Plant nutrition and the soil-plant system. The key-role of fertilizers and their judicious use in crop husbandry is well understood, when one is familiar with the general facts about plant nutrition. It is now known that at least 16 plant-food elements are necessary for the growth of green plants. These plant-nutrients are called essential elements. In the absence of any one of these essential elements, a plant fails to complete its life cycle, though the disorder caused can, however, be corrected by the addition of that element.These 16 elements are: Carbon(C), hydrogen(H), oxygen(O), nitrogen(N), phosphorous(P), sulphur(S), potassium(K), calsium(Ca),magnesium(Mg), iron(Fe), manganese(Mn), zinc(Zn), copper(Cu), molybdenum(Mb), boron(B) and chlorine(Cl). Green plants obtain carbon from carbon-di-oxide from the air; oxygen and hydrogen from water, whereas the remaining elements are taken from the soil. Based on their relative amounts, normally found in plants, the plant nutrients are termed as macronutrients, if large amounts are involved, and micronutrients, if only traces are involved. The micronutrients essential for plant growth are iron, manganese, copper, zinc, boron, molybdenum, and chlorine. All other essential elements listed above are macronutrients.

As mentioned above, most of the plant nutrients, besides carbon, hydrogen and oxygen, originate from the soil. The soil system is viewed by the soil scientists as a triple-phased system of solid, liquid and a gaseous phases. These phases are physically seperable. The plant nutrients are based in the solid phase and their usual pathway to the plant system is through the surrounding liquid phase, the soil solution and then to the plant root and plant cells. This pathway may be written in the form of an equation as: M(Solid)->M(Solution)->N(Plant root)->(Plant top) where 'M' is the plant nutrient element in continual movement through the soil-plant system. The operation of the above system is dependent on the solar energy through photosynthesis and metabolic activities. This is however, an oversimplified statement for gaining a physical concept of the natural phenomenon, but one should bear in mind that there are many physico and physico-chemical processes influencing the reactions in the pathway. The actual transfer in nature takes place through the charged ions, the usual form in which plant-food elements occur in solutions(liquid phase of the system). Plant roots take up plant-food elements elements from the soil in these ionic forms. The positively charged ions are called 'cations' which include potassium(K⁺), Calcium(Ca⁺⁺), magnesium(Mg⁺⁺), iron(Fe⁺⁺⁺), zinc(Zn⁺⁺), and so on. The negatively charged ions are called anions and the important plant nutrients taken in this form include nitrogen(NO^-₃), phosphorous( H₂PO^-₄), sulphur(SO^-₄), Chlorine(Cl), etc.

The process of nutrient uptake by plants refers to the transfer of the nutrient ions across the soil root interfaces into the plant cell. The energy for the process is provided by the metabolic activity of the plant and in its absence no absorption of nutrients take place. Nutrient absorption involves the phenomenon of ion exchange. The root surface, like soil, carries a negative charge and exhibits cation-exchange property. The most efficient absorption of the plant nutrients takes place on the younger tissues of the roots, capable of growth and elongation.

In this respect, root-systems are known to vary from crop to crop. Hence their feeding power differs. The extent and the spread of the effective root-system determines the soil volume trapped in the feeding-zone of the crop plant. This is indeed an important information in a given soil-plant system which helps us to choose fertilizers and fertilizer-use practices. The absorption mechanisms of the crop plants are fairly known now. There are three mechanisms in operation in the soil-water-plant systems. They are:(i) the contact exchange and root interception, (ii) the mass flow or convection, and (iii) diffusion. In the case of contact exchange and root interception, the exchangeable nutrients ions from the clay-humus colloids migrates directly to the root surface through contact exchange when plant roots come into contact with the soil solids. Nutrient absorption through this mechanism is, however, insignificant as most of the plant nutrients occur in the soil solutions. Scientists have found that plant roots actually grow to come into contact with only 3 percent of the soil volume exploited by the root mass, and the nutrient uptake through root interception is even still less. The second mechanism is mass flow or convection, which is considered to be the important mode of nutrient uptake. This mechanism relates to nutrient mobility with the movement of soil water towards the root surface where absorption through the roots takes place along with water. Some are called mobile nutrients. Others which move only a few millimetres are called immobile nutrients. Nutrient ions such as nitrate, chloride and sulphate, are not absorbed by the soil colloids and are mainly in solution. Such nutrient ions are absorbed by the roots along with soil water. The nutrient uptake through this mechanism is directly related to the amount of water used by the plants (transpiration). It may, however, be mentioned that the exchangeable nutrient cations and anions other than nitrate, chloride and sulphate, which are absorbed on soil colloids are in equilibrium with the soil solution do not move freely with water when it is absorbed by the plant roots. These considerations, therefore, bring out that there are large differences in the transport and root absorption of various ion through the mechanism of mass flow. Mass flow is, however, responsible for supplying the root with much of the plant needs for nitrogen, calcium and magnesium, when present in high concentrations in the soil solution, but does not do so in the case of phosphorous or potassium. The nutrient uptake through mass flow is largely dependent on the moisture status of the soil and is highly influenced by the soil physical properties controlling the movement of soil water.

