Soil Fertility – Its Meaning, Causes and Maintenance (With Diagram)

Read this article to learn about Soil Fertility – Its Meaning, Causes and Maintenance!

Soil fertility may be defined as the ability of soil to provide all essential plant nutrients in available forms and in a suitable balance whereas soil productivity is the resultant of several factors such as soil fertility, good soil management practices availability of water supply and suitable climate.

The soil is a natural medium for plant growth and it supplies nutrients to plants. Some soils are productive and they support luxuriant growth of plants with very little human effort whereas others may be unproductive which support almost no useful plant life regardless of every human effort In order for soil to be productive, it must:

(i) Be easily tillable and fertile

(ii) Contain all essential elements in the forms readily available to plants in sufficient amount, and

(iii) Physically good to support plants and contain just the right amount of water and air for proper root growth. The soil must supply these essentials every day in the life of the plant.

Soil fertility and soil productivity appear to be synonymous but in soil science these two terms bear different meanings. Soil fertility may be defined as the ability of soil to provide all essential plant nutrients in available forms and in a suitable balance whereas soil productivity is the resultant of several factors such as soil fertility, good soil management practices availability of water supply and suitable climate.

A soil can be highly fertile, i.e., it has ready supply of nutrients in available form, yet it may not be highly productive. Water-logged soils may be highly fertile but may not produce good crop because of the un-favourable physical conditions.

A fertile soil may be highly saline or alkaline which may not be good for agriculture Sandy soil may be poor in fertility but with the use of fertilizers and water it may be made productive. Soil fertility thus denotes the status of plant nutrients in the soil whereas the soil productivity is the resultant of various factors influencing crop production. In fact there is no standard for either fertility or productivity because both depend upon the crops to be grown. Soil that is productive for potatoes may not necessarily be productive for certain other crops.

Plant Nutrients:

Of the 90 or so chemical elements forming the earth’s crust, 16 are known to be essential for plant growth and reproduction. Seven elements needed in good quantity (macro nutrients) are hydrogen, oxygen, nitrogen and carbon from air and water and phosphorus, potassium and calcium from mineral particles in the soil. The other 9 elements needed only in small amount (micronutrients) are magnesium, sulphur, boron, copper, iron, manganese, zinc, molybdenum and chlorine.

Jacob and Uexkull have listed cobalt and sodium as essential elements for plant growth. With the exception of hydrogen, carbon, and oxygen all other inorganic plant requirements are obtained directly or indirectly from the soil minerals, hence these elements are called mineral nutrients. Strictly speaking, nitrogen is not a mineral element but it has been included in the list because it can also be obtained by plants from soil.

The mineral elements are taken by plants from soils mostly in the form of ions. Plants obtain nutrients from the following four devices:

(i) From the soil solutions through roots,

(ii) From exchangeable ions on the surface of clay and humus particles through roots,

(iii) From readily decomposable minerals, and

(iv) Through the leaves.

The essentiality of an element is proved by the following criteria:

(a) The element may be considered essential if its exclusion from the nutrient medium inhibits or drastically reduces the growth and reproduction of plant.

(b) Acute deficiency of the element produces certain well defined disease symptoms which are not produced by the deficiency of any other element.

(c) Deficiency disease symptoms will disappear if the particular element is supplied before the living system has been damaged beyond repairs.

The capacity of soil to supply the essential elements is a fundamental edaphological problem In natural habitat the plant matter is returned to ground through decay and unless there is extensive leaching and percolation the inorganic nutrients become available again for new growth Many farm crops are removed from ground in to and the supply of essential elements thereby becomes depleted.

To replace these elements taken away from ground by crops, the manures or fertilizers are added. Unless it is done the crop will suffer from deficiencies in the essential elements. Deficiencies become reflected in the growth of plants in several ways; some may cause a reduction in yield as a result of poor plant growth and some may delay maturation of crop a function that may be very vital to crop yield in the places where the growing season is short

The symptoms of mineral deficiencies may be dwarf, spotted, distorted, curled or wilted leaves or rotting of the centre of fruits. Different mineral nutrients have certain specific deficiency symptoms. The physiological roles of various mineral elements in the life of plants and deficiency symptoms caused by them can be found in any plant physiology book.

Soil Fertility Factors:

Several factors are known to govern the fertility of soil. Some of the important factors are discussed below:

1. As a result of cropping, a large amount of organic matter and soil minerals are removed and if the normal cycling of mineral elements is retarded, loss in soil fertility may result.

