields are left with large clods with
some weeds and stubbles partially uprooted. Harrowing is done to a shallow depth to crust the
clods and to uproot the remaining weeds and stubbles. Disc harrows, cultivators, blade harrows
etc. are used for secondary tillage.
Disadvantages
1. In conventional tillage system the soil is subjected to wind and water erosion because
only about 15% organic residues are left on the field surface.
2. The timing of operation is too difficult to meet the requirements and costs of energy and
labour are too high and in most of the cases it is uneconomical.
3. Hard pans formation may take place in the soil by the continuous use of heavy
implements, which restrict root growth of crop.
4. The heavy loss of soil, water and plant nutrients takes place in conventional tillage
compared to conservation tillage.
Due to such problems or limitations associated with conventional tillage the need of optimizing
the type and frequency of tillage operations has become a pressing issue. In this context zero or
minimum tillage or reduced tillage is most often suggested.
B. Modern concept of tillage or Conservation Tillage
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Traditionally it is thought that repeated ploughing is essential during field preparation. By the
analysis of cost benefit ratio of crop production it was observed that repeated ploughing was not
cost effective. Modern concept of tillage is developed by emphasizing minimal cultivation.
Under this system of tillage sowing operations are carried out with little disturbance to the crop
residues. Considering the time loss for tillage operations, minimum and zero tillage have been
developed and this concept is together known as conservation tillage.
The objective of conservation tillage is to reduce the loss of soil, water, plant nutrients etc.
According to this concept a large amount of organic residue should be left in the soil surface to
increase the organic matter content in the soil which helps to protect the soil surface from the
beating action of rain drops, increase the infiltration of water, improve the soil structure and
maintained the soil fertility and productivity also. This system is frequently referred to as
stubble mulching, eco-fallow, limited tillage, reduced tillage, minimum tillage, no tillage,
conservation tillage, direct drill etc. This system of tillage is widely adopted in western countries.
3.2. Definition of primary and secondary and inter tillage, conservation tillage (minimum, zero and mulch
tillage), advantage and disadvantage of conservation tillage.
Based on the purpose and onset of operation, tillage may be classified into following
categories:
Types of tillage
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Tillage operations are carried out in normal season or main season of planting and intercultural
operations of any crop is called on season tillage. According to the types of implements used
and time of operation on-season tillage can be classified under two major headings:
a) Preparatory tillage
b) Inter tillage
a) Preparatory tillage:
Tillage operations that are carried out after the harvest of previous crop and before sowing and /
or planting of succeeding crop are known as preparatory tillage operations. Preparatory tillage
operations include primary and secondary tillage operations.
i) Primary tillage
The operations performed for initial cutting or opening and inverting the hard or compact soil,
(new land or virgin land and cultivated land) to a depth of 10-30 cm. It is performed immediately
after harvesting of the previous crop or untilled fallow or to bring virgin land under cultivation
(as it is in shifting cultivation) at the beginning of the new crop season. During primary tillage
the soil is inverted, weeds are uprooted and stubbles are incorporated into the soil. The
equipments used in these operations are generally heavy implements requiring more energy per
unit area. The main objective of primary tillage operation include deep opening and loosening of
the soil to bring about a desirable tilth through heavy equipments like Mould Board (MB)
plough or disc plough. Opening of trenches or ridges and furrows, shattered, twisted, inverted
and sheared for further preparation are the important operations performed in primary tillage.
This operation is done once, twice or thrice per year in normal and settled agriculture and once in
4-5 years in dry land agriculture which depends upon the soil type, agro-climatic conditions and
the nature of the farming. Primary tillage implements may be bullock drawn and tractor drawn.
Bullock drawn primary tillage implements are mould board plough (MB plough), country plough
(indigenous plough or desi plough) and tractor drawn implements are mould board plough, disc
plough, disc harrow in light soil, sub soil plough, chisel plough etc.
Only secondary tillages may be sufficient as preparatory tillage in cropping under upland soil
conditions and also when the preceding crop is harvested by tillage operations as well as in other
similar situations.
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b) Inter tillage
Tillage operations that are carried out for manipulating the soil after the seed is sown or young
plant has emerged are known as inter tillage operations. Inter tillage operations are also called
intercultural operations. The main objectives of intercultural operations are to control weeds,
increase porosity by pulverizing the soil and make dust mulch in the soil surface for reducing the
evaporation loss. Placement of fertilizers (top dressing), weeding, intercultural hoeing, earthing
up etc are intercultural operations. By increasing porosity of the soil there will be increased in
the initial rate of intake of water in the beginning of the rainy season, increase infiltration of
water, reduce runoff loss and provides aeration in the root zone. The depth of intercultural
operation depends upon the type and condition of crop, rooting depth, season of planting, type of
soil etc. Equipments used during intercultural operations are hoe, spades, cultivators etc.
2. Off-season tillage
Preparatory tillage operations that are performed during the off season or before the main crop is
cultivated is known as off-season tillage. It is done for conditioning the soil suitably for the
forthcoming main season crop. Different working schedules are made during uncropped seasons.
Activities like leveling to desirable grade, leaching to remove salts, lowering of seasonal water
table and reducing the population of harmful flora and fauna in the soil are performed during off-
season. Off season tillage is categorized into four types which are i) post harvest tillage ii)
Summer tillage iii) Winter tillage iv) Fallow tillage.
3. Special Purpose Tillage
Tillage operation performed to serve special purposes are called special purpose tillage. These
are: i) sub soiling ii) leveling iii) blind tillage iv) clean tillage v) contour tillage vi) wet tillage
vii) minimum tillage, viii) zero tillage and ix) mulch tillage. Brief description of some of the
tillage practices are given below.
i) Minimum tillage
Minimum tillage operation is a practice in which the tillage operations are reduced to the
minimum number necessary for ensuring good seed bed preparation. Tillage number can be
reduced by omitting operations which do not give much benefit when compared to the cost and
by combining agricultural operations. This method is normally followed in those situations
where crop residues are left in situ in the field for decomposition. It is easy to adopt in coarse and
medium textured soils and is practiced for a period of 2-3 years.
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Disadvantages
1. Sowing operations are difficult with ordinary equipments.
2. Continuous use of herbicides causes pollution problems and dominance of perennial
problematic weeds.
3. Seed germination is lower; more N has to be added because rate of decomposition of
organic matter is slow.
Zero tillage method is highly effective under sloppy lands where soil and water erosion are
heavy. In mechanize system machines accomplish four tasks in one operation i.e. clean a narrow
strip over the crop row, open the soil for seed insertion, place the seed and cover the seed
properly. No tillage method has been successfully adopted for planting grasses and legumes.
In zero tillage system different herbicides are used to control unwanted vegetation. Before
sowing, broad spectrum and non selective herbicides with relatively short residual effect are
used. During subsequent stages, selective and persistent herbicides are needed. The herbicides
applied should not cause injury to the succeeding crop.
This system is found to be an alternative to the conventional tillage system where soils are
subject to wind and water erosion, the timing of tillage operations is too difficult, the
requirements and costs of energy and labour are too high and performance is insufficient.
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In the rice-wheat system, field preparation is difficult for sowing wheat which may be due late
season for wheat sowing because of long duration varieties of rice, difficultly in field preparation
in marshy land etc. In such condition zero tillage practice is useful to the farmers. Application of
non-selective herbicide like Paraquat @ 2 liters a.i. per ha to kill rice stubbles and other
vegetations is essential. Wheat seed is drilled in between the rice stubbles and covered with
mulch. This mulch provides clothing that adequately protects the soil from erosion without
presenting problems of weed control, soil fertility, infiltration of rain water and aeration.
Undisturbed soil appears more dense and firm and bears the characteristic structure, texture and
other physical, chemical and biological capacities of typical soils rich in organic matter. The
activity of earthworm increases resulting in biological turning and opening of the soil, forming
tunnels and mittens in or on the soil. Undisturbed decayed roots also provide channels.
There are certain disadvantages of zero tillage. The seedling establishment in zero tillage is
about 20% less than in conventional methods that’s why the seed rate should be increased by
20%. This practice reduces labour cost but crowd work into a shorter time period immediately
prior to planting. Land improvement, reclamation of problem soils, cultivation of tuber, root and
rhizome crops that bear economic yield in subterranean parts are seriously affected in the zero
tillage system of farming.
4.1 Definition of seed, seed technology, characteristics of quality seed (genetic, physiological, physical,
entomological, and pathological), importance of quality seed.
Seed
A true seed may be defined as a fertilized mature ovule that posses an embryonic plant, stored
food material and a protective coat or coats, which is viable and has got capacity to germinate.
Basically the seed is made up of the embryo, the endosperm or other food reserves and the seed
coat. However, the broad definition of seed includes all plant propagules including rhizomes,
tubers, bulbs cuttings, grafts and all vegetatively propagated materials besides mature ovules.
Actually these are not true seeds, these are seed materials and used for multiplying the plants.
Grain
Grain is the part of commercial produce used for human and animal consumption. Certain
characteristics of grains are given below:
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Seed Technology
Seed technology comprises techniques of seed production, seed processing, seed storage, seed
testing and certification, marketing and distribution and their related research on these aspects.
Feistrizer (1975) define “Seed technology as the methods through which the genetic and
physical characteristics of seed could be improved. It involves such activities as variety
development, evaluation and release, seed production, processing, storage and certification”.
Seed quality
Seed is said to be quality if it is scientifically produced (under the supervision of seed certifying
agency) and is distinctly superior in terms of genetic purity or varietal purity, freedom from
admixture of weeds and other crop seeds, seed health, high germination and vigor, seed
treatment and safe moisture content etc. Which are the important parameters to determine the
seed quality.
It is the degree of excellence in regards to the characteristics referred to above that determines
the seed quality. If the seed lot posses high genetic purity and high germination percentage and a
minimum of inert, weed and other crop seeds and free from diseases, it is said to have high
quality and if it is lacking in any of these, it is said to be low quality.
Quality seed
To become a quality seed, it should pass the certain standard fixed for certified seeds. It implies
that if a seed lot meets the certification standards, it is good quality seed and if it does not meet
the certification standards it is obviously of a lower quality seed. Seed is said to be quality if it
posses the following characteristics:
1. Improved variety
The variety must be truly superior to existing one. It must be latest and best suited to the area in
regards to production potential and other characteristics.
2. Genetic purity
There should not be any genetic deterioration in the variety. If the seed posses all the genetic
qualities that breeder has placed in the variety it is said to be genetically pure. Genetic purity is
directly responsible for higher yield. There should not be off type plant and no varietal mixture.
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3. Physical purity
Physical purity of a seed lot refers to the physical composition of seed lots. It must be clean and
processed, free from inert materials, weed seeds and other crop seeds or variety. Higher the
content of pure seed the better would be the seed quality.
4. Physiological quality
Quality seed should have high germination capacity and seed vigour. It should have bold and
plumpy grain. It must be dried to proper moisture percent. High germination percentage and
vogour results into raising of an excellent crop having adequate plant population and uniform
growth. Seed moisture is the most critical factor to determine viability during storage. The seed
size, weight and specific gravity have been found positive correlation with seed germination and
vigour in many crops.
5. Entomological quality
The quality seed must be free from insects. The quality seed lot very much depends on its health.
It should be free from insects and must be treated with proper chemicals.
6. Pathological quality
The quality seed must be free from diseases. The quality seed lot very much depends on its
health. It should be free from seed borne diseases and must be treated with proper chemicals.
7. Other characteristics
Seed colour often reflects the condition during seed maturation. Good normal colour and shine
have been regarded as invaluable quality guides by the farmers from the time immemorial.
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was introduced in different countries, farmers started to use fertilizers, irrigation also. This
brought green revolution. Thus quality seed is a carrier of new technology.
4.2 Different classes of seed (Breeder, foundation, certified seed I, certified seed II, improved seed), seed
germination, external and internal condition for seed germination, seed dormancy, causes of seed dormancy,
seed certification.
Classes of seed
The seeds are evolved, tested and if found good they are multiplied and distributed to the farmers
for commercial production of the crop. Therefore according to the nature and precautions with
which the seeds are produced, they are classified into the following groups:
2. Foundation seed
Foundation seed is the progeny of breeder seed and second grade seed in order of its genetic
purity. Production of foundation seed is done generally by government farm or by certain
organizations (NARC, Cooperatives, National Seed Company, NGOs). The foundation seed is
relatively less pure compared to the breeder seed. It has white tag and available in limited
quantity.
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Certified seed 1st generation is the progeny of foundation seed. Its production is done in such a
way that specific genetic identity and purity is maintained according to standards specified for
the crop being certified. This seed is also produced in government farm or by certain
organizations. During the period of seed production, the seed inspectors inspect the field and the
seed thus produced is processed, bagged and tagged in the presence of the seed technicians of the
seed-certifying agency. After proper leveling the seed is sold to the leader farmers or certain
organizations. It has tag with blue border.
5. Improved seed
Improved seed is the progeny of certified seed 2nd generation. It is produced in the farmer's field
with supervision of certifying agencies. They have a wide range of adaptability, tolerance to
adverse condition of environment such as drought, flood and frost. Their quality is acceptable to
the local market and consumers. It is available in sufficient quantity. It has yellow tag and is used
for commercial cultivation of crop.