The third mechanism is diffusion. It is an important phenomenon by which ions in the soil medium move from a point of higher concentration to a point of lower concentration. in other words, the mechanism enables the movement of the nutrients ion without the movement of water. The amount of nutrient-ion movement in this case is dependent on the ion-concentration gradient and transport pathways which, in turn, are highly influenced by the content of soil water. This mechanism is predomionant in supplying most of the phosphorous and potassium to plant roots. It is important to note that the rhizophere volume of soil in the immidiate neighbourhood of the effective plant root receives plant nutrients continously to be delivered to the roots by diffusion. However, when the nutrient concentration builds up far excess of the plant in the reverse direction. These are some of the choice of fertilizers and fertilizer practices for practising scientific agriculture.

The relationship in the soil-plant system stated in the simple equation give in the earlier paragraph reflects the highly dynamic nature of the soil solution. One knows that the roots of the growing plants continuously remove nutrient ions from the soil solutions. At the same time, the breakdown of the soil minerals and the generating of more exchangeable cations, the biological activity and the additions made to the anions, e.g. nitrates, continuously change the composition of the soil solution. At a given point of time, therefore, the available plant nutrients in the soil solution may range from a tiny amount to larger quantities. Under favourable conditions, crop plants, in general, require larger amounts of plant nutrients than the quality found in soil solution at any given time. Hence, the situation of nutrients supply to plants becomes a limiting factor, specially, at the critical stages of plant growth and low crop yeilds result in recognition, therefore, fertilizers application and the use of suitable fertilizers are recommended for higher crop yeilds in productive farming. The knowledge of the specific role of each essential element in the growth of crop plants and their amounts required for efficient crop production is considered necessary in adopting scientific fertilizers use.

PLANT NUTRIENTS AND THEIR FUNCTIONS

The plants require, the following essential nutrients for their normal development:

Carbon	Nitrogen	Calcium
Hydrogen	Phosphorous	Magnesium
Oxygen	Potassium	Sulphur
Iron	Zinc	Chlorine
Manganese	Boron	..
Copper	Molybdenum	..

Carbon is obtained from carbon dioxide of the air; Oxygen from air and water; Hydrogen from water; Nitrogen from air and soil or both, and all other nutrients from the soil. Soil is a the most important source of plant food.

Nitrogen, Phosphorous and Potassium are known as primary plant nutrients; Calcium, Magnesium and

Sulphur

are secondary nutrients; Iron, Manganes, Copper, Zinc, Boron, Molybdenum and Chlorine as trace elements or micronutrients. The primary nutrients and secondary nutrients elements are known as major elements. This classification is based on their relative abundance, and not their relative importance. the micronutrients are required in small quantities, but they are as important as the major elements in plant nutrients.

Air is the primary source of Nitrogen for plant nutrient. Only leguminous crops can directly use this free Nitrogen with the help of symbiotic bacteria of the genus Rhizobium. Other plant derive from soil their Nitrogen in the form of Nitrogen and Ammonium. Nitrogen and Ammonium are produced in the soil by action of micro-organisms on the soil organic matter. Non symbiotic micro-organisms can fix free Nitrogen of the air and make it available to plant in Ammonium and Nitrates forms.