2. Besides cropping, soil erosion and loss of water also causes tremendous loss of plant nutrients from the top soil.

Generally, water is lost through leaching, drainage, evapotranspiration and runoff.

The following adverse affects are observed due to water loss:

(i) Soil becomes very hard.

(ii) The seed germination percentage decreases.

(iii) The nutrients in the soil leach or evaporate.

(iv) The root growth retards, so that plants become stunted and, as a result, the yield is reduced.

(v) Stomata become closed, as a result of which accumulation of gases or metabolic wastes increases in plant tissues leading to death of the plant.

(vi) The activity of soil-micro organisms decreases.

3. Conversion of organic forms of nitrogen locked in humus into ammonia gas and nitrogen gas and leaching out of soluble nitrates and nitrites from surface soil greatly affect the fertility status of soil.

4. Like deficiency, the abundance of certain nutrient elements in soluble form may also be toxic and even the elements, say alkalies, essential for plant growth may be toxic if present in excess. Flowering plants do not grow in the soil containing more than 6 per cent NaCl and other salts. The elements are not equally toxic and the various species of plants differ in their susceptibility to different elements.

5. Toxic chemicals and pesticides in soil:

Several agricultural chemicals being used for controlling various diseases and insect pests are highly toxic and their application adversely affects the soil micro flora and fauna. Prolonged persistence of these pesticides in soil is bound to lower the soil fertility both directly and indirectly.

6. Soil reaction:

The soils may be alkaline or neutral or acidic in their reaction. Some plants find acid soil unsuitable for growth and other plants find alkaline ground un-favourable. pH value of soil solution determines the availability of certain plant nutrients and thus it has bearing on soil fertility problem. Increase in the acidity of the soil makes mineral salts more soluble in soil solution and thus salts may become available in concentrations that may be highly toxic or may damage plants growing in such soils. Janick et al. (1969) have demonstrated that high concentration of both iron and aluminium may damage plants growing in acid soils.

Maintenance of Soil Fertility:

Soil fertility is the most important asset of a nation. Maintenance of soil fertility is an important aspect of agriculture. The soil fertility problem has been studied in many countries and scientists have brought to light several facts concerning soil fertility and its maintenance.

Soil fertility is of two types;

(a) Permanent fertility:

It is derived from the soil itself. It can be improved, maintained or corrected by soil management practices.

(b) Temporary fertility:

It is acquired by suitable soil management but the response of built up soil fertility is highly dependent on the degree of permanent fertility which is already there. Several methods are known for controlling the loss of soil fertility. Here only the important methods are discussed.

1. Application of Organic Manures and Chemical Fertilizers:

Plants absorb water and minerals from the soil, which is essential for growth, flowering, crop yield, and other vital activities. Soil is a store house for organic and inorganic plant nutrients. Some soils are rich in organic and humus content and are considered to be fertile and more productive while others that are deficient in humus and minerals are less productive.

The soil is subjected to a continuous depletion of nutrients due to its continuous use by crops. This requires the addition of mineral resources. The various soil components are being removed by living organisms and are returned to the soil by death and decay of organisms. If the rate of removal or loss of minerals is greater than the rate of addition, the soil will naturally become less fertile. The minerals of the soils are lost due to crops, leaching or soil erosion.

The minerals are often removed from the top layer by rainwater. Cultivation of crops regularly, year after year, makes the soil less productive. In intensive cultivation there are little chances for the restoration of lost nutrients in the soil until they are supplied from outside. The leguminous plants, however, compensate the loss of nitrogenous compounds. Besides this, manure and fertilizers are to be supplemented to restore the fertility of the soil.

The deficiency of mineral nutrients in the soil either can be compensated through organic manures such as green manuring, compost etc. or it can be supplemented by the application of chemical fertilizers from outside sources.

A. Organic Manures:

The organic content of the soil which is a good source of plant nutrients contributes most to the fertility of the soil.

Organic manures improve soil fertility in the following ways:

(i) They modify the physical properties as increase in granulation of the soil and increase in permeability and moisture holding capacity of soil.

(ii) They provide food for soil microbes and thus enhance microbial activities.

(iii) Decomposition products of organic manures help to bring mineral constituents of soil into solution.

(iv) They improve physico-chemical properties of soil, such as cation exchange and buffering action.

Organic manures are of several kinds some of which are discussed below:

(i) Farmyard manures:

Solid and liquid excreta as dung and urine of all farm animals are termed farmyard manures. They are ready made manures and contain nitrogen, phosphorus and potassium. The farmyard manures of different animals vary greatly in their composition but they are good for all types of soils and all the crops. Farmyard manure when collected in field in exposed condition for several months shows considerable loss of fertilizing value as upon decomposition a considerable amount of ammonia is lost by volatilization.

