TEACHING MATERIAL ON

Fundamentals of Agronomy
AAG – 111 (3+1)

S.K. Dutta, A. Roychowdhury, S.S. Acharya,

Seema, S.K. Pathak

Department of Agronomy
Bihar Agricultural College, Sabour
Bihar Agricultural University, Sabour,
Bhagalpur-813 210
 CONTENTS

S.N. Course content Break-up

1. Agronomy and its scope

2. Seeds and sowing

3. Tillage and tilth

4. Crop density and geometry

5. Crop nutrition, Manures and fertilizers

6. Water resources and soil – plant – water relationships

7. Crop water requirement and water use efficiency

8. Scheduling of irrigation and methods of irrigation

9. Quality of irrigation water

10. Weed and its classification

11. Weed management

12. Herbicide classification

13. Allelopathy

14. Growth and development of crops

15. Plant ideotype

16. Crop rotation and its principles

17. Harvesting and threshing of crops

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 Chapter 1

Agronomy and its scope

Agriculture:
The term Agriculture is derived from two Latin words “ager” or “agri” meaning soil
and “cultura” meaning cultivation. Agriculture is an applied science which encompasses all
aspects of crop production including horticulture, livestock rearing, fisheries, forestry, etc.
Agriculture is defined as an art, science and business of producing crops and livestock for
economic purposes.
As an art, it embraces knowledge of the way to perform the operations of the farm in a
skillful manner, but does not necessarily include an understanding of the principles
underlying the farm practices.
As a science, it utilizes all technologies developed on scientific principles such as
crop breeding, production techniques, crop protection, economics etc. to maximize the yield
and profit. For example, new crops and varieties developed by hybridization, Transgenic crop
varieties resistant to pests and diseases, hybrids in each crop, high fertilizer responsive
varieties, water management, herbicides to control weeds, use of bio-control agents to combat
pest and diseases etc.
As the business: As long as agriculture is the way of life of the rural population
production is ultimately bound to consumption. But agriculture as a business aims at
maximum net return through the management of land labour, water and capital, employing
the knowledge of various sciences for production of food, feed, fibre and fuel. In recent
years, agriculture is commercialized to run as a business through mechanization.
Agronomy:
The word agronomy has been derived from the two Greek words, agros and nomos
having the meaning of field and to manage, respectively. Literally, agronomy means the “art
of managing field”. Technically, it means the “science and economics of crop production by
management of farm land”.
Agronomy is the art and underlying science in production and improvement of field
crops with the efficient use of soil fertility, water, labourer and other factors related to crop
production. Agronomy is the field of study and practice of ways and means of production of
food, feed and fibre crops. Agronomy is defined as “a branch of agricultural science which
deals with principles and practices of field crop production and management of soil for higher
productivity.
Importance:
Among all the branches of agriculture, agronomy occupies a pivotal position and is regarded
as the mother branch or primary branch. Like agriculture, agronomy is an integrated and
applied aspect of different disciplines of pure sciences. Agronomy has three clear branches
namely Crop Science, Soil Science and Environmental Science that deals only with applied
aspects. Agronomy is a synthesis of several disciplines like crop science, which includes
plant breeding, crop physiology and biochemistry etc., and soil science, which includes soil
fertilizers, manures etc., and environmental science which includes meteorology and crop
ecology.
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Basic Principles of Agronomy
• Planning, programming and executing measures for maximum utilization of land,
labourer, capital and other factors of production.
• Choice of crop varieties adaptable to the particular agro-climate, land situation, soil
fertility, season and method of cultivation and befitting to the cropping system;
• Proper field management by tillage, preparing field channels and bunds for irrigation and
drainage, checking soil erosion, leveling and adopting other suitable land improvement
practices;
• Adoption of multiple cropping and also mixed or intercropping to ensure harvest even
under adverse environmental conditions;
• Timely application of proper and balanced nutrients to the crop and improvement of soil
fertility and productivity. Correction of ill-effects of soil reactions and conditions and
increasing soil organic matter through the application of green manure, farm yard manure,
organic wastes, bio fertilizers and profitable recycling of organic wastes;
• Choice of quality seed or seed material and maintenance of requisite plant density per
unit area with healthy and uniform seedlings;
• Proper water management with respect to crop, soil and environment through
conservation and utilization of soil moisture as well as by utilizing water that is available
in excess, and scheduling irrigation at critical stages of crop growth.
• Adoption of adequate, need-based, timely and exacting plant protection measures against
weeds, insect-pests, pathogens, as well as climatic hazards and correction of deficiencies
and disorders;
• Adoption of suitable and appropriate management practices including intercultural
operations to get maximum benefit from inputs dearer and difficult to get, low-monetary
and non-monetary inputs;
• Adoption of suitable method and time of harvesting of crop to reduce field loss and to
release land for succeeding crop(s) and efficient utilization of residual moisture, plant
nutrients and other management practices;
• Adoption of suitable post-harvest technologies.
• Agronomy was recognized as a distinct branch of agricultural science only since about
since about 1900. The American Society of Agronomy was organized in 1908.
Irrigation management: Whether to irrigate continuously or stop in between and how much
water should be irrigated are calculated to find the water requirement.
• Crop planning (i.e.,) developing crop sequence should be developed by agronomist (i.e.)
what type of crop, cropping pattern, cropping sequence, etc.
• Agronomists are also developing the method of harvesting, time for harvesting, etc. The
harvest should be done in the appropriate time.
• Decision-making in the farm management. What type of crop to be produced, how much
crop, including marketing should be planned? Decision should be at appropriate time.

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 Chapter 2

Seeds and sowing

Seed – Seed is an embryonic part covered in a seed coat often containing some food. It is
formed from the ripened ovule of a plant after fertilization.
Grain – A grain is a small edible fruit usually hard on the outside, harvested from crops.
Grains basically grow in a cluster on top of the mature plant.

Seed vs Grain –
1. A seed is an ovule containing an embryo while a grain is a fusion of the seed coat and the
fruit.
2. Typically seeds are planted to grow plants while grains are harvested for food.
Grains provide food from the fruit part while seeds mainly food from embryo part.

Seeds are the vital part of agriculture. Selection of good quality seeds is a challenge
for famers. Only good quality seeds which are sown properly can give an expected result or
yield. Seeds of variety of types and strains are available; cultivators have to choose from
these and these have to be sown in the field.
Seed Selection
Healthy, good quality seeds are the root of a healthy crop. Hence selection of seeds is
crucial. Selection helps to obtain healthy seeds; sustain and optimize the quality of crop
strain. Based on plant size, quantity of grains, fruit size or colour, disease resistance etc. seeds
can be selected. Farmers also need to check the germination period, nutrients required so that
the selected seeds will be beneficial in terms of yield and finance. Some seeds are sources of
diseases; they can be used after proper treatment like chemical or hot water treatments etc. A
careful observation of crops and their yield in first year may help farmers to choose best
strains of seeds for successive years. Hence for high yield, sow best seeds.
Classification:
Breeder Seed
Breeder seed is the progeny of nucleus seed of a variety and is produced by the
originating breeder or by a sponsored breeder. Breeder seed production is the mandate of the
Indian Council of Agricultural Research, State Agricultural Universities, Sponsored breeders
recognized by selected State Seed Corporations, and Non-governmental Organizations.
Foundation Seed
Foundation seed is the progeny of breeder seed and is required to be produced from
breeder seed or from foundation seed which can be clearly traced to breeder seed. The
responsibility for production of foundation seed has been entrusted to the NSC, SFCI, State
Seeds Corporation, State Departments of Agriculture and private seed producers, who have
the necessary infrastructure facilities. Foundation seed is required to meet the standards of
seed certification prescribed in the Indian Minimum Seeds Certification Standards, both at
the field and laboratory testing.
Certified Seed

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 Certified seed is the progeny of foundation seed and must meet the standards of seed
certification prescribed in the Indian Minimum Seeds Certification Standards, 1988. The
production and distribution of quality/certified seeds is primarily the responsibility of the
State Governments. Certified seed production is organized through State Seed Corporation,
Departmental Agricultural Farms, Cooperatives etc.
Methods of Sowing
Seeds are sown directly in the field (seed bed) or in the nursery (nursery bed) where
seedlings are raised and transplanted later. Direct seeding may be done by Broadcasting,
Dibbling, Drilling, Sowing behind the country plough, Planting and Transplanting.
(a) Broad casting - Broad casting is the scattering or spreading of the seeds on the soil, which
may or may not be incorporated into the soil. Broadcasting of seeds may be done by hand,
mechanical spreader or aeroplane. Broadcasting is the easy, quick and cheap method of
seeding. The difficulties observed in broadcasting are uneven distribution, improper
placement of seeds and less soil cover and compaction. As all the seeds are not placed in
uniform density and depth, there is no uniformity of germination, seedling vigour and
establishment. It is mostly suited for closely spaced and small seeded crops.
(b) Dibbling - It is the placing of seeds in a hole or pit made at a predetermined spacing and
depth with a dibbler or planter or very often by hand. Dibbling is laborious, time consuming
and expensive compared to broadcasting, but it requires less seeds and, gives rapid and
uniform germination with good seedling vigour.
(c) Drilling - It is a practice of dropping seeds in a definite depth, covered with soil and
compacted. Sowing implements like seed drill or seed cum fertilizer drill are used. Manures,
fertilizers, soil amendments, pesticides, etc. may be applied along with seeds. Seeds are
drilled continuously or at regular intervals in rows. It requires more time, energy and cost, but
maintains uniform population per unit area. Rows are set according to the requirements.
(d) Sowing behind the country plough - It is an operation in which seeds are placed in the
plough furrow either continuously or at required spacing by a man working behind a plough.
When the plough takes the next adjacent furrow, the seeds in the previous furrow are closed
by the soil closing the furrow. Depth of sowing is adjusted by adjusting the depth of the
plough furrow. e.g., ground nut sowing in dry land areas of Tamil Nadu.
(e) Planting - Placing seeds or seed material firmly in the soil to grow.
(f) Transplanting - Planting seedlings in the main field after pulling out from the nursery. It
is done to reduce the main field duration of the crops facilitating to grow more number of
crops in an year. It is easy to give extra care for tender seedlings. For small seeded crops like
rice and ragi which require shallow sowing and frequent irrigation for proper germination,
raising nursery is the easiest way.
Pre-monsoon sowing:
Normally, sowing is taken up after receipt of sufficient amount of rainfall (20 mm) in
the case of dry land farming. Since sowing is continued for two or three days after a soaking
rain, certain amount of moisture is lost during the period between the receipt of rainfall and
sowing. In the case of heavy clay soils (black soils), sowing operation is difficult after the
receipt of rain. To overcome this difficulty, sowing is taken up in dry soil prepared with
summer rains, 7-10 days before the anticipated receipt of sowing rains. The seeds germinate

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after the receipt of the rainfall. This method of sowing is known as dry sowing or pre-
monsoon sowing. By this method, the entire rainfall received is efficiently utilized.
Factors involved in Sowing Management
This can be classified into two broad groups.
1. Mechanical factors - Factors such as depth of sowing, emergence habit, seed size and
weight, seedbed texture, seed–soil contact, seedbed fertility, soil moisture etc.
(i) Seed size and weight: Heavy and bold seeds produce vigorous seedlings. Application of
fertilizer to bold seed tends to encourage the seedlings than the seedlings from small seeds.
(ii) Depth of sowing: Optimum depth of sowing ranges from 2.5–3 cm. Depth of sowing
depends on seed size and availability of soil moisture. Deeper sowing delays field
emergence and thus delays crop duration. Deeper sowing sometimes ensures crop survival
under adverse weather and soil conditions mostly in dry lands.
(iii) Emergence habit: Hypogeal seedlings may emerge from a relatively deeper layer than
epigeal seedlings of similar seed size.
(iv) Seedbed texture: Soil texture should minimize crust formation and maximize aeration,
which in turn influence the gases, temperature and water content of the soil. Very fine soil
may not maintain adequate temperature and water holding capacity.
(v) Seeds–Soil contact: Seeds require close contact with soil particles to ensure that water
can be absorbed readily. A tilled soil makes the contact easier. Forming the soil around the
seed (broadcasted seeds) after sowing improves the soil–seed contact.
(vi) Seedbed fertility: Tillering crops like rice, ragi, bajra etc., should be sown thinly on
fertile soils and more densely on poor soils. Similarly high seed rate is used on poor soil for
non-tillering crops. Although higher the seed rate grater the yield under conditions of low
soil fertility, in some cases such as cotton, a lower seed rate gives better result than a higher
seed rate.
(vii) Soil moisture: Excess moisture in soil retards germination and induce rotting and
damping off disease except in swamp (deep water) rice. Adjustment in depth is made
according to moisture conditions, i.e., deeper sowing on dry soils and shallow sowing on
wet soils. Sowing on ridges is usually recommended on poorly drained soils.
2. Biological factors - Factors like companion crops, competition for light, soil
microorganisms etc.
(i) Companion crop: Companion crop is usually sown early to suppress weed growth and
control soil erosion. In cassava + maize/yam cropping, cassava is planted later in yam or
maize to minimize the effect of competition for light. In mixed cropping, all the crops are
sown at the same time.
(ii) Competition of light: In mixed stands, optimum spacing for each crop minimizes the
competition of light.
(iii) Soil microorganisms: The microorganisms present in the soil should favour seed
germination and should not posses any harmful effect on seeds/emerging seedlings.

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 Chapter 3

Tillage and Tilth

Tillage operations in various forms have been practiced from the very inception of
growing plants. Primitive man used tools to disturb the soils for placing seeds. The word
tillage is derived from the Anglo-Saxon words tilian and teolian, meaning to plough and
prepare soil for seed to sow, to cultivate and to raise crops. Jethrotull, who is considered as
Father of tillage, suggested that thorough ploughing is necessary so as to make the soil into
fine particles.

Definition

Tillage refers to the mechanical manipulation of the soil with tools and implements so
as to create favourable soil conditions for better seed germination and subsequent growth of
crops. Tilth is a physical condition of the soil resulting from tillage. Tilth is a loose friable
(mellow), airy, powdery, granular and crumbly condition of the soil with optimum moisture
content suitable for working and germination or sprouting of seeds and propagules i.e., tilth is
the ideal seed bed.

Characteristics of good tilth

Good tilth refers to the favourable physical conditions for germination and growth of
crops. Tilth indicates two properties of soil viz., the size distribution of aggregates and
mellowness or friability of soil. The relative proportion of different sized soil aggregates is
known as size distribution of soil aggregates. Higher percentages of larger aggregates with a
size above 5 mm in diameter are necessary for irrigated agriculture while higher percentage
of smaller aggregates (1–2 mm in diameter) are desirable for rainfed agriculture. Mellowness
or friability is that property of soil by which the clods when dry become more crumbly. A soil
with good tilth is quite porous and has free drainage up to water table. The capillary and non-
capillary pores should be in equal proportion so that sufficient amount of water and free air is
retained respectively.

Objectives

Tillage is done:

• To prepare ideal seed bed favourable for seed germination, growth and establishment;
• To loosen the soil for easy root penetration and proliferation;
• To remove other sprouting materials in the soil;
• To control weeds;
• To certain extent to control pest and diseases which harbour in the soil;
• To improve soil physical conditions;
• To ensure adequate aeration in the root zone which in turn favour for microbial and
biochemical activities;
• To modify soil temperature;

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• To break hard soil pans and to improve drainage facility;
• To incorporate crop residues and organic matter left over;
• To conserve soil by minimizing the soil erosion;
• To conserve the soil moisture;
• To harvest efficiently the effective rain water;
• To assure the through mixing of manures, fertilizers and pesticides in the soil;
• To facilitate water infiltration and thus increasing the water holding capacity of the soil, and
• To level the field for efficient water management
Types of tilth
1. Fine Tilth refers to the powdery condition of the soil. Coarse Tilth refers to the
rough cloddy condition of the soil.
2. Fine seedbed is required for small seeded crops like ragi, onion, berseem, tobacco.
Coarse seedbed is needed for bold seeded crops like sorghum, cotton, chickpea, lab-
lab etc.

Types of tillage

1. On Season Tillage: It is done during the cropping season (June–July or Sept.–Oct.).

2. Off Season Tillage: It is done during fallow or non-cropped season (summer).
3. Special Types of Tillage: It is done at any time with some special objective/purpose.

On Season Tillage
Tillage operations done for raising the crops in the same season or at the onset of the crop
season are called as on season tillage. They are,

A. Preparatory Tillage

It refers to tillage operations that are done to prepare the field for raising crops. It is divided
into three types viz., (i) primary tillage, (ii) secondary tillage, and (iii) seed bed preparation.

(i) Primary tillage - The first cutting and inverting of the soil that is done after the harvest of
the crop or untilled fallow, is known as primary tillage. It is normally the deepest operation
performed during the period between two crops. Depth may range from 10–30 cm. It includes
ploughing to cut and invert the soil for further operation. It consists of deep opening and
loosening the soil to bring out the desirable tilth. The main objective is to control weeds to
incorporate crop stubbles and to restore soil structure.

(ii) Secondary tillage - It refers to shallow tillage operation that is done after primary tillage
to bring a good soil tilth. In this operation the soil is stirred and conditioned by breaking the
clods and crust, closing of cracks and crevices that form on drying. Incorporation of manures
and fertilizers, leveling, mulching, forming ridges and furrows are the main objectives. It
includes cultivating, harrowing, pulverizing, raking, leveling and ridging operations.

(iii) Seed bed preparation - It refers to a very shallow operation intended to prepare a seed
bed or make the soil to suit for planting. Weed control and structural development of the soil
are the objectives.

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B. Inter Tillage/Inter Cultivation

It refers to shallow tillage operation done in the field after sowing or planting or prior to
harvest of crop plants i.e., tillage during the crop stand in the field. It includes inter
cultivating, harrowing, hoeing, weeding, earthing up, forming ridges and furrows etc. Inter
tillage helps to incorporate top dressed manures and fertilizers, to earth up and to prune roots.

Off Season Tillage

Tillage operation is done for conditioning the soil during uncropped season with the main
objective of water conservation, leveling to the desirable grade, leaching to remove salts for
soil reclamation reducing the population of pest and diseases in the soils. etc. They are:

(a) Stubble or Post harvest tillage - Tillage operation carried out immediately after harvest
of crop to clear off the weeds and crop residues and to restore the soil structure. Removing of
stiff stubbles of sugarcane crop by turning and incorporating the trashes and weeds thus
making the soil ready to store rain water etc., are the major objectives of such tillage
operations.

(b) Summer tillage - Operation being done during summer season in tropics to destroy
weeds and soil borne pest and diseases, checking the soil erosion and retaining the rain water
through summer showers. It affects the soil aggregates, soil organic matter and sometimes
favour wind erosion. It is called as Kodai uzavu in Tamil Nadu state.

(c) Winter tillage - It is practiced in temperate regions where the winter is severe that makes
the field unfit for raising crops. Ploughing or harrowing is done in places where soil condition
is optimum to destroy weeds and to improve the physical condition of the soil and also to
incorporate plant residues.

(d) Fallow tillage - It refers to the leaving of arable land uncropped for a season or seasons
for various reasons. Tilled fallow represent an extreme condition of soil disturbance to
eliminate all weeds and control soil borne pest etc. Fallow tilled soil is prone to erosion by
wind and water and subsequently they become degraded and depleted.

Special Types

Special type tillage includes

(i) Subsoil tillage (sub soiling) is done to cut open/break the subsoil hard pan or plough pan
using sub soil plough/chisel plough. Here the soil is not inverted. Sub soiling is done once in

4–5 years, where heavy machinery is used for field operations and where there is a colossal
loss of topsoil due to carelessness. To avoid closing of sub soil furrow vertical mulching is
adopted.

(ii) Levelling by tillage - Arable fields require a uniform distribution of water and plant
nutrition for uniform crop growth. This is achieved when fields are kept fairly leveled.

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Levellers and scrapers are used for levelling operations. In leveled field soil erosion is
restricted and other management practices become easy and uniform.

(iii) Wet tillage - This refers to tillage done when the soil is in a saturated (anaerobic)
condition. For example puddling for rice cultivation.

(iv) Strip tillage - Ploughing is done as a narrow strip by mixing and tilling the soil leaving
the remaining soil surface undisturbed.

(v) Clean tillage - Refers to the working of the soil of the entire field in such a way no living
plant is left undisturbed. It is practiced to control weeds, soil borne pathogen and pests.

(vi) Ridge tillage - It refers to forming ridges by ridge former or ridge plough for the purpose
of planting.

(vii) Conservation tillage - It means any tillage system that reduces loss of soil or water
relative to conventional tillage. It is often a form of non-inversion tillage that retains
protective amounts of crop residue mulch on the surface. The important criteria of a
conservation tillage system are:

(i) presence of crop residue mulch, (ii) effective conservation of soil and water, (iii)
improvement of soil structure and organic matter content, and (iv) maintenance of high and
economic level of production (refer section 7.10 of this chapter).

(viii) Contour tillage - It refers to tilling of the land along contours (contour means lines of
uniform elevation) in order to reduce soil erosion and run off.

(ix) Blind tillage - It refers to tillage done after seeding or planting the crop (in a sterile soils)
either at the pre-emergence stage of the crop plants or while they are in the early stages of
growth so that crop plants (cereals, tuber crops etc.) do not get damaged, but extra plants and
broad leaved weeds are uprooted.

Factors affecting (intensity and depth of) the tillage operations

Several factors are responsible for deciding intensity and depth of tillage operations.
They are soil type, crop and variety, type of farming, moisture status of the soil, climate and
season, extent of weed infestation, irrigation methods, special needs and economic condition,
and knowledge and experience of the farmer.

(i) Crop - It decides the type, intensity and depth of tillage operations with small sized seeds
like finger millet, tobacco etc. Require a fine seedbed which can provide intimate soil-seed
contact as against coarser seed bed required for larger size seeds such as sorghum, maize,
pulses, etc. Root or tuber crops require deep tillage whereas rice requires shallow puddling.

(ii) Soil type - It dictates the time of ploughing. Light soils require early and rapid land
preparation due to free drainage and low retentive capacity as against heavy soils.

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(iii) Climate - It influences soil moisture content, draught required tilling and the type of
cultivation. Low rainfall and poor water retentive capacity of shallow soil do not permit deep
ploughing at the start of the season. Heavy soils developing cracks during summer (self
tilled) need only harrowing. Light soils of arid regions need coarse tilth to minimize wind
erosion.

(iv) Type of farming - It influences the intensity of land preparation. In dry lands, deep
ploughing is necessary to eradicate perennial weeds and to conserve soil moisture. Repeated
shallow tilling is adequate under such intensive cropping.

(v) Cropping system - In involves different crops, which need different types of tillage. Crop
following rice needs repeated preparatory tillage for obtaining an ideal seedbed. Crops
following tuber crops like potato require minimum tillage. Similarly crops following pulses
need lesser tillage than that of following sorghum, maize or sugarcane.

Depth of ploughing

Desirable ploughing depth is 12.5–20 cm. Ploughing depth varies with effective root
zone depth of the crops. Ploughing depth is 10–20 cm to shallow rooted crops and 15–30 cm
to deep-rooted crops. Deep ploughing is done to control perennial weeds like Cyanodon
dactylon and to break soil hard pans. Since deep ploughing increases the cost, most farers
resort to shallow ploughing only.

Number of ploughing

It depends on soil conditions, time available for cultivation between two crops, (turn
over period) type of cropping systems etc. Small or fine seeded crop requires fine tilth, which
may require more ploughings. Zero tillage is practiced in rice fallow pulse crops or relay
cropping system. Three numbers of puddling is sufficient for rice cultivation. Minimum
numbers of ploughing are taken up at optimum moisture level to bring favourable tilth
depending on the need of the crop and financial resources of the farmer. In fact, this brought
the concept of minimal tillage or zero tillage systems.

Time of ploughing

The time of ploughing is decided based on moisture status and type of soil. The
optimum moisture content for tillage is 60% of field capacity. Ploughing at right moisture
content is very important. Summer ploughing (March–May) can be practiced utilizing
summer showers to control weeds and conserve soil moisture. Light soils can be worked
under wide range of moisture. Loamy soils can be easily brought to good tilth. Pulverization
of clay soils is difficult as they dry into hard clods.

Method of ploughing

Ploughing aims at stirring and disturbing the top layer of soil uniformly without
leaving any unploughed strips of land. Straight and uniformly wide furrows give a neat
appearance to the ploughed field. When the furrows are not straight or when the adjacent

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furrows are not uniformly spaced, narrow strips of land are left unploughed. The correct inter
furrow space is little over the width of the furrow slice. After the harvest of a crop the land is
first ploughed along the length of the field. This reduces the number of turns at the headlands
for opening fresh furrows. The next ploughing is done across the field for breaking furrows of
the previous ploughing. This must increase the turns at the headlands and the empty turns
along the headlands, but is unavoidable. New turns are taken 6 m wide each time, till the
entire field is covered.

Modern concepts of tillage

In conventional tillage combined primary and secondary tillage operations are

performed in preparing seed bed by using animal or tractor, which cause hard pan in sub soils
resulting in poor infiltration of rain water, thus it is more susceptible to run off and soil
erosion. Farmers usually prepare fine seed bed by repeated ploughing, when the animal of the
farm is having less work. Research has shown that frequent tillage is rarely beneficial and
often detrimental. Repeated use of heavy machinery destroys structures, causes soil pans and
leads to soil erosion. Moreover energy is often wasted during tillage processes. All these
reasons led to the development of modern concepts namely the practices like minimum
tillage, zero tillage, stubble mulch farming and conservation tillage, etc.

1. Minimum Tillage

Minimum tillage is aimed at reducing tillage to the minimum necessary for ensuring a
good seedbed, rapid germination, a satisfactory stand and favourable growing conditions.
Tillage can be reduced in two ways by omitting operations, which do not give much benefit
when compared to the cost, and by combining agricultural operations like seeding and
fertilizer application.

(a) Advantages (especially in coarse and medium textured soils)

• Improved soil conditions due to decomposition of plant residues in situ.

• Higher infiltration caused by the vegetation present on the soil and channels formed by the
decomposition of dead roots.

• Less resistance to root growth due to improved structure.

• Less soil compaction by the reduced movement of heavy tillage vehicles.

• Less soil erosion compared to conventional tillage.

(b) Disadvantages

• Seed germination is lower with minimum tillage.

• More nitrogen has to be added as the rate of decomposition of organic matter is slow. This
point holds good only in temperate regions. Contrary to this in tropics, minimum tillage
recommended to conserve organic matter in the soil.

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• Nodulation is affected in some leguminous crops like peas and broad beans.

• Sowing operations are difficult with ordinary equipment.

• Continuous use of herbicides causes pollution problems and dominance of perennial

problematic weeds (weed shift).

Minimum tillage can be achieved by the following methods:

(a) Row zone tillage - Primary tillage is done with mould board plough in the entire area of
the field, secondary tillage operations like discing and harrowing are reduced and done only
in row zone.

(b) Plough-plant tillage - After the primary tillage a special planter is used for sowing. In
one run over the field, the row zone is pulverized and seeds are sown by the planter.

(c) Wheel track planting - Primary ploughing is done as usual. Tractor is used for sowing,
the wheels of the tractor pulverize the row zone in which planting is done.

2. Zero Tillage/No Tillage/Chemical Tillage

Zero tillage is an extreme form of minimum tillage. Primary tillage is completely

avoided and secondary tillage is restricted to seedbed preparation in the row zone only. It is
also known as no-tillage and is resorted to places where soils are subjected to wind and water
erosion, timing of tillage operation is too difficult and requirements of energy and labour for
tillage are also too high. Weeds are controlled using herbicides. Hence, it is also referred as
chemical tillage.

There are two types of zero tillage.

(a) Till Planting is one method of practicing zero tillage. A wide sweep and trash bars clear a
strip over the previous crop row and planter–opens a narrow strip into which seeds are
planted and covered. In zero tillage, herbicide functions are extended. Before sowing, the
vegetation present has to be destroyed for which broad spectrum non-selective herbicides
with relatively short residual effect (Paraquat, Glyphosate etc.) are used and subsequently
selective and persistent herbicides are needed (Atrazine, Alachlor etc.).

(b) Sod planting or sod culture: Sod refers to top few centimeters of soil permeated by and
held together with grass roots or grass-legume roots. Planting of seeds in sods without any
tillage operation is known as sod culture or sod seeding. Usually legumes or small grains are
mechanically placed directly into a sod.