Seed germination
Germination is the emergence and development of a seedling from the seed embryo, which is
able to produce a normal plant under favorable condition. All the viable seeds which have
overcome dormancy (if any) either naturally or artificially will readily germinate under suitable
environmental conditions necessary for seed germination i.e water, oxygen, temperature and in
some case light.
Types of germination
There are two kinds of seed germination, which are:
1. Epigeal germination (cotyledons above the ground).
2. Hypogeal germination (cotyledons below ground)
1. Epigeal germination
In epigeal germination, the cotyledons are raised above the ground where they continue to
provide nutritive support to the growing points. During root establishment the hypocotyls begins
to elongate in an arch which breaks through the soil, pulling the cotyledon and enclosed plumule
(epicotyl) through the ground and projecting them into the air. Afterward the cotyledons open,
plumule growth continues and the exhausted cotyledons wither and fall to the ground. It is found
in bean, soybean, black gram, green gram, groundnut, pigeon pea, sunflower, pine seeds etc.
2. Hypogeal germination
In hypogeal germination the cotyledons remain beneath the soil, while the plumule pushes
upward and emerges above the ground. The plumule elongates in hypogeal germination whereas
in epigeal germination, the hypocotyls is the rapidly elongating structure. Regardless of their
above ground or below ground locations, the cotyledons continue to provide nutritive support to
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the growing points throughout germination. Most cereals or monocots except onion are hypogeal
type of germination. Some winter pulses have also hypogeal germination eg. pea, gram, lentil
etc.
A) External factor
a) Temperature
b) Moisture
c) Air (O2 and CO2)
d) Light
B) Internal factors
a) Reserved food materials
b) Dormancy
c) Viability
d) Poisons and inhibitors
Seed Dormancy
Dormancy is defined as the inactive period of seed embryo, during which growth slows or
completely ceased. During dormant period the growths of the seeds remain suspended and they
are said to be in rest stage or dormant stage and this phenomenon is called as dormancy of seeds.
All the viable seeds have capacity to germinate if placed under suitable conditions necessary for
germination. While in certain plants such seeds will immediately germinate after harvest in other
they fail to germinate, which may due to internal factor and environmental factors or external
factors.
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degree of hardness depends on the degree of maturity, the ripening conditions and the storage
time.
2) Physiological Dormancy
Sometimes, the dormancy of seeds results due to the presence of certain germination inhibitors
(abscisic acid, ferulic acid, dormin etc.) either in some parts of the seeds such as testa,
endosperm, embryo or in embryo surrounding structures like the juice or the pulp of fruit
(tomato) and glumes (oats). Abscisic acid acts as the germination inhibitor in dormant groundnut
(Arachis hypogea), cotton etc. Dormancy due to immaturity of the embryo which fails to develop
fully by the time the seeds are shed. In such case the seeds germinate only after a period of rest
during which the development of embryo inside the seeds is completed.
3) Genetical dormancy
The structural and physiological factors controlling dormancy are under control of specific
genes. In this case dormancy is primarily determined by genetic makeup of seeds and varies
widely among species and even within species. The intensity of dormancy in rice varieties is
controlled by a varying number of partially dominant genes that have cumulative unequal effect.
B) External factor
i) Low temperature or chilling requirement
In certain plants such as apple, rose, peach etc the seeds remain dormant after harvest in the
autumn because they have a low temperature of chilling requirement for germination. In nature
this requirement is fulfilled by the winter temperature. In such case the seeds remain dormant
throughout the winter season and germinate only in the following spring. Such a chilling
treatment is known as stratification. The moistened seeds are usually preconditioned at
temperature between 3-10oC.
Seed certification
Seed certification is a legally organized programme for quality control of seed and propagating
materials of genetically distinct crop varieties during seed multiplication programme. In
certification programme seed is produced by farmers through using careful quality control
mechanisms like field inspection during growing season and seed inspection following harvest
by legally authorized agency. High quality seed should equal or exceed the bench mark of
standards set for genetic and physical purity, germination, vigour and should be free from seed
borne disease and insect pest damage.
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High quality seed can be produced by controlling the production protocol of seed certifying
agency in two ways:
1) By monitoring seed multiplication and processing operations to avoid or minimize the risk of
mechanical or genetical contamination for maximize biological efficiency of seed crop.
2) By fixing minimum field and seed standards of different crop species to facilitate certification
and assuring dependability of the product to the users.
Seed quality control is a very important component of seed programme. Without controlling the
quality of seed during production, cleaning, grading, drying, storage and marketing operations, it
is not possible to carry forward a seed programme. Quality control aims to make available the
seeds of improved varieties and hybrids of assured standards to the farmers so as to improve the
agriculture production and productivity. Seed quality is usually controlled through seed
legislation, certification and seed testing.
Objective of certification
To ensure genuineness and quality of seed to the users or purchasers to increase the production
and productivity of any crop is the main objective of seed certification.
Organization of certification
The organization and structure of a seed certification agency differ country to country. In some
country it is done by either Department of agriculture or State Agriculture Universities or Crop
Improvement Association etc. In Nepal, the by laws of Seed Act (1988) have been approved by
the parliament. Seed certification is done by seed certification agency i.e. Seed Quality Control
Center under Ministry of Agriculture and Cooperatives of Nepal. The process of seed
certification is initiated by an application given by the seed grower for certifying the seed to the
certifying agency. If a seed lot ratifies the prescribed purity and quality requirements, the
certification authority issues suitable tags of certification for affixing them to the seed bags under
certification. The inspections are conducted at three levels: 1) Field inspection 2) Inspection
during seed processing and 3) Laboratory testing
1. Field inspections
The purpose of field inspections is to examine the seed crop in the field and to determine its
suitability for certification. Seed certification inspectors do field inspections. During field
inspections, observations are made on isolation distance, the presence of off-type plants, error in
planting, planting ratio in the case of hybrid varieties, presence of objectionable weeds and plants
of other crops, and the incidence of disease transmissible through seed. Generally 2-4 inspections
are carried out at different phonological stages of crop. Foundation seed crops are also subjected
to the same number of field inspections as those for certified seed, however, the requirements are
more strict. During field inspections, objectionable weed plants and plant infected by designated
(seed borne) diseases are specifically monitored.
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such inspections is to determine whether appropriate care is taken to avoid mechanical mixtures
during seed processing. This is not common practice in Nepal.
Cultivar purity test: This test determines the amount of seeds of other varieties of the same
crop in a seed lot. The sample size should be large, and it can be conducted by examination of
seed in the laboratory, examination of seedlings grown in a growth chamber or green house and
field plot tests or grow-out tests.
c) Moisture test: It is determined as percent water content of seeds. The moisture content is
determined by drying the seed samples in an oven or with the help of moisture meter. Moisture
meter measures the resistance of seeds to an electrical current, which varies with the moisture
content. The use of moisture meters requires calibration and a certain degree of technical skill on
the part of the user. But moisture meter are very efficient and extremely rapid, so a large number
of samples can be handled in a relatively short period. Moisture content is determined easily and
very fast by electronic moisture meters also.
After doing all the above tests, if the seed lot under test meets the requirements set by the
concerned country authority, then the certifying agency duly certified the seed lot, and the seed is
sold for cultivation. If the requirements are not met, the particular seed lot is not permitted to sale
and grows commercially.
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Farming system
Farming system represents an appropriate combination of farm enterprises viz. cropping system,
livestock, poultry, fisheries, forestry and the means available to the farmer to raise them for
increasing profitability. They interact adequately with environment without dislocating the
ecological and socio-economic balance on the one hand and attempt to meet the national goals
on the other.
Cropping system
Cropping system is a land use unit comprising soils, crop, weed, pathogen and insect subsystems
that transform solar energy, water, nutrients, labour and other inputs into food, feed, fuel and
fibre. The cropping system is a sub system of the farming system. Depending on the resources
and technology available, different types of cropping systems adopted on farms are
monocropping, multiple cropping, intercropping, mixed cropping, crop rotation or sequential
cropping etc.
Sole cropping
Sole cropping is a type of cropping system in which single crop or variety is grown alone
in pure stands at normal density, for instance transplanted rice, jute, tobacco, oats, rice
bean etc.
Monoculture
Monoculture or monocropping is the repetitive growing of the same crop on the same piece of
land year after year. It may be due to climatological and socioeconomic conditions or due to
specialization of farmers in growing a particular crop. For instance rice growing in lowland or
canal irrigated area is a normal practice of Nepalese situation where it is not possible to grow any
other crop. Under rainfed conditions groundnut or cotton or sorghum are grown year after year
due to limitation o rainfall.
Cropping pattern
The yearly sequence and spatial arrangement of crops and fallow on a given area is known as
cropping pattern. For example Rice-wheat-maize is a cereal based cropping pattern of inner terai
areas of Nepal.
Multiple cropping
Multiple cropping refers to growing of two or more crops on the same piece of land in one
calendar year is known as multiple cropping. It is the intensification of cropping in time and
space dimensions i.e more number of crops within a year and more number of crops on the same
piece of land at any given period. It includes sequential cropping, intercropping, mixed cropping
etc.
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Sequential cropping
It refers to growing of two or more crops in sequence on the same field per year. The succeeding
crop is planted after the preceding crop has been harvested. Crop intensification is only in the
time dimension. There is no inter crop competition. The following cropping patterns are included
in sequential cropping.
i) Double cropping: growing two crops a year in sequence.
ii) Triple cropping: growing three crops a year in sequence.
iii) Quadruple cropping: growing four crops a year in sequence.
iv) Ratoon cropping: The cultivation of crop regrowth after harvest of previous crop e.g.
sugarcane.
Inter cropping
Intercropping is the cultivation of two or more crops simultaneously on the same land with a
definite row pattern.. Crop intensification is in both time and space dimension. There is inter
crop competition during all or parts of crop growth. Farmers manage more than one crop at a
time in the same field. For example, for growing maize + soybean in 3:1 ratio, i.e. after every 3
rows of maize, one row of soybean is sown.
Legumes and cereal offers minimum competition so legume and cereal intercropping is popular.
Major competition is for light, water, space and nutrients. In tropical climate light is not severe
problem but major problem is nutrient and water.
Advantages of Intercropping
a) Better use of growth resources including light, nutrients and water.
b) Intercropping helps to suppress the weeds.
c) It helps to reduce plant and disease incidence in the crop.
d) Proper selection and management of intercropping yield stability of the crops may take place.
e) Ecological stability i.e. improvement of soil health and agro-ecosystem.
f) Intercropping helps the physical support of one crop to another crop.
g) Different types of produce can be obtained from the same field at the same time.
h) Intercropping helps to minimize the risk of crop failure.
Disadvantages
a) Intercropping is more labour intensive.
b) The control of pests and diseases or chemical weed control may be difficult.
c) Mechanization is also difficult.
d) Adverse competitive effect may reduce the yield of any crop.
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Mixed cropping
Growing two or more crops simultaneously with no distinct row arrangement. It is a common
practice in most of rainfed farming areas of Nepal. Seeds of different crops are mixed in certain
proportion and are sown. The objective is to meet the family requirement of cereals, pulses and
vegetables. It is subsistence farming. To denote mixed planting arrangement a plus sign (+) is
mentioned. Example: Upland rice (ghaiya) + maize -Wheat + mustard – Fallow (One year crop
rotation in inner terai region and foot hills of Nepal).
Relay cropping
Growing two or more crops simultaneously during part of the life cycle of each. A second crop is
planted after the first crop has reached its reproductive stage of growth but before it is ready for
harvest e.g. Wheat in standing potato, fingermillet in standing maize, lentil in standing rice.
5.2 Definition and method to calculate cropping index, cropping intensity, land equivalent ratio. Definition of
crop rotation, principles and advantage of crop rotation.
Cropping index
The number of crops grown per year on a given piece of land multiplied by 100 is cropping
index.
Cropping index = Total number of crops x 100
Net cultivated area
Cropping intensity
Cropping intensity indicates the number of times a field is grown with crops in a year. It is
calculated by dividing gross cropped area with net area available in the farm, region or country.
Rice 2 - 2
Maize 2 2 1
Fingermillet 1 - -
Wheat - 3 1
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Where, Yij = Yield of inter crops, Yii and Yjj = Sole crops yield of component crops.
Example: Suppose in a farmer’s field the yields of maize and soybean grown as pure crops be 2
tons and 1ton/ha respectively. Let the yields of these crops when grown as intercrops be
1.75 and 0.5 t/ha respectively. The land equivalent ratio of maize and soybean
itercropping system is follows:
Crop rotation
Crop rotation is defined as a process of growing different crops in succession on a piece of land
in a specific period of time, with an object to get maximum profit from least investment without
impairing the soil fertility. One cycle may take one or more farming years to complete. Farming
year is 12 months for irrigated areas and is limited to the period of adequate soil and waer
availability for crop growth in rainfed areas.
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6. The crop of the same family should not be grown in succession because they act like
alternate hosts for insects, pests and diseases.