Therefore, it is important to keep manure protected from weather and manure preparation should be carried out in trenches of about a metre depth. When the trenches are filled with dung etc, the surface is covered with a cow dung-earth slurry. In about 3 months the manure becomes ready for use.

(ii) Compost:

Compost manure can be prepared from a variety of refuse materials, such as straw, sugar cane refuse, rice hulls, forest, litter, weeds, leaves, kitchen wastes. It is prepared in pits usually 6-8inlong, 1½ to 2inwide and one metre deep. In the pits, 30 cm thick layer of plant residues moistened with dung, urine and water is formed and then a second layer of about 30 cm thickness of mixed refuse is spread over it and moistened with slurry. The operation is repeated until the heap rises to a height of about 50 cm above the ground level. The top is then covered with a thin layer of moist earth. After three months of decomposition the material is well mixed and again covered. After a couple of months the manure is ready for use.

There are two types of composts:

(а) Farmyard compost which is obtained from animal excreta and plant residues.

(b) Town compost which is obtained by decomposition of kitchen wastes and garbage of towns and cities. Compost manures are rich in all plant nutrients.

(iii) Green manures:

Green manuring is the practice of growing, ploughing and mixing of green crops with soil to improve soil fertility and productivity. Its effects on soils are similar to those of farmyard manures. It is cheap and the best method to increase soil fertility as it can supplement farmyard and other organic manures without involving much cost. Green manures add nitrogen and organic matter to the soil for the improvement of crop yield.

Through green manuring mobilization of minerals, reduction of organic nutrient losses due to erosion, leaching and percolation, and improvement in physical, chemical and biological activities of the soil can be achieved. Green manuring also improves soil aeration and drainage conditions. For green manuring both leguminous and non-leguminous crops are used. In India, leguminous crops such as sannhemp (sanai), dhaincha, berseem, clover, Phaseolus mungo, cowpea, are generally used for green manuring.

(iv) Sawdust:

Sawdust can be used as bedding material to conserve animal urine or for making compost. It is a low fertilizing material but it is definitely richer than wheat straw in calcium.

(v) Sewage:

In modem system of sanitation, water is used for removal of human excreta and other wastes.

Sewage consists of two components:

(a) The solid part, called sludge and

(b) The liquid part, called effluent or sewage water.

Sewage is quite rich in several plant nutrients and can be used for fertilizing the crop by irrigating the soil directly with sewage water but there is a danger for the spread of several human diseases.

B. Chemical Fertilizers:

Of the elements known to be essential for plant growth, nitrogen (N), phosphorus (P) and potassium (K) are required by plants in pretty large amounts, and are therefore, designated as major ox primary nutrients while calcium, magnesium and sulphur are secondary nutrients. For acid soils, use of Ca and Mg is necessary. Seven elements iron, manganese, boron, molybdenum, copper, zinc and chlorine are required in trace amount and hence called micro-nutrients.

Under continuous cultivation our soils are losing organic matter and mineral nutrients faster than they can be replaced. Regular loss of nutrients from the soil results in compact soil, shallow roots, increased drought, daddy and poorly productive soil. So, for the maintenance of soil fertility quick replacement of the organic matter and mineral nutrients removed from the soils is necessary (Table 26.1).

Nitrogen (N), phosphorus (P) and potassium (K), i.e., the primary plant nutrients are commonly applied to soils in the form of commercial fertilizers and hence they are often referred to as fertilizer elements.

Chemical fertilizers are classified into the following three group on the basis of materials supplied:

(i) Nitrogenous fertilizers.

(ii) Phosphorus fertilizers, and

(iii) Potassium fertilizers.

Classification is not so simple as this grouping would imply, several such fertilizer materials as contain two of these elements, as for example, potassium nitrate and ammonium phosphate.

(i) Nitrogenous fertilizers:

Crops usually take nitrogen from the soil in the form of nitrate (NO₃-) and ammonium ions (NH₄⁺).

Nitrogen fertilizers may be divided for convenience into two groups:

(a) Organic nitrogen fertilizers, and

(b) Inorganic nitrogen fertilizers.

(a) Organic nitrogen fertilizers:

Organic materials such as cotton seed meal, guano and fish tank age are nitrogen carriers but because they supply less than 2% of total nitrogen added in commercial fertilizers, their use is costly and hence they are not used extensively. Nitrogen of organic fertilizers is released slowly by microbial action. They are used as special fertilizers for gardens, lawns and potted plants.