Advantages

• Zero tilled soils are homogenous in structure with more number of earthworms. These soil
physical properties are apparent after two years of zero tillage.

• The organic matter content increases due to less mineralization.

Page | 13
• Surface runoff is reduced due to the presence of mulch.

Disadvantages

• In temperate countries highest dose of nitrogen has to be applied for mineralization of

organic matter in zero tillage.

• Large population of perennial weeds appears in zero tilled plots.

• Higher number of volunteer plants and build up of pests are the other problems.

1. Stubble Mulch Tillage or Stubble Mulch Farming

In this tillage, soil is protected at all times either by growing a crop or by leaving the
crop residues on the surface during fallow periods. Sweeps or blades are generally used to cut
the soil up to 12 to 15 cm depth in the first operation after harvest and the depth of cut is
reduced during subsequent operations. When unusually large amount of residues are present,
a disc type implement is used for the first operation to incorporate some of the residues into
the soil.

Two methods are adopted for sowing crops in stubble mulch farming.

• Similar to zero tillage, a wide sweep and trash-bars are used to clear a strip and a narrow
planter-shoe opens a narrow furrow into which seeds are placed.

• A narrow chisel of 5–10 cm width is worked through the soil at a depth of 15–30 cm
leaving all plant residues on the surface. The chisel shatters tillage pans and surface crusts.
Planting is done through residues with special planters.

Disadvantages

• The residues left on the surface interfere with seedbed preparation and sowing operations.

• The traditional tillage and sowing implements or equipments are not suitable under these
conditions.

2. Conservation Tillage

Though it is similar to that of stubble mulch tillage, it is done to conserve soil and
water by reducing their losses. Modern tillage methods are practiced in western countries
especially in USA. In India, it is not suitable due to several reasons. In USA, straw and
stubbles are left over in the field but in India, it is a valuable fodder for the cattle and fuel for
the home. Use of heavy machinery in India is limited and therefore, problem of soil
compaction is rare. The type of minimum tillage that can be practiced in India is to reduce the
number of ploughings to the minimum necessary i.e., unnecessary repeated
ploughings/harrowing can be avoided.

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 Chapter 4

Crop density and geometry

Crop geometry is the pattern of distribution of plant over the ground or the shape of the area
available to the individual plant, in a crop field. It also refers to the shape of the space
available for individual plants. It influences crop yield through its influence on light
interception, rooting pattern and moisture extraction pattern. Crop geometry is altered by
changing inter and intra-row spacing (Planting pattern).

• Wider spaced crops have advantage under this geometry

• Plants which requires no restriction in all directions are given square geometry

• Usually perennial vegetations like trees/shrubs are under these arrangements.

(i) Square planting - Square arrangements of plants will be more efficient in the utilization of
light, water and nutrients available to the individual plants than in a rectangular arrangement.

(ii) Rectangular planting - Sowing the crop with seed drill, wider inter-row and closer intra-
row and closer intra-row spacing leads to rectangularity. Rectangular arrangement facilitates
easy intercultivation. Rectangular planting mainly suits annual crops, crops with closer
spacing etc., the wider section (row) is given for irrigation, intercultural operation etc.

• It is an arrangement to restrict the endless growth habit in order to switch over from
vegetation to the productive phase.

• This method accommodate high density planting

• It can facilitate intercropping also.

(iii) Triangular planting - It is a method to accommodate plant density under perennial/tree

crops.

(iv) Miscellaneous planting - In rice and ragi transplanting is done either in rows or at
random. Skipping of every alternate row is known as skip row planting. When one row is
skipped the density is adjusted by decreasing inter-row spacing. When the inter row spacing
is reduced between two rows and spacing between two such pair are increased then it is
known as paired row planting. It is generally done to introduce an inter crop.

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 Chapter 5

Crop nutrition, Manures and fertilizers

In nature there are 109 elements and out of these only 17 elements are essential.
Arnon and Stout (1939) first proposed the term criteria of essentiality and later Arnon (1954)
revised some of the criteria and concluded the three essential criteria.
Criteria of essentiality of nutrients:
 A mineral element is considered essential to plant growth and development if the
element is directly involved in plant metabolic function.
Ex. N involved in protein synthesis, K involved in stomata opening and closing and sugar
translocation. However, P involved in energy transfer
 Plants are unable to complete its lifecycle if the element is absent.
 Deficiency symptoms in the plant of the element can only be corrected by the supply of
the particular element.
Seventeen elements are considered essential to plant growth. Carbon (C), Hydrogen
(H) and Oxygen (O) are the structural or basic nutrient and not considered mineral nutrients
but are the most abundant element sin plants. The photosynthetic process in green leaves
converts CO2 and H2O into simple carbohydrates from which amino acids, sugars, proteins,
nucleic acid and other organic compounds are synthesized.
The remaining 14 essential mineral elements due to their primary sources are mineral
and are classified as macronutrients & micronutrients, and the classification based on their
relative abundance in plants. The essential nutrients are as follows.
Essential nutrients Type
C, H, and O Structural or basic nutrient, but not mineral.
N, P, and K Primary elements, macro nutrients, require larger quantity.
Ca, Mg, and S Secondary elements, macro nutrients, require lesser quantity.
Zn, Fe, Cu, Mn Metalic, micronutrients or trace elements, require lesser quantity.
B, Mo, Cl Non Metalic, micronutrients or trace elements, require lesser quantity.
Ni Metalic, micronutrient or trace element, requires lesser quantity.
 In addition to the 17 essential nutrients several elements are beneficial to some plants
but are not considered necessary for completion of the plant life cycle. These are
Cobalt (Co), Sodium (Na), Silicon (Si), Selenium (Se), Vanadium (V) and Aluminium
(Al).
 Cobalt (Co) is essential for the growth of symbiotic microorganisms such as
Rhizobia, free living N2 fixing bacteria and blue green algae.
 Sodium (Na) is essential for halophytic plants that accumulate salts in vacuoles to
maintain turgor and growth of the plant.
 Silicon (Si) has specific role in rice, sugarcane crops. It is accumulated in cell wall
which strengthens the stem, prevails cop lodging and increases water use efficiency.

Page | 16
  Selenium (Se) is required by cabbage, nustard with an intermediate amount, while
grasses ad grain crops absorb low to moderate amount of Se.
 Vanadium (V) is essential for the growth of green algae.
 Aluminium (Al) is not an essential plant nutrient, though in plants can be high when
soil contain relatively large amount of Al.

Classification of nutrients

a. on the basis of quantity of nutrient required:

i. Basic nutrients: These constitute 96% of total dry matter of plant. e.g. Carbon,
Hydrogen and Oxygen. Among these, carbon and oxygen constitute 45% each and
hydrogen is 6%.
ii. Macro nutrients: The nutrients which are required by plants in large quantities are
called macro or major nutrients. These are six in number like Nitrogen, Phosphorus,
Potassium, Calcium, Magnesium, Sulphur, Carbon, Hydrogen and Oxygen. Macro
nutrients have again two categories:
 Primary nutrients: Among macro nutrients, Nitrogen, Phosphorus and Potassium are
known as primary nutrients which are required in a proper ratio for a successful
crop.
 Secondary nutrients: Next to primary nutrients, there are three elements such as
Calcium, Magnesium and Sulphur which are known as secondary nutrients.
iii. Micro nutrients: These nutrients required by plants in small quantities and also known
as minor or trace elements. These are eight in number like Manganese, Iron, Zinc,
Copper, Boron, Molybdenum Chlorine and Cobalt.

b. Classification on the basis of mobility of nutrient in the soil:

i. Mobile nutrients: The nutrients are highly soluble and these are not adsorbed on clay
complexes. e.g., NO3-, SO42-,BO32-, Cl- and Mn+2
ii. Less mobile nutrients: They are soluble, but they are adsorbed on clay complex, so
their mobility is reduced. e.g., NH4+, K+, Ca+, Mg2+, Cu2+
iii. Immobile nutrients: Nutrient ions are highly reactive and get fixed in the soil. e.g.,
H2PO4-,HPO42-, Zn2+3

c. Classification on the basis of mobility with in plant:

i. Highly mobile: N, P and K.

ii. Moderately mobile: Zn
iii. Less mobile: S, Fe, Mn, Cl, Mo and Cu
iv. Immobile: Ca and B

Functions of plant nutrients:

Carbon (C): It is the basic molecular component of carbohydrates, protein, lipids and nucleic
acids.

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Oxygen (O): It is somewhat like carbon in that it occurs in virtually all organic compounds
of living organisms.

Hydrogen (H): Play a certain role in plant metabolism. Important in ionic balance and as
main reducing agent plays a key role in energy relation of cells.

Nitrogen (N): Nitrogen is needed for vigorous vegetative leaf and stem growth and dark
green leaf colour (chlorophyll production). It is a component of many important organic
compounds ranging from protein to nucleic acid. It feeds soil microorganisms as they
decompose organic matter. It is part of proteins, enzymes, chlorophyll, and growth regulators.
Uptake inhibited by high phosphorus levels. N/K ratio is important: high N/low K favours
vegetative growth; low N/high K promotes flowering and fruiting.

Phosphorus (P): Phosphorus is very mobile in plants; relatively immobile in soil and does
not leach. It is stored in seeds and fruit. It is most readily available to plants between a pH of
6 and 7.5 (unavailable in very acid or alkaline soils). It has a central role in energy transfer
and protein metabolism. Phosphorus has also a role in fat, carbon, hydrogen, and oxygen
metabolism, in respiration, and in photosynthesis. Found in greatest concentration in sites of
new cell growth. Phosphorus absorption is reduced at low soil temperatures. Phosphorus is
necessary to stimulate early root formation and growth, hasten crop maturity, stimulate
flowering and seed production, give winter hardiness to fall plantings and seedings, and
promote vigorous start (cell division) to plants.

Potassium (K): Potassium (potash - K2O) is highly mobile in plants, and generally immobile
in soil. It tends to leach. Potassium promotes vigour and disease resistance, helps
development of root system, improves plant quality, and increases winter hardiness due to
carbohydrate storage in roots. Increases protein production, and is essential to starch, sugar
and oil formation and transfer and in water relations. It helps in osmotic and ionic regulation.

Calcium (Ca): Calcium is immobile in plants, and relatively immobile in soil. It is

moderately leachable. Calcium is necessary for cell elongation and division, protein
synthesis, root and leaf development, and plant vigour. It influences intake of other nutrients
and increases calcium content of plants, important in cell wall structure and as an enzyme
activator.

Magnesium (Mg): Magnesium is mobile in plants, mobile in acid soils, and fairly immobile
above pH 6.5. It leaches from soil. Magnesium is necessary for formation of sugars, proteins,
oils, and fats, regulates the uptake of other nutrients (especially P), is a component of
chlorophyll, and is a phosphorus carrier.

Sulphur (S): Sulphur is mobile in plants, somewhat immobile in soil. Organic sulphur is
converted into available sulphate sulphur by soil bacteria. It is also leachable. It is rarely
deficient. Sulphur is necessary to maintain dark green colour, stimulate seed production, and

Page | 18
promote root and general plant growth. It is part of proteins, amino acids, and vitamins,
important in respiration.

Iron (Fe): Iron is immobile in plants and mobility decreases in soil with increasing pH. Iron
is necessary for chlorophyll maintenance. It is an essential component of many hemo and
nonhemo Fe enzymes and carriers, including cytochrome (respiratory electron carrier) and
the ferrodoxins. The latter are involved in key metabolic functions such as N fixation,
photosynthesis and electron transfer.

Zinc (Zn): Zinc is important for plant enzyme system function, seed production, and starch
production. It needed for auxin synthesis.

Manganese (Mn): Manganese involved in oxygen evolving system of photosynthesis. It can

substitute for magnesium in many of the phosphorylating and group transfer reactions. It
influences auxin levels in plant. Manganese increases availability of Ca, Mg.
Copper (Cu): Copper is a constituent of enzyme systems. It is involved in photosynthesis
and respiration and the formation of lignin. It has indirect effect on nodule formation.
Molybdenum (Mo): Molybdenum is needed for enzyme activity in the plant and for nitrogen
fixation in legumes. It is an essential component of enzyme nitrate reductase in plant.
Boron (B): Primary functions of B in plants are related to cell wall formation and
reproductive tissue. It is necessary for nodule formation in legumes. It is associated with
translocation of sugars, starches, nitrogen and phosphorus.
Chloride (Cl): Chloride is required by the plant for leaf turgor and photosynthesis. It is
associated with osmoregulation of plants growing on saline soil.
Nickel (Ni): Nickel is required by plants for proper seed germination and is beneficial for N
metabolism in legumes and other plants in which ureides (compounds derived from urea) are
important in metabolism. Ni is the metal component in urease, an enzyme that catalyzes the
conversion of urea to ammonium.
Sources of mineral nutrient elements
Nutrient Sources
C Carbamate
N Organic matter
P Apatite
K Mica, Feldsper
Ca Dolomite, Apatite, Calcite, Gypsum
Mg Dolomite, Muscovite, Biotite, Olivine
S Pyrites, Gypsum, Organic Matter
Fe Pyrites, Magnetites
B Tourmline
Cu Chalcopyrite, Olivine, Biotite
Mn Magnetites, Olivine, Pyrolusite
Mo Olivine
Zn Olivine, Biotite
Cl Apatite
Ni Nickeliferous limonite, Pentlandite [(Ni,Fe) 9S8]

Page | 19
Manures
Organic Manures are plant and animal wastes that are used as sources of plant
nutrients. They release nutrients after their decomposition. Manures are the organic materials
derived from animal, human and plant residues which contain plant nutrients in complex
organic forms. Manures have low nutrient content per unit quantity and have longer residual
effect besides improving soil physical properties compared to fertilizer with high nutrient
content. Major sources of manures are:
1. Cattle shed wastes - dung, urine and slurry from biogas plants
2. Human habitation wastes - night soil, human urine, town refuse, sewage, sludge
3. Poultry litter, droppings of sheep and goat
4. Slaughter house wastes - bone meal, meat meal, blood meal, horn and hoof meal, Fish
wastes
5. Byproducts of agro industries - oil cakes, bagasse and press mud, fruit and vegetable
processing wastes etc.
6. Crop wastes - sugarcane trash, stubbles and other related material
7. Water hyacinth, weeds and tank silt, and
8. Green manure crops and green leaf manuring material
Manures can also be grouped into bulky organic manures and concentrated organic
manures based on concentration of the nutrients.

Bulky organic manures

Bulky organic manures contain small percentage of nutrients and they are applied in
large quantities. FYM, compost and green-manure are the most important and widely used
bulky organic manures. Use of bulky organic manures has several advantages:
 They supply plant nutrients including micronutrients
 They improve soil physical properties like structure, water holding capacity etc.,
 They increase the availability of nutrients
 Carbon dioxide released during decomposition acts as a CO 2 fertilizer
 Plant parasitic nematodes and fungi are controlled to some extent by altering the
balance of microorganisms in the soil.
1. Farmyard manure
FYM refers to the decomposed mixture of dung and urine of farm animals along with
litter and left over material from roughages or fodder fed to the cattle. On an average well
decomposed FYM contains 0.5 % N, 0.2 % P2O5 and 0.5 % K2O.
Partially rotten FYM has to be applied three to four weeks before sowing while well
rotten manure can be applied immediately before sowing. Generally 10 to 20 t/ha is applied,
but more than 20 t/ha is applied to fodder grasses and vegetables. In such cases FYM should
be applied at least 15 days in advance to avoid immobilization of nitrogen.
Vegetable crops like potato, tomato, sweet-potato, carrot, raddish, onion etc., respond
well to the farmyard manure. The other responsive crops are sugarcane, rice, napier grass and
orchard crops like oranges, banana, mango and plantation crop like coconut.
The entire amount of nutrients present in FYM is not available immediately. About
30% of nitrogen, 60 to 70 % of phosphorus and 70 % of potassium are available to the first
crop.

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2. Vermicompost
Vermicompost is the excreta of earthworms, which is rich in humus and nutrients.
Vermicomposting is the process of turning organic debris into earthworm castings. The worm
castings are very important to the fertility of the soil. The castings contain high amounts of
nitrogen, potassium, phosphorus, calcium, and magnesium. The content of the earthworm
castings, along with the natural tillage by the worms burrowing action, enhances the
permeability of water in the soil.

Materials for preparation of Vermicompost

Any types of biodegradable wastes-
1. Crop residues
2. Weed biomass
3. Vegetable waste
4. Leaf litter
5. Hotel refuse
6. Waste from agro-industries
7. Biodegradable portion of urban and rural wastes

Advantages of vermicompost
 Vermicompost is rich in all essential plant nutrients.
 Provides excellent effect on overall plant growth, encourages the growth of new
shoots / leaves and improves the quality and shelf life of the produce.
 Vermicompost is free flowing, easy to apply, handle and store and does not have bad
odour.
 It improves soil structure, texture, aeration, and waterholding capacity and prevents
soil erosion.
 Vermicompost is rich in beneficial micro flora such as a fixers, P- solubilizers,
cellulose decomposing micro-flora etc in addition to improve soil environment.
 Vermicompost contains earthworm cocoons and increases the population and activity
of earthworm in the soil.
 It prevents nutrient losses and increases the use efficiency of chemical fertilizers.
 Vermicompost is free from pathogens, toxic elements, weed seeds etc.
 It enhances the decomposition of organic matter in soil.
 It contains valuable vitamins, enzymes and hormones like auxins, gibberellins etc.

2. Sheep and Goat Manure

The droppings of sheep and goats contain higher nutrients than FYM and compost.
On an average, the manure contains 3% N, 1% P 2O5 and 2% K2O. It is applied to the field in
two ways. The sweeping of sheep or goat sheds are placed in pits for decomposition and it is
applied later to the field. The nutrients present in the urine are wasted in this method. The
second method is sheep penning, wherein sheep and goats are kept overnight in the field and
urine and fecal matter added to the soil is incorporated to a shallow depth by working blade
harrow or cultivator.
3. Poultry Manure

Page | 21
 The excreta of birds ferment very quickly. If left exposed, 50 percent of its nitrogen is
lost within 30 days. Poultry manure contains higher nitrogen and phosphorus compared to
other bulky organic manures. The average nutrient content is 3.03% N, 2.63% P 2O5 and 1.4
% K2O.
4. Green Manuring

It is a practice of ploughing the green plant tissues grown in the field or adding green
plants with tender twigs or leaves from outside and incorporating them into the soil for
improving the physical structure as well as fertility of the soil. It can also be defined as a
practice of ploughing or turning into the soil, undecomposed green plant tissues for the
purpose of improving the soil fertility.
The objective of green manuring is to add an organic matter into the soil and thus,
enrich it with „N‟ which is most important and deficient nutrient.
There are two types of green manuring:
i. Green manuring in-situ:
When green manure crops are grown in the field itself either as a pure crop or as
intercrop with the main crop and buried in the same field, it is known as Green manuring in-
situ. E.g.: Sunhemp, Dhaincha, Pillipesara, Urd, Mung, Cowpea, Berseem, etc.
ii. Green leaf manuring:
It refers to turning into the soil green leaves and tender green twigs collected from
shrubs and tress grown on bunds, waste lands and nearby forest area. e.g.: Glyricidia, wild
Dhaincha, Karanj. Forest tree leaves are the main sources for green leaf manure. Plants
growing in wastelands, field bunds etc., are another source of green leaf manure.
The important plant species useful for green leaf manure are neem, mahua, wild
indigo, Glyricidia, Karanji (Pongamia glabra), calotropis, avise (Sesbania grandiflora),
subabul.
Characteristics/desirable qualities of a good manuring:
1. Yield a large quantity of green material within a short period.
2. Be quick growing especially in the beginning, so as to suppress weeds.
3. Be succulent and have more leafy growth than woody growth, so that its
decomposition will be rapid.
4. Preferably is a legume, so that atm. „N‟ will be fixed.
5. Have deep and fibrous root system so that it will absorb nutrients from lower zone
and add them to the surface soil and also improve soil structure.
6. Be able to grow even on poor soils.
Stage of green manuring: A green manuring crop may be turned in at the flowering stage
or just before the flowering. The majority of the G.M. crops require 6 to 8 weeks after sowing
at which there is maximum green matter production and most succulent.

Page | 22
Advantages of green manuring:
i) It adds organic matter to the soil and simulates activity of soil micro-organisms.
ii) It improves the structure of the soil thereby improving the WHC, decreasing run-off
and erosion caused by rain.
iii) The G.M. takes nutrients from lower layers of the soil and adds to the upper layer in
which it is incorporated.
iv) It is a leguminous crop, it fixes „N‟ from the atmosphere and adds to the soil for being
used by succeeding crop. Generally, about 2/3 of the N is derived from the
atmosphere and the rest from the soil.
v) It increases the availability of certain plant nutrients like P2O5, Ca, Mg and Fe.
vi) Growing of green manure crops in the off season reduces weed proliferation and weed
growth.
vii) Green manuring helps in reclamation of alkaline soils. Root knot nematodes can be
controlled by green manuring.
viii) When green manures are turned into the soil and decompose, they provide nutrition
for soil organisms, thus protecting and enhancing the soil‟s biological activity.
ix) The root mass of a green manure crop loosens and aerates the soil, consequently
improving the soil structure.
x) The roots and top growth maintain or increase the organic matter content of the soil,
which improves soil tilth.
xi) Green manure crops reduce soil compaction. They lessen the impact of rainfall and
vehicle traffic.
Disadvantages of green manuring:
i. Under rain fed conditions, the germination and growth of succeeding crop may be
affected due to depletion of moisture for the growth and decomposition of G.M.
ii. G.M. crop inclusive of decomposition period occupies the field least 75-80 days
which means a loss of one crop.
iii. Incidence of pests and diseases may increases if the G.M. is not kept free from them.
iv. Application of phosphatic fertilizers to G.M. crops helps to increase the yield, for
rapid growth of Rhizobia and increase the „P‟ availability to succeeding crop.

Concentrated organic manures:

Concentrated organic manures have higher nutrient content than bulky organic
manure. The important concentrated organic manures are oilcakes, blood meal, fish manure
etc. These are also known as organic nitrogen fertilizer. Before their organic nitrogen is used
by the crops, it is converted through bacterial action into readily usable ammoniacal nitrogen
and nitrate nitrogen. These organic fertilizers are, therefore, relatively slow acting, but they
supply available nitrogen for a longer period.
1. Oil cakes

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After oil is extracted from oilseeds, the remaining solid portion is dried as cake which can, be
used as manure. The oil cakes are of two types:
 Edible oil cakes which can be safely fed to livestock; e.g.: Groundnut cake, Coconut
cake etc., and
 Non edible oil cakes which are not fit for feeding livestock; e.g.: Castor cake, Neem
cake, Mahua cake etc.,
Both edible and non-edible oil cakes can be used as manures. However, edible oil
cakes are fed to cattle and non-edible oil cakes are used as manures especially for
horticultural crops. Nutrients present in oil cakes, after mineralization, are made available to
crops 7 to 10 days after application. Oilcakes need to be well powdered before application for
even distribution and quicker decomposition.
The average nutrient content of different oil-cakes is presented in the following table.
Average nutrient content of oil cakes
Nutrient content (%)
Oil-cakes
N P2O5 K2O
Non edible oil-cakes
Castor cake 4.3 1.8 1.3
Cotton seed cake (undecorticated) 3.9 1.8 1.6
Karanj cake 3.9 0.9 1.2
Mahua cake 2.5 0.8 1.2
Safflower cake (undecorticated) 4.9 1.4 1.2
Edible oil-cakes
Coconut cake 3.0 1.9 1.8
Cotton seed cake (decorticated) 6.4 2.9 2.2
Groundnut cake 7.3 1.5 1.3
Linseed cake 4.9 1.4 1.3
Niger cake 4.7 1.8 1.3
Rape seed cake 5.2 1.8 1.2
Safflower cake (decorticated) 7.9 2.2 1.9
Sesamum cake 6.2 2.0 1.2
2. Other Concentrated Organic Manures
Blood meal when dried and powdered can be used as manure. The meat of dead animals is
dried and converted into meat meal which is a good source of nitrogen. Average nutrient
content of animal based concentrated organic manures is given as follows.
Nutrient content (%)
Organic manures
N P2O5 K2O
Blood meal 10 - 12 1-2 1.0
Meat meal 10.5 2.5 0.5
Fish meal 4 - 10 3-9 0.3 - 1.5
Horn and Hoof meal 13 - -
Raw bone meal 3-4 20 - 25 -
Steamed bone meal 1-2 25 - 30 -

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Fertilizer
A fertilizer is any material of natural or synthetic origin (other than liming materials)
that is applied to soils or to plant tissues (usually leaves) to supply one or more plant nutrients
essential to the growth of plants.
Organic Manures Fertilizers
1. Nutrients from natural sources. 1. Nutrients from artificial sources.
2. Natural or organic origin 2. Mineral origin
3. Low nutrient compared to fertilizers. 3. High nutrient content
4. Very complex 4. Simple salts.
5. 30 days or more to decompose. 5. Soluble or give rapid response.
6. Organic nutrients contain all the nutrients. 6. Only specific nutrient.
7. Do not cause side effects 7. Cause side effects
8. Examples: Excrete of animals, animal 8. Examples: urea, DAP, MOP,
matter (blood, bones, flesh, horn) Superphosphate.

Classification of Fertilizers:
1. Straight fertilizers: Straight fertilizers are those which supply only one primary plant
nutrient, namely nitrogen or phosphorus or potassium.
eg. Urea, Ammonium sulphate, Potassium chloride and Potassium sulphate.
2. Complex fertilizers: Complex fertilizers contain two or three primary plant nutrients of
which two primary nutrients are in chemical combination. These fertilisers are usually
produced in granular form.
eg. Diammonium phosphate, Nitrophosphates and Ammonium phosphate.
3. Mixed fertilizers: are physical mixtures of straight fertilisers. They contain two or three
primary plant nutrients. Mixed fertilisers are made by thoroughly mixing the ingredients
either mechanically or manually.
Fertilisers can also be classified based on physical form: i.e., Solid and Liquid
fertilizers
Solid fertilizers are in several forms viz.
i. Powder (single superphosphate),
ii. Crystals (ammonium sulphate),
iii. Prills (urea, diammonium phosphate, superphosphate),
iv. Granules,
v. Supergranules (urea supergranules) and
vi. Briquettes (urea briquettes).
Liquid fertilizers:

Page | 25
1. Liquid form fertilizers are applied with irrigation water or for direct application.
2. Ease of handling, less labour requirement and possibility of mixing with herbicides have
made the liquid fertilisers more acceptable to farmers.
Based on the concentration of primary plant nutrient (N, P, K), fertilisers are
classified into:
1. High analysis fertilizer: The total content of primary plant nutrient is more than
25%. e.g. Urea (46%N), Anhydrous ammonia (82%N), DAP (18:46), Ammonium
Phosphate(20:20)
2. Low analysis Fertiliser: The total content of primary plant nutrient is less than 25%.
e.g. SSP (16%P2O5), NaNO3 (16%N)
Acidity and Basicity of Fertilizers:
Acid forming fertilizer: The fertilizer which leaves an acid residue is called an acid forming
Fertilizer. It should be applied to alkaline soils. The amount of CaCO3 required to neutralize
the acid residue of an acid forming fertilizer is called Equivalent Acidity.
Fertilizer Equivalent Acidity
Ammonium Nitrate 60
Urea 80
Ammonium Phosphate 86
Ammonium Sulphate Nitrate 93
Ammonium Sulphate 110
Ammonium Chloride 128
i.e., 100 kg of Ammonium Sulphate produces acidity for which 110 kg of CaCO 3 is required
for its neutralization.
Alkaline forming/ Basic Fertilizers: The fertilizer which leaves an alkaline residue is called
an alkaline forming Fertilizer. It should be applied to acid soils.
Fertilizer Equivalent Basicity
Calcium Nitrate 21
Sodium Nitrate 29
Di-calcium Phosphate 25
Calcium Cyanamide 63
Nitrogenous Fertilizers:
Nitrogenous fertilizers take the foremost place among fertilizers since the deficiency of
nitrogen in the soil is the foremost and crops respond to nitrogen better than to other
nutrients. More than 80 per cent of the fertilizers used in this country are made up of
nitrogenous fertilizers, particularly urea. It is extremely efficient in increasing the production
of crops. This type of fertilizer is divided into different groups according to the manner in
which the Nitrogen combines with other elements. These groups are Nitrate form,
Ammonium form, Chemical compounds that contains both Nitrate and Ammonium form and
Amide form.