Nitrogenencourages the vegetative development of plants by importing a healthy green colour to the leaves. It also controls, to some extent the efficient utilization of phosphorous and Potassium. Its dependency retards growth and root development, turns the foilage yellowish or pale green, histens maturity, causes the shrivelling of grains and lowers crop yield. The older leaves are affected first. An excess of Nitrogen produces leathery(sometimes crinkled), dark-green leaves and succulent growth. It also delays the maturation of plants, impairs the quality of crops like barley, potato, tobacco, sugarcane, and fruits; increases susceptibility to diseases and causes 'lodging' of cereal crops by inducing an undue lengthoning of the stem internodes.

Phosphorousinfluences the vigour of plants and improves the quality of crops. It encourages the formation of new cells, promotes root growth(particularly the development of fibrous roots), and hastens leaf development through emergence of ears, the formation of grains, and the maturation of crops. It also increases resistence to diseases and strengthens the stems of cereal plants, thus reducing their tendency to lodge. It offsets the harmful effects of excess nitrogen in the plant. When applied to leguminous crops, it hastens and encourages the development of nitrogen-fixing nodule bacteria. If phosphorous is deficient in the soil, plants fail to make a quick start, do not develop a satisfactory root-system, remain stunted and sometimes develop a tendency to show a reddish or purplish discolouration of the stem and foilage owing to an abnormal increase in the sugar content and the formation of anthoscyanin.

However, the deficiency of this element is not easily recognised as that of nitrogen. It has also been observed that cattle feeding on the produce of deficient soils become dwarfed, develop stiff joints and lose the velvetty feel of the skin. Such animals show an abnormal craving for eating bones and even soil itself.

Potassiumenhances the ability of plants to resist diseases, insect attacks, and cold and other adverse conditions. It plays an essential part in the formation of starch and in the production and translocation of sugars, and is thus of special value to carbohydrate-rich crops, e.g. sugarcane, potato and sugar-beet. The increased production of starch and sugar in legumes fertilized with potash benefits the symbiotic bacteria and thus enhances the fixation of nitrogen. It also improves the quality of tobacco, citrus etc. With an adequate supply of potash, cereals produce plump grains and strong straws. But an excess of element tends to delay maturity, though, not to be the same extent as nitrogen.

Plants can make up and store potassium in much larger for correcting zinc deficiency. The symptoms of zinc deficiency appear generally in younger leaves, starting with intervienal chlorosis leading to a reduction in shoot growth and the shortening of internodes. Mottle leaf, little leaf, etc. in the case of trees are symptoms of zinc difficiency. The buds of several defficient maize plants become white; in citrous interveinal chlorosis and mottled leaf occur. In calcareous soils and in soils with very high phosphorus content, zinc defficiency is commonly expected to occur. The principal function of zinc in plants is as a metal activator of enzymes. In highly weathered coarse textured soils zinc deficiency appears under an intensive cropping programme. The availability of zinc is least between pH 5.5 and 7, but its availability increases at a lower pH. At a higher pH above 7, zinc availability becomes a complex problem, as the positively charged zinc ion gets converted into a negatively charged zincate complex whose availability tends to be reduced in alkaline soils. When the calcium ion is predominent, the highly insoluble calcium zincate is formed and zinc availability gets seriously limited. The application of soluble zinc salts or zinc chelates to the soil is generally recommended to correct its defficiency. Foliar sprays are advocated, especially for orchard trees for amending zinc defficiency. About 5 to 50 kg of zinc sulphate per hectare is used for such purposes.

The symptoms of boron defficiency vary with the kind and age of the plant, the conditions of growth and the severity of the deffiency. Each crop produces its characteristic growth abnormalities associated with boron defficiency, such as yellows and rosetting in lucerne, snakehead in wallnuts, die-back and corking of fruits in apple, corking and pitting of fruits in tomatoes, hollow stem and the bronzing of curd in cauliflower, the brown-heart diseases in table-beets, turnips, etc.

Molybdenumdeficiency produces whip-tail in cauliflower, broccoli and other Brassica crops. The deficiency of this element reduces the activity of the symbiotic and non-symbiotic nitrogen-fixing micro-organisms.