7. An ideal crop rotation is one which provides maximum employment to the family member
as farm labour, the machine and equipments are efficiently used and all agricultural
operations are done on time and simultaneously maintaining the soil productivity.
c) Pest control: An ideal crop rotation can helps in controlling insects, pests, diseases and
weeds.
e) Higher yield: The farmer get higher yield and a better price for his produce because of its
higher demands in the locality and market.
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6.1 Definition of soil fertility and soil productivity, criteria of essentiality of elements, classification of
essential elements (structural, mineral, macro and micro nutrients), forms of elements absorbed by plants,
dynamics of nutrients in soil plant environments.
Soil fertility and soil productivity are two terms, which always create confusion in our minds.
The simple definition of these terms is given below.
Soil Fertility
Soil fertility may be defined as the ability of a soil to supply all the essential plant nutrients in
readily available forms to the crop plants. When soils are deficient in some of the essential
elements, the deficient elements are supplemented from out side sources in the form of manures,
fertilizers and lime. A soil may be fertile, that is having chemical capacity but may not be
productive because of excessive acidity or alkalinity or the presence of toxic substances, poor
physical properties or an excess or deficiency of water.
Soil productivity
Soil productivity refers to the capacity of a soil for producing a specified plant or sequences of
plants under a specified system of management i.e the capacity of the soil to produce crops per
unit area of the field. A fertile soil may or may not be productive depending upon crop
production conditions and several other factors but a productive soil is always fertile. Soil
productivity is influenced by aerial environment and soil environment.
Therefore it is very essential for farmer to manage soil fertility in such a way that he gets
maximum production from his land. To maximize production a soil must be productive and a
productive soil must be fertile. For better fertility management farmer should consider what
elements are needed for a particular crop and in what quantity and how much is present in the
soil. When the soil does not furnish adequate quantities of the nutrients necessary for normal
growth and development, it is necessary to know the amounts and kinds of fertilizers to use
because unnecessary fertilizer is expensive and the wrong fertilizer may also be harmful.
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2. It is one of the factor for crop production 2. It is the interaction of all the factors that
and other factors are moisture, topography, determine the magnitude of yield.
water table, tillage practice, varieties,
organic matter content of soil etc.
Nutrients
Dictionary meaning of nutrient is “any substances that provides essential nourishment for the
maintenance of life”. In other words nutrients may be defined as the chemical compounds
required by an organism for their nourishment and maintenance of their life. Plants have the
ability to build up organic tissues directly from inorganic materials. They live, grow and
reproduce by taking up water and mineral substances from the soil, carbon dioxide from the air,
energy from the sun to form plant tissues.
By the analysis of plant tissues, there are a large number of elements that have been identified;
out of them only sixteen have been found to be more essential for growth, development and
reproduction of plants. These essential elements are called nutrients.
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Plant analysis using modern techniques reveals that plant body contains about 30 elements and in
some cases as many as 60 elements. The presence of several elements in plant does not mean that
all these are essential for plants. For an elements to be considered an essential plant nutrient, the
following three criteria as proposed by Arnon and Stout (1938) and again refined by Arnon
(1954) must be satisfied. These are:
1The plant cannot grow or complete its life cycle in absence of the element.
2.The element is very specific and cannot be replaced by another elements.
3. The element plays a direct role in metabolism.
2. Macronutrients
Macronutrients are needed in large amounts and large quantities have to be applied if the soil is
deficient in one or more of them. Elements which are required by plants in considerable
concentrations (greater than 1 ppm) are called macronutrients e.g. C (45%), H (6%), O (43%)
which are used by plants from air and water constitute 94%, N (1-3%), P (0.005-1%), K (0.3-
6%), S (0.05-1.5%), Ca (0.1-4%), Mg (0.004-1%). Soils may be naturally low in nutrients, or
may become deficient due to nutrient removal by crops over the years, or high yielding varieties
(HYV) are grown which are more demanding in nutrient requirements than local varieties.
All plant nutrients except carbon, hydrogen and oxygen are taken up by plants from soil. The
three primary constituents (namely C, H, O) combined will form the organic part of a bulk of
plant tissue and are called structural components.
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Among macronutrients plant utilize greater quantities of N, P and K from the soil and these to be
replaced in greater quantities, so they are called major nutrients or primary nutrients and Ca, Mg
and S are utilized by plants from the soil in less amount compared to primary nutrients, which
are called secondary nutrients. But they are just as important as primary nutrients to fulfill
fertility.
3. Micronutrients
Elements, which are required by plants in minute quantities (0.001-1000 ppm) or plants also take
them up in considerable amounts are termed micronutrient or trace elements e.g. Mn, Cu, Zn, B,
Mo, Cl, and Fe. They are the part of the key substances in plant growth and are comparable with
the vitamin in human nutrition. Their plant availability depends primarily on the soil reaction.
Some beneficial nutrients important for some plants are sodium (Na) eg. For sugarbeets and
silicon (Si) e.g. for cereals (strengthening cereal stems to resist lodging), cobalt (Co) e.g.
required in the process of N fixation of legumes and vanadium (V) for green vegetables.
Individual elements have a number of functions at the different stages of the growth and
development of plants. Individual plant parts such as roots, stems, leaves, flowers, fruits and
seeds nutrients differ with respect to the composition and concentration of nutrients. The
individual plant species also differ with the distribution of the elements within the plants.
1 Potassium K+
2 Calcium Ca++
3 Magnesium Mg++
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7 Zinc Zn++
8 Chlorine Cl-
9 Cobalt Co++
10 Sodium Na+
Thus mineral nutrients are available to plants both in ionic and molecular forms, the proportion
depending on the nature of the soil solutions and other conditions. For proper growth and
development of field crops the nutrient should fulfill the following conditions:
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Soil solution contains at least a trace of every plant nutrient element. The uptake of any nutrient
by a plant from the soil solution is rapidly replenished by equilibrium between soil solution and
the cation exchange sites and the soil solution and the mineral surfaces. Changing the
concentration of a given nutrient in the solution by addition of fertilizer or plant uptake results in
shifts in the movement of the nutrient in all the other components of the soil-plant environments.
Addition of fertilizers or manures increases the content of the nutrient in the soil-plant
environment. This increase is desirable as long as the ions remain in balance and do not exceed
the toxic limit of concentration. The objective of soil fertility management, then, is to provide the
nutrient required in amount and times as required by crops.
6.2 Manures and fertilizers: Importance of organic manures, classification of manures (bulky and
concentrated organic manures), brief description of FYM, compost, vermicompost, animal manures,
night soil, sewage and sludge, biogas slurry, oil seed cakes, green manures.
Plant nutrients are essentially supplied through manures and fertilizers. Manures are organic in
nature and applied in large quantities. They are also called as organics or organic manures.
Nutrient content in the organic manures is low. Fertilizers are inorganic or synthetic and the
nutrient content is higher than in manures. They are available for a particular nutrient or
combination of nutrients.
Organic manure
Organic manures are those complex materials, which are organic in origin, bulky and
concentrated in nature and capable of supplying plant nutrients and improving physical, chemical
and biological environment of the soil. They have no definite chemical composition and low
analytical value prepared from animal, plant and other organic wastes and byproducts.
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repulsion takes place) and accumulated with gravitational water and make the water
pollution due to which blue baby diseased problem is seen some times in the society.
5. When sulfur containing fertilizers are applied large amount in the soil it forms sulphuric
acid (H2SO4) in the atmosphere and takes acid rain in some times. Using organic manures
solves this problem.
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On an average well-rotted FYM contains 0.5%, 0.25% and 0.5% N, P and K respectively. The
characteristic and relative concentration of FYM vary widely. Some factors affecting
composition of FYM are: kind of animal, age and condition of animal, animal feed, kind and
amount of litter used, digestibility of the feed consumed or function of animal, handling and
storage procedure of manure etc.
Compost
Compost is the product of organic residues (straw, chaff, leaves, paddy and ground nut husk,
sugaracane trash, weeds, and other agricultural as well as industrial and habitation waste) and
soil that have been piled, moistened and allowed to undergo biological decomposition. The quick
breakdown of organic materials by micro-organisms needs a warm, moist and aerated
environment. Ingredients used to make compost may vary from place to place but the basic steps
are similar. Similarly the compost making can be carried out in any scale from large-scale
compost making on the community level to a small and simple form of compost making on the
farm.
Farm compost can be made from almost any plant materials such as cereal straws, crop stubbles,
leaves, stems, farm weeds, grasses, forest litters, animal beddings, dung as well as household
garbage etc. As a source of plant nutrient the value of compost will depend on the composition of
the plant materials used in composting. Poor plant materials will produce compost with relatively
low manurial value. For the faster decomposition different nitrogenous and phosphatic fertilizers,
and lime can also be added on various layers as starters.
Recent weeds, grasses and forest litters take relatively shorter period to decompose than crop
residue such as straws, stubbles, husk etc, which may be due to low carbon-nitrogen (C/N ratio).
If cereal straws, stubbles and similar materials with high C/N ratio are used for composting it is
preferable to chop them in to small pieces and mixed with a large amount of new tender weeds
and liquid dung before composting to speed up the processes.
Vermicompost
Compost that is prepared with the help of earthworms (Pheretima posthuma) is called
vermicompost. Earthworms consume large quantities of organic matter and excreted soil as casts.
The weight of the material passing through the body each day is almost equal to the weight of the
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earthworm. The earthworms may be of local species or more vigorous exotic ones. The casts of
earthworm have several enzymes and are rich in plant nutrients, beneficial bacteria and
mycorrhizhae. On an average vermicompost contains 3%, 1% and 1.5% N, P 2O5 and K2O
respectively.
Animal manures
The excreta’s of animals like sheep, goat, poultry etc are used as manure is called animal
manure. The droopings of sheep, goats and poultry contain higher nutrients than FYM and
compost. On an average sheep and goat manure contains 3% N, 1% P 2O5 and 2% K2O. Poultry
manure contains higher N and P2O5 compared to other bulky organic manures. On an average
poultry manure contains 3.03% N, 2.63% P2O5 and 1.4% K2O.
Night soil
It is human excreta both solid and liquid form. Night soil is richer in NPK than FYM and
compost. The disposal of night soil is a serious problem in towns where facilities for it’s
composting are not available. Trenching the materials as such takes a long time for it to dry and
causes nuisance of fowl smell and profuse fly breeding. Dehydration of night soil by mixing it
with any absorbing materials like soil, ash, dry broken leaves, paddy husk etc. is al highly
effective method of disposal of the offensive waste which yields poudrette manure of high
manural value. One of the effective materials for this purpose is saw dust. Night soil contains
on an average 5.5% N, 4% P2O5 and 2% K2O.
Green Manures
Green undecomposed plant materials used as manure into the soil for the purpose of improving
soil physical, chemical and biological environments is called green manure and the process is
called green manuring. Annual leguminous crops as well as green leaves, twigs or succulent
stems of non leguminous perennial trees or shrubs are used for green manuring.
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main crop. In this system, green manuring plants, especially legume species are grown in the
field and they are slashed and incorporated in the same field where they were grown. Dhaincha
(Sesbania spp, Sesbania rostrata), sunhemp (crotolaria juncea), guar (Cyamopsts tetragonoloba)
are the most commonly used green manure species in Nepal. However, they have some problems
e.g. latitudinal limitation, difficulty in germination etc.
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6.3 Fertilizers: Classification of fertilizers, nitrogenous, phosphatic and potassic fertilizers, biofertilizers:
saprophytes, symbiotic bacteria, blue green algae, azolla, azotobacter and mycorrhiza
Classifcation of fertilizers
1. On the basis of primary nutrient content mainly fertilizers are classified in two groups, which
are:
a) Straight fertilizers
Fertilizers that contain only one primary nutrient are referred to straight fertilizers e.g.
ammonium sulphate, urea etc (they supply nitrogen only).
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b) Multi-nutrient fertilizers
Those fertilizers that contain two to three primary nutrients are called multi-nutrients fertilizers.
Binary fertilizers contain two major nutrients e.g. potassium nitrate (13%N and 44% K 2O) and
they are also called incomplete fertilizer (having lack of any 3 major nutrient elements) and
ternary fertilizers contain three major nutrients e.g. complete fertilizer (15:15:15% NP and K
respectively. Multi nutrient fertilizers are more beneficial than straight fertilizer because multi
nutrient fertilizers are easy of handling, transport, storage and application with high fertilizer
efficiency. These fertilizers are usually produced in granular form.
2. Fertilizers are also classified as high analytic and low analytic fertilizers. High analytic
fertilizers containing more than 25% of major plant nutrients e.g. urea (46%N) and low analytic
fertilizers containing less than 25% of the major plant nutrients e.g. single super phosphate (16%
P2O5), sodium nitrate (16%N) etc.
3. Fertilizer can also be classified based on physical form, which are: a) Solid and b) Liquid form
Most of the fertilizers are in solid form. They are in several form viz. powder (SSP), crystals
(A/S), prills (urea, DAP), super granules (urea supergranules).