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Nitrate Fertilizer:
The Nitrogen is present in the form of Nitrate (NO -3). This Nitrogen is highly mobile
in soil and immediately available to plants. Hence it is usually suitable as top- and side-
dressing. Due to its high solubility and mobility, it is subjected to leaching. In waterlogged
soil, there is denitrification (microbial reduction of NO-3). It increases alkalinity in soil, hence
should be used for acidic soil.
1. Sodium Nitrate: 15.6% N
2. Calcium nitrate [Ca(NO3)2]: 15.5% N and 19.5% Ca. The NO3– is readily available, but
the material is extremely hygroscopic.
3. Potassium nitrate [KNO3]: N (13%) and K2O (45%).
Ammoniacal Fertilizer:
Ammoniacal fertilizers contain the nitrogen in the form of ammonium. These
fertilizers are readily soluble in water and therefore readily available to crops. Except rice, all
crops absorb nitrogen in nitrate form. These fertilizers are resistant to leaching loss, as the
ammonium ions get readily absorbed on the colloidal complex of the soil. Hence well suited
to submerged soils. All Ammoniacal fertilisers are acidic. Hence used for basic/alkaline soils.
1. Ammonium Sulphate [(NH4)2 S04]: 20.6% ammoniacal N and 24% S
2. Ammonium Chloride (NH4Cl): 26% ammoniacal N
3. Ammonium phosphates:
a. Monoammonium phosphate (MAP) [NH4H2PO4] : 11–13% N and 48–62% P2O5
b. DAP: [(NH4)2HPO4]: N- 18% and P2O5 46%
4. Anhydrous ammonia (NH3): This fertilizer type is a colourless and pungent gas
containing 80-82% of nitrogen. It is volatile in nature. Hence should be applied 10-20
cm deep in the soil.
5. Aqua Ammonia: It results from the absorption of Ammonia gas into water, in which it
is soluble. It is used for preparation of other fertilisers.

Fertilizer containing N in both Nitrate & Ammoniacal Form:

1. Ammonium Nitrate: (NH4NO3): contains 33 to 35% nitrogen, of which 50% is
nitrate nitrogen and the other 50% in the ammonium form. This type of fertilizer can
be explosive under certain conditions, and, should thus be handled with care.
3. Calcium ammonium nitrate (CAN): containing 26 per cent of N and 10% Ca. Half
of its total N is in the ammoniacal form and half is in nitrate form.
4. Ammonium Sulphate Nitrate [(NH4)2SO4 NH4NO3]: This fertilizer type is
available as a mixture of ammonium nitrate and ammonium sulphate and is
recognizable as a white crystal or as dirty-white granules. This fertilizer contains
26% N, 3/4 of it in the ammoniacal form and 1/4 (i.e. 6.5%) as nitrate nitrogen. In
addition to nitrogen it contains 12.1% S.

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Amide Fertilizer:
1. Urea [CO(NH2)2]
This is the most widely used fertilizer, available in a white, crystalline, organic form. It is
produced by reacting NH3 with CO2 under pressure and high temperature. It is a highly
concentrated nitrogenous fertilizer and is hygroscopic. It contains 46% N. Its high
concentration of N brings about savings in storage, transportation, handling and application.
Urea is also produced in granular or pellet forms and is coated with a non-hygroscopic inert
material.
It is highly soluble in water and therefore, subject to rapid leaching. It is, however,
quick-acting and produces quick results. When applied to the soil, its nitrogen is rapidly
changed into ammonia. The application of Urea as fertilizer can be done at sowing time or as
a top-dressing, but should not be allowed to come into contact with the seed.
2. Calcium cyanamide (CaCN2)
 Calcium cyanamide contains 20.6 per cent of nitrogen.
 It is a greyish white powdery material that decomposed in moist soil giving rise to
ammonia.
Phosphatic Fertilizer Types
Phosphatic fertilizers are chemical substances that contain the nutrient phosphorus in
absorbable form (Phosphate anions). The nutrient phosphorus present in phosphate fertilizers
are usually expressed in terms of phosphoric anhydride or simply as phosphorus pentaoxide
(P2O5). The amount of phosphorus available to the plants depends upon the extent to which
the fertilizer supplies HPO4---or H2PO4 – ions.
According to the solubilities, the phosphatic fertilizers are divided in following
groups.
a. Water soluble phosphatic fertilizers: Superphosphates [Ca(H2PO4)2]. There are two
types of superphosphates.
 Single superphosphate (SSP) with 16% and 12% S.
 Triple (or concentrated) superphosphate (TSP or CSP) with 44% P2O5 is made by
acidulating rock phosphate with phosphoric acid, so it has only 1–1.5% S.
The common examples of these fertilizers are:

S.N. Fertiliser % P2O5

I Single Superphosphate 16% P2O5

Ii Double superphosphate 32% P2O5

Iii Triple superphosphate 46 - 48% P2O5

Iv Ammonium phosphate 20% P2O5

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b. Citric acid soluble phosphatic fertilizers
Citric acid soluble phosphatic fertilizers are not soluble in water but are readily
soluble in acidic water or weak acids like 2 per cent citric acid. They also contain phosphorus
in available form, i.e., HPO4. The fertilizers are suitable for acidic soils where they can easily
dissolved and become available to plants. The citric soluble fertilizers are suitable for acidic
soils because at low pH citrate soluble phosphorus is converted to monocalcium phosphate.
Phosphorus is not fixed as iron and aluminium phosphate. The examples of these fertilziers
are:
a) Basic slag -18% phosphate (P2O5): a by-product of iron and steel industries
b) Dicalcium phosphate -34-39% P2O5
c. Water and citrate insoluble phosphatic fertilizers: These mineral fertilizers contain
phosphorus, which is insoluble in water as well as in citric acid. They are suitable in
strongly acid soils or organic soils. The phosphorus is very slowly released by microbes at
action and remains in soil for long time.
Rock Phosphate Ca3 (PO4)2CaF2 : 20 - 30% P2O5
Bone meal (Ca(PO4) 2) 3 CaF2 : 21 - 25% P2O5
Potassium Fertilizer types
Chemical Potassium fertilizer should only be added when there is absolute certainty
that there is a Potassium deficiency in the soil. Potassium fertilizers also work well in sandy
garden soil that responds to their application. Crops such as chilies, potato and fruit trees all
benefit from this type of fertilizer since it improves the quality and appearance of the
produce. There are basically two different types of potassium fertilizers:
Muriate of Potash: It is a gray crystal type of fertilizer that consists of 60% potash. It should
not be applied as top dressing as the chlorine content has harmful effect on the chlorophyll.
Sulphate of Potash: Sulphate of potash is a fertilizer type manufactured when potassium
chloride is treated with magnesium sulphate. It dissolves readily in water and can be applied
to the soil at any time up to sowing.
NUE is a critically important concept for evaluating crop production systems and can be
greatly impacted by fertilizer management as well as soil- and plant-water relationships. NUE
indicates the potential for nutrient losses to the environment from cropping systems as
managers strive to meet the increasing societal demand for food, fiber and fuel. NUE
measures are not measures of nutrient loss since nutrients can be retained in soil, and systems
with relatively low NUE may not necessarily be harmful to the environment, while those with
high NUE may not be harmless.

The efficiency is expressed in different ways such as the percent utilization of Nitrogen
(Apparent nitrogen recovery), economic yield per unit of Nitrogen applied (Agronomic
efficiency) or grain yield in relation to the nitrogen uptake (Production efficiency).

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Apparent nitrogen Recovery (ANR) = N uptake in the fertilized plot – N uptake in the control plot (kg/ha) × 100
(%) Fertilizer N applied (kg/ha)

Agronomic Efficiency (AE) = Grain yield in fertilized plot – Grain yield in control plot (kg/ha)
(kg grain per kg Nitrogen applied) Fertilizer N applied (kg/ha)

Production Efficiency (PE) = Grain yield in fertilized plot – Grain yield in control plot (kg/ha)
(kg grain per kg Nitrogen absorbed) N uptake in the fertilized plot – N uptake in the control plot (kg/ha)

High nutrient uptake and less loss lead to high ANR. High AE is achieved if the incremental
yield per unit of N applied is high. This is usually so when the N rates applied are low and the
soil is low in N. High N in the grains as compared to the other plant parts leads to a higher
PE. Under Indian conditions the use efficiency of nitrogenous fertilizers are only about 50%
but under flooded or submerged condition in rice fields it is only about 28 – 34 % or about
30%.

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 Chapter 6

Water resources and soil – plant – water relationships

Sources of water for crop plants
Plants get their water supply from natural sources and through irrigation. Natural
sources supply the largest part of water required by the crop plants in most of the places
particularly under humid climate. However crop yields fluctuate widely when it is grown
under rainfed condition due uncertainties in rainfall. Irrigation on the other hand involves
high capital for its exploitation and supply to crop fields.
A. Natural sources:
i. Precipitation – Rain, snow, hail and sleet are received on earth from the atmosphere
that constitutes the precipitation. Rain is the largest part of precipitation and also the
most important source of water for crops. In humid and sub humid areas where
rainfall is moderate, crops are grown depending on rainfall. In low rainfall areas low
water requiring crops are grown. Where irrigation water is available it is used as a
supplement for rain water for growing crops. In cold climates, snow contributes to
soil water as it melts with rise in temperature. Hail and sleet are very minor sources
that are limited to their places of occurrence.
ii. Atmospheric water other than precipitation – Atmospheric water constitutes of dew,
fog, cloud and atmospheric humidity which serves as a very minor source of water
for crop plants. High atmospheric humidity, fog, dew and cloud are quite effective in
reducing evaporation from soil surface and transpiration from plants owing to
reduction in atmospheric demand. They thus reduce the soil water use thereby
making it available for a longer period for crop plants. They sometimes make
growing of crops possible with scanty rainfall. Cereals and vegetables are
extensively grown in North Bihar under unirrigated conditions where dew acts as a
supplementary water source.
iii. Ground water – The free water found beneath the ground surface is referred to as
ground water. When a hole is bored sufficiently deep into the soil, free water
accumulates into the hole and the surface of the water in the hole is termed as water
table. Water table is dynamic in nature and rises up during the rainy season due the
recharge of the ground water by heavy rainfall. During the summer season the water
table goes down due to evapotranspiration and subsurface flow. When the water
table rises and comes near the crop root zone, a considerable amount of water is
utilized by the crop plants. Besides due capillary movement water rises to some
distance above the water table depending upon the soil texture. The capillary rise of
water is more in finer soils like silt or clay compared to coarser soil like sandy soils.
iv. Flood water – Occurrence of flood is a common phenomenon during the rainy period
in many parts of India. Though occurrence of flood causes havoc damage both to
human beings and crops but while passing over the land it infiltrates into the soil and
recharges the ground water.
B. Irrigation water sources:

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 i. Surface water – Rain and melting snow form streams, rivers and fill reservoirs, ponds
and tanks. These form the sources of surface water. Surface water forms the largest
source for irrigation purpose. Dams are constructed across the rivers and water is
diverted to agricultural fields through canals and distributaries by gravity flow.
Supply of water from dams across rivers and streams are often seasonal. Tanks,
ponds and lakes store a limited quantity of water and provide irrigation mostly on
seasonal basis.
ii. Ground water – it is another important source of irrigation water. Seepage water from
canals, reservoirs and lakes, influent drainage from rivers and percolating flood
water recharge the ground water. Dug wells are constructed and shallow, medium
and deep tube wells are constructed to pump out the ground water for irrigation
purpose.
Role of water in plants
1) Water is a constituent of protoplasm. It is a structural constituent of plant cell and it
maintains the cell form through turgor pressure. When plenty of water is available,
cells are turgid and plants retain their normal structural form. Water accounts for the
largest part of the body weight of an actively growing plant and constitutes 85 to 90
percent of the body weight of young plants and 20 – 50 percent of mature plants.
2) Water is a source of two essential elements, oxygen and hydrogen required for
synthesis of carbohydrates during photosynthesis.
3) Water serves as a solvent of substances and a medium in plants allowing metabolic
reactions to occur.
4) Water acts as a solvent of plant nutrients and helps in the uptake of nutrients from
soils. Plants also absorb nutrients through leaves from nutrient sprays. These nutrients
are carried to different plant parts in soluble form for use.
5) Food manufactured in green parts is distributed to various parts of the plant in soluble
form where water acts as a carrier of the food materials.
6) Transpiration is a vital process in plants and occurs at a potential rate as long as water
is available in adequate amounts. When there is deficit of water the transpiration is
reduced thereby affecting the growth and yield of the plants. Transpiration also helps
in absorption of nutrients from the plants.
7) Water is essential in hydraulic process in the plant. It helps in the conversion of starch
to sugar.
8) Water helps to maintain the turgidity of cell walls. Water helps in cell enlargement
due to turgor pressure and cell division which ultimately increase the growth of plant.
9) Water is essential for the germination of seeds, growth of plant roots, and nutrition
and multiplication of soil organism.
10) Water helps in the chemical, physical and biological reaction in soil.
11) Leaves get heated up with solar radiation. Plants dissipate heat by inceased
transpiration. Water acts as a buffer against high or low temperature injury as it has
high heat of vaporization and high specific heat.

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Irrigation Definition:
Irrigation is artificial application of water to soil for the purpose of supplying the moisture
essential for normal plant growth and development”. It is supplementary to water available
from rainfall & ground water. Irrigation is applied into the soil for the following purposes:
1. To add water to the soil for supplying moisture essential for normal plant growth and
development.
2. To provide crop insurance against short duration droughts.
3. To leach or dilute excessive salts in the crop root zone, thereby providing a favourable
environment in the soil profile for absorption of water and nutrients.
4. To soften tillage pans.
5. To cool the soil and atmosphere, thereby making more favourable microenvironment
for plant growth
History of irrigation
Irrigation is an age old art. Civilizations grew up at locations where water was available. In
North India the canal system is found by a network of perennial rivers which have their
source in the snow clad Himalayan Mountains. During the whole winter season, the rivers
carry enormous amount of water for feeding the canals. But in the South they are mainly
rainfed and in off season particularly, no water is left in rivers to do irrigation in winter. So
agriculture in southern India is solely dependent on monsoons or the water stored during the
rainy season in the tanks.
Irrigation development in India
Medieval India
There is evidence that irrigation was practiced in India during Vedic periods. The
concepts of storing river flows behind a dam, distribution of stored water through canals so as
to ensure equity among farmers and adequate irrigation to the crops were well known and
practiced even before 3000 B.C. Further, the remains of Indus Valley Civilization that
flourished up to 1750 B.C also revealed the existence of the farm communities in the Indian
sub-continent.
British period
Irrigation development under British rule began with the renovation, improvement
and extension of the then existing works. However, as a result of the famine during 1876 –
1878, the country received serious setback in agricultural production. Consequently, the First
Famine Commission was setup by the Government in 1880, which recommended for
irrigation development in droughtprone areas.
The last two years of the 19 Century (1899 – 1900) again witnessed devastating
famines. This led to the appointment of First Irrigation Commission in the year 1901 to
ascertain the usefulness of irrigation against famines. Big spurt in irrigation development was
thus, observed in the first quarter of 20th Century.
Pre Independent India
Large scale irrigation in India began in the third decade of the 19 th century with the
construction of Cauvery Delta System in South India. One of the major irrigation projects
that came up during this period was Triveni in Champaran District of Bihar.

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Irrigated area in India
The net cultivated area in India is 141.4 mha while the gross cropped area is 195.1 mha. The
gross irrigated area in India 88.4 mha while the net irrigated area is 63.2 mha.
Irrigated area in different states
The status of net and gross irrigated area in different regions shows that North India
has the highest irrigated area followed by Western India. The Eastern India has the least
irrigated area.Uttar Pradesh has the highest gross irrigated area followed by Punjab, Madhya
Pradesh, Rajasthan, Andhra Pradesh, Haryana, Bihar and Gujarat. However considering the
net irrigated area to net cultivated area Punjab has the highest irrigated area followed by
Haryana, U.P, Tamil Nadu, Bihar and Andhra Pradesh.
Irrigation by different sources
Among the different sources of irrigation tube wells and other wells accounts for the
highest source of irrigated area (62%) followed by canals (26%), other sources (9%) and
tanks (3%) in descending order. More than half of the area has been under irrigation through
tube wells and dug wells. Tube wells may be deep medium and shallow. Uttar Pradesh,
Madhya Pradesh, Andhra Pradesh, Punjab, Rajasthan and Haryana in descending order share
the largest area irrigated by canals. Tube wells form an important source of water in Uttar
Pradesh, Punjab, Bihar and Haryana.
There are three major sources of irrigation in India. They are
a) Canals
b) Wells and tube wells
c) Tanks
wells and tube wells are the major source of irrigation. Canals ranks second while tanks stand
third. Tank irrigation is common in the eastern and southern states. With the introduction of
diesel and electric pumps well and tube well irrigated areas have increased considerably. The
canals in India are of two types –
1. Inundation canals - which are drawn directly from the river without making any kind of
Dam at their head to regulate the flow of the river. Such canals are used for diverting the
excess water from rivers at the time of flood. When the flood subsided the level of the river
falls below the level of the canal and therefore the canal dries up.
2. Perennial canals - canals which are constructed by putting some form of barrage across the
river which flows throughout the year and divert the water by means of Canal to agricultural
fields. Majority of the canals in India are of perennial type.
Water balance in India
India has a vast water wealth. The precipitation provides huge amount of water to fill
tanks, lakes and reservoirs and a good flow of water through streams and rivers. The mean
annual rainfall in the country is 1194 mm when considered over total geographical area of
328.7 mha, it makes available 392.5 mham of water. Thus India receives about 400 million
hectare meters (mham) of rain and snowfall. Another 20 mham flow in as surface water from
outside the country. This total 400 mhamof water goes to account for 70mhamwhich is lost as
evaporation from the top thin layer of soil, 115 mham of runoff direct from rainfall and snow
and 215 mham of water is infiltrated into the soil.

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 Out of 215 mham infiltrated water 165 mham remains as soil water and another 50mham
is available as groundwater. The major part of annual precipitation infiltrates into the soil and
contributes to ground water. The soil water constitutes of 172 mham of water which includes
165 mham of infiltrated rain water and 7 mham of water as contributed from ground water.
The annual ground water recharge constitutes 50 mham from infiltrated rain water, 5 mham
from infiltrated flood water and seepage from river and stream flows and 12 mham seepage
from irrigation systems which makes the ground water wealth of about 67 mham. The
country has asurface flows of 180mham of which 115 mham comes from runoff from rainfall
and snow, 20 mham flows from outside the country and 45 mham from ground water flow.
Out of 180 mham, 165 mham flows as river and stream and 15 mham is stored in reservoirs
and tanks.

Rains in small amounts soak the top thin layer of surface soil and get evaporated quickly.
This accounts for about 70 mham of evaporation from top thin soil layer. Another 65 mham
of evaporation from soil water and 5 mham evaporation from the free water surfaces of tanks
and reservoirs accounts for a total evaporation of 140 mham which is 35 percent of total
precipitation in the country.
Transpiration by irrigated and unirrigated crops is estimated to be about 13 and 42 mham
of water. Forests and other vegetation transpire upto 55 mham. This totals to 110 mham of
water transpired by forests and other vegetation.
Water Resources of Bihar
Agriculture in Bihar is crucially dependent on monsoon. Although around 57 percent
of its gross cultivated area is irrigated, irrigation itself is crucially dependent on monsoon as it
largely depends on the use of surface water. According to the soil quality and climatic
conditions of the relevant areas, Bihar has been classified in 3 agro-climatic zones : North-
West Alluvial Plane ( Zone1), North-East Alluvial Plane ( Zone 2), and South Alluvial Plane
(Zone 3), the last zone being further classified in two sub-zones 3A and 3B. Monsoon

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arrives earliest in the northeastern part (Zone2), which also receives the highest rainfall
among all three zones. Zone 3 receives monsoon showers last of all three zones and also the
least amount. Total irrigated area in the State is 45.67 lakh hectares, of which nearly 30
percent is fed by canal water. This highlights the monsoon dependence of even irrigated lands
as catchment areas of nearly all the major rivers in the State are outside the state.
Soil water relationship
Soil water relations deal with those physical properties of soils and water that
affectmovement, retention and absorption of water by plants and which must be considered
inorder to plan or improve an irrigation system.
Soil – A three phase disperse system
Soil is a three phase system consisting of solid, liquid and gases. The mineral and
organic matter in soil together constitute the solid phase which is the soil matrix, the
liquidphase consists of soil water, which always contains dissolved substancesso that it
shouldproperly be called the soil solution and the gaseous phase is the soil atmosphere.
Mineral matter comprise the largest fraction of soil and exist in the form of particles of
different sizes and shapes encompassing void spaces in soil called soil pore space. Organic
matter is interspersed in soil minerals. The amount and geometry of soil pores depend on the
relative proportions of different sizes and shapes of soil particles, their distribution and
arrangement. The pore spaces remain filled with air and water in varying proportions, which
are mainly manipulated by the amount of water present in the soil. The soil air is totally
expelled out of soil when water is present in excess amount as in water logged soils.
Soil properties influencing soil-water relations
Soil depth
Soil depth refers to the thickness of soil cover over hard rock or hard substratum
below which roots cannot penetrate. The soil depth is directly related to the development of
root system, water storage capacity, nutrient supply and feasibility for land leveling and land
shaping. Soil Conservation Division, Ministry of Agriculture, New Delhi, recognizes the
following classes for irrigation purposes:
Soil depth classification
Soil depth Class
Less than 7.5cm Very shallow
7.5 – 22.5 Shallow
22.5 – 45.0 Moderately deep
45.0 – 90.0 Deep
More than 90 Very deep

A shallow soil has limited moisture holding capacity, restricted feed zone and root
growth, therefore would need frequent irrigations with less water depth. Shallowness of soil
is further unfavourable in areas needing land leveling and shaping because it affects soil-
water relations besides nutrient retention & availability. Deep soil on the other hand, has
good moisture holding capacity, larger feeding zone and good possibilities for development
of root system. Soil depth is also important for interpreting water storage capacity.

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Soil texture
Soil texture is the most important and fundamental property of the soil that is most
intimately related to soil water relationship. It refers to the relative proportion of mineral
particles of various sizes in a given soil i.e., the proportions of coarse, medium and fine
particles, which are termed sand, silt and clay, respectively. Various combinations of these
fractions are used to classify soil according to its texture. Using the name of the predominant
size fraction designates texture. The relative sizes of sand, silt and clay as proposed by United
States Department of Agriculture (USDA) and International Soil Science Society (ISSS) are:
Soil separates Particle diameter (mm)
USDA ISSS
Coarse sand 1.0 – 0.5 2.0 – 0.2
Fine sand 0.25 – 0.10 0.2 – 0.02
Silt 0.05 – 0.002 0.02 – 0.002
Clay < 0.002 < 0.002
A sandy soil has greater proportions of large sized particles and is commonly termed
as coarse or light soil. A clay soil has a high percentage of fine particles and is referred to as
fine or heavy soils. A loam soil having almost equal amount of sand and clay is called as
medium textured soil or medium soil.
The soil texture is closely related to:
1. Water holding capacity of the soil.
2. Quantity of water to be given at each irrigation i.e., irrigation water depth.
3. Irrigation interval and number of irrigations.
4. Permeability i.e., ability of the soil to transmit water & air.
5. Infiltration rate
For example, coarse textured soils (sandy soils) have low water holding capacity
and facilitate rapid drainage and air movement. Therefore, crops grown on these soils require
frequent irrigations with less irrigation water depth at each irrigation. On the other hand, fine
textured soils (clayey) have relatively high water holding capacity, however the permeability
for water and air is slow thus resulting in poor drainage and sometimes the soils get
waterlogged. Considering its various effects, the soils with loamy texture are the ideal soils
for growing most crops under irrigated conditions.
Soil structure
The structure of a soil refers to the arrangement of the soil particles and theadhesion
of smaller particles to form large ones or aggregates. On the surface, soil structure is
associated with the tilth of the soil.
The soil structure influences primarily:
1. Permeability for air and water
2. Total porosity and in turn water storage capacity in a given volume of soil
3. Root penetration and proliferation
Soils without definite structure may be single grain types, sands or massive type such as
heavy clays. For example a structure-less soil allows water to percolate either too rapidly or
too slowly. Platy structure restricts the downward movement of water. Crumbly, granular and

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prismatic structural types are most desirable for efficient irrigation water management and
normal crop growth.
Physical properties of soil
Physical properties of soil play an important role in determining its suitability for
economic crop production. Density of individual soil particles and of bulk is reported in
relation to density of water, which is 1.0 g/cc. solid rock particles that go to form the soil
normally weigh about 2650 kg/m3. Weight of water being 1000 kg/m3, specific gravity of soil
is thus equal to 2650/1000 = 2.65.
Soil has solids, liquid and air and their relative masses and volume are often required
for proper soil and crop management. The relationship may be expressed as:
Vt = Vs + Vw + Va
Mt = Ms + Mw + Ma
Where,
Vt = total soil volume
Vs = volume of soil solids
Vw = volume of soil water
Va = volume of soil air
Mt = total mass of soil
Ms = mass of soil solids
Mw = mass of soil water
Ma = mass of soil air (negligible)
Particle density: The particle density, also called is also called density of soil solids, is the
ratio of mass of soil solids (Ms) of total volume of soil solids (Vs) and is expressed in g/cc or
Mg/cc. density of soil solids or particle density of 2.6 g/cc means that its weight is 2.65 times
that of water. In most mineral soils, the mean density of particles is about 2.6 to 2.7 g/cc.
presence of soil organic matter lowers its value.
P.D = Ms/Vs
Dry Bulk density: A given bulk of soil is not all solid. On volume basis, it may contain
about 50 percent pore space occupied by water and air. The dry bulk density or simply bulk
density is the ratio of mass of oven dry soil solid particles (Ms) to the total volume of the soil
(Vt). The volume includes the volume of soil solids (Vs), soil water (Vw) and soil air (Va).
Bulk density is sometimes referred to as the apparent specific gravity. The difference between
the two terms is that the bulk density is expressed as g/cc. while the apparent specific gravit y
is a dimensionless quantity.
B.D = Ms/Vt = Ms/ (Vs + Vw + Va)
Soil texture, structure, organic matter content and soil management practices
influence bulk density of soil. In sandy soils the bulk density can be as high as 1.6 g/cc. in
extremely compacted soils, bulk density might approach but never reach particle density.
Ideal bulk density for optimum crop growth varies from 1.2 g/cc for a clay soil to about 1.4
g/cc for a sandy soil.
Total or wet Bulk density: It is the ratio of total mass of soil (Mt) to the total volume of soil
(Vt).
Wet B.D = Mt/Vt = (Ms + Mw)/ (Vs + Vw + Va)
The wet bulk density depends more on the soil wetness or moisture content of soil.

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Total Porosity: Soil pores are those parts of soil bulk not occupied by solid soil particles. In
a field, soil pores are filled with water, air and other gases. Porosity (f) is the ratio of total
volume of pore spaces (Vf) to the total volume of soil (Vt) and is expressed as a fraction or as
percentage.
f = Vf/Vt = (Vw + Va)/ (Vs + Vw + Va)
= (Vt – Vs)/Vt = (1 – Vs/Vt) = 1 – (B.D/P.D)
Total porosity value generally lies in the range of 30 to 60% for arable soils. Coarse
textured soils tend to be less porous (35 – 50%) than the fine textured soils (40 – 60%),
though the mean size of individual pores is greater (>0.06mm in diameter) in the former than
in the latter. Total porosity is inclusive of both, capillary (micro pores) and non-capillary
porosity (i.e., macro pores). In a sandy soil, in spite of the relatively low total porosity, the
movement of air and water is surprisingly rapid because of the dominance of the macro pores.
Therefore the size of the individual pore spaces rather than their combined volume is an
important consideration for optimum soil-water relations. For ideal conditions of aeration,
permeability, drainage and water distribution, a soil should have about equal amount of
macro and micro pore spaces. Knowledge of porosity in a given volume of soil is very
important with respect to irrigation water management, because it is an index of moisture
storage capacity and aeration conditions, the two most important factors that influence the
plant growth and development.