It was in 1954 that chlorine was proved to be an essential micronutrient. Its defficiency under field conditions has not been reported so far. In water-culture solutions, the leaves of chlorosis, necrosis and an unusual bronze discolouration on tomatoes.

Sodiumis not an essential element for plant growth. But some crops, such as beet, celery, cabbage, kale, knol-khol, radish, rape and turnip, benefit greatly by application of soluble sodium salts, specially if the soil is deficient in potassium. Sodium is also of direct benefit to plants indigneous to the sea-shore or to irrigated arid regions. Salts of this element are said to release more of potassium from the exchange complex and to help to maintain phosphorus in a more available form. They also serve as a partial substitute for potassium in the case of potatoes and cotton.

MAINTENANCE OF SOIL FERTILITY

No two soils are alike either in respect of their nature or in respect of quantities of plant nutrients they contain. Under a given situation, the system of farming, soil management and manuring practices, etc., influence the productiovity of soils and crop yields obtained from them. The quantities of the three primary nutrients- N, P₂O₅ and K₂O removed from a hectare of land by some of the important crop are shown in table 1.

It is estimated that the different agricultural crops in

India

remove about 4.27 million tonnes of nitrogen, 2.13 million tonnes of phosphoric acid, 7.42 million tonnes of potash and 4.88 million tonnes of lime per year. The production of larger yields through improved varities of crops and intensive cultivation will increase the depletion of nutrients still further. But erosion and leaching cause additional losses. The present production of synthetic nitrogenous fertilizers in the country reached 1.5 million tonnes of nitrogen in 1975-76, and the bulky organic manures might supply another 1.5 million tonnes of total nitrogen. The amounts of phosphorous, potash, etc., added to the soil are very small. It is thus obvious that the current huge drain on nutrient supplies will continue to impoverish the soils unless these supplies are replenished by natural or by artificial means, the principal methods of supplementing natural recuperation and for improving the productive capacity of the soils are :(i) to add organic matter to the soil, so that through decay, it may furnish a more or less continuous supply of nuttrients for crops, and (ii) to restore or increase the amount of defficient nutrients by the application of fertilizers. The urgent need of the constantly expanding agriculture production to meet the requirements of the continually increasing human and cattle populations in

India

makes the supply of additional plant nutrients through fertilizers and organic manures, a problem of supreme importance.

Table 1. The quantities of plant nutrients removed from soil by different crops (Kg/ha)

TYPES OF MANURES AND FERTILIZERS

Indian soils are usually very poor in organin matter as well as in nitrogen. Pohsphate deficiency is less wide-spread and potash deficiency generally occurs in com-pact areas. In acid soils the addition of

lome

steps up production.

Table 2. The average nutrients contents of manures

Materials which are commonly used to maintain and improve soil fertility may be classified as follows:

(1) MANURES. These are relatively bulky materials, such as animal or green manures, which are added mainly to improve the physical condition of the soil, to replenish and keep up its humus status, to maintain the optimum conditions for the activities of soil micro-organisms and make good a small part of the plant nutrients removed by crops or otherwise lost through leaching and soil erosion. They, thus, supply practically all the elements of fertility which crops require, though not in adequate proportions. The plant-food elements contained in a manure are released in an available form after it is applied to the soil and is decomposed by soil micro-organisms. Similarly, the green manures add not only substantial amounts of organic matter but also nitrogen.

(2) FERTILIZERS. Fertilizers are inorganic materials of a concentrated nature; they are applied mainly to increase the supply of one or more of the essential nutrients, e.g. nitrogen, phosphorous and potash. Fertilizers contain these elements in the form of soluble of readily available chemical compounds. This distinction is, however, not very rigid. In common parlance the fertilizers are sometimes called 'chemical','artificial' or 'inorganic' manures.

(3) CONCENTRATED ORGANIC MANURES. Some of the concentrated materials, such as oil-cakes, bone-meal, urine and blood are of organic origin. The use of manures and fertilizers is complementary and not as a substitute for each other.