(b) Inorganic nitrogen fertilizers:

Several inorganic chemicals are used to supply nitrogen to plants. The most important of these are presented in Table 26.1.

(ii) Phosphorus fertilizers:

Phosphorus has rightly been called ‘master key’ to agriculture as low crop production is due more often to lack of phosphate than to the deficiency of any other element except nitrogen. In phosphorus fertilizers this element is present in the form of phosphate or superphosphate salts and it is available to the plants when it is combined with organic matter or with calcium and magnesium. Phosphorus is also found in combination with iron and aluminium and is present in certain rock minerals as apatite.

Plants take up phosphorus chiefly as phosphate (PO₄)^–, HPO₄^– and H₂PO₄^– ions and the availability of these ions depends chiefly upon the acidity of ground. They become nearly insoluble in strongly acid or strongly alkaline soils. Release of phosphorus from phosphate rocks is slow. The breakdown of phosphate fertilizers produces phosphoric acid (P₂O₅) in soluble form that is absorbed by plants.

Use of phosphate fertilizers on alkaline soils is not suitable. Phosphorus fertilizers are classified into (i) water soluble, (ii) citrate soluble, and (iii) insoluble. When the term P.O, is used it means water soluble plus citrate soluble P₂O₅. The following are the important phosphate fertilizers being used in all parts of the world including tropical Asia (Table 26.2).

Superphosphate:

It is water soluble fertilizer. It does not affect the soil adversely. It contains mono-calcium phosphate, di-calcium phosphate and tri-calcium phosphate, gypsum, silica, iron aluminium sulphate and calcium fluoride and water.

Ammonium phosphate:

It is a fertilizer containing both nitrogen and phosphorus. It is rich in phosphoric acid content but comparatively low in nitrogen content. Ammonium superphosphate (NH₄H₂PO₄). Ca₃ (PO₄)₂ (NH₄)₂ SO₄. It is the cheapest fertilizer and is a mixture of nitrogen and phosphorus fertilizers. It contains nitrogen 3 to 4 per cent and phosphorus pentaoxide (P2O5) 16 to 18%.

Nitro-phosphate:

It is highly hygroscopic. It contains nitrogen 13-18 per cent and phosphorus 20 per cent. It is suitable for acid soils.

Bone meal:

It is derived from bone. Bone ash and bone char are the bone products. It is suitable for acidic soils.

Basic slag:

Basic slag, a by-product in the manufacture of steel, is one of the cheapest sources of phosphorus. It is a double compound of silicate and phosphate of lime. It is dark brown in colour and alkaline in reaction.

Rock phosphate:

It occurs in natural deposits. It is light grey in colour. It is a very cheap fertilizer suitable for acid soils.

(iii) Potassium fertilizers:

These fertilizers are soluble in water which means that potassium is readily available to plants. Total potassium of potassium fertilizers is usually expressed in terms of water soluble potassium (K) or potash (K₂O). Soils of arid and semiarid areas are generally well supplied with potassium. Acid soils usually need potassium fertilizers more than neutral or alkaline soils because acid soils develop in the areas of high rainfall that leaches out available potassium. All potassium fertilizers are physiologically neutral in reaction.

The following are some common potassium fertilizers:

(i) Potassium chloride:

It is also called muriate of potash. It contains 48—62% K₂O. It is also cheap and neutral in reaction.

(ii) Potassium sulphate:

It contains about 50% potash (K₂O). It is expensive fertilizer.

(iii) Kainite:

It is natural potassium mineral which contains 14—20% potassium. It is suitable for alkaline soils.

(iv) Wood ashes:

It is used in the form of ash as a manure. Potassium occurs in the form of potassium carbonate and the percentage of potash is from 2 to 6.5. It is suitable for alkaline soils.

Application of Micronutrients:

In order to correct the deficiency of micronutrients, especially if it is very necessary, micronutrients should be added only after ascertaining the amount required. Copper, manganese, iron zinc are supplied generally as their sulphate and boron is applied as borax. Molybdenum is supplied as sodium molybdate. In recent years there has been an increase in use of chelates to supply iron, zinc, manganese and copper.

Soils vary in their ability to supply available nutrients. Some soils may be deficient in nitrogen, some may be deficient in nitrogen and phosphorus, and still some others may be deficient in nitrogen, phosphorus and potassium. To suit the variable requirements of different soils and crops, fertilizer mixtures are prepared. Fertilizer mixtures or mixed fertilizers contain two or more fertilizer materials. If the ingredients and their amounts are known, the formula is referred to as open and if they are not disclosed the formula is termed closed one.