Soil wetness:It refers to the relative water content of the soil and is expressed on weight basis
or volume basis. Usually the soil water content is expressed on weight basis.
Mass wetness:Mass wetness is the ratio of mass of water to the mass of soil solids which is
sometimes called gravimetric water content. It is expressed in percent.
Mass wetness = Mw/Ms*100
Volume wetness: It is the ratio of volume of water to the total volume of soil. It is also
termed as volumetric water content. It expressed in percent.
Volume wetness = Vw/Vt*100
A relationship exists between mass wetness and volume wetness, which is given by
Volume wetness = Mass wetness × Apparent specific gravity
Classification of Soil Water:
When water is added to dry soil either by rain or irrigation, it is distributed around the soil
particles, where it is held by adhesion and cohesive forces. It displaces air in the pore spaces
and eventually fills the pores. When all the pores, large and small are filled, soil is said to be
saturated and it is at its maximum retentive capacity.
Although the soil water cannot be sharply demarcated, yet for sake of understanding and
as per utility of water to plant it is mainly classified into following categories.
Soil water can mainly be classified into three heads:
 Gravitation water
 Capillary water
 Hygroscopic water
i) Gravitational water:when sufficient water is added to the soil, water gradually fills the
pore system expelling the air completely from soil. A well drained soil cannot reach

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 this stage of complete saturation as water starts moving downwards under gravity
through the soil pores when the gravity exceeds soil water tension. The water in the
macro pores are generally affected. This water is not available to the plants.
ii) Capillary water: With increasing supply of water, the water film held around the soil
particles thickens. The water retained in the soil after the cessation of the downward
movement is the capillary water. The soil water tension at this stage is 1/10 to 1/3 atm.
Once this stage has reached the soil cannot hold any more water, and the excess water
tends to move downwards under gravity. Capillary water is also known as water of
cohesion. This water is held at a tension of 1/3 to 31 atm and much of it is in fluid state.
Principal factors influencing the amount of capillary water in soils are the structure,
texture, organic and colloidal matters present. A greater amount of water is held by a
fine textured soil than coarse textured soil. The granular structure exhibits a higher
capillary capacity. The more the organic and colloidal matter contents, the greater is the
capillary capacity of soils.
iii) Hygroscopic water: The water that an oven dry soil absorbs when exposed to air
saturated with water vapour is termed as hygroscopic water. It occurs as a very thin
film over the surface of soil particles and is held tenaciously at a tension of 31
atmospheres. Thus hygroscopic water represents the water held by soil in between
10,000 to 31 atmospheric tension. It is non-liquid and immobile at this stage. It is also
termed as water of hydration or water of adhesion. This water is not available to plants.
Soil Moisture Constants
Field capacity
Field capacity denotes the water content retained by an initially saturated soil against the
force of gravity. This stage is reached when the excess water from a saturated soil after
irrigation or rainfall has fully percolated down. Field capacity presupposes the conditions that
evaporation and transpiration are not active, downward movement of water has practically
stopped and all the hydrostatic forces acting on soil water are in equilibrium. Soil water
tension at field capacity ranges from 0.1 to 0.33 atm for different soils. It is 0.1 atm for sandy
soils and 0.33 for clayey soils. However the value of 0.33 atm is commonly accepted. Field
capacity is considered the highest limit of available water range. Soil water content at field
capacity is usually higher in soils with higher content of silt and clay, organic matter and
other colloidal matters.
Figure 2.1 – Soil at field capacity Spaces between the soil particles filled with water and
air

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Permanent wilting point:
It refers to the water content of soil at which plants do not get enough water to meet
the transpiration demand and wilt permanently. This stage of soil water is designated as
permanent wilting percentage, wilting coefficient or permanent wilting point. Two stages of
wilting point are recognized: 1.) temporary wilting point and 2.) Permanent wilting point.
Temporary wilting point denotes the soil water content at which plants wilt during the day
time but recovers during night or when kept in a humid chamber. Permanent wilting point
represents the soil water content at which plants wilt permanently and fail to recover even
when they are kept in humid chamber. Permanent wilting point is considered as the lowest
limit of available water range as most of the plants do not get enough soil water for survival
beyond this point. Sunflower is often used as an indicator plant in determining this point.
Figure 2.2– Soil at wilting point Spaces mostly filled with air, with a small amount of
water held tightly around the soil particles

Saturation capacity
It is the water content of a fully saturated soil with all its pores completely filled with water
under restricted drainage. It is also referred to as maximum water holding capacity. The
soil water at this stage is in a free state and its tension is 0. The saturation capacity varies with
soils. It increases with the presence of greater quantities of silt, clay, organic matter and
colloidal matter. The water between field capacity and saturation is not available to the
plants.
Fig 2.3. Saturated soil spaces between the soil particles totally filled with water

Hygroscopic coefficient: It is the maximum quantity of water absorbed by any soil in a

saturated atmosphere (i.e. at 99 percent relative humidity) at 25 degree Celsius temperature.
The hygroscopic coefficient varies with the type of soil, its texture and organic matter
content. This constant is equal to a force of about 31 atmospheres and determined by placing

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the soil in a saturated atmosphere at 25oC temperature. Water held by the soil at this constant
is not available to plants because it is mostly in vapour form but it is useful to certain
bacteria.
Available water
The water held by the soil between field capacity and wilting point and at a tension
between 0.1 to 0.33 and 15 atm is available to the plants and is termed as available water. It
consists of the greater part of the capillary water. Amount of available soil water depends on
the texture, structure and the amount of organic matter and colloidal matter present therein.
The granular structure and organic matter in soil increase the void space in soil resulting in
greater storage and availability of soil water. The amount of water available within Field
capacity and PWP is called the total available water (TAW) and the water available between
half of F.C and PWP is called readily available water (RAW).
Unavailable water
There are two situations at which soil water is not available to most plants, i) when
the soil water content falls below the Permanent wilting point and is held at tension of 15 atm
and above and when the soil water is above Field capacity and is held at a tension between 0
and 1/3 atm. Gravitational water and hygroscopic water come under this class.
Energy concept of soil water
Soil water has energy in different quantities and forms. Out of two principal forms of energy
i.e kinetic and potential energy, as the movement of soil water is very slow its kinetic energy
is considered negligible. The potential energy which is the potential ability to do work results
from the position of the water with regard to some reference point or level. Potential energy
is very important in determining the state and movement of soil water. Movement of water
between two points in a soil is caused by the difference in potential energy of water between
two points. The natural tendency is that water moves from the region of higher potential
energy to the region of lower potential energy to reach the equilibrium. Water molecules at
the surface a body of water are considered to have no potential energy (zero potential)
whereas the water held by a soil possesses negative potential. It is defined as the amount of
work done by a unit quantity of water to transport reversibly and isothermally an infinitesimal
quantity of water from a pool of pure water at a specified elevation at atmospheric pressure to
the point of soil water under consideration.
Forces acting on soil water
Soil water is constantly subjected to various forces that cause its retention by the soil matrix
and movement through the soil medium. The forces acting on soil water are:
i) Matric forces
ii) Osmotic forces
iii) Gravitational forces
The matric and osmotic forces are negative forces and are known as matric tension and
osmotic tension.
Matric forces
Matric forces consist of a group of forces that are (i) Adsorptive forces and (ii) Capillary
forces.

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Absorptive forces: Adsorptive forces cause water molecules adsorbed on clay particles in
clay crystal lattices and around certain cations adsorbed on clay particles. A water molecule
possesses an electrical charge and is a dipole. Clay particles in soil carry a negative charge
and attract the water molecules that get adsorbed around the particles. The effectiveness of
the attractive forces due to electrostatic field diminishes rapidly with distance from the clay
particles.
Capillary forces: Capillary tension (negative force) is mainly responsible for retention of
water around soil particles in the micro pores. When the water comes up from the soil below
i.e from the water table below, the soil becomes moist for a considerable distance. This
movement is due to capillarity and is similar to the rise of water in a capillary tube. Capillary
forces comprise of two different forces, i) force of cohesion i.e liquid to liquid attraction and
ii) force of adhesion i.e solid to liquid attraction.
i) Force of cohesion: The force of mutual attraction of water molecules in air – water
interface is known as the cohesive force. The attraction of water molecules for each
other is termed as surface tension. The surface tension is responsible for retention of
water around soil particles as a very fine film.
ii) Force of adhesion: The other force involved in the capillarity is the adhesive force that
acts in a solid – liquid interface. It represents the mutual attractive force between soil
particles and water and is responsible for retention of water as a much thicker film.
Capillarity depends on both cohesive and adhesive forces. If the adhesive force is greater than
the cohesive force the liquid will rise on the surface of the solid. If the adhesive force is
greater than the cohesive force, the contact angle between the glass and water would be zero
which is also considered same for water in soil.
The height to which water rises in a tube of capillary dimension depends on the
surface tension and the weight of the water column. The weight of water column elevated to
height h, is supported by the vertical component of surface tension acting around the
perimeter of the tube.
Thus as the capillary tube gets finer the value of „r‟ becomes smaller and this makes
the water rise to a greater height. Thus in clay soils the water rises above the water table to a
great height because of the smaller sized pore compared to sandy soils.
Osmotic force
Soil water contains some amount of dissolved salts and solutes and is termed as soil
solution. Presence of solutes in water decreases the potential energy of water in it. Osmotic
pressure is the property of aqueous solution. When aqueous solution is separated by a semi –
permeable membrane from pure water or from a solution of lower concentration, water tends
to diffuse or osmose into the concentrated solution through the membrane. The pressure that
must be applied to prevent the diffusion of water is termed as osmotic pressure. Besides
capillary tension, the osmotic tension is responsible for retention of water in soil.
Gravitational force
The gravity acts on soil water simultaneously with matric and osmotic tensions. As
long as the gravity is lesser in magnitude than the matric and osmotic suctions (negative
force) there is no downward movement of water. When the soil gets wet after rainfall or
irrigation the combined effect of matric and osmotic suction decrease and become lower in
magnitude than gravity. Thus the water has a downward movement. Downward movement
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ceases when the combined effect of matric and osmotic suctions are equal in magnitude to
that of the gravity.
Soil moisture tension
The moisture held in the soil against gravity may be described in terms of moisture
tension. Thus, soil moisture tension is a measure of the tenacity with which water is retained
in the soil and reflects the force per unit area that must be exerted by plants to remove water
from the soil. Several units have been used to express the force (energy) with which water is
held in the soil. A common means of expressing tension is in terms of a bar or atmosphere.
For instance, a pressure of one bar is approximately equal to the hydrostatic pressure exerted
by a vertical column of water having a height of 1023 cm or a hydraulic head of 1023 cm.
Again a pressure of 1 atmosphere is equivalent to the weight of 1036 cm of water column or
76.39 cm of mercury column over 1 square centimetre area. Similarly 1.0 bar is equivalent to
0.9869 atmospheres. The suction of water having a height of 10cm is equal to 0.01 bars or 10
millibars, that of a column of 100 cm high about 0.1 bar or 100millibars. Similarly 1.0 bar is
equal to 100 centibars. Thus the higher the height of water column or bars or atmospheres the
greater the tension or suction measured.
pF
In attempting to express the matric potential (or soil moisture tension) of soil water in
terms of an equivalent hydraulic head (or energy per unit weight), it is understood that this
head may be of the order of -100 cm or even -100000 cm of water. To avoid the use of such
cumbersomely large numbers, Schofield (1935) suggested the use of pF (by analogy with the
pH acidity scale), which is defined as the logarithm of the negative pressure (soil water
tension or suction) head in cm of water. A tension of 10 cm of water is, thus, equal to a pF of
1. Likewise, a tension head of 1000 cm is equal to a pF of 3, and so forth. Approximate
equivalents among expressions of soil water tension are given below in Table 2.1.
Table 2.1 Approximate equivalents among expressions of soil water tension
Soil moisture tension Soil water potential Hydraulic head pF
(bars) (kPa) (cm) value
-0.01 1 10.2 1.0
-0.1 10 102 2.0
-0.33 33 337 2.52
-1.0 102 1023 3.0
-15.0 1534 15345 4.2
-31.0 3171 31713 4.5

Soil water tension: It is the force per unit area that must be exerted to remove water from a
non – saline soil at any water content. Tension or suction represents the negative force. Soil
water tension is often referred to as soil water suction or matric suction. It measures the
potential energy of water in soil with respect to free pure water. It presupposes that the soil is
non – saline or the soil water exhibits a very negligible osmotic pressure.
Soil water stress: Soil water contains some amount of dissolved salts and thus exhibit some
amount of osmotic tension. Salts and other solutes in soil water increase the force that must
be exerted to extract water and influence the amount of water available to the plants. A saline

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soil has a stronger osmotic tension. The soil water tension together with the osmotic tension
constitutes the soil water stress. In non – saline soils, soil water stress equals to soil water
tension.
Total soil water potential
The total soil water potential is the sum of potentials resulting from different force
fields. It may be defined as the amount of work done by unit quantity of water to transport
reversibly and isothermally an infinitesimal quantity of water from a pool of pure water at a
specified elevation at atmospheric pressure to the point of soil water under consideration.
ψsoil = ψg + ψp(m) + ψo
ψg= gravitational potential
ψp(m) = pressure or matric potential
ψo= osmotic potential

Gravitational potential
Everybody on the earth's surface is attracted toward the earth's center by a
gravitational force equal to the weight of the body, that weight being the product of the mass
of the body and the gravitational acceleration. To raise a body against this attraction, work
must be expended, and this work is stored by the raised body in the form of gravitational
potential energy. It is evaluated at any point by the elevation of the point relative to some
arbitrary reference level within the soil or below the soil profile in consideration so that the
gravitational potential can always be taken as either positive or zero. Gravitational potential
may be defined as the amount of work that a unit quantity of water in an equilibrium soil
water system at an arbitrary level is capable of doing when it moves to another equilibrium
identical in all respects, except that it is at a reference level. The gravitational potential is
independent of the chemical and pressure conditions of soil water, and dependent only on
relative elevation.
Matric potential
Matric potential is the negative pressure potential resulting from the capillary forces
originating from the soil matrix. It is sometimes called the capillary potential or soil – water
suction or matric suction. It results from the interactive capillary and adsorptive forces
between water and the soil matrix, which in effect bind water in the soil and lower its
potential energy below that of bulk water. The soil water in an unsaturated soil has no
pressure potential, but has only matric potential.
Osmotic potential
While this phenomenon may not affect liquid flow in the soil significantly, it does
come into play whenever a membrane or diffusion barrier is present that transmits water more
readily than salts.The presence of solutes in soil water affects its thermodynamic properties
and lowers its potential energy. The osmotic effect is important in the interaction between
plant roots and soil, as well as in processes involving vapour diffusion.
Soil moisture characteristics curve
Soils differ considerably in their capacity to retain water. Soil characteristics such as
texture and structure of soils, size and amount of pore space, amount and nature of organic
colloidal matters and quantities of exchangeable cations present influence primarily the
retention of water. The relative proportion of soil – water interfaces and the size and amount

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of pore space are most important in water retention. The soil moisture characteristic curve is
strongly affected by soil texture. The greater the clay content, in general, the greater the water
retention at any particular suction, and the more gradual the slope of the curve. In a sandy
soil, most of the pores are relatively large, and once these large pores are emptied at a given
suction, only a small amount of water remains. In a clay soil, the pore size distribution is
more uniform, and more of the water is adsorbed, so that increasing the suction causes a more
gradual decrease in water content. The soil moisture characteristic curves have marked
practical significance. They illustrate retention-energy (suction) relationships, which
influence various field processes, the two most important of which are the movement of
water in soils and the uptake and utilization of water by plants. Thus help in scientific
scheduling of irrigation‟s to field crops at optimum time and in proper quantity.

Figure 2.4 Soil moisture characteristic curves for soils varying in texture

Soil structure also affects the shape of the moisture characteristic curve, particularly at
low suction range. Soil compaction decreases the total porosity, especially decreases the
volume of large interaggregate pores. Hence, the saturation water content and initial decrease
of water content at low suction is reduced. On the other hand, the volume of intermediate size
pores is likely to be relatively greater in a compacted soil, while the interaggregate
micropores remain unaffected. Hence, the curves for compacted and uncompacted soil may
be nearly identical at high suction range. At very high suction range, water is held primarily
by adsorption and hence retention is a textural than structural attribute.
Hysteresis
The moisture retention curve, i.e. the relationship between matric potential and water content
can be obtained in two ways (i) by wetting a dry soil (sorption), (ii) by drying a saturated soil
(desorption)
1. Sorption, by gradually wetting an initially dried soil, while reducing the suction.
2. Desorption by taking an initially saturated sample and increasing the suction to
gradually dry the soil.
Each of these methods will give a continuous curve, but the two curves will not be identical.
The soil moisture content at a given suction is greater in desorption than in sorption. This
phenomenon is known as hysteresis. The hysteretic effect may be due to geometric non-
uniformity of individual pores, entrapped air or swelling and shrinkage of the soil. Large
pores which are bounded by smaller openings, will not empty until the pressure potential

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(ψp)< 15/d, where d is the diameter of the small pores. However, these same pores will not
fill until (ψp)> 15/d, where d is the diameter of the large pores. Therefore, the same moisture
content can occur at two different tensions (pressure potentials) in the same soil (when the
soil is being wetted and when the soil is being dried).
Movement of Water in Soil
Soil water is dynamic and moves constantly in the soil medium in different directions
under different forces acting on it. Downward and lateral movements of water occur during
and after irrigation or rainfall and upward movement takes place when upper soil layers start
drying up owing to evaporation or evapotranspiration. Movements of water in soil may either
occur in liquid or vapour form or both.
Infiltration
Infiltration is the process of entry of waterdownwards from the air medium, precisely
the soil surface, into the soil medium. In irrigation practice it is the term applied to the
process of water entry into the soil, generally by downward flow through all or part of the soil
surface is termed as infiltration. Infiltration rate or infiltrability is defined as the volume of
water flowing into the profile per unit of soil surface area per unit time. Infiltration rate is
very rapid at the start of irrigation or rain, but it decreases rapidly with the advance of time
and eventually approaches a constant value. When water is applied it enters the soil as fast as
it is supplied as long as the supply rate is less than the intake rate. When the supply rate
exceeds the intake rate, water ponds over the area or moves down the slope as runoff.
i = Q/ (A×T)
i = Infiltration rate (mm or cm/min or h)
Q = Volume quantity of water (m3) infiltrating,
A = Area of the soil surface (m2) exposed to infiltration, and
T = Time (min or h).

Figure. 2.5 Infiltration rate and cumulative infiltration

The infiltration rate is not constant over time. Generally, infiltration rate is high in the initial
stages of infiltration process, particularly where the soil is quite dry, but tends to decrease
monotonically and eventually to approach asymptotically a constant rate, which is often
termed as basic intake rate or steady state infiltration rate. Whereas, the cumulative
infiltration, being the time integral of the infiltration rate, has curvilinear time dependence,
with a gradually decreasing slope. The infiltration rate of a soil may be easily measured using

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a simple device known as a Double Ring Infiltrometer. The variation of infiltration rate in
different soil textures.

Figure 2.6 Infiltration rate in different soil type

Infiltration rate is grouped in to four categories
1. Very Slow: soils with less than 0.25 cm per hour e.g. - very clay soils.
2. Slow: infiltration rate of 0.25cm to 1.25 cm per hour e.g. Soils with high clay.
3. Moderate: infiltration rate of 1.25 to 2.5 cm per hour. e.g. - sandy loam/ silt loam
soils.
4. Rapid: infiltration rate is more than 2.5cm per hour e.g. deep/sandy silt loam soils.
Factors affecting the rate of infiltration:
 Compactness of soil surface: A compact soil surface permits less infiltration
whereas more infiltration occurs from loose soil surface.
 Impact of rain drop: the force (speed) with which the rain drop falls on the ground is
said to be impact of rain drop. Ordinary size varies from 0.5 to 4mm in diameter. The
speed of raindrop is 30ft per second and force is 14 times its own weight. When
impact of raindrop is more then it causes sealing and closing of pores (capillaries)
especially in easily dispensable soils resulting in infiltration rate
 Soil cover: Soil surface with vegetative cover has more infiltration rate than bare soil
because sealing of capillary is not observed.
 Soil Wetness: If soil is wet, infiltration is less. In dry soil, infiltration is more.
 Soil temperature: Warm soil absorbs more water than cold soils.
 Soil texture: In coarse textured soils, infiltration rate is more as compared to heavy
soils. In coarse textured soil, the numbers of macro-pores are more. In clayey soils,
the cracking caused by drying also increases infiltration in the initial stages until the
soil again swells and decreases infiltration.
 Depth of soil: Shallow soils permit less water to enter into soil than too deep soils.
A coarse surface textured, high water stable aggregates, more organic matter in the
surface soil and greater number of micro pores, all help to increase infiltration. As it is a
dynamic and quite variable character of soil, it can be controlled by management practices.

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Cultivation practices that loosen the surface soil make it more receptive for infiltration e.g.
course organic matter mulches increases infiltration.
Water intake time relationship
The relationship is important in order to decide the time to be allowed for application of a
specified depth of water to a crop. A shorter period is allowed for infiltration in a soil with
high intake rate compared to a soil with low intake rate. The stream size should be larger for
soils with higher intake rate so that the irrigation water front advances at a faster rate and
quickly covers the whole area.
Permeability
Permeability may be defined as the characteristics of a porous medium of its readiness to
transmit a liquid. It is dependent on the pore size distribution in the soil. The larger the
proportion of macro – pores, the greater is the permeability. Permeability usually decreases
with depth as subsoil layers are more compact and have a usually small number of macro
pores compared to the surface soil layers. The organic matter content, soil aggregates,
texture, structure, colloidal matters, plough pan sodium concentration of water, tillage and
crop management practices influence greatly the permeability of soil. Permeability decreases
as the soil becomes drier following saturation.
Seepage
The lateral movement of water through soil pores or small cracks in the soil profile
under unsaturated condition is known as seepage.
Water movement in saturated soil
Darcy’s law
Experience shows that the discharge rate or flow rate Q (the volume V is flowing
through the column per unit time) is directly proportional to the cross-sectional area and to
the hydraulic head drop ∆H, and inversely proportional to the length of the column L:
Q ~ V/t ~ A∆H/L

The usual way to determine the hydraulic head drop across the system is to measure
the head at the inflow boundary H1 and at the outflow boundary H0 relative to some reference
level. Hydraulic head can be measured with help of Piezometer. In the following equation,
∆H is the difference between these two heads:
∆H = H1 – H0
Obviously, no flow occurs without a hydraulic head difference, that is, when ∆H = 0.
The head drop per unit distance in the direction of flow is in fact, the driving force. The
specific discharge rate Q/A (i.e., the volume of water flowing through a unit cross-sectional
area per unit time t) is called the flux density (or, simply, the flux) and is indicated by q.
Thus, the flux is proportional to the hydraulic gradient:
q = Q/A = V/(A×t) ~ ∆H/L
The proportionality factor K is termed the hydraulic conductivity. It can be measured with the
help of Permeameters.
q = K∆H/L
This equation is known as Darcy‟s law, after Henry Darcy. This equation gives an
empirical relationship between water flux and energy gradient. Water flow in saturated soils
is considered to follow Darcy‟s law.

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 The above equation can also be written as
Q = A K∆H/L
Q = A Ki
Where
i is the hydraulic gradient i = ∆H/L, dimensionless
Hydraulic gradient is the head drop per unit distance in the direction of the flow.
When the hydraulic gradient becomes unity that is the driving force is equal in magnitude to
the force of gravity, then
V/t = K
i.e the velocity of flow (V/t) is equal to the hydraulic conductivity.
Limitations of Darcy’s law
The law applies only when the flow is laminar. Laminar flow usually occurs in silt and clay
soils. Hydraulic gradient more than unity may result in non- laminar flows in coarse sands,
where Darcy‟s law cannot be applied. The usual index to find the tendency of flow to be
laminar is the Reynold‟s number Rn, where Reynold‟s number less than unity indicates
laminar flow.
Hydraulic conductivity
It is the rate of flow of liquid through a porous medium under unit hydraulic gradient
and is the proportionality factor K in Darcy‟s law. A soil with high porosity and large number
of macro pores has high hydraulic conductivity.
Soil water – plant relationship
Plants that inhabit water saturated domains are called Hydrophytes or aquatic plants.
Plants adapted to drawing water from shallow water tables are called Phreatophytes. In
contrast, plants that can grow in arid regions by surviving long periods of thirst and then
recovering quickly when water is supplied are called Xerophytes or desert plants. Some
plants are specially adapted to growing in saline environment and are called Halophytes.
Plants that grow best in moist but aerated soils generally in semi-humid to semiarid climates
are called Mesophytes. Most crop plants belong to this category.
Plants grow on soil that provide them water and nutrients. They absorb the water from
soils mainly through roots and use only 1.0 to 1.5 percent of the volume of water absorbed
for building their vegetative structures and performing various biochemical and physiological
activities. Soil, plant and ambient atmosphere taken together constitute a physically
integrated dynamic system in which various flow processes occur independently like links in
a chain which in a unified form is called soil plant atmosphere continuum (SPAC). In this
system water flow always takes place from regions where its potential energy state‟s higher
to where it is lower. The flow path includes liquid water movement in the soil towards the
roots, liquid and perhaps vapour movement across the root to soil contact zone, absorption
into the roots and across the membranes to the vascular tubes of the xylem, transfer through
the xylem up the stem to the leaves, evaporation in the intercellular spaces within the leaves,
vapour diffusion through the substomatal cavities and out of the stomata perforations into the
air layer in direct contact with the leaf surface to the atmosphere.