(4) BULKY ORGANIC MANURES. the properties and role of organic matter and humus in the soil have been explained already. Table2 gives the average nutrient contents of manures and other organic raw materials which may be used to maintain the humus content of the soil.

(1) Farmyard manure. Good-quality farmyard manure is perhaps the most valuable organic matter applied to a soil. It is the most commonly used organic manure in India. It consists of a mixture of cattle dung, the bedding, used in the stable and of any ramnants of straw and plant stalks fed to cattle. Though its crop-increasing value has been recognised from time immemorial, more than 50 per cent of the cattle dung produced in the country today is burnt as fuel and is thus lost to agriculture. Not only this tremendous waste, but also the tradition method of preparing and storing the farmyard manure is generally faulty. The cattle-dung, together with stable-waste and house sweeping, is first collected in the open backyard, and when a cartload has been collected, it is removed to another heap or to an uncovered pit in a common plot outside

the village. The loose heaps lie exposed to the sun, with the result that the raw organic matter dries up quickly and does not rot properly. Very often, a part of the dry dung is blown off by wind or washed away by rain. Cattle urine is either not conserved or is stored in a defective manner. American studies on the distribution of soil derived elements between urine and faeces of dry cows have shown that 95 per cent pf Potassium, 63 per cent of nitrogen and 50 per cent of sulphur are contained in the urine. The wastage of nitrogen-rich urine, the loss of nitrogen(in the form of ammonia) due to the fermentation of exposed cattle dung, and the washing away of soluble mineral elements be leaching reduce its manurial value in India to a great extent. Its average content of plant nutrients under Indian and European conditions is shown below for comparison:

 

Percentage content

About half of this nitrogen, one-sixth of phosphorous and more than half of potash are readily soluble and subject to dissipation. However, the loss of nitrogen and minerals elements caused by careless handeling can be reduced greatly by using absorbent bedding for cattle, storing dung in stone or brick-line pits, mixing large quantioties of straw and other vegitable matter with cattle dung, and keeping the heap compact and moist. Thus, if urine is properly conserved, the loss of soluble mineral elements through seepage is prevented, bacterial decomposition of raw organic matter is encouraged, plant nutrients are made soluble, and nitrogen losses are minimised. The relative absorbent capacity of different materials that may be used as bedding for cattle may be judged from the following figures given in table 3.

 

Table 3. The relative absorbent capacity of different materials used as bedding for cattle

Material	Quantity of water (in kg) retained by one kg of the following materials after 24 hours of soaking
Wheat straw	2.20
Peat straw	2.80
Dry leaves	2.00
Peat	6.00
Sawdust	4.35
Soil	0.50
Sand	0.25

If urine is not conserved in the bedding used for cattle it must be collected in covered pucca cistern and then, added to the dung in the manure pit. Nitrogen in the urine is mainly in the form of urea, which readily changes into the highly volatile ammonium carbonate through bacterial action, and quickly loses ammonia thereafter by evaporation. This loss can be reduced to a great deal if the manure and the urine-soaked absorptive itter for bedding are kept compacted in a pit. The pit may be 1 m in depth, 1.3 to 1.5 m in width and 4.5 to 6 m in length, depending upon the no. of cattle on a farm. The filling of the pit should be 'sectional' and when each section of three or 1.3 m in length is filled to about 45 cm above the ground level, it should be clustered with 2.5 cm layer of a mixture of mud and dung in equal proportions. Before plastering, 4 to 5 buckets of water should be added to the manure in the pit. Plastering conserves moisture and nitrogen and also prevents housefly nuisance. The manure becomes ready for use in about 4 to 5 months after plastering.

The quality of manure is also improved by the concentrated feeds given to cattle. Cotton-seed, cotton-seed cake, linseed-meal, wheat bran, grain husk, groundnut cake, gram, horse-gram, etc. are rich in nitrogen, phosphorous, potassium, magnesium and sulphur. It has been found that in the case of adult working-cattle about 80 per cent of nitrogen and the other mineral elements contained in the feed is recovered in urine, faeces and other animal by-products. Accordingly, manure from cattle fed on cereal straws and grass hay is much less valuable than that from animals fed on legume hays, grains and concentrates.