The kinds and amounts of fertilizers to be applied to soil are determined considering the following points:

(a) Kinds of crop to be grown—particularly its economic value, nutrient removal and absorbing ability.

(b) Chemical condition of soil in respect of total nutrients and available nutrients.

(c) Physical state of the soil, especially its moisture content and aeration. For recommending the kind and amount of fertilizers or soil amendments, the analysis of soil is essential.

2. Application of Soil Conservation Practices:

Loss of plant nutrients and water from the soils due to soil erosion can be checked effectively and the fertility of soil can be maintained by application of various biological and engineering methods of soil conservation. A detailed account of these methods has already been given in soil conservation topic.

3. Water management Practices (Irrigation and Drainages):

Water supply is critical factor in crop production in most areas of the world. Soil moisture greatly affects the availability of mineral nutrients in the soil. It has been proved beyond doubt that fertilizer response is much higher with adequate irrigation.

Drainage and moisture control influence micronutrient availability in soils. Improving the damage of acid soils encourages the formation of less toxic oxidized forms of iron and manganese.

4. Prevention and Elimination of Inorganic Chemical Contamination of Soil:

Loss of soil fertility due to application of toxic chemicals as pesticides can be eliminated if:

(i) Application of toxic chemicals to soil is reduced and

(ii) The soil and crop are so managed as to prevent cycling of toxic chemicals.

5. Stabilization of Soil pH:

The stabilization of pH through application of soil amendments and buffering seems to be an effective guard against the problems of non-availability of certain plant nutrients and radical changes in microbial activities arising due to change in soil pH.

Irrigation Systems:

Water is a very important natural resource, which is the basis of all life forms. For sustainable agricultural production, water is one of the most precious important inputs. Plants need water in huge amount throughout their life. Water is also one of the main factors that influence most of the metabolic process such as photosynthesis, respiration, adsorption, opening and closing of stomata and translocation of food material. The growth and yield of crop plants is very much affected by the availability of water.

Water is used in two ways:

1. Withdrawal or off-channel use

2. Non-withdrawal or on-channel use.

The amount of water taken out of a streams or pumped out from underground water reservoir or surface water reservoirs to be supplied to the points of major use, such as public water supply systems, irrigation and industries, is referred to as off channel use. In non-withdrawal use, water is used without being removed from its natural source such as for navigation, swimming bodies, wildlife habitats and other recreation purposes.

Need for Irrigation:

Irrigation is the artificial watering of soil to sustain plant growth. Irrigation has become necessary because of the limitation of using natural rainfall as the reliable source of water for agriculture. It is also difficult to store the rainwater for immediate irrigation purposes.

In India, monsoon is usually erratic; sometimes delayed, sometimes scarce or sometimes in excess. Through the monsoon season usually lasts for four months, most of the rains occur only during two months. Therefore, it is very difficult to plan the cropping pattern depending solely on the rams. The sufficient recharging of ground water is essential for sustainable farming, but usually this objective is not fulfilled due to unpredictable and fluctuating rains.

The efficient utilization of water resources is essential for better crop production. It includes the suitability of land and water for irrigation, planning of crops and suitable water management practices. Water management includes irrigation and drainage.

The suitable irrigation depends on:

Time of irrigation

Amount of irrigation, and

Efficient method of irrigation

Similarly, suitable drainage depends on:

How much to drain

How best to drain

How rapidly to drain

Stages of Crop when Irrigation is required:

The growth span of a crop plant passes through various phases and stages of growth. The rate of irrigation varies during the different stages of plant growth, i.e., from seedling to maturity stage. The growth period of irrigated crops can generally be divided into three phases, namely vegetative, flowering and maturity stage. At vegetative stage, light and intermittent irrigation is required whereas at flowering stage moderate and frequent irrigation is needed and during crop maturation stage again light irrigation is required.

Systems of Irrigation:

There are different water sources from which irrigation is carried out, for example, canals, wells, open wells, tube wells, tanks etc.

Depending upon the crops, soil types, water resources, climate conditions and costs involved, several systems of irrigation are used which are as follows:

1. Surface irrigation systems

2. Subsoil irrigation systems

3. Drip irrigation systems

Surface Irrigation System:

In this system, water is directly used on the surface of the soil and water follows the slope of the land, the surface irrigation system may be of following types:

Flood irrigation:

Flood irrigation is used for close-grown crops such as rice and where farm fields are leveled and water is abundant. A sheet of water is allowed to advance from different sources and remains on a field for a given period, depending on the crop, the porosity of the soil and its drainage (Fig. 26.1 a).