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 Fig. 2.7 Moisture absorption pattern by crops
Absorption of Moisture by Crops
Absorption of water is not dependent of process but it is related to transpiration.
Absorption is controlled by rate of water loss in transpiration at least when water is readily
available to the roots. Absorption and transpiration are linked by the continuous water
column in xylem system of plants. Due to the loss of water in transpiration, it produces the
energy gradient which causes the movement of water from soil in to the plants and from
plants to atmosphere. In the maintenance of water column in xylem, the cohesive and
adhesive properties of water play important role. Moisture enters in to plant roots by process
of osmosis (movement of liquid through semi permeable membrane caused by unequal
concentration on the two sides). The concentration of soluble material in cell sap of roots is
increased because of loss of water through transpiration. When concentration of soluble
material in cell sap within roots is greater than the soil moisture, the water passes in the roots
to equalize the concentration. A more correct view to consider the concentration of water
molecule in cell sap reduced because of quantity of soluble substances present and hence the
number of water molecules in the soil solution is greater. As a result more water molecules
strike against cell wall and water passes into the roots from the zone of higher concentration
of water to a zone of lower concentration of water. When the concentration of soluble
substances in the soil moisture exceeds that cell sap, situation will be reserved and water will
pass out of the roots to the soil. Plants growing in saline soils with high concentration of
soluble salts absorb water with difficulty due to high osmotic pressure of the soil solution.
The absorption of water by plants is closely related with transpiration. The sun provides
energy for vaporization of water from leaves. Loss of water from leaf cells cause an increase
in interior osmotic pressure which causes water to move in to them from xylem vessels. The
xylem vessels of leaf are continuous with that of stem and roots and cause a tension created
by loss of water from leaf to be transmitted to roots. Increased osmotic pressure in root cells
occurs and uptake of water is encouraged. The absorption of water takes place in terminal
portion of roots but the maximum absorption takes place in the zone of root hairs, 1 to 10 cm
behind root tip. In other words, water is absorbed mainly through roots hairs. Root absorbs
water both passively and actively. Passive absorption takes place when water is drawn into
the roots by negative pressure in the conducting tissues created by transpiration. Under the
conditions during which there is little transpiration, the roots of many plants absorb water by
spending energy that is called active absorption. Under normal conditions of transpiration, the
contribution of active absorption to the water supply of plant is negligible and it is usually

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less than 10 percent of total absorption. Certain plants are able to absorb moisture from the
atmosphere when soil is at permanent wilting point. This is known as aerial absorption or
negative transpiration. Direct absorption of water by leaves that are wetted by rain, dew or
overhead irrigation can help to resaturate dehydrated leaf tissue. The leaves are borne through
out the stem in all plants which are mainly responsible for the loss of water. The leaf surface
shows small pores surrounded by two cells. The pores are called stoma and cells surrounding
them are called guard cells. The stoma (stomata) regulates the loss of water as vapour and
exchange of CO2 in leaf and other organs. It is thus the efficiency of these structures which
possibly determine water loss from plant. The efficiency of the stomata up on their size and
number per unit area.
Energy concept of water absorption
Pure water has zero water potential, ψ. When solutes are present in water, the
potential decreases below zero. A cell therefore has negative water potential. When a cell is
placed in pure water, water moves into the cell due to gradient of decreasing ψ. This
movement produces turgor pressure or pressure potential, ψ p inside the cell and reduces the
osmotic potential, ψs by diluting the concentration of the cell sap. The turgor pressure acts
against the forces responsible for movement of water in the cell and is considered positive.
Cell = ψs+ ψm+ ψp
Where, ψcell = cell water potential
ψs = osmotic potential
ψm = matric potential
ψp= pressure potential
Value of ψs and ψm are negative while that of ψp is positive. The ψcell is usually negative,
unless the cell is fully turgid. The cell water potential becomes zero when the cell becomes
fully turgid. With the entry of water into the cell owing to the osmotic and matric potential,
the pressure potential increases as the volume of the cell increases. The elasticity of the cell
wall puts a limit to the increase in the cell volume.
A cell inside the plant system is surrounded by other cells while epidermal cells of the
root are surrounded by soil water outside and the cortical cells inside. The gradient of
decreasing water potential from epidermal cellsto xylem results in the radial movement of
water in the roots.
Water movement in soil – plant – atmosphere system
When the soil – plant – atmosphere system is considered, difference in the magnitude
of the water potential at different points in the system creates the driving force for the water
to move from soil to the atmosphere through the plants. This movement occurs so long ψair is
less than soil water potential ψ soil.
Water when moves from soil through plants to the air takes the path along;
i) Epidermal cells in root
ii) Cortical cells and intercellular spaces in the cortex
iii) Conductive system of the xylem
iv) Leaf cells
v) Intercellular spaces in the leaf
vi) Stomatal cavities and stomata
vii) Air layer in the immediate vicinity of the leaf

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In this system water takes the path of least resistance and moves as a continuous cohesive
liquid from epidermal cells of root to the leaf cells. Water from leaf cells moves through the
stomatal cavity to the air in vapour form. The evaporation from the leaves sets up
imbibitional forces in leaf cell walls that are transmitted to epidermal cells of roots through
the hydrodynamic system and causes the water absorption and then its ascent through the
plant body.
Active absorption: A well-watered slowly transpiring plant absorbs water by active
absorption under the tension developed in the root xylem due to matric effect of solid and the
osmotic effects of the solutes present in it. This tension is also called the root pressure. Root
pressure is only detectable during periods of low transpiration. The amount of water absorbed
by active absorption is very negligible and is usually less than 5%of the total water required
by a rapidly transpiring plant.
Passive absorption: In rapidly transpiring plant water loss from leaves exceeds the volume
of water that the plant can absorb by active absorption. Thus a tension or diffusion pressure
deficit is created in the mesophyll tissues of the leaves which is then transmitted through the
hydrodynamic system into the xylem system in the roots and then to the root surface. Under
conditions of rapid transpiration and high diffusion pressure deficit in the xylem system,
water is literally pulled into the roots from the soil by mass flow. However, root tissues offer
resistance to this movement and water absorption tends to lag behind the transpiration rate.
The absorption lag causes development of water deficit and tension. Sometimes the water
deficit is so high that plants show signs of wilting even when the water supply is adequate
especially during summer mid days.
Factors affecting water absorption
1. Atmospheric factors: Evaporative demands of the atmosphere decides the rate of
transpiration and consequently the rate of absorption. Temperature, relative humidity,
winds and solar radiation are the principal atmospheric factors that decide the evaporative
demand. High temperature, high wind, low relative humidity and greater solar radiation in
combination cause transpiration at a higher rate thereby increasing absorption of water.
2. Soil factors: Available water, concentration of the soil solution, hydraulic conductivity of
soil, soil temperature and soil aeration are the principal soil factors that affect the water
absorption. In soils, where the hydraulic conductivity is high, movement of water towards
roots occur faster resulting in greater availability of water to the plants. As long as the
potential of the water is higher than plant water potential, the movement of water occurs
towards plant.
Concentration of soil solution in saline soils and arid soils remain high resulting in higher
osmotic pressure of the soil solution. This reduces the gradient of water potential from soil
to plant resulting in reduced absorption of water.
Low soil temperature reduces the permeability of root cells and increases the viscosity of
water causing reduction in water absorption. Again at low temperatures, root growth is
restricted providing a smaller absorbing surface. Water absorption becomes significantly
reduced at soil temperature below 200C and the reduction is more prominent in warm
season crops. The amount of water absorption is linearly related to the temperature in the
range of 100C to 250C. It declines beyond 250 C. Temperatures beyond 400C in the
rhizosphere often do not support water absorption and plants show symptoms of wilting.

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 Soil aeration becomes a problem in heavy soils particularly in high rainfall areas under
poor drainage condition. Water logging causes poor aeration and interferes with the root
growth and restricts water absorbing surfaces. As a result crops like maize, cowpea and
mungbean show signs of wilting when the sun is bright after continuous rain.
3. Plant factors: Rate of transpiration, expanse of the root system and permeability
characteristics of root cells are the principal plant factors that influence water absorption.
Root growth, nature of the root system and distribution of the roots in the soil decides the
volume of water available to the plants. A plant with deeper root system has access to a
greater volume of water than a shallow rooted plant which can suffer from water stress
even when the water is present in the deeper layers of the soil. New growth of roots is
always desirable for better and greater absorption of water by the plants.
Water deficit and plant responses
Plants absorb water to do the normal function of nutrient absorption, transpiration and
metabolic activities leading to growth and yield. When available soil water is not enough to
meet the normal transpiration losses, a deficit in plant is created and under severe cases the
growth ceases and finally death of plants occur.
Soil water deficit and plant stress condition:
The primary effect of water stress is the reduction of cell growth and cell wall
synthesis. This is followed by changes in various biochemical processes such as reduction in
carbohydrate assimilation, protein synthesis and nitrate reductase activity and accumulation
of abscisic acid (ABA) and prolein. Water stress affects the growth and yield of plants in
various ways such as root development, tiller formation, branching, flowering, seed
formation and seed development are affected. Water stress causes reduction in internodal
length of sugarcane, leaf area per plant in tobacco, incomplete filling of grains in cereals and
fruit drop. Protein content of wheat grains and nicotine content of tobacco leaves increases
with an increase in stress. Yields of vegetables and fodder in which succulent vegetative parts
are wanted, are depressed considerably even by mild stress. Occurrence of stress in certain
plant stages when the cell division and differentiation are significant, plants undergo some
significant changes in their growth behaviour. A water deficit during crown root initiation
stage in wheat, spike development stage in cereals and branching, flowering or seed
development stages of crop plants is harmful and depresses the growth and yield
significantly.
The field capacity and wilting point are generally considered as the uppermost and
lower most limits of available soil water. The soil water within these two limits is termed as
available soil water and the range of the available soil water between these two water
constants is termed as available soil water range. It is also observed that yield declines
drastically when the available soil water falls below a particular point within this range. This
point is referred to as critical soil water tension for crop yield. Crops give optimum yield in
most cases when the soil water is maintained from field capacity to 50% of available soil
water and sometimes from field capacity to 25% of available soil water. The upper region of
available soil water range provides the maximum amount of available water in the plants. It is
usually within the soil water tension of one to two atmospheres that most of the available soil
water is released.

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 Chapter 7

Crop water requirement and water use efficiency

Evapotranspiration
The crop water need (ET crop) is defined as the depth (or amount) of water
needed to meet the water loss through evapotranspiration. In other words, it is the amount
of water needed by the various crops to grow optimally.
The crop water need always refers to a crop grown under optimal conditions, i.e. a
uniform crop, actively growing, completely shading the ground, free of diseases, and
favourable soil conditions (including fertility and water). The crop thus reaches its full
production potential under the given environment.
The crop water need mainly depends on:
 The climate: in a sunny and hot climate crops need more water per day than in a
cloudy and cool climate
 The crop type: crops like maize or sugarcane need more water than crops like millet or
sorghum
 The growth stage of the crop; fully grown crops need more water than crops that have
just been planted.
Evapotranspiration (ET = Evaporation + Transpiration)
Evaporation is a diffusive process by which water from natural surfaces, such as free
water surface, bare soil, from live or dead vegetation foliage (intercepted water, dewfall,
guttation etc) is lost in the form of vapour to the atmosphere. It is one of the basic
components of hydrologic cycle. Likewise transpiration is a process by which water is lost in
the form of vapour through plant surfaces, particularly leaves. In this process water is
essentially absorbed by the plant roots due to water potential gradients and it moves upward
through the stem and is ultimately lost into the atmosphere through numerous minute stomata
in the plant leaves. It is basically an evaporation process.
Thus, evapotranspiration is a combined loss of water from the soil (evaporation) and
plant (transpiration) surfaces to the atmosphere through vaporization of liquid water, and is
expressed in depth per unit time (for example mm/day). Quantification of evapotranspiration
is required in the context of many issues:
1. Management of water resources in agriculture.
2. Designing of irrigation projects on sound economic basis.
3. Fixing cropping patterns and working out the irrigation requirements of crops.
4. Scheduling of irritations.
5. Classifying regions climatologically for agriculture
Consumptive use
The term consumptive use (CU) is used to designate the sum of losses due to evaporation
+ transpiration from the cropped field as well as that water utilized by the plants in its
metabolic activities for building up of the plant tissues. Since the water used in the actual
metabolic processes is insignificant (about 1% of evapotranspiration losses) the term
consumptive use is generally taken equivalent to evapotranspiration. It is expressed similar to
ET as depth of water per unit time i.e., mm/day or cm/day.

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 a) Daily consumptive use: It is the total amount of the water used in ET plus water
usedin metabolic activities by a crop during a single day or 24-hours period and is
expressed in mm/day or cm/day.
b) Seasonal consumptive use: The total amount of water used by the crop in ET and
metabolic activities for building up of plant tissues during its total growing season. It
is essential to evaluate and decide the seasonal water supply to a command area of an
irrigation project. It is important for planning the cropping pattern and cropping
sequencein an area. It is expressed as surface depth of water in cm per hectare or
hectare – cm.
c) Peak period consumptive use: The average daily water use rates in terms of ET plus
that consumed in metabolic process during the highest consumptive use period (6 – 10
days) of the season is called peak period consumptive use rate. This is the design rate
to be used in planning an irrigation system. The peak-use consumptive period
generally occurs when the vegetation is abundant, temperature is high and crops are in
flowering stage. The peak use rate for a shorter period of two to three days is higher
than that for a longer period and is lower than the peak daily use rate. The peak use
period is usually shorter in shallow soil and in soil with low water holding capacity. It
is also shorter for crops with shallow root system.

Potential evapotranspiration
It refers to the highest rate of evapotranspiration by a short and actively growing crop
or vegetation with abundant foliage completely shading the ground surface and abundant soil
water supply under a given climate.
(The potential evapotranspiration concept was first introduced in the late 1940s and
50s by Penman and it is defined as “the amount of water transpired in a given time by a short
green crop, completely shading the ground, of uniform height and with adequate water status
in the soil profile”. Note that in the definition of potential evapotranspiration, the
evapotranspiration rate is not related to a specific crop. The main confusion with the
potential evapotranspiration definition is that there are many types of horticultural and
agronomic crops that fit into the description of short green crop.)
Reference crop evapotranspiration
Doorenbos and Pruitt (1975) used the term reference crop evapotranspiration. It refers
to the rate of evapotranspiration from an extended surface of 8 – 15 cm tall green grass cover
of uniform height, actively growing, completely shading the ground and not short of water.
ET0 can be computed with any of the empirical formulae such as Blaney – Criddle,
Modified Penman, Radiation and Pan evaporation methods for a month or a shorter period.
(Reference evapotranspiration is defined as "the rate of evapotranspiration from a
hypothetical reference crop with an assumed crop height of 0.12 m (4.72 in), a fixed surface
resistance of 70 sec m-1 (70 sec 3.2ft-1) and an albedo of 0.23, closely resembling the
evapotranspiration from an extensive surface of green grass of uniform height, actively
growing, well-watered, and completely shading the ground". In the reference
evapotranspiration definition, the grass is specifically defined as the reference crop and this
crop is assumed to be free of water stress and diseases. In the literature, the terms “reference
evapotranspiration” and “reference crop evapotranspiration” have been used

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interchangeably and they both represent the same evapotranspiration rate from a short,
green grass surface. Historically two main crops have been used as the reference crop, grass
and alfalfa.)
Actual crop evapotranspiration
It refers to the rate of evapotranspiration by a particular crop in a given period under
prevailing soil water and atmospheric conditions. The ET crop varies under different soil water
and atmospheric conditions and at different stages of crop growth, geographic locations and
periods of the year.
ETcrop = Kc × ET0
Changes in the values of Evapotranspiration components during crop period
The two components of evapotranspiration are evaporation and transpiration.
Transpiration loss accounts for the largest portion of ET. The evaporation occurring from the
time of sowing to germination of the crop forms wholly the ET. After germination of the
crop, transpiration becomes a constituent part of ET. Initially when the crop cover is
insignificant, evaporation exceeds transpiration. As the crop grows there is development of
vegetative cover shading the ground, transpiration rate goes on increasing with parallel
decrease in evaporation rate. At this stage ET reaches its peak and further vegetative
development does not bring any change in evapotranspiration. At maturity the transpiration
and ET fall rapidly with simultaneous increase in evaporation.
Water Requirement
It is defined as the quantity of water regardless of its source, required by a crop or
diversified pattern of crops in a given period of time for its normal growth & development
under field conditions at a given place. In other words it is the total quantity of water required
to mature an adequately irrigated crop. It is expressed in depth per unit time. Water
requirement, if considered as a demand, it includes the quantity of water needed to meet the
losses due to evapotranspiration (ET), plus the losses during the application of irrigation
water (unavoidable losses) and the additional quantity of water required for special operations
such as land preparation, transplanting, leaching of salts below the crop root zone, frost
control etc.
WR = ET or CU + Application Losses + Special needs
Water requirement of crops can also be expressed in terms of source of water-
WR = IR + EP + ∆SW
When the water requirement is supplied entirely by irrigation, irrigation requirement and
water requirement will be same.
Water requirement of crops
In crop fields, transpiration and evaporation go on simultaneously changing with time
after rain or irrigation. Owing to the variable crop structures, root systems, nature of soils and
soil conditions and energy status of water in plants and soil variable quantity of water escapes
in to the atmosphere as evapotranspiration.
Water Requirement of Different Crops
Water requirement of crops refers to the amount of water required to raise a
successful crop in a given period. It comprises thewater lost as evaporation from crop field,
water transpired and metabolically used by crop plants, water lost during application which is
economically unavoidable and the water used for special purpose such as land preparation,

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puddling of soil, salt leaching, retting of jute, harvesting of potato, ginger and groundnut and
germinating seeds etc. It is usually expressed as the surface depth of water in mm or cm.
WR = ET + Wm + Wu + Ws
Where, WR – water requirement of a crop
E – Evaporation, T – Transpiration, Wm – Water used for metabolic activities by the plants,
Wu – Unavoidable water loss during application, Ws – Water applied for special operations.
Amount of water required by a crop in its whole production period is called water
requirement. The amount of water taken by crops vary considerably.
Crop Water Requirement (mm)
Puddled Rice 1800-2000
Direct Seeded rice 1100 -1200
Wheat 350-400
Rabi Maize 400-450
Jowar 450-500
Barley 200-250
Chickpea 150-200
Lentil 120-180
Field Pea 200-250
Summer Greengram 250-300
Summer/Post Kharif Black Gram 270-330
Pigeonpea 210-280
Mustard 180-220
Linseed 250-310
Groundnut 400-450
Soybean 400-450
Sunflower 350-500
Sugarcane 1500-2500
Ragi 400-450
Potato 500-600
Onion 450-550
Berseem 500-700
Water required by the crops is essentially met from water sources such as rainfall,
irrigation, soil water and ground water.
WR = P + I + ∆SW + ∆GW – (R+DP)
WR = EP + I + ∆SW + ∆GW
Where WR – water requirement
EP – effective precipitation
∆SW – change in soil water storage
∆GW – ground water contribution
I – Gross Irrigation requirement of the crop
Consumptive use or consumptive water use:
It is the sum of the volumes of water used by vegetation (crop) over a given area in producing
plant tissue, in transpiration (T), plus that evaporated (E) from adjacent soil or from moisture

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intercepted on plant foliage. Since the volume of water used in producing plant tissue is
negligible (<1%) compared with the volumes used in E and T, the CU can be taken to be
approximately equal to ET.
Effective precipitation– The proportion of rainfall that is stored in the rhizosphere.
EP = P – (R+DP)
Where, EP = Effective precipitation
P – Precipitation
R – Runoff
DP – Deep percolation
Part of the rain may be lost as a surface run-off, deep percolation below the root zone of the
crop or by evaporation of rain intercepted by foliage. When rainfall is of high intensity, only
a portion of rainfall can enter the soil and stored in the root zone. In case of light rains of low
intensity depending on the amount of moisture already present in the root zone of the crop,
even the amount and intensity of rainfall, rate of consumption use, moisture storage capacity
of soil, initial moisture content and infiltration rate of the soil. It is difficult to predict
effective rainfall because of variation of soils, crops, topography and climate. However, in
India it is assumed that 70% of the average seasonal rainfall to be effective in arid and semi-
arid regions while 50% considered effective humid regions.
Irrigation requirement:
It is the total amount of water applied to a cropped field for supplementing effective
rainfall, soil profile and groundwater contribution to meet the crop water requirements for
optimum growth. In other words irrigation requirement is exclusive of ER + ∆SW + Gws
IR =WR – (EP + ∆SW)
Net irrigation requirement (NIR):
It is the amount of water, exclusive of precipitation and profile soil moisture contribution,
required for optimum crop production. In other words, it is the amount of irrigation water that
must be stored in the root zone to meet the consumptive use requirement of a crop. In other
words, 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 in depth or percentage soil
moisture between field capacity and the soil moisture content in the root zone before starting
irrigation.
NIR = ∑ M2i – M1i ×Ai × Di
100
NIR = net amount of irrigation water to be applied at each irrigation
n = number of soil layers considered in root zone depth D
M1i = soil moisture percentage at first sampling
M2i = soil moisture percentage at second sampling
Ai = Apparent specific gravity of ith soil layer
Di = depth of ith soil layer.

Gross irrigation requirement:(I) refers to the amount of water applied to the field from the
start of land preparation to the harvest of the crops together with the water lost in conveyance
through distributaries and field channels during irrigation to the crop field.
GIR = NIR / Irrigation efficiency

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Seasonal irrigation requirement: It can be obtained by adding NRI values at each
irrigation.

Irrigation efficiency
Irrigation efficiency is generally defined as the ratio of water output to the water input i.e. the
ratio or percentage of the irrigation water consumed by the crop (Wc) to the water delivered
to the field (Wf).
Ei = Wc/Wf × 100
Irrigation efficiency indicates how efficiently the available irrigation water is used for crop
production.
Factors influencing irrigation efficiencies
 Finer the soil texture higher the surface runoff and lesser the deep percolation losses
compared with coarse sandy soils.
 Irregular land surface, compact and shallow soils reduce the irrigation efficiency.
 Irrigation efficiency will be low with small or too large irrigation streams.
 Long irrigation runs and excessive single applications contribute to large losses of
irrigation water.
Types of irrigation efficiencies
1. Reservoir Storage Efficiency: It measures the fraction of storage utilised for
irrigation. It also measures the volume of water lost or retained in the reservoir.
Es = Vol. of water delivered from the reservoir/ Vol. of water delivered to the reservoir for
irrigation
2. Water Conveyance efficiency: Conveyance losses include direct evaporation or deep
seepage in transit from source of supply to the point of supply. It is the ratio between
water delivered to the irrigated plot and total quantity delivered from source. It is
mathematically expressed as:
Ec = Wf/Wd × 100
Where:
Ec = Water conveyance efficiency (%)
Wf = Water delivered to the plot (l/sec)
Wd = Water delivered from the source (l/sec)
In irrigation distribution network i.e., distributaries, water courses, etc., the
waterconveyance efficiency is used to find out what percentage of the released water at the
head gate actually reaches the farm and is an indicator of the seepage losses in the
conveyance losses. Thus a low Ec implies that much of the water released from the source is
lost due to seepage in transit from source to the field.
3. Water Application Efficiency: Operational or delivery losses due to inefficient water
handling during conveyance and losses on farm due to uneven distribution, poor
handling, evaporation and deep percolation further reduces the efficiency of irrigation
water. It is the ratio between quantity of water stored in the root zone and water
delivered to the plot. It is mathematically expressed as:
Ea = Ws/ Wf × 100
Where:

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 Ea = Water application efficiency (%)
Ws = Water stored in the root zone (cm)
Wf = Water delivered to the plot (cm)
The concept of water application efficiency can be applied to a project, a farm or a field
to evaluate the irrigation practices. All the factors, which influence the design of thesurface
irrigation system therefore directly, affect the application efficiency. Thus a low Eaimplies
that much of the applied water has been lost due to deep percolation or runoff.
4. Water Distribution Efficiency: Uneven surface distribution due to uneven land
levelling, leaves some pockets unirrigated in the field, unless excess irrigation water is
applied. This excess water lowers the irrigation efficiency.It is the ratio between the
average numerical deviations in depth of water stored from average depth stored
during irrigation (y) and the average depth stored during irrigation (d). It is
mathematically expressed as:
Ed = [1 – y/d] × 100
Where:
y = Average numerical deviation in depth of water stored from average depth stored
during irrigation
d = Average depth of water stored during irrigation
It is a measure of water distribution within the field. Low distribution efficiencymeans
non-uniformity in the irrigation water penetration in the soil due to uneven landlevelling. The
irrigation water cannot flow over the soil smoothly. There are low patcheswhere water will
penetrate more and there are high patches where water cannot reach.This leaves some spots
unirrigated unless excess irrigation water is applied. Excess waterapplication lowers
irrigation efficiency.
5. Water Storage Efficiency: It indicates how efficiently the irrigation has met the crop
needs. If only a fraction of the water needed is applied, Ea is 100 percent.
Consequently, the storage efficiency (Es) is used to calculate how efficiently the soil –
water deficit has been removed by the irrigation. When only a fraction of the needed
water is being applied, the application efficiency is automatically 100%. Under such
conditions, this will be a very poor irrigation practice since only a fraction of the
water needed by the crop is added, although the application efficiency is 100%. Thus
water storage efficiency is the ratio between water stored in the root zone (Ws) and
the water needed (Wn) in the root zone prior to irrigation.
Es = Ws/ Wn × 100
Where:
Es = Water storage efficiency (%)
Ws = Water stored in the root zone (cm)
Wn = Water needed in the root zone (cm)
The concept of water storage efficiency is useful in evaluating the irrigation methods
especially under limited water supply conditions. It is also important when soils with low
infiltration rates are to be irrigated. In such cases adequate time is to be allowed for the
required amount of water to penetrate into the soil. This concept is also useful when salt
balance of the root zone has to be taken into consideration and leaching requirement needs to
be calculated. In such cases higher water storage efficiencies must be desirable to leach out

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the salts from the root zone. A low storage efficiency implies that water application is much
less than actually needed. In a stretch of land one may get poor application efficiency for the
upstream part and poor storage efficiency for the downstream section.
6. Water Use Efficiency: It is determined to evaluate the benefit of applied water
through economic crop production. It is described in the following two ways:
i) Field water use efficiency: It is defined as the ratio of the amount of economic crop
yield to the amount of water required for crop growing.
Eu = Y/WR
ii) Crop water use efficiency: It is defined as the ratio of the amount of economic crop
yield to the amount of water consumptively used by the crop.
ECU = Y/CU or ET
7. Project Efficiency:It is the ratio between the average depth of water stored in the root
zone during irrigation and water diverted from the reservoir. It is mathematically
expressed as:
Ep = Ws/Wr × 100
Where:
Ep = Project efficiency (%)
Ws = Water stored in the root zone (cm)
Wr = Water diverted from the reservoir (cm)
The overall irrigation efficiency of a farm is a product of:
Ef = Ea × Es × Ed
i.e. Ef = Water Application Efficiency × Water Storage Efficiency × Water Distribution
Efficiency
The overall irrigation efficiency for a project (i.e., considering irrigation channels) is the
product of Ep = Ea × Es × Ed × Ec

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 Chapter 8

Scheduling of irrigation and methods of irrigation

Scheduling Irrigation
It is a means of supplying water in accordance with the crop needs. It a process of
determining when to irrigate and how much water to apply.

Approaches for scheduling irrigation

Crops differ in their tolerance to depletion of soil moisture. Crops such as rice respond to
continuous land submergence or very high frequency irrigation. Some crops such as potato
and most winter vegetables, require moist conditions (<40 to 50 DASM). Other crops such as
small millets and fruit trees and several others with deep root system may show little
reduction in yield until nearly all the available water has been depleted in the soil depth from
which extraction has been most rapid. Irrigation scheduling decisions are to be made for
mainly two situations:
1. Where water is expensive, irrigation should be scheduled to maximise crop
production per unit of applied water.
2. Where good land is scarcer than water, irrigation should be scheduled to maximise
crop production per unit of planted area.

Advantages of Irrigation Scheduling

Irrigation scheduling offers several advantages:
a) It enables the farmer to schedule water rotation among the various fields to minimize
crop water stress and maximize yields.
b) It reduces the farmer‟s cost of water and labor through fewer irrigations, thereby
making maximum use of soil moisture storage.
c) It lowers fertilizer costs by holding surface runoff and deep percolation (leaching) to a
minimum.
d) It increases net returns by increasing crop yields and crop quality.
e) It minimizes water-logging problems by reducing the drainage requirements.
f) It assists in controlling root zone salinity problems through controlled leaching.
g) It results in additional returns by using the “saved” water to irrigate non-cash crops
that otherwise would not be irrigated during water-short periods.

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The different approaches include:

i. Soil moisture regime approach:

In these methods, soil moisture content is estimated to know the deficit available soil
moisture at which it is proposed to irrigate based on predetermined soil moisture content to
bring the soil to field capacity.

1) Soil water content approach: Irrigation scheduling on the basis of gravimetric soil –
water content is based on two assumptions: assuming threshold moisture content
below which the plant growth is adversely affected or determination of optimum
fixed interval between two successive irrigations. Both these assumptions vary with
soil texture. As, such, the soil water content approach may not be an ideal approach
for irrigation scheduling.
2) Depletion of available soil water: This approach consists of determining the lower
limit of available water in an assumed shallow root zone of the crops at which
irrigation must be applied to avoid yield reduction. Soil moisture content is
estimated by gravimetric sampling.
3) Soil water tension or soil moisture potential: Available water in soils at specific
soil depths can be measured in terms of corresponding range of soil water potential
or soil water tension by tensiometers/ irrometers or electrical resistance blocks for
scheduling irrigation. Soil moisture tension approach is more useful for orchards and
vegetable crop, particularly on coarse textured soils, where most of the ASM is held
at low tensions. In soils with higher moisture holding capacity, properly calibrated
gypsum blocks can be used for irrigation scheduling. One of the major drawbacks of
this method is that this approach does not indicate the amount of irrigation to be
applied directly but require soil moisture characteristic curve to interpret the soil
moisture content.
4) Feel and appearance method:With experience, farmer can judge soil water content
by the feel and also appearance of the soil. Soil samples are taken with a probe or
soil auger from each quarter of the root zone depth, formed into a ball, tossed into air
and caught in one hand. From the description given in Table 1, available moisture
percentage is estimated for different textures of soils. Considerable experience and
judgment are necessary to estimate available soil moisture content in the sample
within reasonable accuracy.