Liquid fertilizers are of two types: a) Clear liquid fertilizers: When the nitrogenous, phosphatic
and potassic and other fertilizers are completely dissolved in water these are called clear liquid
fertilizer.
b) Suspension liquid fertilizers: Those fertilizers in which some of the fertilizer materials are
suspended as fine particles.
Fertilizer grade:
Fertilizer grade refers to the guaranteed minimum percentage of N, P2O5 and K2O contained in
fertilizer material. The number representing the grade is separated by hyphens and are always
stated in the sequence. Example: Urea (46-0-0), DAP (18-46-0) etc.
Nitrogenous fertilizers
Those fertilizers, which are sold in the market for their nitrogen content. They are classified into
four classes on the basis of N present.
1. Nitrate (NO3-) containing nitrogenous fertilizers: Most of the field crops except rice in the
early stage of plant growth take up in nitrate form. They are suitable for top and side dressing
and on dry soils. In moist soils they leach rapidly e.g. Sodium nitrate (NaNO 3) (16%N), Calcium
nitrate [Ca (NO3)2 ] (15.5%N).
3. Both ammonium and nitrate containing fertilizers: These fertilizers contain both
ammonium and nitrate These are acidic in nature. Leaching losses are less. e.g. Ammonium
nitrate (NH4NO3) (33-34% N), Calcium ammonium nitrate (CAN) (20% N).
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4. Amide fertilizers: These are organic form of N containing fertilizers, which are readily
soluble in water and are easily decomposed in the soil where they are quickly changed into
ammonical and thence to nitrate form e.g. Urea CO (NH2)2 (46%N), Calcium cyanamide
(CaCN2) (21%N). These fertilizers are also known as organic fertilizers since they contain
carbon atoms.
B) Phosphatic fertilizers
The phosphate content in such fertilizers is expressed in terms of phosphorus pentaoxide (P2O5),
which is readily dissolved in water and produces salts of phosphoric acid (H 2PO4, HPO4). They
are classified according to solubility and availability to crops are:
a) Water soluble or monocalcium phosphate: These fertilizers are available in the form of
monocalcium phosphate of ammonium phosphate. Water soluble phosphates can be absorbed
quickly by plants. They should be used on neutral to alkaline soils. However they form insoluble
iron and aluminium phosphate in acid soils eg. single super phosphate (16% P2O5), Triple super
phosphate (46-48% P2O5), Ammonium phosphate (20% P2O5).
b) Citric acid soluble or dicalcium phosphate: Citrate soluble phosphates are soluble in acid
soils where they convert into soluble phosphates and there are less chances of fixation e.g Basic
slag (14-18% P2O5), Dicalcium phosphate (34-39% P2O5). These are suitable in acidic soils due
to presence of calcium.
c) Insoluble or tricalcium phosphate: These are soluble in strongly acidic or organic soils.
These fertilizers are suitable in strongly acidic or organic soils. The availability of phosphorus
from these fertilizers can be increased by ploughing in along with green manures. e.g. Rock
phosphate (20-40% P2O5), Raw bone meal (20-25% P2O5), Steamed bone meal (22% P2O5).
These are suitable for plantation crops like tea, coffee, rubber etc.
Phosphate content in fertilizers is expressed in oxidized form (P 2O5) while its content in
soil and plant is expressed in elemental form The conversion factors for elemental to
oxidized form and vice versa are 2.29 and 0.43 respectively.
C) Potassic Fertilizers
Potassic fertilizers are classified on the following basis:
a) Having K in the chloride form: Chloride form of K fertilizers are used extensively in all
crops except where no chlorine is desired in the fertilizer. Potassium chloride is the most
common and cheap fertilizer among potassic fertilizer. e.g. Muriate of potash (KCl) (58-60%
K2O.
b) Having K in non chloride form: Non chloride form of K fertilizers are in demand by
cultivators growing special crops such as tobacco, potato and tomato to obtain better quality e.g.
sulphate of potash (48% K2O).
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Bio-fertilizers:
Bio-fertilizers are defined as preparations containing live or latent cells of efficient strains of
nitrogen fixing and phosphate solubilizing micro-organism used for inoculation of seed, and
application of soil or composting areas with the objectives of increasing the population of such
beneficial micro-organisms and accelerate certain microbial processes to augment the extent of
the availability of nutrients in a form which can be easily assimilated by plants.
Bio-fertilizer is a carrier-based product in which live cells of efficient microorganism are mixed
in maximum number to increase soil fertility and availability of nutrients to plant through seed
treatment or soil application. There are various types of bio-fertilizers like Rhizobium,
Azotobacter and Azospirillum , Blue green algae (cyanobacteria), Azolla etc which can fix N
and acts as a bio-fertilizer augmenting N in the soil.
Recently, the interest in bio-fertilizers has been increased. There is a world wide increased trend
towards the use of azolla, blue green algae, mycorrhiza and various bacteria on the cropping
system to enhance the soil fertility.
Advantages of bio-fertilizers
1. Chemical fertilizers are costly, causing environmental pollution and human health hazards,
while bio-fertilizers are eco-friendly, non-toxic and cheaper natural resources.
2. They help in the establishment and growth of crop plants and trees by providing plant
nutrients and increase the fertility status of the soil also.
3. They enhance bio-mass production and grain yields by 10-20%.
4. Approximately 25% of chemical fertilizer can be substituted with the use of bio-fertilizer
therefore bio-fertilizers are useful for sustainable agriculture.
5. They play an important role in agro-forestry or silvipastoral systems.
6. They protect plants from several fungal diseases by producing fungi static substances.
7. Bio-fertilizers also increase seed germination by producing plant growth substances and
hormones.
8. Algal bio-fertilizer can be used for reclamation of sodic saline soil also.
9. They are suitable in organic farming.
Types of Bio-fertilizers
Based on the function of bio-fertilizers, they are classified as under:
A Nitrogen fixing bio-fertilizers
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The fertilizer preparation with Rhizobium culture is known as “Nitrogin”. Important strains of R.
bacteria are R. japonicum (better for soybean inoculation), R. meliloti (alfalfa), R.
leguminosarum (peas), R. phaseoli (beans).
ii) Azolla
A small floating water fern, azolla is commonly seen in low land fields and shallow fresh water
bodies. Azolla forms a green mat over water which often becomes reddish colour due to the
accumulation of anthocyanin pigments. This fern harbours a blue green algae (Anabaena
azollae). The Azolla anabaena association is a live floating nitrogen factory using energy from
photosynthesis to fix atmospheric N amounting to 100-150 kg /ha N from about 40-60 tonnes of
bio-mass. Important strains of bacteria are A. caroliniana, A. nilotica, A. mexicana and A.
pinnata.
ii) Azospirillum
Azospirillum lipoferum has associative symbiosis with higher plant system. They don not
produce any visible nodules on the root tissues. The crops, which respond to Azospirillium
inoculation are maize, barley, oats sorghum, pearl millet and forage crops. Its application
increases grain productivity of cereals by 5 -20% and fodders by over 50%.
2. Non-symbiotic
i) Azotobacter
The beneficial effects of Azotobacter bio-fertilizer on cereals, millets, vegetables, cotton and
sugarcane under both irrigated and rainfed field condition have been substantiated and
documented. Application of Azotobacter has been found to increase the yield of wheat, rice,
maize, pearl millet and sorghum upto 30% over control. Apart from N, this organism is also
capable of producing antibacterial and anti fungal compounds, hormones and siderophores. The
bacterial fertilizer of azotobacter of Azotobacter chrococcum is known as “Azotobacterin”.
Research done in Nepal show that the amount of nitrogen to be applied to wheat can be cut down
to 15% if inocualtion with effective strain of azotobacter is practiced (Karki and Baral, 1977).
According to Maskey et al (1974) the azotobacter inoculation should be preferred under resource
constraints or for farmers with limited resource of fertilizer input.
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a) Phosphate absorber
i) Mycorrhizae or Vesicular Arbuscular Mycorrhiza (VAM)
Mycorrhiza is a fungal bio-fertilizer. It is a symbiotic association of fungi with roots of vascular
plants. The main advantages of micorrhizae to the host plants lies in the extension of the
penetration zone of the root fungus system in the soil, facilitating and increase phosphorus
uptake. The inner connected the net work of external hyphae acts as an additional catchment and
absorbing surface in the soil beyond the depletion zone that would other wise be inaccessible to
plant roots. Endotrophic mycorrhizae have been sown to be present in a wide range of
horticultural species including Apple, Walnut, Almond, Citrus, Avocado, Strawberry and Grape.
Mycorrhizal fungi's assists the uptake of phosphate and trace metals and possibly influence water
and nutrient via hormonal influences is not in doubt.
b) Phosphate solubilizers
A group of heterotropic microorganisms are known to have the ability to solubilize P from
isoluble sources. Phosphate solubilizers are Pseudomonas spp, Bacillus megatherium,
Aspergillus awamori, Pencillium digitum, Trichoderma spp etc., which are responsible to
solubilize the phosphates in the soil.
6.4. Factors affecting fertilizer use, time of fertilizer application, method of fertilizer application, use and
limitation of organic manures, green manures, bio-fertilizer and chemical fertilizers
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Bio-fertilizers like Azolla sp may be grown in a standing crop of wet land rice and incorporated
thereafter. Blue green algae can be grown in moist bare or cropped fields and incorporated
before sowing or planting the crop. Bacterial fertilizer lime Rhizobium, azotobacter may be used
as seed or soil inoculation before sowing.
Moisture content of the soils also play the important role in nutrient availability and their loss. In
moist soil both bulky and concentrated manures can be applied by broadcasting or by localized
placement method. In dry lands manure and fertilizers should be placed below the seed as pocket
or contact placement. All the fertilizers and manures should be applied in the moist zone in case
of dry lands. If they are not placed in the moist zone the solubility and release of nutrients are
less. In wet soil the loss of N is more therefore to increase nitrogen use efficiency, slow release N
fertilizers may be used. Ammonical fertilizer should be applied in the reduced zone and nitrate
fertilizers in wet land rice as top dressing in splits.
Bulky organic manures and green manures may be applied at least once in a year in case of
multiple cropping system. In mono or double cropping systems each crop may be supplied with
such manures during land preparation.
Nitrogen should be stopped much before maturity to obtain better quality yield in those crops
which are used the vegetative parts as economic yield such as sugarcane, potato, tobacco etc. In
seed crops the last application of N may be during seed development phase to improve the
quality and germinability of seeds.
In determinate grain crops like rice, maize, wheat etc the supply of N at the beginning of the
reproductive stage as the last dose increase the number and weight of grains and in case of
indeterminate crops like rape seed and mustard, sesame, cotton etc an application of N at the
flowering and another at the late flowering stage increases the yield and quality of the produce.
Phosphatic fertilizers are move very little from its site of application. So the entire dose may be
applied as basal dose. In dry lands and acid soils P fertilizers should be placed near the roots.
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The potassic fertilizers become available slowly to the crop plants therefore the entire quantity of
K fertilizers should be applied at sowing. K fertilizers move slowly from their site of application,
therefore they should be applied in the rhizosphere.
B) Placement application
i) Plough sole placement: Manure and fertilizers are paced in the plough sole after opening the
furrow by the plough. Such furrows are covered immediately during the next run of the plough.
This method is popular in dry soils where there is moisture only in plough sole layer.
ii) Deep placement: This method is adopted in wetland rice field, where nitrogenous fertilizer
(ammonium sulphate) is placed deep in the reduced layer to avoid denitrification loss.
iii) Sub soil placement: It is followed in strongly acidic soils where P and K fertilizers are
placed in deeper layers by heavy machinery to avoid fixation.
C) Localized placement
i) Contact placement: The small quantities of well decomposed manures, ashes and phosphatic
and potassic fertilizers are placed along with seeds during sowing. Seed cum fertilizer drill is
used for such placement.
ii) Band placement: In this method both manures and fertilizers are placed in bands on one sides
of the row at about 5 cm away from the seed or plant in any direction. There are two types of
band placement.
a) Hill placement: This method is applied in wide spaced crops like cotton, castor, cucurbits
where manure and fertilizers are placed on both side of the plants only along or across the row
but not along the entire row.
b) Row placement: The wide spaced row crops like sugarcane potato, maize, tobacco etc the
manure and fertilizers are placed on one or both sides of the row in continuous bands.
iii) Pocket placement: In dry lands and in wide spaced crops like cotton, castor, cassava,
cucurbits, chillies etc manures and fertilizers are placed deeper in to the pocket and seeds are
sown in the same pocket about 5 cm above the fertilizer and manure or their mixture.