Basin flooding:

It is used in widely spaced trees, such as in orchards, with basins built around trees and filled with water (Fig. 26.1c).

Check basin:

This system of irrigation is widely used in India, as it is more suitable to all types of soils and to a variety of crops.

Furrow irrigation:

In furrow irrigation, water moves in the fields in furrows, between two ridges (Fig. 26.1b). It is employed in the fields with row crops such as cotton and vegetables. Parallel furrows, called corrugations, are used to spread water over fields that are too irregular to flood.

Sprinkler Irrigation System:

In this system, irrigation is done through pressure, to the surface of any crop or soil, in the form of a thin spray. Sprinkler irrigation system uses less water and provides better control. Each sprinkler, spaced along a pipe, sprays water in a continuous circle until the moisture reaches the root level of the crop. Centre-pivot irrigation uses long lines of sprinklers that revolve in a circular field. It is used especially for feed crops such as alfalfa, tall crops and orchards (Fig 26.2a).

1. Sprinkler irrigation system conveys water from the source to the field, through pipes under pressure, and distributes over the field in the form of spray of ‘rain like’ droplets (Fig. 26.2b).

2. 10-20% of area is not irrigated at the comers of square of rectangular plot.

3. This system requires high energy and involves huge cost of the equipment.

This system can be followed in conditions when:

1. The soil is too shallow.

2. The land is too steep.

3. Less and frequent irrigations are needed.

4. The soils are very sandy.

This system is disadvantageous in the following conditions when:

1. Strong winds cause improper distribution of water.

2. Evaporation losses are high from sprinkler irrigation, especially under high temperature and low relative humidity conditions.

3. The initial cost is high.

Sub-Soil Irrigation System:

In this system, irrigation is done into a series of ditches in the field deeply to the impervious layer. Then it moves laterally and vertically through capillaries saturating the root /one. In this system, continuous supply of water in the root zone is assured from the artificial water table created by the ponding of irrigation water on the impervious layer. This system is very efficient because the water losses through evaporation from surface can be reduced. This system is more common in Gujarat and Jammu and Kashmir, for cash crops growing on sandy loam soils.

Drip Irrigation System:

It is also called trickle irrigation. This irrigation system involves the slow application of water, drop by drop, to the root zone of a crop. It is done through mechanical devices called emitters, located at selected points along water delivery lines. Drip irrigation is extensively used in areas of acute water scarcity and especially for crops such as coconut, grape, banana, citrus, sugarcane, cotton, maize, tomato and plantation crops (Fig. 26.3).

Advantages of Drip Irrigation:

1. Water loss through transpiration is low.

2. It is possible to obtain better yield and quality of crops by controlling soil moisture-air- nutrient levels.

3. We can save the fertilizers by monitoring the supply of nutrients as per the need of the crop.

4. Improvements in biological fertility can be achieved by avoiding pollution.

Disadvantages of Conventional Irrigation Methods:

i. Major part of the water goes waste, only small quantity of water is utilized by the plants.

ii. Water is not uniformly distributed due to uneven and poor leveling of the field.

iii. Crops are usually subjected to cyclic changes of flooding and water stress situations by providing heavy irrigation at one time and leaving the fields to dry up for about 10 to 15 days.

iv. The low lying fields always get excess water that causes prolonged water logging, due to lack of leveling of fields.

v. In the fields, about 10-15% of land is utilized for making channels and distributaries etc. which decreases the area of cultivation.

vi. Excessive irrigation and poor water management leads to water logging and accumulation of salty in the upper layer of the soil.

vii. In conventional irrigation, unmanageable and undesirable weeds grow.

Problems of Excess Irrigation:

i. Excess irrigation causes several changes in the soil and plants, resulting in reduced growth and sometimes even death of plants.

ii. Germinating seeds are sensitive to water logging, since they are totally dependent on the surrounding soil space for oxygen supply

iii. Yield of cereals is reduced if excess irrigation is given.

iv. Excess water causes injury to the plant due to low oxygen supply to the root system and accumulation of toxic substances in the soil.

v. Leaching of nitrates and de-nitrification occur which result in nitrogen deficiency.

vi. Permeability of roots decrease due to shortage of oxygen. It results in decreased uptake of water and nutrient.