Available Coarse texture Moderately Medium Fine texture (clay

soil (loamy sand) coarse texture texture (loamy loamy and silty clay
moisture (sandy loamy) and silt loamy) loamy)
range
Field On squeezing, no Similar symptoms
capacity free water appears
(100%) on soil, but wet
outline is left on
hand

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75 to Tends to stick Forms weak ball, Forms a ball, Easily ribbons out
100% together slightly, breaks easily, very pliable, between fingers, has
sometimes forms a don‟t slick slicks readily slick feeling
very weak ball
under pressure
50 to 75% Appears to be dry Tends to form aForms a ball Forms a ball, ribbons out
don‟t form a ball ball under somewhat between thumb and fore-
with pressure pressure but plastic, some- finger
seldom holds times slick
together slightly with
pressure
25 to 50% As above, but ball Appears to be Somewhat Somewhat pliable, forms
is formed by dry, don‟t form a crumbly but a ball under pressure
squeezing very ball unless holds together
firmly squeezed very with pressure
firmly
0 to 25% Dry, loose, single Dry, loose, flows Powdery dry, Hard, baked, cracked,
grained flows through fingers sometimes sometimes has loose
through fingers slightly crusted crumbs on surface.
but easily
broken down
into powdery
conditions.

ii. Climatological approach

1) PET measurement: PET can be estimated from any of the empirical formulas and
irrigation can be scheduled if the level of DASM in the root zone and evaporation
during the crop period is known. PET can be estimated by several techniques viz.,
lysimetric methods, energy balance, aerodynamic approach, combination of energy
balance and empirical formulae etc., and irrigation‟s can be scheduled conveniently
based on the knowledge of PET or water use rates of crops over short time intervals of
crop growth.
2) Cumulative pan evaporation: Earlier investigations have shown that transpiration of a
crop is closely related to free water evaporation from an open pan evaporimeter. Thus,
the open pan evaporimeter being simple and as they incorporate the effects of all
climatic parameters into a single entity i.e., pan evaporation could be used as a guide
for scheduling irrigation‟s to crops. For example,
i) Wheat required 75 to 100 mm CPE at Ludhiana
ii) Sugarcane required 75 mm CPE in Maharashtra
iii) Greengram required 180 mm CPE at Ludhiana
iv) Sunflower required 60 mm CPE at Bangalore
3) IW/CPE approach: Pan Evaporation (Epan) can be used for scheduling irrigations.
Priharet al (1974) suggested relatively practical approach of IW/CPE as the basis for
scheduling irrigation. An IW/CPE ration of 1.0 indicates scheduling irrigation with
quantity of water equal to that lost in evaporation. If 5.0 cm of irrigation water is
applied when the cumulative pan evaporation is 10 cm, the ratio will be 0.5 (5/10). This
approach has been evaluated extensively to develop optimum irrigation schedules for
different crops and agro climatic regions of the country.

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iii. Plant indicator approaches:
Any physical measurement related directly or indirectly to plant water deficits and
which responds readily to integrated influence of soil – water – plant factors and
evaporative demand of the atmosphere may serve as a criterion for timing of irrigation
to crops.

1) Visual plant symptoms: Symptoms of plant wilting such as drooping, curling and
rolling of leaves in maize are visual indicators of plant needs for water. Change in
foliage colour and leaf angle is used as indicator to irrigate beans. Water stress in some
crops lead to appearance of carotenoid and anthocyanin pigments, shortening of
internodes in sugarcane and cotton, retardation of stem elongation in grapes lack of new
growth in terminal growth points of almond can be used as indices for scheduling
irrigation to crops. Although this approach is simple and rapid, it suffers from many
drawbacks like error in judgement, poor wilting of certain crops under moderate to
severe stress and growth reduction in some crops even before the plant is visibly wilted.
Adoption of this approach is constrained by inadequate standardization of techniques,
nonavailability and high cost of equipment, selection of suitable growth parameters,
lack of precision in growth measurements and variation of growth - water relationship
with stages.
2) Plant water content or plant water potential: Plant water content is generally indexed
from measurements of relative leaf water content and leaf water potential. Values of
these parameters at any time of the day depend upon the time lag between evaporative
demand of the atmosphere and uptake rate by the crop. As these values fall below
certain critical limits, specific to plant species and their growth stages, the important
physiological and growth phenomenon are adversely affected. Relative water content is
the actual water content of the leaf or plant when sampled relative to the water at
saturation or turgid.

RWC = (fresh weight - dry weight)/ (turgid weight - dry weight)

3) Plant and Canopy temperature: Leaf or canopy temperature is a sensitive index to

plant water status. Canopy temperature at 1400 hrs is a better index of plant water
status than that recorded at other times of the day. It is believed that difference between
canopy temperature and air temperature is a better criterion of water stress than plant
temperature alone. Jackson et al (1977) suggested the use of Stress Degree Day Index
computed as ∑(canopy temperature – midday air temperature) for a period for
determination of timings and amount of irrigation.
4) Critical crop growth stages: As a result of extensive experimentation, critical growth
stages (moisture sensitive stages) of various crops for water demand have been
identified. If irrigation water is scarce, irrigation are to be scheduled at least at these
critical growth stages for maximum water use efficiency

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 Crops Critical Stages
Rice Initial tillering, flowering
Most critical stage: Crown root initiation, tillering,
Wheat
jointing,. booting, flowering, milk and dough stages
Wheat Boot stage; dough stage
Pulses Flowering and podding.
Peas Pre bloom stage.
Berseem After each cutting.
Gram Pre flowering and flowering.
Pigeonpea Flower initiation, pod filling.
Sorghum Initial seedling, pre flowering, flowering, grain formation.
Barley Boot stage, dough stage
Maize Early vegetative, taselling and silking stage.

5) Soil cum mini plot technique: In this method, 1x1x1 m size of pit is dug in the
middle of the field. About 5% of sand (by volume) is added to the pit, mixed well with
soil and the pit is filled up in natural order. Crops are grown normally in all areas
including pit area. The plants in the pit show wilting symptoms earlier than the other
areas. Irrigation is scheduled as soon as wilting symptoms appear on the plants in the
pit.
6) Sowing high seed rate:In an elevated area, one square metre plot is selected and crop is
grown with four times thicker than the normal seed rate. Because of high plant density,
plants show wilting symptoms earlier than in the rest of the crop area indicating the
need of scheduling of irrigation.
7) Indicator plants: there are few references about use of indicator plants as a guide for
scheduling irrigation. In wheat scheduling irrigation on the basis of wilting symptoms
in maize and sunflower gave the highest grain yields.

Comparison of the above irrigation approaches leads to the conclusion that an

estimation of permissible soil moisture depletion is essential before the crop yield starts
declining. Among the approaches, the IW/CPE ratio method appears to be ideal because of its
simplicity when the water supply is adequate. When irrigation water is inadequate, irrigation
may be scheduled at critical growth stages or at variable IW/CPE ratios. However the
emphasis should lie on optimum yield with high water use efficiency rather than potential
yield.

Methods of irrigation , surface, sprinkler and drip irrigation

Applications of irrigation water to cropped field by different types of layouts are

called as irrigation methods. The methods of irrigation initially might have been started to
check the over flow of water from one field to another. But today, it has become necessary to
save the water by proper methods to arrest run-off loss, percolation loss, evaporation loss etc.,
and to optimize the crop water need. Hence, irrigation method can be defined as the way in
which the water is applied to the cropped field without much application and other losses,

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with an objective of applying water effectively to facilitate better environment for crop
growth.

Classification of Irrigation Methods

The irrigation methods are broadly classified as:
1. Surface method or gravity method of irrigation
A. Complete flooding of soil surface
i)Wild flooding ii) Border or border strip (a. Straight border b. Contour border)
iii)Check or check basin( a. rectangular check b. contour check)
iv) Contour ditch /contour channel irrigation
B. Partial flooding of soil surface
i) Furrow irrigation (a. Straight level furrow b. Straight graded furrow c. Contour
furrow d. Alternate furrow e. Raised bed furrow f. Corrugation g Basin or
ring irrigation)
C. Surge irrigation

2. Sub surface or sub irrigation

i) Irrigation by lateral supply trenches ii) Irrigation by underground pipe or tiles

3. Pressurized or micro irrigation - Drip irrigation, sprinkler irrigation and rain gun
irrigation.

I. Surface or gravity irrigation

It is the common method of irrigation practiced all over the world. In this method,
water is applied directly to the surface by providing some checks to the water flow:
Advantages
• Easy to maintain
• Low cost
• Technical skill is not required.
Prerequisites
• Uniform soil
• Smoothness of field surface or levelled surface
• Adequate quantity of water.
Classification
1. Border strip method - The field is divided into number of long parallel strips by
providing small parallel earthen bunds or levees or dykes along both sides of the strips. The
end along the strip may or may not be closed, which is based on the length of the strips. If the
length of the strip is very long, the end will be closed to have a uniform distribution and to
avoid run off loss. Each strip is irrigated independently from upper end (turned on) and water
flow as thin sheet and uniformly spread along the strips. The water is turned off when the
required volume is delivered to the strip. The application efficiency of this system is 75–85%.
Crop - All closely spaced crops like pulses, wheat, barley, alfalfa, berseem, grasses, ragi, and
small grains.

2. Check basin method (beds and channel) - It is the common and simple method of
irrigation mainly adopted in levelled land surface. It is also known as Beds and channel
method of irrigation. The land is divided into small basins/beds. The area of basin is
surrounded by earthen bunds or levees or dykes. The applied water is kept within the basin
and not allowed for run off. This is the most common method adopted for most of the crops.

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The size of the levees or ridges or bunds depends upon the depth of water to be impounded in
the basin. The water is turned on the upper side and after applying the required quantity of
water it is turned off.

Fig. 5.1 Check basin method of irrigation

Crops - Cereals, millets, pulses, oilseeds.

3. Basin method - Basin method of irrigation is used in soil submergence method of

irrigation in low land rice, bunded rainfed rice and forage grasses, where water is stagnated to
the required depth by providing bunds on all the sides to sufficient width and height. The
optimum size for efficient water management to rice crop is 0.25-0.40 ha. The field is to be
levelled thoroughly for uniform depth of water. Provision of separate irrigation and drainage
channels is more efficient than field-to-field irrigation.
4. Ring basin - This method is mostly adopted for wide spaced orchard crops. The rings are
circular basins formed around the individual trees. The rings between trees are interlinked
with main lead channel by sub channels to get water to the individual rings. As water is
allowed in rings only, wastage of water spreading the whole interspaces of trees as in the
usual flooding irrigation method is reduced. Weed growth in the interspaces around the rings
are discouraged. This method ensures sufficient moisture in the root zone and saves lot of
irrigation water.

Fig 5.2 Ring basin

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B. Partial flooding of soil surface
1. Furrow method of irrigation - It is the common method adopted for row planted crops
like cotton, maize, sugarcane, potato, beetroot, onion, sorghum, vegetable crops etc. In this
method, small evenly spaced shallow furrows or channels are formed in the beds. Another
method of furrow irrigation is forming alternate ridges and furrows to regulate water. The
water is turned at the high end and conveyed through smaller channels. Water applied in
furrows infiltrate slowly into the soil and spread laterally to wet the area between furrows.
2. Straight furrow - Best suited to soils where land slope does not exceed 0.75%.
3. Contour furrow - This method is similar to graded and level furrow method. Furrow
carries water across slopping field rather than downwards. They are designed to fit the
topography of field. Furrows are given a gentle slope along its length as in graded furrow.
Field supply channels run down the land slope to feed the contour furrow and are provided
with erosion control structure. Successfully used in all irrigable soils. All row crops including
grains, vegetables and cash crops are adapted to this method. Light soil can be irrigated
successfully across slopes up to 5% slope. Up to 8-10% can be irrigated by contour furrow.
Contour furrow may be used on all types of soil except in light sandy soil and soil that crack.
4. Corrugation irrigation - It consists of running water in small furrows, which direct the
flow down the slope commonly used for irrigation in non-cultivated close growing crops such
as small grains, pasture on steep slopes. Corrugation can be made with a simple bamboo
corrugation or cultivators equipped with small furrows. Corrugations are „V‟ or „U‟ shaped
channels about 6-10 cm deep spaced 40-75 cm apart. This method is not recommended for
saline soil or for saline water irrigation. The permissible length of corrugation varies from 15
cm within light textured soil with slopes of 2-4% to about 150 cm in heavy texture soil up to
2% slope.
5. Surge irrigation - Surge irrigation is a method of surface irrigation through furrows or
border strips wherein water is applied intermittently in a series of relatively short on and off
time periods during the irrigation (Humphrey, 1989). Water is let into a long furrows or
border strips in an intermittent flow instead of conventional continuous flow. Each flow is
termed as a surge.
Surge irrigation practiced under favourable conditions can improve the performance of
surface irrigation system compared to the other methods of surface irrigation. Irrigation is
given in an on-off cycle or by cut back method. The cycle time means the time from the
beginning of one surge to the beginning of next surge. Cycle ratio is the ratio of flow time
(continue) to the cycle time. Assuming the cycle time as 20 minutes and cycle ratio as 1:2
(0.5), the on-time is 10 minutes and off time is 10 minutes. This cycle ratio can also be the
ratio of on-time and off-time as 1:1, if the on time is 10 minutes. Water is allowed for 10
minutes and stopped for 10 minutes. This 20 minutes is the surge time or cycle time. This
surge is repeated until the water reaches the whole furrow or strip.

Fig. 5.3 Contour irrigation Fig. 5.4 Graded contour-furrow Irrigation

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Fig. 5.5 Corrugated irrigation

Fig. 5.6 Graded or level-furrow irrigation: Different types of furrow irrigation

II. Subsurface irrigation

Water is applied below the ground surface through the network of pipes or some devices. The
main aim of this type of irrigation is to reduce the evaporation loss and to maintain an
artificial water table near the root zone of the crop.
Suitability - It is mainly suitable for the high temperature area where ET losses are very high
wherein controlling and maintenance of surface water and application is very difficult.
Pitcher pot irrigation method - It is one way of applying water below the ground or soil
surface. In this method, in a mud pot, some small holes are made and the holes are closed by
either threads or material, which is able to conduct water very quickly. The pots are kept
around the root zone in pits made for it. The pits are completely covered tightly with sand
mulch mix. The pots are filled with water and closed. The water slowly penetrates to root
zone through the holes and wet the root zone area. This method is mostly suitable for widely
spaced tree crops under water scarce conditions.
III. Pressurized irrigation methods (Micro irrigation)
It includes both sprinkler and drip irrigation methods where water is applied through network
of pipelines by means of pressure devices.
1. Sprinkler irrigation system/point source method - In this method the irrigation water is
sprayed to the air and allowed to fall on-the ground surface more or less resembling rainfall.
The sprinkling of water or spray of water is made by pumping water under pressure through
network of pipelines and allowing to eject out by means of small orifices or nozzles or holes.
The water required by the crop is applied in the form of spray by using some devices,
wherein the water application rate should be somewhat lesser than the soil infiltration rate to
avoid run off or stagnation of water in the field.
Suitability and advantages
• It is highly suitable for sandy soil where infiltration rate is more.
• For shallow soil where levelling operation is technically not possible.

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• For lands having undulating topography or steep slopes where levelling is economically not
advisable.
• Irrigation steam size is very small where surface flow is low.
• It is almost suitable for all crops except crops like rice, which needs stagnation of water, but
under water scarcity it can be tried for rice also. Reproductive phase in cotton sprinkler
irrigation is not advisable.
• Application of fertilizer (fertigation), pesticides (pestigation) and herbicides (herbigation)
are possible through irrigation systems which reduce labour cost and increase the use
efficiency of any chemical.
• It controls crop canopy temperature.
• In crust soil, it facilitates early germination and establishment by means of light and
frequent irrigation.
• Wastage of land for basin, ridges and furrows and irrigation channels are reduced.

Fig. 5.7 Components of a sprinkler irrigation system.

Disadvantages
In heavy windy areas the distribution efficiency is reduced due to drifting of water droplets.
In saline water conditions, it causes leaf burns besides clogging and corrosion of the pipeline.
Continuous power supply is required to operate the system to maintain pressure. It is very
costly to install and to maintain. Uniformity of application is difficult due to over application
or neglected corners in the field.
Major components
• Pump set
• Network of pipelines (main, lateral, sub lateral, etc.)
• Riser pipes with tripod stand
• Sprinkler head
Classification - There are two types viz., (1) Rotation head system and (2) Perforated pipe
system.
(a) Rotating head system - A special device to sprinkle the water called “Sprinkler Head” is
used in this system. The sprinkler head consists of small nozzles and metal ring or vane with
a spring. The water ejected through the nozzle strike the metal ring which changes its
direction by the help of the spring attached to this which in turn causes the spray of water in

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all directions. The whole sprinkler head system is fitted on the riser pipe, which is erected
from lateral pipes at uniform intervals. Rotating sprinkler heads are of two types viz., single
nozzle type and twin nozzle type (main nozzle and driving nozzle).
(b) Perforated pipes system - In this method, small holes are made in lateral pipes based on
the nature of the crops to distribute water uniformly.
Uniform distribution of water - Irrigation efficiency of sprinklers depends upon the degree
of uniformity of water applied. Uniformity coefficient is computed with field application.
Open cans are placed at regular interval within sprinkled area. Depth of water collected in
open cans is measured and the coefficient of uniformity is computed by Christiansen (1942)
equation.
Cu = 100(1-ΣX/m.n)
Where,
Cu = uniformity coefficient
m = average value of all observations
n = total number of observation points
X = numerical deviation of individual
observation from average application rate.
A uniformity coefficient of 85% or more is considered to be satisfactory. The uniformity
coefficient is affected by pressure–nozzle size relation, sprinkler spacing and wind condition.
Sprinkler selection and spacing - The choice depends on diameter of coverage required,
pressure available and discharge of sprinkler. The data given in tables 1 and 2 may serve as
guidance in selecting the pressure and spacing desired.

2. Drip or Trickle Irrigation System/line source irrigation

Water is applied through network of pipelines and allowed to fall drop by drop at crop root
zone by a special device called emitters or drippers. These drippers or emitters control the
quantity of water to bedropped out. In this system, the main principle is to apply the water at
crop root zone based on the daily
ET demand of the crop without anystress. Hence, the root zone is always maintained at field
capacity level.

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Components
• Overhead tank or pressure system (Motor pumps).
• Main Lines - To take water from source to field which is usually made of black poly
alkathene pipes having an inner diameter of 50 mm
Sub main - If the area is larger, the sub mains are used to take water from main pipes to field
which is normally having an inner diameter of 37 mm.
Laterals - These pipelines are normally having lesser diameter than mains and sub mains
usually of 12 mm made of black poly alkathene pipes which deliver water from main or sub
mains to crop root zone. The length of lateral depends upon the pressure created in pump as
well as spacing of the crop and length of the field. Normally about 25 m length of lateral can
be adopted to have a uniform distribution of water.
Emitters - Emitters control the water drops and the quantity of water to be delivered. Various
designs of drippers with various discharge capacity are available (5, 7, 8, 10 and 20 lph, etc.
Button types, spray type, tap type etc.). Instead of drippers micro tubes are inserted into the
laterals and water is allowed to drip in the root zone of crops or trees.
Advantages
• Application of water in slow rates facilitates the easy infiltration into the soil.

Fig 5.8 Drip irrigation system

The required quantity of water is applied near the root zone alone which in turn save water.
• The root zone is always maintained with field capacity level and hence plants do not suffer
for want of water.
• There is no seepage or percolation or evaporation loss.
• Weed growth is restricted due to limited area of wetting zone.
• Fertilizers (fertigation), chemical like pesticides (chemigation) and herbicide (herbigation)
can be applied through irrigation. Hence, saving of input quantity and labour cost besides
increase in their use efficiencies is possible.
• Reduce the salt content near the root zone and dilute it in saline soil.
• The saline water also can be put under use if irrigation is applied through drip irrigation.
• It can be adopted for any type of topography.
• Yield increases due to optimum maintenance of soil moisture at root zone.
• More area can be maintained with little quantity of water.
• It cab be used for widely spaced crops like cotton, sugarcane, tomato, brinjal, coconut and
orchard crops.

Disadvantages
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• Clogging in emitters due to salt content of water and other impurities like moss, dust etc.
• Damage of pipe lines by rodents.
• It is not economical for closely spaced crops which require more number of pipes and
drippers per unit area.
• Proper maintenance and periodical cleaning of drippers and pipelines (with 1%
hydrochloric acid) are very important to maintain the system efficiency.

Page | 75
 Chapter 9

Quality of irrigation water

All irrigation waters are not pure and may contain some soluble salts. In arid and semi-arid
regions successful crop production without supplemental irrigation is not possible. Irrigation
water is usually drawn from surface or ground water sources, which typically contain salts in
the range of 200 to 2000 ppm (= 200 to 2000 g/m). Irrigation water contains 10 – 100 times
more salt than rain water. Thus, each irrigation event adds salts to the soil. Crop removes
water from the soil to meet its water needs (ETc) leaving behind most of the salts to
concentrate in the shrinking volume of soil water. This is a continuous process. Application
of saline water may hinder the crop growth directly and may also cause soil degradation.
Beyond its effect on crop and soil, irrigation water of low quality can also affect environment
by introducing potentially harmful substances in to surface and ground water sources.
Therefore, a salt balance in the soil has to be maintained through proper water management
practices for continuous and successful cultivation of crops.

Fig. 8.1 Salinity build up process in irrigated soils

Criteria to determine the quality of irrigation water

The criteria for judging the quality of irrigation water are: Total salt concentration as
measured by electrical conductivity, relative proportion of sodium to other cations as
expressed by sodium adsorption ratio, bicarbonate content, boron concentration and soluble
sodium percentage.
1. Total soluble salts: Salinity of water refers to concentration of total soluble salts in it. It is
the most important single criterion of irrigation water quality. The harmful effects increase
with increase in total salt concentration. The concentration of soluble salts in water is
indirectly measured by its electrical conductivity (ECw). The quality of saline waters has
been divided into five classes as per USDA classification given in Table 8.1.

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Table 8.1 Salinity classes of irrigation water
Salinity class Electrical conductivity
Micro mhos/cm Milli mhos/cm
C1 - Low <250 <0.25
C2 – Medium 25 - 750 0.25 – 0.75
C3 – Medium to high 750 - 2250 0.75 – 2.25
C4 – High 2250 - 5000 2.25 – 5.00
C5 – Very high >5000 >5.00

Adverse effects of saline water include salt accumulation, increase in osmotic potential,
decreased water availability to plants, poor germination, patchy crop stand, stunted growth
with smaller, thicker and dark green leaves, leaf necrosis & leaf drop, root death, wilting of
plants, nutrient deficiency symptoms and poor crop yields.
2. Sodium Adsorption Ratio (SAR): SAR of water indicates the relative proportion of
sodium to other cations. It indicates sodium or alkali hazard.

SAR = Na+ / √(Ca++ + Mg++/2)

The ion concentration is expressed as meq per litre. Increase in SAR of water increases the
exchangeable sodium percentage (ESP) of soil.

As per USSSL, the sodicity classes of water are shown in Table 8.2
Sodium class SAR value
S1 – Low <10
S2 – Moderate 10 – 18
S3 – High 18 – 26
S4 – Very high >26

Harmful effects of sodic water include destruction of soil structure, crust formation, poor
seedling emergence, and reduction in availability of N, Zn and Fe due to increased soil pH,
Na toxicity and toxicity of B & Mo due to their excessive solubility.
3. Residual sodium carbonate: Bicarbonate is important primarily in its relation to Ca and
Mg. There is a tendency for Ca to react with bicarbonates and precipitate as calcium
carbonate. As Ca and Mg are lost from water, the proportion of sodium is increased leading
to sodium hazard. This hazard is evaluated in terms of Residual Sodium Carbonate (RSC) as
given below:
RSC (meq/litre) = (CO3-- + HCO3-) – (Ca+++ Mg++)
RSC is expressed in meq per litre. Water with RSC more than 2.5 meq/L is not suitable for
irrigation. Water with 1.25 to 2.5 meq/L is marginally suitable and water with less than 1.25
meq/L is safe for use.

4. Boron content: Though boron is an essential micronutrient for plant growth, its presence
in excess in irrigation water affects metabolic activities of the plant. For normal crop growth
the safe limits of boron content are given in Table 8.3.
Table 8.3 Permissible limits of boron content in irrigation for crops
Boron (ppm) Quality rating
<3 Normal
3–4 Low
4–5 Medium

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 5 – 10 High
More than 10 Very high

Leaching requirement
Leaching requirement (LR) is that fraction of total crop water requirement which must be
leached down below the crop root zone depth to control salts within the tolerance level (ECe)
of the crop.
Leaching Requirement (LR) = ECw/(5(ECe) –Ecw)
Where:
ECw = Salinity of applied water in dS/m
ECe = Threshold level soil salinity of the crop in dS/m

Management practices for using poor quality water

Whenever, it is inevitable to use water of poor quality water for crop production appropriate
management practices helps to obtain reasonable yield of crops. Some of the important
management practices are as follows:
a. Application of gypsum: Chemical amendments such as gypsum, when added to water
will increase the calcium concentration in the water, thus reducing the sodium to calcium
ratio and the SAR, thus improving the infiltration rate. Gypsum requirement is calculated
based on relative concentration of Na, Mg & Ca ions in irrigation water and the solubility
of gypsum. To add 1 meq/L of calcium, 860 kg of gypsum of 100% purity per ha m of
water is necessary.
b. Alternate irrigation strategy: Some crops are susceptible to salinity at germination &
establishment stage, but tolerant at later stage. If susceptible stages are ensured with
good quality water, subsequent tolerant stages can be irrigated with poor quality saline
water.
c. Fertilizer application: Fertilizers, manures, and soil amendments include many soluble
salts in high concentrations. If placed too close to the germinating seedling or to the
growing plant, the fertilizer may cause or aggravate a salinity or toxicity problem. Care,
therefore, should be taken in placement as well as timing of fertilization. Application of
fertilizers in small doses and frequently improve uptake and reduce damage to the crop
plants. In addition, the lower the salt index of fertilizer, the less danger there is of salt
burn and damage to seedlings or young plants.
d. Methods of irrigation: The method of irrigation directly affects both the efficiency of
water use and the way salts accumulate. Poor quality irrigation water is not suitable for
use in sprinkler method of irrigation. Crops sprinkled with waters having excess
quantities of specific ions such as Na and Cl cause leaf burn. High frequency irrigation in
small amounts as in drip irrigation improves water availability and uptake due to
microleaching effect in the wetted zone.
e. Crop tolerance: The crops differ in their tolerance to poor quality waters. Growing
tolerant crops when poor quality water is used for irrigation helps to obtain reasonable
crops yields. Relative salt tolerance of crops is given in Table 26.4.
f. Method of sowing: Salinity reduces or slows germination and it is often difficult to
obtain a satisfactory stand. Suitable planting practices, bed shapes, and irrigation
management can greatly enhance salt control during the critical germination period.
Seeds have to be placed in the area where salt concentration is less. Salt accumulation is
less on the slope of the ridge and bottom of the ridge. Therefore, placing the seed on the

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 slope of the ridge, several cm below the crown, is recommended for successful crop
establishment.
Table 8.4 Relative salt tolerance of crops
Tolerant Field crops: Cotton, Safflower, Sugarbeet & Barley
Fruit crops: Date palm & Guava
Vegetables: Turnip & Spinach
Forage crops: Berseem & Rhodes grass
Semi tolerant Field crops: Sorghum, Maize, Sunflower, Bajra, Mustard, Rice & wheat
Fruit crops: Fig, Grape & Mango
Vegetables: Tomato, Cabbage, Cauliflower, Cucumber, Carrot & Potato
Forage crops: Senji & Oats
Sensitive Field crops: Chick pea, Linseed, Beans, Greengram & Blackgram
Fruit crops: Apple, Orange, Almond, Peach, Strawberry, Lemon & Plum
Vegetables: Radish, Peas & Lady‟s finger

g. Drainage: Provide adequate requirement depending on crop and EC of water. This is

necessary to avoid build of salt in the soil solution to levels that will limit crop yields.
Leaching requirement can be calculated from water test results and tolerance levels of
specific crops.
h. Other management practices
1) Over aged seedlings in rice: Provide adequate internal drainage. Meet the
necessary leaching depending on crop and EC of water. This is necessary to
avoid build of salt in the soil solution to levels that will limit crop yields.
2) Mulching: Mulching with locally available plant material help in reducing salt
problems by reducing evaporation and by increasing infiltration. Mulching with
locally available plant material help in reducing salt problems by reducing
evaporation and by increasing infiltration.
3) Soil management: All soil management practices that improve infiltration rate
and maintain favourable soil structure reduces salinity hazard. soil management
practices that improve infiltration rate and maintain favourable soil structure
reduces salinity hazard.
4) Crop rotation: Inclusion of crops such as rice in the rotation reduces salinity.
Inclusion of crops such as rice in the rotation reduces salinity.

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 Chapter 10

Weed and its classification

Definition of a Weed:

Undesirable and unwanted plants growing out of their proper place

Or

A plant which grows voluntarily at places where it is not wanted and grows at places
where other useful plants grow
Or
A weed is a plant which interferes with human activity or welfare.

Origin and Evolution of weeds:-

In stable (climax) vegetation, all plant species are equally naturally adapted.