In foreign countries, considerable attention has been given to the use of preservatives on manure. Calcium sulphate or gypsum and superphosphate have proved most promising in preventing the escape of ammomnia. Gypsum has been found specially effective as an ammonia-absorbing agent. Superphosphate, besides absorbing ammonia, supplies additional phosphorous and, thus, improves the crop producing capacity of the manure.

 

Partially rotten farmyard manure should generally be applied to the soil about three to four weeks before the sowing of a crop. In case there is sufficient moisture in the soil, there sill be enough time for its decomposition and for improving the soil structure. Its application too long before sowing a crop will either cause a drying up of the rotted manure or too quick decomppostion, depending on the incidence of rains. But in each case, there will be a serious loss of ammonia and nitrogen. If the manure is already well rotted, it is advisable to apply it just before sowing to a crop. This procedure is perticularly essential in the case of light soils. In any case, after the manure is carted to the field, it should be evenly spread and worked into the soil soon to avoid the loss of nitrogen. The existing practice of leaving the manure in small heaps scattered in the field for several days, before spreading it in the field and incorporating it into the soil, results in the serious deterioration of its quality, particularly if strong winds blow. In vagitable and fruit cultivation, the application of well-rotten manure, in conjunction with fertilizers to young plants individually, has been founnd to give the best results. In

Egypt

, even the cotton crop, which is invariably grown on ridges, is given a top-dressing a handful of the rotten manure being applied to the soil at the base of each plant before an irrigation, and is worked into the soil with a hand hoe.

The practice of penning cattle, sheep and goats in the fields in summer is common in some parts of the country. Folding 7,000 sheep for one night is said to add the equivalent of 149.3 quintals(14.93 tonnes) of cattle dung. The fresh dung left in the field in such cases rapidly dries up. This drying checks ammonification and loss of nitrogen. With the first fall of rain, the dung is worked into the soil. It, therefore, does not lose much of its fertilizing value. Further more, its beneficia effects on the physical condition of the soil are undeniable. However, sheep-folding is said to make the land more weedy.

There must be adequate moisture in the soil for the proper decomposition of organic matter. Farmyard manure can, therefore, be applied to all crops grown in the rainy season or grown under irrigation. The quantity of manure to be applied to unirrigated crops varies from 1.5 to 2 cartloads per hectare in areas of heavier rainfall. If sufficient farmy manure is not available, it may be applied at the usual rate to a part of the land,say, to one-third or one-forth of the area, in rotation every year, so that all parts of the field receive the manure regularly once in three or four years. For irrigated field crops, the rate varies from 10 to 20 cartloads. Sugarcane, maize and garden crops, such as potatoes, turmeric, ginger, vegetables and fruits receive still higher doses, amounting sometimes to 15 to 25 cartloads. A cartload of manure, measuring 9 cubic metres, weighs about half a tonne.

It must be stressed that the value of farmyard manure in soil improvement is due to its content of principal nutritive elements and its ability to (i) improve the soil tilth and aeration, (ii) increase the water-holding capacity of the soil, And (iii) stimulate the activity of micro-organisms that make the plant-food elements in the soil readily available to crops. The supply of organic matter, which is later converted into humus is a property of farmyard manure.

One tonne of carttle dung can supply only 2.95 kg of nitrogen, 1,59 kg of phsophoric acid and 2,95 kg of potash.

The use of farmyard manure alone causes an imbalance in nutirtion owing to its relatively low content of phosphoric acid. Therefore, to keep the soils well supplied with all the essential elements of plant food in a readily available form, and also to keep them in good 'heart', it is advisable to use the bulky organic manures in conjuction with superphosphate and such other artificial fertilizers as contain the particular plant food or foods in which a soil may be deficient or which the crop to be grown may specially require.