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iv) Side dressing: In this method manures and fertilizers are applied along the side of a row or
around a plant.
v) Pellet application: The nitrogenous fertilizers are pelleted in various types of mud bolls and
placed deep into the soft saturated soils of wet land rice to increase nitrogen use efficiency
(NUE).
i) Starter solutions: The fertilizer solutions in low concentrations are used for soaking
seeds, dipping roots after uprooting or spraying on the seedlings to strengthen the seeds
or seedlings for early rooting, establishment and growth.
ii) Foliar application: The fertilizer solutions (nitrogenous and mineral fertilizers) in low
concentrations are sprayed to the foliage of the standing crop in the form of spray. The
general principle is that the applied nutrients are absorbed by the plant leaves through
their natural opening.
iii) Direct application to the soil: Liquid fertilizers such as anhydrous ammonia are
applied directly to the soil with special injecting equipment. Liquid manure such as urine,
sewage water and shed washing are let in the field.
iv) Application through irrigation water: The water soluble fertilizers are dissolved and
diluted with irrigation water and applied either through surface, sub surface or over head
irrigation. Liquid and slurry manures are also diluted with irrigation water and supplied through
surface irrigation.
6.5. Integrated nutrient management, agronomical practices to be adopted for soil fertility and soil
productivity maintenance
Apart from balanced nutrient management, there are several other factors to be taken care off. So
productive management can be done through balanced use of organic manure, green manure,
bio-fertilizers and fertilizers in the cropping system rather than individual crops. The residual
effect of previous crop on succeeding crop and residual effects of manure and fertilizers should
be taken into account. Fertilizer application on one crop based is not efficient. So more emphasis
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is given to find the fertilizer requirement of whole crop sequence. Three general
recommendations have been formulated in intensive cropping system.
i) It is accepted that phosphorus should be applied in winter crop so that residual effect
of P can be found in rainy season crop.
ii) For optimum nitrogen economy, organic manure should be added in rainy season
crop so that it will be sufficiently decomposed and benefits the succeeding winter and
spring season crops.
iii) Any inorganic fertilizer nutrient should be applied to the crop, which should
maximize the response in cropping sequence. For example if potato based sequence is
taken then potassic and phosphatic fertilizer should be added because potato is most
responsive to potash and phosphorus.
For the better utilization of sources and to produce crop with less expenditure, integrated nutrient
management is the best approach. In this approach all possible sources of nutrients are applied
based on economic consideration and the balanced required for the crops. The appropriate
estimation of amount of nutrient added to the soil by crop residues should be done and chemical
fertilizers application can be reduced. Application of organic matter in any form reduced the
form of N fertilizer and increase the fertilizer use efficiency because release of N from organic
matter is slow so it gives durability to soil fertility.
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viii) It release more carbondioxide and which is dissolved in water form carbonic acid
which reduce pH and availability of inorganic phosphorus in alkali soil.
Concentrated organic manure contains higher percentage of major plant nutrients, which are oil
cakes, blood and meat meals, fish meals, poultry manures etc.
Saprophytes are not capable of fixing atmospheric N but capable of decomposing organic matter
at faster rate. So they can be used for quick release of nutrients from the organic matter.
Example: Aspergillus spp., Trichoderma etc.
Blue green algae, azolla, azotobactor, rhizosprilium, mycorrhiza or phospo micro-organism are
free living microorganisms. The inoculation of these microorganisms with seeds or soil can
increase the availability of N or P into the soil.
Rhizobium spp. is symbiotic bacteria and fixed atmospheric N in association with legumes crops.
Different species enters the root of host plant and for nodules on the root surface. Bacterial
depend on host plant in the form of asparagin and glutamin (amino acids). Different Rhizobium
species multiplied in the laboratories and can be used in three wars i.e. seed treatment, soil
treatment and soil application.
c) Beneficial nutrients eg. Sodium, cobalt, vanadium, silicon. These are not essential for higher
plants. Na is essential for Chinopodiacea, silicon is essential for rice, Co is essential for
microorganisms.
To supply above plant nutrients we have different artificial fertilizers in the market and can apply
to fulfill the requirements of crop plants.
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7. Weed Management
7.1 Definition of weed, losses caused by weeds, benefits from weeds
Definition of weed
“ Weeds are unwanted and undesirable plants which interfere with the utilization of land and
water resources and thus adversely affect human welfare”. Jethro Tull (1731) was the first
person to use the word weed in this sense in the literature of his famous writing “Horse Hoeing
Husbandry”. He defined that “a weed is a plant growing where it is not desirable”. Weeds are
that species of plant, which grow unwanted or are not useful, often prolific and persistent,
interfere with agricultural operations, increase labour cost and reduce the crop yield.
From these definitions it can be said that as long as a plant is not interfering with human
activities it is not called weed.
Characteristics of weeds
Weeds are extremely noxious, useless and unwanted.
Weeds are persistent and resistant to control.
Remain dormant and viable for several years (grassy weeds for 10 years and broad leaved
weeds for 50 years).
Weeds are prolific or having high reproductive capacity.
Some weeds have very deep roots.
Some weeds propagated vegetatively.
Some weed seeds are very similar to crop seeds.
Weeds have competitive and aggressive habits.
Dispersal of weed seeds exposes weeds to different ecosystems.
Weeds are hardy and resist to adverse climatic, soil and disease conditions.
Weeds are self sown plants.
Evasiveness of weed because of their better taste, disagreeable odour, and spiny nature
and mimicry.
Thus weeds are uncultivated plants that are not desired by man with respect to place and time
occurrence. They don’t belong to a particular group. Under certain circumstances, each plant
species can be a weed. All weeds are unwanted plants but unwanted plants may not be weeds.
For e.g. Cynodon dactylon (Dubo grass) is a world worst weed of the crop field but it is a
desirable plant in lawns, rangelands and permanent bunds. Agropyron repens (Quack grass) is a
very good soil binding grass on erodable and non-crop lands but it is a serious weed when it
infest crop fields and orchards. Some times two persons may differ about the weedy nature of a
plant at the same place and time.
Thus from the above situation “ weeds are plants growing in places and at times when we wanted
either some other plants to grow or no plants to grow at all”.
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The direct effect of weeds may not be apparent in many cases but they eventually incur heavy
loss of the crop reflected by the severe reduction of the crop yield. The weeds compete with crop
plants mainly for nutrients, soil moisture, sunlight and space. The plants that germinate first and
grow fast tend to exclude others. The major harmful effect of weeds in crop fields can be realized
from the following exhaustive data also.
Insects (30%)
Weed loss (45%)
Diseases (20%)
Others (5%)
4. Allelopathic effect
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Many seeds and propagules of weeds may contain allelochemicals ((derivatives of benzoic acids,
cinnamic acids, phenolic acids, coumarins, hydroquinones, benzoquinones and cineoles) certain
toxic substances), which rendered the antagonistic effect (impair germination and growth) to the
neighboring plants. This effect is called allelopathy. Both weeds and crop may possesses such
allelopathic compounds, yet unfortunately the weed species often possess much higher levels of
these than the crop plants. The important weed species that show allelopathic effect on crops are
Agropyron repens, Sorghum halapenge, Lantana camera, Abutilon theophrastic, Cyperus
rotundus, Eupporbic maculta, Ambrosia psitostachya etc.
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5. Economic utilization
A bulk of weeds can be economically useful for various purposes, some of them are given
below:
Imperata cylindrica (siru), Saccharum spp (kans), Typha elephantina are used for
thatching roofs of huts and hermitages.
Eulaliopsis binate and Sansevieria roxburghiana are used to prepare ropes and strings.
Phragmites karka and Andropogon squarrosus are used for making mats and screens.
Weeds are also used as raw materials for paper making, basket making and solid fuel and
extracting plant growth hormones and pesticides.
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7. Reclamation of the soil: Argemone mexicana and Cynodon dactylon help to reclaim the
alkalinity of soils.
8. Valued for protecting bunds: Weeds like Cynodon dactylon, Saccharum squarrosus etc are
generally used to protect different types of bunds, irrigation and drainage channels,
embankments of river, ponds and pools as well as sides of rail and roadways.
9. Valued as ornamental plants.
10. Valued for religious and ritual purposes.
11. Valued for maintaining biological equilibrium.
12. Valued for cleaning and purifying water.
13. Some weeds are used for fencing purpose.
7. 2 Classification of weeds based on life cycle, cotyledons and morphological characters, modes of weed seed
dispersal (wind, water, animals and humans)
Classification of weeds
There are over 30,000 plant species considered as weeds among which only about 18,000 species
cause serious damage in man’s affairs and need effective control. It would be impossible to
control all these weeds if each of them need specific control measures. Thus the knowledge of
growth habit, leaf characteristic, growing habitat etc. is essential for formulating an effective
control measures.
B) Biennials: These weeds need two years to complete their lifecycle and may propagate either
by seed or by vegetative means or by both. Example: Daucus carota, Zingiber casumonar,
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Plantago spp etc. Generally these remain vegetative in first year and in the second year they
produce seeds.
C) Perennials: These weeds continue their lifecycle within three or more years and produce
seeds more than once in their lifecycle. They may reproduce either by seeds or by propagules or
by both. Example: Lantana camara, Cynodon dactylon, Agropyron repens, Convolvulus arvensis
etc.
b) Sub-aerial with storage organ: These weeds have under ground stems with storage
tissue which helps them to propagate. Example: Nuts (Cyperus rotundus) and rhizomes
(Inula indica).
c) Sub-aerial stem without storage organ: These weeds have subaerial modified stem but
have no storage organs such as runners (Oxalis corniculata, Cynodon dactylon) and off-
set (Pistia spp).
b) Crop bound weeds: They are parasites of host crop because they depend on their host
crop for survival. Some of them are total parasite while some are semi parasite. Example:
Orobanche spp. are total parasite on rapeseed and mustard, tobacco and sunflower. Striga
spp are semi parasite on maize sugarcane etc.
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c) Crop associated weeds: These are also crop specific and may be associated with certain
crops. They are similar with crop plants due to their similar agro-climatic requirements
need for specific microclimate, mimicry, easily contamination of crop seeds with weed
seeds. For e.g. Phalaris minor, Avena fatua are specific to wheat, Echinochloa colonum
is specific to maize and rice.
1) Wind
The agent of air disperses majority of weed seeds. Such weed seeds possess special organs to
keep them float in air e.g. pappus (a parachut like modification of calyx into hairs or cotton like
structure), comose (seeds are covered with hairs) and wings. Which help them to cross long
distance with wind and germinate in a new habitat. Example: Ageratum conyzoides (gandhe
jhar), Eclipta prostrata etc.
2) Water
Aquatic weeds largely dispersed through water. The seeds have special structure and lower
weight per unit of seed with which they can float in water and carried away by the current of
water. By runoff these seeds are deposited in the crop lands. Irrigation and drainage also act as
the carrier of weed seeds. Example: Pistia, Monochori etc.
3) Animals
Many weed fruits and seeds are eaten by animals and birds. Depending upon the digestive
mechanism and nature of the weed seeds 0.2-9.6% of the ingested weed seeds are passed in
viable form with the animal excreta, which is dropped wherever the animal moves. This
mechanism of weed seeds dispersal is called endozoochory. Several birds pickup weed fruits
and seeds on their wings, feet and beaks and drop these during their flight. Dissemination of
Lantana seeds for e.g. is chiefly through the birds like Indian Maina and Chinese Dove.
Xanthium, Tribulus etc. are dispersed by animal through their hoof, skin and hairs.
4. Man
Careless operations of man (transplanting, harvesting, threshing, transportation of crop seeds),
are largely responsible for the dispersal of weed seeds from the infected areas to the new habitat.
Weed also dispersed through FYM or compost also because during decomposition of FYM or
compost many weed seeds do not loose their viability, even if proper temperature and acidity are
maintained. Example: Echinochloa colonum (sama) may get transplanted with rice and Vicia spp
with seeds of wheat. Similarly farm implements are the possible agent since many weed seeds
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are get attached with the tools when used in the infested areas and are dispersed in the new areas
cultivated by the tools as such.
7.3 Concept of weed management, prevention, eradication, control, physical, chemical, biological and
chemical control methods, relative merit and demerit of different biological and chemical control
methods.
To deal with problems posed by weeds some methods of management are to be adopted. Such
methods are based on some basic principles. These principles are related to:
a. Life cycle of weeds 6. Area
b. Characteristics of weeds 7. Farming and cultural practices
c. Mode of reproduction of weeds 8. availability of resources
d. Habitat, location and season 9. Economics of the method
e. Soil and weather conditions
1. Preventive measures
In this method the principle “prevention is better than cure” is applied. Prevention has two
dimensions with respect to time and space: the measures taken to prevent the infestation prior to
weed germination and to prevent the introduction or spread to new areas. Weed prevention also
includes measures to check the every year spread of even the existing weed species on the farm.
Weed prevention is a long term planning so that later the weeds could be controlled or managed
more effectively and economically than is possible when these are allowed to disperse freely.
The following methods can be adopted to prevent the introduction and infestation of weeds in
crop fields.