Weeds evolved
i. When the stable environment is disturbed through human activities.
ii. Fromecotypes that have evolved from wild colonizers in response to continuous habitat
disturbances and selection pressures.
iii. As a result of the products of hybridization between wild domestic races of crop plants.
Characteristics of Weeds
• Can tolerate adverse climatic conditions
• Competitive and aggressive in nature
• Resist control/eradication
• Morphological similarities
• High reproductive capacity
• Persistent in nature
• Early seed setting
• Repeated germination in different phases
• Deep root system
• Similarity of seed
• Seed dormancy: could be innate, induced or enforced.

Harmful effect of weed-

Weeds have serious impacts on agricultural production. It is estimated that in general
weeds cause 5% loss in agricultural production in most of developed countries, 10% lossin less
developed countries and 25% loss in least developed countries. In India, yield losses due to
weeds are more than those from pest and diseases. Yield losses due to weeds vary with the crops.
Every crop is exposed to severe competition from weeds. Most of these weeds are self-sown and
they provide competition caused by their faster rate of growth in the initial stages of crop growth.
In some crops, the yields are reduced by more than 50% due to weed infestation.
Reduction in crop yield through:-
Physical Interaction (Allelospoly: competition for growth resources including water, light,
nutrient, air, space.Chemical interaction (Allelopathy)

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Reduction in crop quality through
- Direct contamination of cultivated rice and maize grain by wild rice(Oryza longistaminata) and
itch grass (Rottboelliaco chinchinensis) respectively
- Contamination of forage, silage or pasture crop .by C. rotundus seeds.
-Reduction in Sugarcane juice quality bythe presence of sida.
-Contamination of cotton lint by dried weed fragments
-Damage of underground tuber of yam and cassava through piercing of Spear grass rhizomes
 Interference with field operations (harvest,pesticideapplication,etc.)
 Some are poisonous to grazing animals e.g. Euphorbia heterophylla,
Halogetonglomeratus contain high oxalate content, it can kill livestock when eaten in dry
season.
 Weeds compete with crops for water soil, nutrients, light, and space, and thus reducethe
crop yields.
 Some are harmful to grazing animals e.g. Amaranthus spinosus, Acanthospermum
hispidus
 Increase cost of production; high cost of labour and equipment during harvesting.
 Presence of weeds can impede water flow in irrigation canals
 Weeds present in lakes and reservoirs can increase loss of water by evapo-transpiration
 Reduction in quality of pasture land; it reduces the carrying capacity of grazing lands and
pastures through their physical presence and weediness
 Reduction in quality of animal products;it affects the palatability of pastures, hay; silage
etc. protein content in alfalfa wild garlic (Alliums spp) when eaten by cattle spoils the
meat and the milk.
 Weeds reduce the quality of marketable agricultural produce.
 Serve as alternate hosts for many plant diseases and animal pests e.g. insects, rodents,
birds. Cyperusrotundus serve as alternate to nematodes and athropods
 Impose limitation to the farm size of a farmer
 Can serve as sources of fire hazards

Beneficial Effects of Weeds:-

In spite of all the difficulties caused by weeds, they can offer some beneficial
properties,particularly when occurring at low densities. These aspects should be utilised in the
farmingsystem, although this may make organic management more complicated than chemical
basedsystems. Some of the potential benefits of weeds are listed below:
 Helping to conserve soil moisture and prevent or Reduce erosion problem through the
production of protective cover
 Help in nutrient recycling through decay of vegetative part.
 Food/vegetables for humans e.g. leaves of Talinumtriangulare, and tubers of
Colocasiaesculentus .
 Serve as hosts and nectar for beneficial insects
 Beautification of the landscape e.g. Cynodondactylon
 Feed for livestock and wildlife and aquatic organisms in form of hay, silage and forage /
pasture, fruit seeds and branches and whole plant.
 Source of pesticides e.g. Chrysanthemum cinerariifolium
 Source of genetic material for useful traits in crop improvement.
 Medicinal use e.gneem (Azadirachtaindica), Ageratum conyzoides
 Some serve as trap crop for parasitic weeds.
 Habitat for wildlife and plant species hence biodiversity conservation.

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  Major role in carbon recycling through carbon sequestration. Field of exposed soil always
suffers a net loss in organic matter and releases carbon dioxide, while a field covered with
crops and/or weeds takes up carbon dioxide. This concept of carbon sequestrations an
added advantage of sustainable and organic farming.

Classification of weeds
Weeds can be classified based on :
Life cycle or history (Ontogeny): Annual, Biennials and Perennial weeds
a. Annual Weeds
Weeds that live only for a season or a year and complete their life cycle in that season
or year are called as annual weeds.
Kharif annuals:-Exa. Digeraarvensis, E. crusgalli
Rabi annuals:-Exa. Phalirs minor, Chenopodium album
b. Biennials weeds:- Exa. Daucuscarota, Cirsiumvulgare
c. Perennial weeds:-Exa.Cyperusrotundus, Sorghum halepense

2. Based on Habitat:-
a. Upland (terrestrial) weeds or dry land weeds (Agrestal /Weeds of arable or cultivated
crops, andRuderal weeds /weeds of disturbed non- cropped area such as rubbish heaps,
landfills, paths, roads, compost heaps
b. Aquatic weeds (Submerged aquatic, Floating aquatic, Emergent aquatic weeds

3. Based on soil type (Edaphic)

a. Weeds of black cotton soil: These are often closely allied to those that grow in dry
condition. Eg., Aristolo chiabracteata
b. Weeds of red soils: They are like the weeds of garden lands consisting of various
classes of plants. Eg. Commelina benghalensis
c. Weeds of light, sandy or loamy soils: Weeds that occur in soils having good
drainage. Eg. Leucas aspera
d. Weeds of laterite soils: Eg. Lantana camara, Spergula arvensis

4. Based on Growth habit:

Free living (autotrophic) weeds
Parasitic plants(Root parasitic weeds or obligate parasite, Stem parasitic weeds,
Semi parasitic weeds, Total parasites floating aquatic Emergent aquatic weeds
5. Based on Degree of undesirability: ease and difficulty in controlling weeds.
6. Based on Morphology :
e.g. i. Woody Stem e.gAzadirachta indica,
ii. Semi Woody weeds- e.gChromolaena odorata, Sidaacuta.
iii.Herbaceous weeds: e.g Ageratum conyzoides, Talinum triangulare,
b.Leaf Type: i) Narrow leaf: grass like (ii) Broad leaf weeds (Dicotyledons):, Sedges; e.g.
Cyperusrotundus, C. esculentus, Mariscusalternifolius
7. Scientific classification (Binomial nomenclture): based on their taxonomy (family, genera
and specific epithet
8. Ecological affinities: dryland weeds, gardenland weeds and wetland weeds

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 Chapter 11

Weed management
Crop –weed competition
When plants grow close to each other, they interact in various in ways.
Interference: It is the detrimentaleffects of one species on another resultingfrom their
interactions with each other. When plants are far apart they have no effect on each other.
Interaction generally involves competition and amensalism.
Commensalism: This is the relationship between unrelated organism (different
species) in which one derives food or benefit from the association while the other remains
unaffected.
Competition (allelospoly): It is the relationship between two plants (weed/crop,
crop/crop, weed/weed) in which the supply of a growth factor falls below their combined
demand for normal growth and development. The growth factor competed for include
water, nutrients, light, space and air/gasses (oxygen, carbon dioxide).
Types of competition
• Above-ground (Aerial) competition Takes place in the leaves and the growth factors
involve are light and carbon dioxide.
• Below-ground(Subterranean) competition: Takes place mainly in the roots while the
growth factors involve are water, nutrients and oxygen.
• The perceived consequence of competition with crop is reduction in the economic
yield of affected crop plants.
Forms of competition:
Intraspecific competition: competition for growth factors among individuals of a plant
species
Interspecific competition: competition for growth factors between two different plant
species i.e., crop/weed, weed/weed,or crop/crop.
Critical Period of Weed competition/interference:
This is the minimum period of time during which the crop must be free of weeds in
order to prevent loss in yield.
a. It represents the overlap of two separate components (a) the length of time weeds can
remain in a crop before interference begins
b. The length of time that weed emergence must be prevented so that subsequent weed
growth does not reduce crop yield.
Factors affecting weed-crop competition
• Competitiveness of weed species
• Weed density and weight
• Onset and duration of weed-crop association
• Growth factors
• Type of crop and seeding rate
• Spatial arrangement of crops
• Plant architecture
• Growth factors availability
• Cropping patterns
• Crop type (C3 or C4 plants)
• Crop variety( tolerance, resistance, aggressiveness)

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Environmental factors
• Climatic factors e.g. rainfall, temperature, wind, light etc
• Tillage
• Ground water management
• Soil (Edaphic)

• Amensalism (Allelopathy)
• Allelopathyis the production of chemical(s) or exudates by living and decaying plant
species which interfere with the germination, growth or development of another plant
species or microorganism sharing the same habitat.
There are two types of allelopathy:(True and Functional )
True allelopathy involves the release into the environment compounds that are toxic in
the form they are produced. Functional allelopathyinvolves the release into the environment
substances that are toxic as a result of transformation by microorganism.
Allelochemical complex commonly encountered in plants include:
coumaric acid, terpenoids, - syringic acid, butyric acid, flavonoids, phenolic
compounds.

Examples of allelopathic plants:

1. Black walnut (Juglansnigra)
2. Gmelinaarborea
3. Soghum bicolor
4. Casuarina
5. Lantana camara
6. Imperatacylindrica is allelopathic on tomato, cucumber, maize rice, glnut,
olera, cowpea, pepper.
7. Cyperusesculentus– is allelopathic on rice, maize
8. C. rotundus – is allelopathic on barley.

• Parasitism- It is a relationship between organisms in which one lives as a parasite in

or on another organism.
• Parasitic weeds are plants that grow on living tissues of other plants and derive part
or all of their food, water and mineral needs from the plant they grow on (host
plants)
• Hemi parasite (Semi parasite) a plant which is only partially parasitic, possessing its
own chlorophyll (green colour) and photosynthetic ability (may be facultative or
obligate). e.gStrigahermonthica
• Holo parasite – a plant which is totally parasitic, lacking chlorophyll thus unable to
synthesize organic carbon. E.gOrobanchespp
• Obligate parasite – a plant which cannot establish and develop without a host
• Facultative parasite – a plant which can grow independently but which normally
behaves as a parasite to obtain some of its nutrition.
• Predation: It is the capture and consumption of organisms by other organisms to
sustain life.
• Mutualism: It is an advantageous relationship between two organismsof different
species that benefits both of them. It is obligatory and the partners are mutually
dependent. Both partners are stimulated when the interaction is on. Example is the
case between fungus and algae. The fungus protects the algae while the algae provide
carbohydrate for the fungus.
• Neutralism: This is the situation where plant exert no influence on one another.

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 • Protocooperation: This is a condition whereby two plants interact and affect each
other reciprocally. Both organisms are stimulated by the association but unaffected by
its absence.
Weed management- Principles and methods
Weed Management refers to how weeds are manipulated so that do not interfere with the
growth, development and economic yield of crops and animals. It encompasses all aspects of
weed control, prevention and modification in the crop habitat that interfere with weed ability to
adapt to its environment.

Weed control: Refers to those actions that seek to restrict the spread of weeds and destroy or
reduce their population in a given location. The effectiveness of weed control is affected by
i. Type of crop grown
ii. Timing of weeding operation
iii. Nature of the weed problem
iv. Methods of weed control available to the farmer
v. Type of weeds to be controlled
vi. Cost of the operation
vii. Available labour or cash resources
viii. Environmental condition before during and after the time of operation.
Weed prevention: This refers to the exclusion of a particular weed problem from the system that
has not experienced that weed problem. It involves those measures necessary to prevent the
introduction of new weed species into a given geographical area as well as the multiplication and
spread of existing weed species.
It includes the following:
Fallowing
Preventing weeds from setting seeds
Use of clean crop seed for planting
Use of clean machinery
Controlling the movement of livestock
Quarantine laws services

Weed eradication:This involves complete removal of all weeds and their propagules from a
habitat.Eradication is difficult to achieve in crop production and uneconomical. However in
situations where weed problem becomes so overwhelming, eradiation may be desirable in long
term goal. E.g. Strigaasiatical, S. hermonthica.Eradication may be considered if :
i. Other weed control methods are ineffective
ii. Weeds have many buried seeds that cannot be controlled by conventional practice.
iii. The infested field is small
iv. Benefits from eradication outweigh those of the alternate methods for copping with weeds.
Methods of weed control: -

1. Physical –
a. Tillage
b. Hand pulling
c. Hand hoeing
d. Inter culture
e. Flooding
f. Flaming
g. Mowing

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 2. Cultural Method –
a. Crop rotation
b. Date of sowing
c. Plant density
d. Planting pattern
e. Methods of fertilizer application
f. Selection of quick growing varieties
g. Dab system
h. Mulching
i. Irrigation management
j. Soil solization

3. Chemical methods
Histories of herbicides/chemical weed control
• The use of chemical weed control started with inorganic copper salts e.g CuSO 4 for
broadleaf weed control in cereals in Europe in 1896.
• Other inorganic salts that were tested between 1900-1930 included nitrates and
borates.
• In 1912, sulphuric acid (H2SO4) was used for selective weed control in onions and
cereals. In 1932, the first organic herbicide, Dinitro-ortho Cresol (DNOC) was
introduced.
• In the 1950s triazine was introduced. In 1974, Glyphosate, frequently sold under brand
name Roundup for non-selective weed control was introduced.
• Agriculture witnessed tremendous changes through the production of organic
herbicides, which came at a time when field workers were reducing, high cost labour
and productive cost of production. Thus, farmers in advance countries almost
depended on herbicide because it met their production challenges in agriculture and
relatively ignored other methods of weed control.

• Limitation of chemical methods –

• Lack of application technology.
• Weed resistance
• Herbicide drift
• When crop fails no choice for succeeding crops
• Chemical crop war
• Cost of few herbicides is high
• Pollution hazards

4. Biological methods: - This method is an effective, environmentally safe, technical

appropriate, economical viable and socially acceptable methods of weed management.

Qualities of bio agents

a. Host specific
b. Adjustment to field environment
c. Easy to multiply
d. Feeding habbits

Kinds of bio agents

a. Insects
b. Plant pathogens

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 c. Carp fish
d. Competitive plants

Integrated weed management

a. This method is more effective because the left over weeds with one methods can be
controlled with other methods. So this methods helps in reducing seed bank status in
the field.
b. Many problems such as shift in weed flora, development of resistance in weed plants
etc. can be avoided.
c. IWM approaches are environment friendly as farmers should not entirely depends on
herbicide.
d. No danger of herbicide residue in soil or plant.
e. It is very suitable for high cropping intensity
Higher net returns are achieved with the adaptation of this method

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 Chapter 12

Herbicide classification
Herbicides- classification

Herbicides are classified according to their:-

 Selectivity
 Mode of action
 Timing of application.
 Chemical group
 Mechanism of action

SELECTIVITY

1. A non-selective herbicide kills or damages all plant life in a treated area (e.g.,
Roundup).
2. A selective herbicide will kill weeds in a germinating or growing crop without harming
the crop beyond the point of recovery (e.g., 2,4-D used to control broadleaved weeds in
a grass pasture; Avadex to control wild oats in cereals.)

MODE OF ACTION (or how the herbicide works to kill a weed)

1. Contact herbicides – kills plant parts covered by the herbicide and are directly toxic to
living cells. There is little or no translocation or movement of the material through the
plant. Contact herbicides are effective against annual weeds but they only “burn off”
the tops of perennial weeds – chemically mowing them. Contact herbicides may be
selective, such as Torch (bromoxynil) which kills broadleaved weeds in cereals
without damaging the crop, or nonselective, such as Gramoxone (paraquat) which
kills any green plant material.
2. Systemic herbicides – absorbed by either the roots or above ground parts of plants,
these herbicides move or are translocated in the plant. They exhibit a chronic effect;
that is, the full effects may not show for a week or more after treatment. An overdose
on the leaves may kill the leaf cells more quickly, thus preventing translocation to the
site of action in a plant. Systemic herbicides can be selective, as in the case of 2,4-D,
MCPA, Banvel and Tordon or non-selective, as with Roundup.
3. Soil Sterilants– chemicals which prevent growth of plant life when present in the soil.
These products will prevent plant growth for periods of a few months to a number of
years. Examples include bromacil, tebuthiuron and atrazine at high rates.

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TIMING OF APPLICATION

1. Pre-Plant Soil Incorporated – these herbicides are applied to the soil before the crop
is sown. They are incorporated in the soil to prevent loss due to vapourization and
breakdown by sunlight. Trifluralin and EPTC are examples.
2. Pre-Emergence – applied to soil prior to seeding or after the crop is sown but before
crop and weeds emerge. In most cases, the weeds germinate in treated soil while the
crop germinates below the herbicide zone.
3. Post-Emergence – sprayed directly on the weeds after they are up and growing.

Comparison of Soil-Applied and Foliar-Applied Herbicides

Source: Weeds ‘81 Alberta Agriculture

HERBICIDE TYPE: PRE-PLANT INCORPORATED (Soil Applied)

Advantages:
1. Early control of weeds, minimizing competition.
2. Weeds are controlled where wet or windy weather after emergence can delay
spraying.
3. Work load is distributed.
Disadvantages:
1. Perennial weeds are generally not controlled.
2. Less effective under dry or cold soil conditions.
3. Residue may restrict crop rotation the following year.
4. Soil erosion may be a problem, as additional tillage for incorporation is required.
HERBICIDE TYPE: PRE-EMERGENCE INCORPORATED (Soil Applied)
Advantages:
1. Early control of weeds, minimizing competition.
2. Weeds are controlled where wet or windy weather after emergence can delay
spraying.
3. Planting and herbicide application may be done in one operation.
Disadvantages:
1. Less effective under dry or cold soil conditions.
2. Perennial weeds are generally not controlled.
3. On sandy soils, heavy rains may leach the herbicide down to the germinating crop and
cause injury.
4. Wet or windy conditions after seeding can delay application until crop emergence and
prevent herbicide application.
5. Planting may be slowed down by combining planting and herbicide application.
6. Residue may restrict crop competition the following year.
7. Soil erosion may be a problem, as additional tillage for incorporation is required.
HERBICIDE TYPE: POST-EMERGENCE (Foliar applied)
Advantages:
1. Type and density of weed can be seen before herbicide application.
2. Soil texture does not directly affect herbicide choice or performance.
3. Soil moisture has little influence on level of control.
4. Few post emergent herbicides leave a soil residue which will restrict subsequent
cropping rotation.
5. Incorporation tillage is not required.

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 6. Top growth control of several perennial weeds is possible.
Disadvantages:
1. Specific stage of application required on both crop and weed variable emergence may
be a problem.
2. Flush of weeds after spraying generally not controlled.
3. Wet or windy weather can delay application.
Based on Mechanism of action

Mechanism of action Chemical family Active ingredients

Inhibitors of acetyl CoA Aryloxyphenoxy clodinafop-propargyl
carboxylase ACCase. propionate fenoxyprop-p-ethyl
These chemicals block an enzyme called (Fop) quizalofop-p-ethyl
ACCase. This enzyme helps the formation Cyclohexanediones clethodim
of lipids in the roots of grass plants. Without (Dim) sethoxydim
lipids, susceptible weeds die. tepraloxydim
tralkoxydim
Phenylpyrazolin pinoxaden
(Den)
ALS/AHAS inhibitors. These chemicals Imidazolinones AC 299, 263, 120 AS
block the normal function of an enzyme imazamethabenz
called acetolactate (ALS) actohydroxy acid imazamox
(AHAS). This enzyme is essential in amino imazamox +
acid (protein) synthesis. Without proteins, imazethapyr
plants starve to death. imazapyr
imazethapyr
Sulfonylamino- flucarbazone sodium
carbonyltriazolinones
Sulfonylureas chlorsulfuron
ethametsulfuron methyl
metsulfuron-methyl
nicosulfuron
rimsulfuron
thifensulfuron-methyl
tribenuron-methyl
triflusulfuron methyl
Triazolpyramidines florasulam
pyroxsulam
Triazolones thiencarbazone-methyl
Microtubule assembly Dinitroanilines ethalfluralin
inhibitors. These chemicals inhibit the trifluralin
cell division in roots.
Synthetic auxins. These chemicals disrupt Benzoic acids dicamba
plant cell growth in the newly forming stems Carboxylic acids clopyralid
and leaves; they affect protein synthesis and aminopyralid Page | 90
normal cell division, leading to malformed fluroxypyr
growth and tumors. picloram
Phenoxy 2,4-D
dichlorprop (2,4-DP)
2,4-DB
MCPA
MCPB
mecoprop (MCPP)
quinclorac
Photosynthetic inhibitors Phenyl-carbamates desmedipham
at Photosystem II, phenmedipham
Site A. These chemicals interfere Triazines atrazine
with photosynthesis and disrupt plant simazine
growth, ultimately leading to death. Triazinones hexazinone
metribuzin
pyrazon
Uracils bromacil
Photosynthetic Benzthiadiazoles bentazon
inhibitors at Nitriles bromoxynil
Photosystem II, Site II
Photosynthetic Ureas diuron
inhibitors at linuron
Photosystem II, Site B.
Lipid synthesis Thiocarbamates EPTC
inhibitors (not ACCase triallate
inhibition). These chemicals inhibit the cell Pyrazolium difenzoquat
division and elongation in the seedling
shoots before they emerge above ground.
Inhibitors of EPSP None glyphosate
synthesis. These
chemicals inhibit the
amino-acid synthesis.
Inhibitors of glutamine synthetase. None glufosinate-ammonium
Carotenoids biosynthesis inhibitors. These Triazole amitrol
chemicals inhibit the carotenoids
biosynthesis.
Inhibitors of cell growth Chloroacetamides metolachlorpropyzamide
and division.
Cell membrane Bipyridyliums diquat
disrupters. (Inhibitors of P.S.-I)
Chemicals that disrupt the internal cell paraquat
membrane and prevent the cells from
manufacturing food.

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Based on chemical groups
Dalapon, FCA, Glyphosate, Methyl bromide, Cacodylic acid,
1 Aliphatic acids
MSMA, DSMA
Alchlor, Butachlor, Propachloi, Metalachlor, Diphenamide.
2 Amides
Propanil
3 Benzoics 2,3,6, TBA, Dicamba, tricamba. Chloramben
4 By Pyridillums Paraquat, Diquat
5 Carbamates Prop ham, Chlorpropham. Barban. Dichlormate. Asulam
Butylate, Diallate, EPTC, Molinate, Triallate, Benthiocarb,
6 Thiocarbamates
Metham
7 Dithiocarbainates CDEC, Metham
8 Nitriles Bromoxynil, Ioxynil, Dichlobenil
9 Dintroanilins Fluchloralin, Trifluralin, Pendimethalin, Nitralin, Isoproturon
10 Phenols Dinoseb, DNOC, PCP
11 Phynoxy acids 2,4 D, 2,4,5-T, MCPA, MCPB, 2,4-DB, Dichlorprop
12 Traizines Atrazine, Simazine, Metribuzine, Amytrin, Terbutrin
Monuron, Diuron, Linuron, Metoxuron, Isoproturon, Methabenz
13 Ureas
thiozuron
14 Uracils Bromacil, Terbacil, Lenacil
15 Diphenyl ethers Nitrofen, Oxyfluorfen, Nitrofluorfen
Aryloxyphenoxy
16 Diclopop Fenoxaprop-p, Quizalofop-p, Haloxyfop-p, Fluazifop-p
propionate
17 Cyclohexanedione Sethoxydim, Clethodim, Tralkoxydim, Cycloxidim
18 Imidazolines Imazapyr, Imazamethabenz, Imazaquin, Imazamax, Imazethapyr
19 Isoxazolidinones Clomazone
20 Oxadiazoles Oxadiazon
21 Oxadiazolides Methazole
22 N-phenylphthalamides Flumiclorac
23 Phenylpyridazones Sulfentrazone
24 Phthalamates Naptalam
25 Pyrazoliums Difenzoquat, Metflurazone
26 Picolinic acids Pyridine Picloram, Dithiopyr, Pyrithiobac, Fluridone, Thiazopyr
27 Quinolines Quinclorac
Bensulfuron, Chlorimuron, Metsulfuron, Sulfosulfuron,
28 Sulfonylureas
Triasulfuron
29 Triazolinones Pyridates
30 Cineoles Cinmethylin
31 Others Pichloram, Pyrazon, Endothal, Oxadiazon, Amitrole, Anilofos

Herbicide Selectivity
It is a phenomena by which in a given mixed crop stand some species eg weeds are
preferably controlled while others (eg crops) remains unaffected or marginally affected when
a herbicide is applied to them.

Selectivity Index (S.I.)

S.I. = Max. dose of herbicide tolerated by crop

Min dose of herbicide required to control weed

If SI <2 it is safe for use.

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Fundamental principle of selectivity:
More toxicant reaches to the active site of action in more active form inside the target species
than in non-target species.
Selectivity mechanism
1. Differential absorption
2. Differential translocation
3. Differential metabolism
Differential absorption
Eg. 2,4-D slow absorbed in wild cucumber ((Sicyos angulatus) and makes it tolerant to 2,4-D
whereas quick absorption in cucumber (Cucumis sativa) makes it susceptible.
Causes:
 Difference in morphology & growth
 Difference in time and method of application
 Difference in herbicide formulation
 Use of absorbents and antidotes
Difference in morphology & growth
It causes differential retention of aquas spray. Limited retention of spray may cause due to:
 Narrow upright leaves
 Corrugated/ finely ridged leaf surface
 Waxy leaf surface
 Pubescent leaves
These protects against contact and selective herbicides but not useful for translocated
herbicides.
Difference in growth habit:
 Directed spray in a situation where high crops and short weeds exist.
 Herbicide mulch in standing crop row can cause effective control of germinating
weeds.
 In case of slow germinating crops like sugarcane, potato etc weeds germinate before
crop emergence. In that case spray of selective and contact herbicides can selectively
control weeds.
 Depth protection: Weed seed bank exists between top 1.25 – 1.5 cm of soil whereas
crop seeds are placed in 5.0 cm depth. In this case pre-emergence herbicide which
leaches upto 2.5 cm can kill weeds but cannot reach upto the depth where crop seeds
exist. This is the basic selectivity mechanism of all pre-emergence herbicides.

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 Eg. Selectivity of Monilate between rice and Echinochloa
Use of absorbents and antidotes
Absorbents like activated charcoal is a strong absorbent of 2,4-D., Butachlor. Germinating
seedlings surrounded by layer of activated charcoal escape phyto toxicity of several
herbicides.
Herbicide formulation
Granular formulation of herbicides imparts selectivity in case of cotton against Diuron. It
filters through crop foliage and accumulates in moist ground and finally absorbed by weeds
and kill them.
Differential translocation
Eg. 2,4-D slowly translocated in sugarcane (tolerant) but quickly translocated in beans
(Susceptible).
Differential metabolism:
In this case herbicides are converted in non-phytotoxic compounds inside the non targeted
species while it becomes phytotoxic in susceptible species.
There are several mechanisms of metabolism:

1. Conjugation: Coupling of intact herbicide molecule with some plant cell constituent
in living plants. It takes phyto toxic compounds out of the main stream of plants and
thus become tolerant.

Eg. Selectivity of Atrazine in sorghum due to conjugation of Atrazine in sorghum leaf by the
enzyme Glutathione-S-Transferase (GST) enzyme.

2. Hydroxylation: Selectivity of Atrazine in maize due to hydroxylation of Atrazine in

maize roots by the enzyme Benzoxazinone.

3. Hydrolysis: Selectivity of Propanil between Echinochloa and rice is due to hydrolysis

of Propanil in rice due to presence of an enzyme called Aryl- acyl amidase.

4. Oxidation:

 Selectivity of 2,4DB, MCPB, MCPA in leguminous crops is due to β-

oxidation of these herbicides in non-leguminous weeds which makes them more
phytotoxic than the parent compounds. This is called reverse metabolism.

 Selectivity of Isoproturon between wheat and Phalaris is due to presence of P-

450 monooxygynase in wheat which oxidizes the compound.

5. N-Dealkylation: Substitution of alkyl groups from N –position of several herbicides.

Eg. Selectivity of Monuron/Diuron in cotton.

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Herbicide resistance & its management
Herbicide resistance is a phenomenon by which a plant/biotype is capable to survive and
reproduce seeds even after a exposure to a dose of herbicide normally lethal to the wild type.

Herbicide resistance is measured by Resistance Factor (GR50) values – based on the %

inhibition of growth / dry wt. of plant.