1. Avoid using crop seeds that are infested with weed seeds.
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2. Curative measures: Curative measures are applied after the infestation of weeds in the crop
field. This practice is done to check the growth of the weeds or totally eradicate the weeds from
the field. Mainly the following measures are adopted under curative measures:
a) Eradication method
This method is followed when and where a new species is found it must be destroyed
immediately before its multiplication, dispersion and acclimatization. Eradication can be done by
:
a) Destroying the species at the initial stage of introduction or early growth stage.
b) Degenerate the buried dormant but viable seeds by fumigation, flooding, heating and
other methods.
b) Control method
It is the process of limiting the weed infestation so that the crop can be grown profitably and
other operations can be conducted efficiently. The objective of weed control is to limit the
growth of unwanted plants with out any attempt to eliminate them from the scene. Now the weed
scientist prefer to use the term weed management. Important weed management practices
followed in relation to agriculture are:
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It refers to the combination of cultural practices being carried out in field in favor of crop
suppressing weed growth without environmental degradation. These practices are good land
preparation or tillage, growing smother competitive crops (sunnhemp, cowpea and rice bean),
mulching, crop rotation and land rotation, intercropping, stale seed bed technique, pre sowing
irrigation, summer fallowing or solarization, use of minimum tillage, green manuring, puddling,
selection of adaptable variety, optimum date, use of quality seed, seed treatment, seed rate and
method of sowing, stale seed bed, skipping the basal dose of fertilizer, correction of soil reaction,
insect, pest and disease management, appropriate method and time of harvesting etc.
Limitations:
1. Labour intensive method.
2. It required timely operation.
3. Usually limited by either too wet or too dry soil when crop needs weeding, depending upon
the weather conditions.
4. Soil should be workable.
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Benefit of herbicides
Herbicides were developed in the western world primarily to overcome shortage of farm labour
for weeding crops. The benefits are:
a) Herbicides can be used where physical weeding is not possible.
b) From very beginning even before they emerge from the soil, weed can be controlled
by using herbicides.
c) Herbicides can kill many weeds that survive by mimicry, e.g. Wild oat in wheat field.
d) They are convenient to use on spiny weeds which can not removed manually.
e) Herbicides can kill weeds insitu without permitting their dissemination.
f) Lower cost of farm produce.
Limitation of herbicides
a) Lack of technical know-how b) Environmental pollution. c) Variety of herbicides needed to
control weeds. d) Required considerable skill on the part of the users. e) Possibility of crop
injury. f) Military use of herbicides is a greatest misfortune of their discovery because of
possible hazards to human, animals, soil and environment. g) Development of resistance on the
part of weeds.
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8. Irrigation, drainage and rainfed farming
8.1 Role of water, water requirement of crops, water use efficiency, definition, objective and principles,
requirement and frequency of irrigation
Role of water
Water is one of the most important inputs essential for the production of crops. Plant need it in huge
quantities continuously during their life. Water received in the soil from precipitation and irrigation
is stored in the soil as soil moisture after the losses from runoff, drainage and evapotranspiration.
About 400-500 liters of water is necessary for the production of a kilogram of plant dry matter. The
main role of water is given as under:
Water moves in the plant body in liquid and vapour phases. The movement of water as a liquid
phase takes place from the soil to the root hair to mesophyll cells in the leaves through the root
epidermis, cortex, endodermis, pericycle, root xylem, stem xylem and leaf xylem. There after it
moves to the stationary air and ultimately to the turbulent air as a vapour phase through palisade
cells and sub stomatal cavity.
a) Free water
It is not bound to the soil but percolates it and drains under the influence of gravity.
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c) Hygroscopic water: Water hold tightly to the surface of soil particles by adsorption forces and is
not available to the plants.
d) Gravitational water: Water that moves freely in response to gravity and drains out of the soil.
The water, which is lost and goes below the ground due to the pull of gravity, is called gravitational
or super flow water. This water is not available for the plants.
2. Biological classification
a) Available water
The amount of water between field capacity (FC) and permanent wilting point (PWP) is considered
as available water for plant use. But the availability of water to plants is a function of soil-water-
plant system rather than soil-water system alone.
b) Unavailable water
Water held at tensions greater than 15 bars is said to be unavailable to plants. Depending upon the
reduction in availability of soil water, crop plants are subjected to water stress of varying degrees
ranging from mild to severe stress.
Water requirement of any crop is fulfilled through precipitation oreffective rainfall (ER), soil profile
contribution including that from shallow water table (S).
WR = IR + ER + S
The water requirements of crops vary from area to area, and even from field to field in a farm
depending on the above mentioned factors.
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Water use efficiency (WUE)
Water use efficiency is defined as the yield of marketable crop produced per unit of water used in
evapotranspiration.
WUE = Y
ET
Where WUE is water use efficiency (kg/ha mm); Y the marketable yield (kg/ha) and ET is
evapotranspiration (mm).
If yield is proportional to ET, water use efficiency has to be a constant but it is not so. Actually Y
and ET are influenced independently. Yield is more influenced by crop management practices, while
ET is mainly dependent on climate and soil moisture. Fertilization and other cultural practices for
high crop yield usually increase WUE, because they relatively increase crop yield more than crop
water use. Any practice that promotes plant growth and the more efficient use of sun light in
photoslynthesis without causing a corresponding increase in ET will increase WUE.
Irrigation
Irrigation is the artificial application of water to soil for the purpose of crop production. Irrigation
water is supplied to supplement the water available from rainfall and contribution to soil moisture
from ground water. In addition; irrigation can also be applied for leaching of soluble salts from
saline soils, to regulate soil-plant temperature, field preparation etc.
Objectives of irrigation
i) To increase productivity (the crop yield per unit area). The productivity of the crop
increase from 30-60% due to irrigation.
ii) To expand area under cropping.
iii) To increase cropping intensity.
iv) To minimize induce fluctuation in food production.
Principals of irrigation
i) Maximization of water use efficiency (WUE).
ii) Irrigate upto field capacity (FC) except rice.
iii) Standing water even for an hour except rice.
iv) Application efficiency should be maximum (leveling, bunding, and special shaping).
v) Irrigation water should be soaked the root zone and water management zone by
mulching and weed control.
vi) Irrigation interval and intensity should be based on soil, crop cultivation and
environment.
Irrigation requirement
The net irrigation requirement is the depth of irrigation water exclusive of precipitation, carry over
soil moisture or ground water contribution or other gains in soil moisture; that is required for crop
production. It is the amount of irrigation water required to bring the soil moisture level in the
effective root zone to field capacity. Thus it is the difference between the field capacity and the soil
moisture content in the root zone before starting irrigation.
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8.2 Methods of irrigation: surface irrigation (flooding, check basin, basin/ring, border strip, furrow), subsurface
method, sprinkler irrigation, drip irrigation, advantage and disadvantage of sprinkler and drip irrigation.
System of irrigation
The selection of systems of irrigation depends upon several factors viz. type of crop to be grown,
topography and texture of the soil, climatic conditions, water resource and economic conditions of
the cultivator. The irrigation system could be divided into following groups:
a) Surface irrigation system
b) Sub surface irrigation system
c) Drip irrigation system
d) Sprinkler irrigation system
Limitation
1) Greater loss of water and nutrients 2) More soil erosion 3) Depth of irrigation varies from place to
place due to varied topography. 4) Greater percolation in certain pockets.
2) Controlled flooding: In this method of irrigation field plots, which are to be irrigated are divided
into several plots convenient sizes of more or less even surface. The water is let into the field
through main and sub channels for irrigation plot one after another. The different methods of
controlled flooding are given as under:
a) Check basin method: Check basin method is applied in those areas where small stream of water
is available, ground is nicely leveled and the crop needs a carefull distribution of water. Bunds are
constructed around the area forming basin within which the irrigation water can be controlled. The
water is conveyed through main channel and branch channels which used to connect two
consecutive parallel rows of beds or basins. Rectangular or square beds of 10-100 m 2 areas are
prepared. The basins are filled to the desire depth and the water is retained until infiltrate. Crops
like onion, garlic; rice can be irrigated by this method.
Merits
i) Different kinds of crops can be grown in sequence in the same field without making
major changes in design, layout or operating procedure.
ii) Check basins are useful when leaching is required to remove salts from soil profiles.
iii) This method usually results in high water application and distribution efficiency.
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iv) This method enables the conservation of rainfall and reduction in soil erosion by
retaining a large part of the rain in the basin to be infiltrated gradually, without loss due
to surface runoff.
Demerits
i) Very expensive as preparation of ridges for making channels.
ii) Fairly large area is occupied by ridges and channels which remain uncropped.
iii) Ridges interfere in movement of animal drawn or tractor drawn implements for
interculture or harvesting of the crops.
iv) Precise land grading and shaping are required.
v) This method is not suitable for irrigated crops which are sensitive to wet soil conditions
around the stem of plants.
Merits
i) Border ridges are easily constructed with simple farm tools.
ii) Labour requirement is greatly reduced.
iii) Uniform distribution of water is maintained with higher application efficiency.
iv) Operation system is easy and simple.
v) Surface drainage can be easily made from the cross ridges.
vi) This method is more suitable to the soils having moderately low to moderately high
infiltration rates.
Demerits
1. It is not suitable for those crops which require water stagnation through out their cropping
period e.g. rice, jute etc.
2. This method is not suitable in sloppy and undulated land areas and having coarse sandy soils
(having high infiltration rates).
3. It is also not well suited to soils having very low infiltration rates.
c) Furrow irrigation method: This method is generally used for those crops which are sensitive to
saturated conditions at the root zone, these are root and tuber crops. It is adopted for irrigated row
crops where furrow made between the crop plant during the land preparation and planting. The crop
is sown on the ridges and the irrigation water is applied in the furrow so that most of the roots
remain above the saturation zone and there is no soil com,paction. Field is divided into ridge and
furrows along or across the slope and the furrows are connected with main channels. Sometimes ‘V’
shaped furrows are prepared along the slope of the land which are called corrugated or corrugation
method of irrigation. The length of time, the water is to flow in furrows depends on the ampunt of
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water required to replenish the root zone and the infiltration rate of the soil and the lateral spread of
water in the soil.
Merits
1. Water in the furrows contacts only one half to one fifth of land surface, thereby reducing
puddling and crusting of the soil, and evaporation losses.
2. Earlier cultivation is possible which is a distinct advantage in heavy soils.
3. The labour requirements in land preparation and irrigation is greatly reduced.
4. No wastage of land in field ditches.
Merits
i) High water use efficiency. ii) Needs least labour. Iii) Low evaporation loss through ground
surface.
Demerits
i) Very expensive ii) A slight negligence in applying water may lead to water logging in root zone
iii) Water having a high salt contain can not be used.
Merits
1. Drip irrigation method can achieve a 90% or more application efficiency, which can hardly
be achieved by any other methods of irrigation.
2. The method reduces salt concentration in the root zone when irrigated with poor ground
water.
3. Soluble fertilizers and pesticides can also be applied through this method of irrigation.
Demerits
1. High initial cost
2. The requirement that the water must be relatively clear, otherwise clogging problems may occur.
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3. Poor water distribution efficiency when a low pressure system is installed on steep slopes or uneven
land.
Merits
i) Better method for ground having uneven topography or land leveling ins not essential for
sprinkler irrigation.
ii) Better for light textured soils.
iii) Soluble fertilizer, insecticides and herbicides can also be sprayed easily through this
system.
iv) It is detachable and portable and can be carried at any location and may be shifted to
other locations after the irrigation is over.
v) Sprinkler irrigation can be used for almost all crops (except rice and jute)
vi) Small streams of irrigation can be used efficiently.
vii) Sprinkler method of irrigation can be used to protect crops against frost and high
temperatures that reduce the quantity and quality of the produce.
viii) Labour costs are usually less than for surface methods on soils having high infiltration
rate and on steep and rolling land.
ix) No wastage of land for bunds and ridges.
x) The irrigation method does not interfere with the movement of farm machinery.
Demerits
i) Sprinkler irrigation is 2-2.5 times costlier than surface irrigation for the same depth of
water application.
ii) If the wind velocity is greater than 6 km per hour drift losses increases or evaporation
losses is increases and wind distort sprinkler pattern and causes uneven distribution of
water also.
iii) Clay soils that have a slow intake rate coupled with hot, dry windy areas are not suitable
for sprinkler irrigation.
iv) Sprinkling water may cause fungal disease, wash pollen and reduce fruit set.
v) If the water containing large quantity of dissolved salts, this method may not be useful.
vi) Power requirement is high.
8.3 Scheduling irrigation: soil moisture depletion approach, IW/CPE approach, can evaporimeter, critical stage
approach.
Irrigation scheduling
To achieve better productivity, it is important to workout an efficient and economic irrigation
schedule for water use under any given set of agro-climatic conditions. There are several approaches
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for scheduling irrigation based on crops, soil atmosphere and plant water relations. The most
important approaches are:
a) Soil moisture depletion approach
b) Physical stage or critical stage approach.
c) Leaf water potential
d) Irrigation scheduling based on calculations.
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Tobacco Topping
Irrigation scheduling considers rainfall, evapo-transpiration, crop growth stages. For effecting
scheduling indicators of plant water stress should be identified. Available soil moisture can be
measured from the following instruments.
Example:
Calculate cumulative pan evaporation required for scheduling irrigation at 0.5, 0.5 and 0.75 and 0.8
with 5 cm of irrigation water.
Solution:
Cumulative pan evaporation at IW/CPE ratio of 0.5 = IW/CPE = 0.5
5 = 0.5
CPE
CPE x 0.5 = 5
CPE = 5 = 50 = 10 cm
0.5 5
Therefore irrigation of 5 cm is given when cumulative pan evaporation is 10 cm.
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4. Can evaporimeter approach
Can evaporimetry can be used by the farmers. In this small cans of one liter capacity (14.3 cm height
and 10 cm diameter) are used to indicate evaporation from the cropped field. These cans are painted
white and covered with 6/20 size mesh. An indicator pointer is fixed at 1.5 cm below the brim.
When irrigation is given bringing the soil to field capacity, the can is filled up with water to pointer
level and ke pt at the crop height. Evaporation from can is directly related to crop
evapotranspiration. Irrigation is scheduled when the water level in the can falls to a predetermined
level (equal to the amount of water to be applied at each irrigation) and can is filled again to the
pointer level.
8.4 Drainage: adverse effect of water logging, types of drainage: surface drainage (open ditch drainage, random
field ditch drainage, land smoothing, bedding/dead furrow), subsurface drainage
Drainage
Drainage is the removal of excess water either from agricultural land or barren land. Agricultural
drainage is the provision of a suitable system for the removal of excessive irrigation of rain water
from the land surface so as to provide suitable soil conditions for better plant growth. Excess water
becomes a problem when it interferes with tillage, land preparation, development of plants and
harvesting operation.
Much of excess water is removed naturally by surface runoff, deep seepage, evaporation and
transpiration but these processes are often too slow to prevent damage to crop and thus removal of
excess water must be carried out with the help of drainage. The excess water can be collected from
the source of excess rainfall, snow melt, irrigation water, overland flow or under ground seepage
from adjacent areas, artesian flow from deep aquifers and flood water from channels or water
applied from special purposes such as leaching salt from the soil or for temperature control.
Objectives of drainage
The main objectives of drainage are: removal excess water from the soil to improve the productive
capacity of soil, improvement in soil structure, increase in depth of plant rooting zone, improve air
circulation, to warm soil, improve organic matter decay and nitrification, reduced erosion,
diminished effect of drought, increased leaking of soil, prevention of freezing in temperate soil,
removal of salts from the soil by drainage of saline soil from irrigated land and check the water
logging condition in agricultural land.
Principles of drainage
1) The main drainage lines should follow the lines of natural drainage.
2) Laterals should be laid along lines of greatest slope.
3) Where possible, long parallel laterals should be used.
4) Drainage lines should be made straight or with gradual errors, sharp curve check the
flow of water and coarse silt deposition.
5) Silt wells or traps should be put in low spots.
6) The outlet should be protected from erosion and screened against burrowing animals.
7) In heavy clay soils of flat tops surface drainage is preferred.
Benefits of drainage
Drainage plays a vital role in agriculture. Irrigation and drainage should be given equal importance
during crop production. The main importance are given below:
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i) Drainage facilitates early ploughing and planting.
ii) It lengthens the crop-growing season.
iii) It helps to increase root zone depth.
iv) It helps to decrease soil erosion.
v) It leaches excess salt from soil and prevents their accumulation in soils.
vi) It improves soil structure and the infiltration capacity of soil.
vii) It hastens the warming of soil and maintains desirable soil temperature.
viii) It helps to aerate the soil.
ix) It helps to favour growth of soil bacteria.
x) It helps in reclamation of arable soil, low lying or swamp areas.
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In localities where drainage is a problem, crops are seen to be stunted with yellowing leaves in low
areas of field. If the excess water remains for sometime, the plants usually die. This is due to the
result of root damage caused by lower supply of O2 and accumulation of CO2.
Agricultural drainage
Agricultural drainage is the removal of excess water known as free water or gravitational water from
the surface or below the surface of farmland so as to create favourable soil conditions for plant
growth. Agricultural drainage is of two types:
Shallow ditches with gentle side slopes are used to remove the water but they may involve deep and
rather narrow field ditches. A surface drainage system includes:
a) Collection ditches
b) Disposal ditches.
Collection ditches are furrow and field ditches, which collect water within field and disposal ditches
are lateral and mains, which transport the collected water to an outlet.
4) Bedding system
The bedding system of surface drainage is designed, constructed and maintained so that surface
water drains laterally from crowned stripes of lands into dead furrows then into collection ditches
and finally into an outlet. The area between two adjacent dead furrow is known as a bed. The bed
should be laid out with the dead furrows running in the direction of greatest slope.
Merits
1) Unlike open drainage; land is not wasted and there is no interference to farming operations
by subsurface drainage.
2) This system requires less maintenance.
Demerits
1) Require high initial investment
2) Failure of the system is difficult to detect.
3) This system is ineffective in soils with low permeability.
4) Inlets and outlets should be maintained properly.
2) Vertical drainage
Vertical drainage is the disposal of drainage water through wells into a porous layer of earth or an
open rock formation. Such a layer formation must be capable of taking large volumes of water
supply.
3) Mole drains: Mole drains are unlined circular earthen channels formed highly cohesive or fibrous
soil by a mole plough. Mole channels are usually ranged in diameter from 7.5-10 cm. Spacing ranges
from 1.5-9 m and depth from 50-75 cm. The mole plough has a long blade like shank to which
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attached a cylindrical bullet-nose plug known as mole. As the plough is drawn through the soil, the
mole forms.
8.5 Rainfed farming: difference between dry land farming and rainfed farming, importance of rainfed farming in
Nepal, management of rained farming.
Dry farming
Dry farming is a system of crop farming where water becomes a major limiting factor for production
with no provision of any planned irrigation. Crop production is solely dependent on rainfall.
Prolonged dry spell during crop period are most common. Crop failure is more frequent under dry
farming conditions. In dry farming areas the average annual rainfall is less than 750 mm. Dry
farming regions are equivalent to arid regions and moisture conservation practices are important in
this region.
Rainfed farming
Rainfed farming is the practice of growing crops, entirely depending on rainfall as source of
moisture where the mean annual rainfall is above 750 mm. The quantity of rainfall should be
adequate to meet the crop demand. It is practiced in humid regions where crop failure is rare and
drainage is the most important problem.
3. Crop growing season is short i.e below 3. Growing season is long compared than
200 days only. dry land farming i.e. more than 200
days.
4. Growing regions are arid and semiarid as 4. Growing regions are humid and sub
well as uplands of sub humid and humid humid regions.
regions.
6. Erosion may be due to wind or water and 6. Erosion may be due to water and
adoption of soil and moisture drainage is the important problem. Soil
conservation practices are necessary. conservation practices are also
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necessary.
With the increase in population, the need for higher food grain production of some associated crops
have increased many folds particularly of cereals and grain legume crops. Nepalese farmers still
farm in a traditional way irrespective of the many changes that have taken place and modern
technology diffusion. There have been many efforts in the past, important contributions were made,
but nevertheless some serious problems could not be solved. The decline in productivity has been
caused mainly by intensified agriculture due to over mining and the improper use of FYM/compost,
green manure and other local resources as recycling of organic wastes.
Rainfed agriculture supports mainly for human and livestock population of Nepal. To meet the food
security in general and in hilly districts in particular, augmented food production to cope with the
need of the increasing population is a great challenge for us. We have majority of rainfed areas
which do not receive good amount of rainfall sufficient for optimum field crop production. More
number of dry areas is found in far and mid development regions of our country. That is why
western and far western region of Nepal are always in food deficient.
Rainfed areas suffer from a number of constraints. The aberrant behaviour of the monsoon causes
frequent drought. Prolonged dry spells during crop period causes crop failure. Soils are highly
degraded due to soil erosion with low water retentive capacity and low nutrient status. Crop
production in dry lands is attendant with high risk due to which farmers hesitate to invest on inputs.
Poor adoption of improved technology leads to low yield and farmers are poor. At present 3 ha of
rainfed area produces cereal grains equivalent to 1 ha of irrigated area. There is scope of rapidly
doubling the average yield in dry farming areas.
ii) Reduce water loss through evaporation: Prevention of water loss through evaporation can be
achieved through mulching. There are two types of mulch i.e. organic (straw, stubble, FYM, saw
dust, rice husk etc) and synthetic (petroleum product like ESSO or ENCAP form thin layer on soil
surface, polythene mulch etc).
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b) Inter row water harvesting: It provides ridge and furrow system. It is done in case of winter and
spring crops. Crops are grown in the furrows in winter and spring and ridges in rainy season.
c) Broad raised bed and furrow: On the bed mixed cropping lime maize + arhar or sorghum +
arhar can be grown. In the furrows rain water is collected which is utilized by the crops. If there is
excess water from furrows could be led to the tanks.
d) Inter plot water harvesting: Rain water falling in the micro-catchments is harvested in to the
cultivated strips. Micro catchment is sloping towards cultivated strips. Example: 40 cm rain becomes
70 cm rain to cropped area (addition of 30 cm). If the flat is there, then earthwork is needed and if
undulated land and then try to adjust the slope lime this. This can be done in light soil because of
high infiltration.
Uncultivated strip
4m
2m
2m
Cultivated strip
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should be selected. Example: sorghum, bajara, cotton, groundnut, cluster bean, gram, barley castor,
saff-flower, mustard, linseed etc.
iii) Intercropping
Intercropping should be widely adopted. It gives better utilization of moisture and fertility apart from
insurance. Example: Bajara + cluster bean, Bajara + Mung, castor + mung, Castor + cowpea, cotton
+ groundnut. Gram + linseed etc.
In dry areas, lower plant population then irrigated areas is maintained because limited soil moisture
can support limited number of plants. Higher plant population will exhaust soil moisture before
onset of reproductive organs, but at the time of sowing 10-15% more seed rate then irrigated area is
used. When the germination is good then after 15 days thinning is done to maintain the plant
population to the desirable level. Row to row spacing is maintained more than irrigated areas. So the
mulching can be easily done.
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9. Soil Erosion
9.1 Definition of soil erosion, types of water erosion (sheet, rill, gully, ravines, stream bank and landslides), factors
affecting water erosion, losses due to water erosion.
2. Accelerated erosion
Accelerated erosion is the removal of the surface soil from areas denuded of their natural protective
covers results of human and animal interference takes place at a much faster rate than that at which it
is buildup by the soil forming process. It results from man activities when preparing land for the
production of food and fibre and as a place to build homes. Industrial plants and transport facilities.
Based on causing agent soil erosion is classified as: a) Water erosion and b) Wind erosion
A) Water erosion
Water erosion causes several types of damages by removing soil gradually. These characteristic soil
losses are: i) Overland flow or sheet erosion ii) Micro-channel or rill erosion, iii) Gully erosion iv)
Land slides or slip erosion, v) Stream bank erosion vi) Ravines
a) Sheet erosion
It is the first stage of erosion and removes a thin covering of soil from large areas, often from entire
fields, more or less uniformly during every rain which produces a runoff. In the early stage of
erosion, rain drops churn the top soil and along with runoff the muddy water moves away from the
soil. It is often unnoticed as it occurs gradually. It is generally neglected, although the soil
deteriorates slowly and imperceptibly. Its existence is however, can be detected by muddy colour of
the runoff from the field.
b) Rill erosion
This is second stage of erosion. When sheet erosion is allowed to continue unchecked, the silt-laden
runoff forms a well defined but minute finger shaped grooves over the entire field. Such thin
channeling is known as rill erosion. These shallow channels can be seen easily on the ground
surface. This is more apparent than sheet erosion.
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c) Gully erosion
When rill erosion is neglected, the tiny grooves develop into wider and deeper channels, which may
assume a huge size. This is called gully erosion. By the large volume and velocity of moving mass
increases, large number of gullies are formed on the ground surface, which are the most spectacular
symptoms of erosion. The gullies tend to deepen and widen with every heavy rainfall. If the gullies
are not checked in time, cultivation of crop may become difficult.
d) Ravines
Ravines are deep and wide gullies which are formed after the prolonged process of gully erosion. It
is advanced stage of gully erosion.
2. Vegetation
Vegetation is most important factor for influencing soil erosion. Vegetation helps to protect the soil
aggregates from detachment or breakdown. In addition plant roots bind the soil particles and
vegetation add the organic matter in to the soil which helps for binding the soil aggregates.
Depending on the type of vegetation, canopy and height, rainfall interception differ and extent of
erosion also differ.
3. Soils
Soil characteristics have considerable influence on soil erodibility. Different characteristics of soil
are topography, physical, chemical and biological properties of soil. Among them topography is the
most important character that influences runoff and sediment transport. Higher the degree and length
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of slope there will be higher amount of runoff and extent of erosion due to higher force of gravity.
Velocity of flowing water detaches soil particles and carries them. When the runoff attains a velocity
of about 60-90 cm/sec, it is capable of eroding of soil.
Physical properties like soil texture and structure also influence soil erosion. Light soils like sandy
soils and sandy loams are easy to detach, but difficult to transport as the particles are heavy and the
infiltration rate is also high due to which the runoff is less. In case of heavy soils, the detachment is
difficult, but transport is easy because most of the particles are light in weight.
Soil chemical and biological properties are also influence soil erosion through their effect on soil
aggregate formation and dispersal. Soils with higher cation exchange capacity, calcium and
magnesium content of the exchange complex, have favourable influence on soil structure and are
therefore susceptible to erosion.