GR50 = GR50 values of resistant population

GR50 values of susceptible population
Types of resistance : -

1. Cross resistance: - It is the resistance of a weed biotype to two on more herbicides of

same on different chemical groups having the same mode of action by a single
resistance mechanism.
Cross resistance evolve when a weed biotype already resistant to a herbicide shows
resistance to other herbicides of same/ different chemical groups to which it had never
been exposed.
Eg:- Phalaris minor – already resistant to Isoproturon shows resistance to dictofop
methyl, clodina-fop prropargyl
Multiple resistance: - It refers to the herbicide resistance where a weed species
shows resistance to two or more herbicides of different chemical class having two
distinctly different mode of action through two different resistance mechanism.
Eg: - Lolium rigidum in Australia
Factors affecting herbicide resistance : -
a. Weed factors
1. Initial frequency of resistant weed species in a mixed population: - Higher the
initial frequency greater & quicker is the chance of developing resistance.
2. Hypersensitivity of weed spp. :- Some weed sp. are hypersensitive to a particular
herbicide which – kills – 90-95 % of its susceptible population with a single
application. In this case selection – pressure is higher & there is quicker chance of
resistance development.
3. Biological fitness: - It is the relative evolutionary advantages of a phenotype based on
its survival and reproductive success. If a resistant biotype is biologically more fit –
there is quicker establishment of resistance.
4. Weed biology (seed dormancy, germination, mode of pollination, seed production
capacity) & soil seed bank.
The development of resistance gets delayed if continuous recruitment of susceptible
individuals takes place from the soil seed bank by presowing tillage. This is further
influenced by dormancy germination characteristics of weed seeds, their seed
production ability etc.
5. Mode of inheritance of gene : - Inheritance of a single gene which confer resistance
against herbicide for a specific target site may dominate under field condition, inherit
and express readily under heterozygous condition resulting from out crossing of
weeds at field level.

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 b. Herbicide factor:-
1. Application of highly potent herbicide: - It increases selection pressure of resistance
biotypes and increase resistance.
2. Application of herbicide having a single target site specific mode of action: -
Frequently application of such herbicides over locations imparts high selection
pressure towards evolution of resistance weed biotypes.
3. Overdependence and frequent application of herbicide without rotation.
4. Application of herbicide having longer residual activity on soil.
5. Time & dose of application.
c. Crop management factor: -
1. Tillage : - Zero/min. tillage – imparts resistance
2. Monoculture : - Selective influence of particular weed to grow & consequently – use
of same herbicides to control- without rotation.
Management of herbicide resistance
Where resistance has already cropped up: -
1. Farmer‟s awareness, training & participatory approaches.
2. Abandonment of the herbicide to which weeds showing resistance.
3. Stopping of any sort of transaction of crop seed from an area having resistance to
anew area.
4. Clean tillage & having equipment.
5. Rouging and prevention of seed production & contamination of crops at harvest.
6. Use of competitive - & high yielding variety smothering effect.
7. Use of pure & certified seed.
8. Stale seed bed technique – for Phalaris minor
[fushes allowed to sprout – followed by killing up those flushes by non selective
herbicide like Glyphosate @ 0.4 – 0.5 Kg a.i./ha]
9. Crop rotation/substitution: - It facilitates – herbicides rotation which is very effective.
10. Proper – residue management
11. Evaluation of alternative herbicide having different mode of action & using them in
appropriate dose and time .
12. Herbicide mixture, sequence & rotation to avoid / delay development of cross /
multiple resistances.
13. Herbicide rotation: - Once in every three years.
14. Use of herbicide resistance crops (HRCS) / GM crops / transgenics.
Herbicide resistant crops (HRC)
A. Alteration of a crop to provide resistance to a herbicide that normally would kill the
crop
1. Traditional means of obtaining selectivity was to screen thousands of chemicals
hoping to find a herbicide that could be used on a crop without causing injury
2. HRC involve screening genes for selectivity, rather than screening chemicals
3. As it has become more difficult to identify selective herbicides (easy ones already
discovered), it is less expensive to screen genes
B. Methods of development

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1. Traditional breeding techniques
a. Triazine resistant canola – canola was crossed with a weedy mustard (field
mustard) that had developed resistance to triazines following repeated use
of atrazine (insensitive target site)
b. ALS-resistant corn – created by mutagenesis of pollen by UV light. A
mutation was found that resulted in an insensitive target site for ALS
herbicides
2. Transgenic crops (genetic engineering)
a. Gene that will provide resistance to a herbicide identified in some other organism and
transferred to crop plant
b. Glyphosate resistant (GR) crops (Roundup Ready)
i. Most RR crops use a gene for an insensitive target site (EPSPS) found in
bacterium. In some GR crops, a gene for an enzyme that metabolizes
glyphosate is included along with the modified target site. A second gene for
an insensitive enzyme has been identified from mutated corn is used in some
GR crops.
ii. Current RR crops: corn, soybean, cotton, sugarbeet, canola.
iii. Numerous other crops developed, including wheat, creeping bentgrass,
Kentucky bluegrass, etc. Registration is pending or on hold.
iv. RR alfalfa was approved in 2006, but a court order in 2007 stopped planting of
any new seed and established fields need to be closely monitored. Court
decided that the movement of the RR gene into conventional alfalfa could
cause loss of market for persons wanting to grow non-transgenic alfalfa
v. A gene that codes for an enzyme that degrades glyphosate has been identified
by DuPont and will be used in Optimum GAT crops. These crops will also
contains a gene for resistance to ALS herbicides
c. Glufosinate resistant crops
i. Gene for an enzyme that degrades glufosinate identified in bacteria and
inserted in crops
Current LL crops include corn, cotton, soybean and canola.

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 Chapter 13

Allelopathy

What Is Allelopathy?
Allelopathy refers to the beneficial or harmful effects of one plant on another plant, both crop
and weed species, from the release of biochemicals, known as allelochemicals, from plant
parts by leaching, root exudation, volatilization, residue decomposition, and other processes
in both natural and agricultural systems. Allelochemicals are a subset of secondary
metabolites not required for metabolism (growth and development) of the allelopathic
organism. Allelochemicals with negative allelopathic effects are an important part of plant
defense against herbivory (i.e., animals eating plants as their primary food) (Fraenkel 1959;
Stamp 2003).

The term allelopathy is from the Greek-derived compounds allelo and pathy (meaning
“mutual harm” or “suffering”) and was first used in 1937 by Austrian scientist Hans Molisch
in the book Der Einfluss einer Pflanze auf die andere - Allelopathie (The Effect of Plants on
Each Other) (Willis 2010). First widely studied in forestry systems, allelopathy can affect
many aspects of plant ecology, including occurrence, growth, plant succession, the structure
of plant communities, dominance, diversity, and plant productivity.

Nature of Allelopathy
Commonly cited effects of allelopathy include reduced seed germination and seedling
growth. Like synthetic herbicides, there is no common mode of action or physiological target
site for all allelochemicals. However, known sites of action for some allelochemicals include
cell division, pollen germination, nutrient uptake, photosynthesis, and specific enzyme
function. For example, one study that examined the effect of an allelochemical known in
velvetbean, 3-(3‟,4‟-dihydroxyphenyl)-l-alanine (l-DOPA), indicated that the inhibition by
this compound is due to adverse effects on amino acid metabolism and iron concentration
equilibrium.
Allelopathic Chemicals
 Phenolic acids
 Coumarins- block mitosis in onion by forming multinucleate cells
 Terpinoids
 Flavinoids
 Scopulatens- inhibits photosynthesis without significant effect on respiration

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 Ways of releasing allelochemicals
Allelopathic chemicals are released from the plants as:
 Vapour- from roots and leaves from stomata
 Foliar lechate
 Root exudates
 Breakdown/decomposition product of dead plant parts
 Seed extract
1. Volatilization: Allelopathic tress release a chemical in a gas form through small
openings in their leaves.
2. Leaching: Some plants store protective chemicals in their leaves. When the leaves
fall n the ground, they decompose and give off chemicals that protect the plant. Water
soluble phytotoxin may be leached from roots and above ground plant parts or they
may be actively exuded from living roots. Rye and quack grass release allelopathic
chemicals from rhizomes or cut leaves.
3. Exudation: Some plants release defensive chemicals into the soil through their roots.
The released chemicals are absorbed by the roots of nearby trees. Exuding
compounds are selectively to other plants. Exudates are usually phenolic compounds
(e.g. coumarins) that tend to inhibit development.
Types of allelopathy
1. Weeds on crop:
 Agropyron repens (Quack grass) generate ethylene in rhizomes due to
microbial activity in soil, which interferes with uptake of nitrogen and
potassium in maize and ultimately decrease in yield of it.
 Avena fatua (Wild oat) residues inhibit germination of certain herbaceous
species like wheat.
 Cynaodon dactylon (Bermuda grass) residues remains in the field inhibits
seed germination, root and top growth of barley.
 Sorghum halpense (Jhonson grass) is a perennial weed in sugarcane,
soybean, maize etc. Root exudates from decaying Jhonson grass is found
to have inhibitory effect on these crops.
2. Weed on weed:
 Imperata cylindrica (Cogon weed) inhibits the emergence and growth of
annual broad leaf weed, i.e., Borreria hispada by exudation of inhibitory
substance through rhizomes.

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  Sorghum halpense (Jhonson grass)- living and decaying rhizomes inhibit
the growth of Setaria viridis (Giant Foxtail), Digitaria Sanguinalis (Large
carb grass) and Amaranthus spinosus (Spiny amaranth).
3. Crop on weed:
 Oat, pea, wheat suppress the growth of Chenopodium album
(Lambsquater).
 Coffea arabica (Coffee) release 1,3,7 trimethylxanthin which inhibits
germination of Amaranthus spinosus (Spiny amaranth).
Factors affecting allelopathic effect
1. Varieties: There can be great deal of difference in the strength of allelopathic effects
between different crop varieties.
2. Specificity: The crop which shows strong allelopathic effect against one weed may
show little or no effect against other weeds.
3. Autotoxicity: Sometimes plant species may also suppress the germination and growth
of its own species. Eg. Lucerne
4. Crops on crop effect: Residues from allelopathic crops can hinder germination and
growth of following crops as well as weeds.
5. Environmental factors: Low fertility increases allelopathic effects due to more
production of allelochemiocals. Warm, wet condition can cause faster decline of
allelopathic effect as against slowest decline under cold and wet condition.

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 Chapter 14

Growth and development of crops

Plant growth: It is the irreversible, quantitative increase in size, mass, and/or volume of a
plant or its parts. It occurs with an expenditure of metabolic energy. Therefore, the events
leading to leaf formation and the increase in height of a plant are growth, but the increase in
volume of a seed due to uptake of water or imbibition is not growth. There are various ways
of quantifying plant growth. These include cell number, fresh weight, dry weight, plant
height, length, width, area, and volume. Each one has limitations. Growth is in general a
combined effect of cell division and cell enlargement. But in some instances, growth can
occur even without cell division and the reverse is also true. Likewise, early growth of the
embryo in the flower can be quantified by the increase in cell number although these cells
being small do not increase the size of the embryo.
Plant development: It is an overall term which refers to the various changes that occur in a
plant during its life cycle. Development consists of both growth and differentiation involving
quantitative and qualitative changes (Hopkins 1999). It is characterized by change in size,
shape, form, degree of differentiation and state of complexity (Abellanosa and Pava 1987).
However, there can be growth without differentiation and likewise there can be
differentiation without growth.
Factors affecting growth and development
Plant growth factors control or influence plant characteristics as well as adaptation. In
general, there are two factors affecting plant growth and
development: genetic and environmental. The genetic factor is also called internal factor
because the basis of plant expression (the gene) is located within the cell. The environmental
factor is considered external, and refers to all factors, biotic and abiotic, other than the genetic
factor. The genetic factor determines the character of a plant, but the extent in which this is
expressed is influenced by the environment. The environmental factors are divided into two
main groups: biotic and abiotic factors. The descriptive word biotic means living
while abiotic means non-living or dead.
The climatic factors include rainfall and water, light, temperature, relative
humidity, air, and wind. They are abiotic components, including topography and soil, of the
environmental factors that influence plant growth and development.

Moisture:
In crop agriculture, water is an important climatic factor. It affects or determines plant growth
and development. Its availability, or scarcity, can mean a successful harvest, or diminution in
yield, or total failure. Most plants are mesophytes, that is, they are adapted to conditions with
moderate supply of water. But some, called hydrophytes, require watery or water-logged
habitats while others, called xerophytes, are more tolerant to dry conditions.
Light:
Light is a climatic factor that is essential in the production of chlorophyll and
in photosynthesis, the process by which plants manufacture food in the form
of sugar (carbohydrate).
Temperature:
The degree of hotness or coldness of a substance is called temperature. It is commonly
expressed in degree Celsius or centigrade (C) and degree Fahrenheit (F). This climatic factor
influences all plant growth processes such as photosynthesis, respiration, transpiration,
breaking of seed dormancy, seed germination, protein synthesis, and translocation. At high

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temperatures the translocation of photosynthate is faster so that plants tend to mature earlier.
In general, plants survive within a temperature range of 0 to 50 0C.
Air:
The oxygen and carbon dioxide in the air are of particular importance to the physiology of
plants. Oxygen is essential in respiration for the production of energy that is utilized in
various growth and development processes. Carbon dioxide is a raw material in
photosynthesis. The favourable or optimal day and night temperature range for plant growth
and maximum yields varies among relative humidity crop species.

Relative humidity:
The relative humidity affects the opening and closing of the stomata which regulates loss of
water from the plant through transpiration as well as photosynthesis. A substantial
understanding of this climatic factor is likewise important in plant propagation. Newly
collected plant cuttings and bare root seedlings are protected against desiccation by enclosing
them in a sealed plastic bag. The propagation chamber and plastic tent are also commonly
used in propagating stem and leaf cuttings to ensure a condition with high relative humidity.

Wind:
Moderate winds favour gas exchanges, but strong winds can cause excessive water loss
through transpiration as well as lodging or toppling of plants. When transpiration rate exceeds
that of water absorption, partial or complete closure of the stomata may ensue which will
restrict the diffusion of carbon dioxide into the leaves. As a result, there will be a decrease in
the rate of photosynthesis, growth and yield.

Sigmoid Growth Curve

The curve can be shown appearing slowly along the line and stabilizing. During the initial
stage, i.e., during the lag phase, the rate of plant growth is slow. Rate of growth then
increases rapidly during the exponential phase. After some time the growth rate slowly
decreases due to limitation of nutrients. This phase constitutes the stationary phase.

The curve obtained by plotting growth and time is called a growth curve. It is a typical
sigmoid or S- shaped curve.

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Parameters used in growth analysis:

Leaf Area Index (LAI)

Leaf area is important for photosynthesis. Its estimation indicates both assimilating area and
growth. For crop production leaf area per unit land area is more important than leaf area of
individual plant. Leaf area index is the ratio between one sided leaf area to ground area.
Total leaf area for a given land area
LAI =
Land area considered
Crop growth rate (CGR):
It indicates at what rate the crop is growing i.e. whether the crop is growing at a faster rate
slower rate than normal. It is expressed as g of dry matter produced per day.
CGR = W2 – W1
T2 – T1
Where, W2 and W1 are the final and initial dry weights at times t2 and t1 respectively. It is
expressed in g/m2/day.
Relative growth rate (RGR):
This parameter indicates rate of growth per unit dry matter. It is similar to compound interest,
wherein interest is also added to the principal to calculate interest. It is expressed as g of dry
matter produced by a g of existing dry matter in a day.

It is expressed in g/g/day
Net Assimilation rate (NAR):
It indirectly indicates the rate of net photosynthesis. It is expressed as g of dry matter
produced per dm2 of leaf area in a day. For calculating NAR, leaf area of individual plants
has to be used but not leaf area index.
(W2 – W1)(LogeL2 – LogeL1)
NAR (g m-2 day-1) = (T2 – T1) (L2 – L1)
Leaf Area Duration (LAD):
Yield of dry matter is a function of leaf area, net assimilation rate and duration of leaf area.
Leaf area duration of a crop is a measure of its ability to produce leaf area on unit area of land
throughout its life cycle.

It is expressed in days.

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 Chapter 15

Plant Ideotype
According to Donald, ideotype is a biological model which is expected to perform or behave
in a particular manner within a defined environment: "a crop ideotype is a plant model,
which is expected to yield a greater quantity or quality of grain, oil or other useful product
when developed as a cultivar.

Features of Crop Ideotype:

The crop Ideotype consists of several morphological and physiological traits which contribute
for enhanced yield or higher yield than currently prevalent crop cultivars. The morphological
and physiological features of crop Ideotype is required for irrigated cultivation or rainfed
cultivation. Ideal plant whether the Ideotype is required for irrigated cultivation or rainfed
cultivation. Ideal plant types or model plants have been discussed in several crops like wheat,
rice, maize, barley, cotton, and bean. The important features of Ideotype for some crops are
briefly described below:

Wheat:

The term Ideotype was coined by Donald in 1968 working on wheat. He proposed Ideotype
of wheat with following main features:

1. A short strong stem. It imparts lodging resistance and reduces the losses due to lodging.
2. Erect leaves. Such leaves provide better arrangement for proper light distribution resulting
in high photosynthesis or CO2 fixation.
3. Few small leaves. Leaves are the important sites of photosynthesis, respiration, and
transpiration. Few and small reduce water loss due to transpiration.
4. Larger ear. It will produce more grains per ear.
5. A presence of owns. Awns contribute towards photosynthesis.
6. Presence of awns. Awns contribute towards photosynthesis.
7. A single culm.

Thus, Donald included only morphological traits in the Ideotype. However, all the traits were
based on physiological consideration. Finally (1968) doubted the utility of single clum in
wheat Ideotype. Considered tillering as important features of wheat flag type a wheat plant
with moderately short but broad flag leaf, long flag leaf sheath, short ear extrusion with long
ear, and moderately high tillering capacity should give yield per plant (Hsu and Watson,
1917). Asana proposed wheat Ideotype for rainfed cultivation. Recent workers included both
morphological and physiological characters in wheat Ideotype.

Rice:

The concept of plant type was introduced in rice breeding by Jennings in 1964, through the
term Ideotype was coined by Donald in 1968. He suggested that the rice an ideal or model
plant type consists of 1) Semi dwarf stature. 2) High tillering capacity, and 3) Short, erect,
thick and highly angled leaves (Jennings, 1964, Beachell and Jennings, 1965). Jennings also

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included morphological traits in his model. Now emphasis is also given to physiological traits
in the development of rice Ideotype.

Maize:

In 1975, Mock and Pearce proposed ideal plant type of maize. In Maize , higher yields were
obtained from the plants consisting of 1) Low tillers, 2) Large cobs, and 3) Angled leaves for
good light interception. Planting of such type at closer spacings resulted in higher yields.

Barley:

Rasmusson (1987) reviewed the work on Ideotype breeding and also suggested ideal plant
type of six rowed barley. He proposed that in barley, higher yield can be obtained from a
combination of 1) Short stature, 2) Long awns, 3) High harvest index, and 4) High biomass.
Kernel weight and kernel number were found rewarding in increasing yield

Cotton:

In cotton, genotypes with zero branch, short stature, compact plant, small leaves and fewer
sympodia were considered to enhance yield levels. Singh et al. (1974) proposed and ideal
plant type of uplant cotton growing belt. The proposed Ideotype includes

1) Short stature (90-120 cm),

2) Compact and sympodial plant habit making pyramidal shape,
3) Determinate the fruiting habit with unimodal distribution of bolling,
4) Short duration (150-165 days),
5) Responsive to high fertilizer dose,
6) High degree of inter plant competitive ability,
7) High degree of resistance to insect pests and diseases, and
8) High physiological efficiency, Singh and Narayana (1993) proposed an Ideotype of above
two species for rainfed conditions. The main features of proposed Ideotype include, earliness
(150-165 days), fewer small and thick leaves, compact and short stature, interminate habit,
spares hairness, medium to big boll size, synchronous bolling , high response to nutrients, and
resistance to insect and diseases.

Sorghum and Pearl millet:

Improvement in plant type has been achieved in Sorghum and Pearl millet through the use of
dwarfing genes. In these crop dwarf F1 hybrids have been developed which have made
combine harvesting possible.

Genetic improvements have been achieved thorough modification of plant type in several
crop species. New Ideotype have been proposed for majority of crop plants. Swaminathan
(1972) has listed several desirable attributes of crop Ideotype with special reference to
multiple cropping in the tropics and sub tropics. These features include:

1) Superior population performance,

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2) High productivity per day,

3) High photosynthetic ability,

4) Low photo respiration,

5) Photo and thermo sensitivity,

6) High response to nutrients,

7) High productivity per unit of water,

8) Multiple resistances to insect and diseases

9) Better protein quantity and quality

10) Crop canopies that can retain and fix a maximum of CO 2, and

11) Suitability to mechanization

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 Chapter 16
Crop rotation and its principles
Crop Rotation
It refers to recurrent succession of crops on the same piece of land either in a year or
over a longer period of time. It is a process of growing different crops in succession on a
piece of land in a specific period of time, with an objective to get maximum profit from least
investment without impairing the soil fertility.
Principles of Crop rotation:
1. It should be adaptable to the existing soil, climatic and economic factors.
2. The sequence of cropping adopted for any specific area should be based on proper
land utilization. It should be so arranged in relation to the fields on the farm that the
yields can be maintained and soil losses through erosion reduced to the minimum.
3. The rotation should contain a sufficient acreage of soil improving crops to maintain
and also build up the OM content of the soil.
4. In areas where legumes can be successfully grown, the rotation should provide for a
sufficient acreage of legumes to maintain the N supply of the soil.
5. The rotation should provide roughage and pasturage for the livestock kept on farm.
6. It should be so arranged as to help in the control of weeds, plant disease & insect-
pests.
7. It should provide for the acreage of the most profitable cash crops adapted to the area.
8. The rotation should be arranged as to make for economy in production & labour
utilization exhaustive (potato, sugarcane) followed by less exhaustive crops (oilseeds
& pulses).
9. The crops with tap roots should be followed by those which have fibrous root system.
This helps in proper & uniform use of nutrients from the soil & roots do not compete
with each other for uptake of nutrients.
10. The selection of crops should be problem and need/demand base.
a. According to need of people of the area & family.
b. On slop lands alternate cropping of erosion promoting and erosion resisting
crops should be adopted.
c. Under dryland or limited irrigation, drought tolerant crops (Jowar, Bajra), in
low lying & flood prone areas, water stagnation tolerant crops (Paddy, Jute)
should be adopted.
d. Crops should suit to the farmer‟s financial conditions, soil & climatic
conditions.
e. The crops of the same family should not be grown in succession because they
act like alternate hosts for insect pests & disease pathogens and weeds
associated with crops.
f. An ideal crop rotations is one which provide maximum employment to the
family & farm labour, the machines and equipments are efficiently used so all
the agricultural operations are done timely.

Advantages of Crop Rotation: An ideal crop rotation has the following advantages:

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 1. There is an overall increase in the yield of crops due to maintenance of proper
physical condition of the soil and its OM content.
2. Inclusion of crops having different feeding zones and different nutrient requirements
help in maintaining a better balance of nutrients in the soil.
3. Diversification of crops reduces the risk of financial loss from unfavourable weather
conditions and damage due to pests & diseases.
4. It facilitates more even distribution of labour.
5. There is regular flow of income over the year.
6. The incidence of weeds, pests and diseases is reduced and can be kept under control.
7. Proper choice of crops in rotation helps to prevent soil erosion.
8. It supplies various needs of farmer & his cattle.
9. Agricultural operations can be done timely for all the crops because of less
competition. „The supervisory work also becomes easier.”
10. Proper utilization of all the resources and inputs could be made by following crop
rotation:

Cropping System: It represents a cropping pattern (i.e. the proportion of area under various
crops at a point of time in a unite area) used on a farm and their interaction with farm
resources, other farm enterprises and available technology, which determine their makeup. It
is defined, as the order in which the crops are cultivated on a piece of land over a fixed period
or cropping system is the way in which different crops are grown. In the cropping systems,
sometimes a number of crops are grown together or they are grown separately at short
intervals in the same field.

Cropping pattern:

The yearly sequence and spatial management of crops and fallow on a given area is known as
cropping pattern.

Cropping pattern Cropping system

Crop rotation is practiced by majority of Management of cropping pattern for
farmers in a given locality maximum benefits from a given resource
base in a given environment
Type and arrangement of crops in time and Cropping pattern used on a farm and their
space. interactions with farm resources, other farm
enterprises and available technology which
determine their makeup.
The yearly sequence and spatial management Pattern of crops taken up for a given piece of
of crops and fallow on a given area is known land or order in which the crops are grown on
as cropping pattern. a piece of land over a fixed period, associated
with soil management practices such as
tillage, maturing and irrigation.
The proportion of area under different crops
at a point of time in a unit area.

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 Chapter 17

Harvesting and threshing of crops

Removal of entire plant or economic parts after maturity from the field is called
harvesting. It includes the operation of cutting, picking, plucking or digging or a combination
of these for removing the useful part or economic part from the plants/crops. The portion of
the stem that is left in the field after harvest is called as stubble. The economic product may
be grain, seed, leaf, root or entire plant.

Harvest Index (H.I): It is the ratio of the economic yield to the total biological yield
expressed as percentage. H.I = (Economic yield/Biological yield) × 100

Time of Harvesting: If the crop is harvested early, the produce contains high moisture and
more immature ill filled and shriveled grains. High moisture leads to pest attack and
reduction in germination percentage and impairs the grain quality. Late harvesting results in
shattering of grains, germination even before harvesting during rainy season and breakage
during processing.

External Symptoms of Physiological Maturity

The major symptoms of physiological maturity of some field crops are as follows:

• Wheat and Barely–Complete loss of green colour from the glumes.

• Maize and Sorghum–Black layer in the placental region of grain

• Pearl millet–Appearance of bleached peduncle

• Soybean–Loss of the green colour from leaves.

• Redgram–Green pods turning brown about 25 days after flowering.

Harvest Maturity Symptoms

The harvest maturity symptoms of some important crops are as follows:

• Rice–Hard and yellow coloured grains.

• Wheat–Yellowing of spikelets.

• Sorghum, Pearl millet, foxtail millet–Yellow coloured ears with hard grains.

• Ragi–Brown coloured ears with hard grains

• Pulses–Brown coloured pods with hard seeds inside the pods.

• Groundnut–Inner side of the pods turn dark from light color.

• Sugarcane–Leaves turn yellow.

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• Tobacco–leaves slightly turn yellow in colour and specks appear on the leaves.

Criteria for Harvesting of Crops

The criteria for harvesting of crops are given in Table.

Crop Criteria for Harvesting of Crops

Rice 32 days after flowering, Green grains not more than 4-9%

Wheat About 15% moisture in grain, Grain in hard dough stage.

Maize 25–30 days after tasselling, Seed moisture content is at 34%
Sorghum 40 days after flowering
Cumbu 28–35 days after flowering
Redgram 35–40 days after flowering
Black/Green gram Pod turn brown/black
Rapeseed/mustard 75% of the silique turn yellow, Seed moisture at 30%
Sunflower Back of heads turns to lemon yellow
Groundnut Yellowing of leaves and shedding Development of purple colour of
the testa
Cotton Bolls fully opened
Jute 50% pod stage (120–150 days)
Sugarcane Brix 18–20%, Sucrose 15%
Determination of harvesting date is easier for determinate crops and difficult for
indeterminate crops because at a given time, the indeterminate plants contain flowers,
immature and mature pods or fruits. If the harvesting is delayed for the sake of immature
pods, mature pods may shatter, if harvested earlier, yield is less due to several immature
pods. This problem can be overcome by

• harvesting pods or ears when 75% of them are mature (or)

• periodical harvesting or picking of pods

• inducing uniform maturity by spraying Paraquat or 2, 4-D sodium salt.

In fodder crops, toxins present in the crop, nutritive value, purpose of harvest
(whether for stall feeding or for storage) and single or multi cut are also to be considered
during harvest. Example–HCN toxin content in sorghum is high up to 30–45 DAS.

Methods of Harvesting

Harvesting is done either manually or by mechanical means.

(i) Manual: Sickle is the important tool used for harvesting. The sickle has to be sharp,
curved and serrated for efficient harvesting. Knife is used for harvesting of plants with thick
and woody stems. Now-a-days improved type of sickle is available which reduce the
drudgery of harvesting labourers.

(ii) Mechanical: Harvesting with the use of implements or machines.

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