Another problem in erosion is the loss of a siltly or sandy surface soil and the leaving of heavy clay
layer exposed at the surface. Under such conditions, erosion severely damages the soil, because of
the heavy clay layer may not contain enough aeration porosity to support a good crop.
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9.2 Water erosion controlpractices, wind erosion (saltation, surface creep, suspension), factors affecting wind
erosion, losses due to wind erosion, wind erosion control
2. Contour cultivation
Contour refers to a line drawn through points of equal heights on the ground. These are suitable on
land with slope less than 5-6%. Contour cultivation includes contour ploughing, contour bunding,
contour sowing and other intercultural operations. These operations are done across the slope. Each
row of the crop, each bund, each ridge of plough and furrow act as an obstruction to runoff,
providing more opportune time for water to enter into the soil and reduce the soil loss.
3. Conservation tillage:
Conservation tillage is disturbing the soil to the minimum extent necessary and leaving crop residues
on the soil. Conservation tillage system includes minimum and zero tillage, which can reduce soil
loss. While the conventional tillage includes ploughing twice or thrice followed by harrowing and
planking. It leaves no land unploughed and leaves no residue on the field. The chances of soil loss by
conventional tillage is more than 50% over conservation tillage.
4. Mulching:
Mulches can cover more soil surface and protects the soil from rain drop impact. By increasing the
amount of mulch, the sediment present in runoff water can also be reduced. Mulching with plant
materials reduces soil loss upto 43 times compared to bare soil and 17 times compared to cropped
soil without mulches.
5. Cropping system
Soil erosion depends on cropping systems adopted. Growing a crop which produces the maximum
cover, reduces runoff and soil loss. Cowpea and green gram are important cover crops for the rainy
season. These crops give early and dense (85%) ground cover which generally coincides with peak
rate of runoff. In multiple cropping systems where the soil is covered with crops throughout the year
and there may be runoff but soil loss is minimum as the falling raindrops are intercepted by the crop.
6. Use of chemicals
Soils with stable aggregates resist break down and thus resist erosion. Breakdown of aggregates by
the falling raindrops is the main cause of detachment of soil particles. Aggregate stability can be
increased by spraying chemicals like Polyvinyl alcohol @ 480 kg/ha, the rate however, depending
on the type of soil.
B) Wind erosion
Wind erosion is a process in which soil particles on the land surface are lifted and blown off as dust
storms. When the velocity of the dust bearing winds is retarded coarser soil farticles are deposited in
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the forms of dunes and thus fertile lands are rendered unfit for cultivation. In other places, fertile soil
is blown away by winds and the subsoil is exposed, as a result the productive capacity of the soil is
considerably reduced. Wind erosion takes place normally in arid and semi arid areas devoid of
vegetation, where wind velocity is high.
i) Saltation
The major portion (50-75 % of the total wind erosion) of the soil carried by the wind is moved in a
series of short bunches called saltation. The soil carried in saltation consists of fine particles ranging
from 0.1-0.5 mm in diameter. Saltation is caused by the direct pressure of wind on soil particles and
their collision with other poarticles. After being pushed along the ground surface by the wind, the
particles leap almost vertically in the first stage of saltation. Some grains rise only a short distance;
other leap 30 cm or higher, depending directly on the velocity of the rise from the ground.
iii) Suspension
Very fine soil particles, less than 0.1mm in diameter, are carried into suspension, being kicked up
into the air by the action of particles in saltation. The movement of fine dust in suspension is
completely governed by the characteristic movement of wind. Suspension material is carried long
distances from its original location and is thus a complete loss to the eroded area, where the soil
moved in saltation and surface creep usually remains within the eroded area, especially when erosive
winds are from different directions.
2. Damage to crops
Crop damage, particularly in the seedling stage, serious stand and subsequent yield and quality
losses are incurred and in the extreme, tender seedlings may be completely killed. Often, sufficient
soil is removed to expose the plant roots or ungerminated seed and this results in complete crop
failure. Covering of stabilized crops or pasturage by drifting soil is another result. It is probable that
annual damage to crops by wind erosion exceeds that by water erosion.
Principles of Agronomy
B . B Adhikari
Lamjung Campus-063
3. Soil loss
Fertile top soil is lost by wind erosion. Finer soil fractions (silt, clay and organic matter) are removed
and carried away by the wind, leaving the coarser fractions behind. This sorting action not only
removes the most important material from the standpoint of productivity and water retention, but
also leaves a more sandy and thus a more erodible soil than the original.
4. Socio-economic effects
Wind control is beyond the capacity of human being. The economy of any country depends
primarily on the soil and its products, and thus on its crops and livestock farmers. Soil erosion can
seriously affect the development and progress of any nation. Food, housing, clothing or other goods
depends directly and indirectly on soil and water. Peoples living in heavy wind blowing areas suffer
more than other areas. Due to this reason the living standard of the people is also directly related to
the soil loss from his field.
Principles of Agronomy
B . B Adhikari
Lamjung Campus-063
10. Crop ideotype and crop density
10.1 Ideotype concept, traits for ideotype, characteristics ideotype of rice, wheat and maize, concept of economic
yield and biological yield, harvest index
Ideotype
Ideotype refers to plant type in which morphological and physiological characteristics are ideally
suited to achieve high production potential and yield reliability.
Ideotype concept
Model characters influences yield and growth. Modal character has been incorporated in major crops
like wheat, rice, maize, barley etc. We can see the differences between traditional and improved
variety of these crops. In most of the crops traditional variety of these crops have less modal
character as compare to improved variety. That’s why improved variety gives more yield than
traditional variety. The difference in yield is due to differences in plant type.
2. Presence of own
Presence of awn is modal character in case of rice wheat, barley, oats etc. that leads to higher
production. Awn less variety has less photosynthetic efficiency. Birds damage awn less variety,
where awn helps to protects the grains against the birds. Awn contributes 10% towards total grain
dry weight. Under rainfed condition this contribution is higher because awn is xerophytic in nature.
Hence for dry area awn is very good character.
3. Erect foliage
Wheat, rice and maize ideotype must have erect leaves. This is important in terms rate of
photosynthesis. Erect foliage provides more population or more population could be accumulated in
an area so more yields can be expected. Erectness is highly responsible to take high inputs such as
fertilizer and irrigation. So erect type of canopy or erectophyle is desirable modal character.
Principles of Agronomy
B . B Adhikari
Lamjung Campus-063
6. Erect ear
In case of wheat, rice , barley, oats, fox tail millet ear should be of erect type. Ear head at initial
stage (green stage) contributes towards photosynthesis and the erect ear heads are more active for
photosynthesis or contribution for dry matter accumulation then drooping types.
7. Single culm
Multiculm variety is less preferable than single culm variety in case of rice, wheat and barley. Many
tillers do not produce ear heads and there is problems barrenness or sterility. Size of the ear from
side tiller is smaller than main shoot. In multiculm variety the efficiency of resource is less than
single culm variety that’s why multiculm varieties are poor yielder than single culm variety. Single
cob having small tassel variety is better than multicob with large tassel variety in case of maize.
8) Leaf senescence
Dry matter accumulation will be continue due to efficient photosynthesis if the maximum number of
leaves are presence upto maturity stage or there is slow senescence of leaves. This is most important
desirable ideal character in almost crops.
9) Other characters
a) Early maturing b) Well adopted c) More disease resistance d) Photo insensitive e) Strong
competitor against weeds f) Cold tolerance variety for winter.
Characteristics ideotype
a) Rice
High yield potential in a rice cultivar is associated with a combination of morphological and
physiological characteristics of plant.Morphological characteristics like short stature, high tillering,
stiff culms and compact panicles to hold the plant erect, erect leaves to reduce shading and utilize
solar radiation efficiently, and well filled heavy panicles. Physiological characteristics like seedling
vigour, early maturity to permit growing more than one crop of rice per year, photoperiod
insensitivity to permit growing a cultivar in any crop season or in different latitudes, and N
responsiveness.
b) Maize
High yield, strong root and stalk, total husk covering, disease and insect resistance, compact
endosperm, resistance to ear dropping, rapid dry down, resistant to heat and drought, response to soil
fertility, cold tolerance etc.
c) Wheat
Stable yield, early maturity, lodging resistance (development of cultivar with a vigorous and healthy
root system, short and sturdy straw, resilient straw that does not break in the wind, shorter straw),
winter hardiness (resistance to winter injury), drought resistance, disease resistance, insect resistance
etc.
Economic yield: It is a measure of the only economically utilizable parts of the crop e.g. grains in
case of cereals, tuber, rhizomes, bulbs etc. are economic yield.
Biological yield: It is a measure of the total biomass production from the crop and is often used as
an expression of yield e. g. rice grain + straw yield, cobs + strover yield of maize etc.
Principles of Agronomy
B . B Adhikari
Lamjung Campus-063
Harvest index
It is the ratio of economic yield to biological yield and expressed in percentage. It is a measure of
efficiency of a given grain crops.
10.2 Crop density, optimum plant population, factors affecting optimum plant population
In rainfed condition crop are grown on stored soil moisture, so population should not be high to
deplete the moisture before crop mature and plant population should not be low to leave moisture
unutilized. Under condition of sufficient soil moisture and nutrients, higher population is necessary
to utilize other growth factors efficiently. When soil moisture and nutrients are not limiting, yield of
a crop is limited by solar radiation. The level of plant population should be such that maximum solar
radiation should be intercepted.
Relationship between yield of individual plant and yield of community influenced by plant
population
Full yield potential of individual plant i.e yield per plant is obtained when sown at wider spacing i.e.
lowest plant population level. When sown densely, competition among plant is more for growth
factor (moisture, nutrients, light etc) resulting changed in size and yield of the plant. Yield per plant
decreases gradually as plant population per unit area is increased. The yield per unit area is increased
due to efficient utilization of growth factors. So maximum yield per unit area which is our main
objective, can be obtained when the individual plants are subjected to serve competition.
Principles of Agronomy
B . B Adhikari
Lamjung Campus-063
Yield
Plant population
Fig. Yield of individual plant and community as influenced by plant population.
1) Time of sowing
The crop is subjected to different weather conditions when sown at different periods. The day length
(for photosensitive varieties) and temperature are most important factor that influences the optimum
plant population.
2) Irrigation
In rainfed condition, the number of plant population should be less because if the plant population is
high the residual moisture of soil will be depleted due to maximum transpiration and creates the
moisture stress condition in last phase of crop. Under adequate irrigation or under evenly distributed
rainfall condition, higher plant population is recommended.
3) Fertilizer application
Dense plant stand is necessary to fully utilize higher level of nutrients in the soil to achieve potential
yields. Nutrient uptake increases with increase in plant population. Higher plant population under
low fertility condition leads to develop the nutrient deficiency.
Principles of Agronomy
B . B Adhikari
Lamjung Campus-063
4) Planting pattern
Planting pattern influences the crop yield through influence on light interception, rooting pattern and
moisture extraction pattern. Same density of plant in the field can be maintained by different crop
geometry. Out of various crop geometry which gives more yield can be called better planting
pattern. Crop geometry is altered by changing inter and intra-row spacing. There are different
patterns of planting which are:
a) Square planting: Square arrangement of planting is more efficient in utilization of light, water
and nutrients available to the individual plant. In wheat decreasing inter-row spacing below the
standard 15-20 cm i.e. reducing the rectangularity generally increase yield slightly. In crops like
tobacco, inter cultivation in both direction is possible in square planting and helps in effective weed
control.
But square planting is not adventitious in all crops. For example ground nut sown with 30 x 10 cm
(3.33 lakh plants/ha) gives higher yield than with same amount of population by square planting.
b) Rectangular planting: Sowing the crop with seed drill is standard practice. Wider inter-row
spacing and closer intra-row spacing is very common for most of the crops and this practice is called
rectangular planting. This rectangular practice is mainly adopter to facilitate intercultivation.
Sometimes only inter-row spacing is maintained and inter-row spacing is not followed strictly and
seeds are sown continuously or closely i.e. plant to plant space is continuous.
c) Miscellaneous planting pattern: Crops are sown with seed drills in two direction to
accommodate more number of plants and mainly to reduce weed population. The important
practices are:
i) Skip row planting: Crops like rice, fingermillet are transplanted at the rate of 2-3
seedlings per hill. Transplanting is done either in rows or randomly. Skipping of every
alternate row is known as skip row planting.
ii) Paired-row planting: When one row is skipped and the required population is adjusted
by decreasing intra-row spacing, this method of planting is known as paired-row planting.
It is generally done to introduce intercrop.
6) Thinning
Thinning is done to obtain optimum plant population by removing excess population. In certain
situation where germination and emergence is a problem, high seed rate is used. During favourable
season this gives very high population and if thinning is not done, results in weak seedlings due to
over crowding. Low yields are obtained due to severed competition. Barren plants are also observed
under excess population.
7) Seed rate
The required number of plants per unit area is decided by calculating the seed rate. The seed rate
depends on spacing, test weight (1000 seed weight) and germination percentage.
Principles of Agronomy