(2) Composted manureAnother method of augmenting the supplies of organic is the preparation of compost from farmhouse, and cattle-shed wastes of all types. Composting has been advocated and adopted extensively during the past 25 years. Composting is the process of reducing vegetable and animal refuse(rural or urban) to a quickly utilizable condition for improving the maintaining soil fertility. Research conducted in India and abroad has shown that good organic manure similar in appearance and fertilizing value to cattle manure similar in appearance and fertilizing value to cattle manure can be produced from waste materials of various kinds, such as cereal straws, crop stubble, cotton stalks, groundnut husk, farm weed and grasses, leaves, leaf-mould, house refuse, wood ashes, litter, urine-soaked earth from cattle-sheds and other similar substances. These raw vegetables materials are rich in cellulose and other readily decomposable carbohydrates and have a carbon-nitrogen ratio of 40 or more to 1. The direct application of such undecomposed, low nitrogen organic matter as manure brings about a temporary deficiency of mineral nutrients(specially nitrates and ammonium compounds) in the soil by stimulating the growth of micro-organisms, which in turn, compete with crop plants for available nitrogen, phosphorous and other elements. Hence, before using them as manure, it is necessary to compost or partially decompose them. This process lowers the carbon-nitrogen ratio to about 10 or 12 to 1.

Two methods of composting waste organic materials are usually recommended. One depends on aerobic and other one unaerobic decomposition. In both cases, the farm wastes have to be used as a bedding for cattle in order to absorb a large of the animal urine. In the aerobic process, the used bedding, the sweepings from cattle sheds and some urine-soaked earth from the stable floar are removed everyday, mixed with a little cattle dung and 2 or 3 handfuls of wood ashes are deposited on a well drained site to gradually builed up a lowpile about 30 or 45 cm in height, about 5 m in width and of any convenient length. The pile is built up before to start of rainy season. After the first heavy shower, the waited material in 1.2 strip on each side of the long heap is turn with a rake on to 2.4 m wide stripe in the middle, so raising the height of the heap to nearly 1 m. This process prevents loss of misture and ensures a quick start of decomposition. When the heap sinks appreciably and such a sinking takes about 3 to 4 weeks, it is given a turning and made into fresh heap, thus mixing the outside material with that from inside. After about a month or more, depending on incidence of rains the heap is given a final turning on a cloudy or moderately rainy day and rebuilt the vacant part of the original position. The composed becomes ready for use in about 4 months. This method is eminently suited for composting in the rainy season. The following proposition of raw materials is considered suitable for compost making:

	Parts by weight
Mixed farm residues and cattle-shed	400
Urine-soaked earth	56
Fresh cattle dung	60
Wood ashes	6

In Tamil Nadu, the application of 90 kg of partially fermented dung in the form of a thin suspension, with 22.50 kg of bone-meal per tonne of dry material to be composted is recommended.

If urine-soaked earth and cattle-dung are not available, the raw organic materials can still be composted, provided more than one-third of the residues is soft and finely broken, such as fallen leaves, leaf-mould, kitchen wastes, grass clippings, green and succulent weeds, plant trimming and clopped wheat, barley and soft cereal straw. The use of ordinary soil and wood ashes or lime is, however, essential.

In the anaerobic process, the mixed farm residues are collected in pits of a convenient size, say, 4.5 m*1.5 m*1 m. Each day's collection is spread in a thin layer, sprinkled with a mixture of fresh cowdung(4.5 kg), ashes(140 to 170 g) and water (18 to 22 litres) and compacted. The pit is filled till the raw material stands 38 to 46 cm above its edge, and then is then plastered with a 2-5 cm layer of a mixture of mud cowdung. Under such conditions, decompostion is anaerobic and high temperatures do not develop. Insoluble nitrogen compunds gradually become soluble and the carbonaceous matter is broken down into carbon dioxide and water. The loss of ammonia is negligible, because in high concentrations of carbon dioxide, ammonium carbonate is stable. The plastered pit also prevents the fly nuisance. The well-made compost contains 0.8 to 1 per cent of nitrogen and has all the good properties of farmyard manure. It can be used in the same way as the latter. The anaerobic process is particularly suited for use by gardeners in or near cities and towns.

COMPOSTING METHODS

Raw Materials

The materials are needed are mixed plant residues, animal dung and urine,earth, wood ash and water. All vegetables wastes available on a farm like weeds,stalks,stems,fallen purnings,chaff,fodder remnants,green matter and so on, are collected and stacked in a pile. Hard woody material like cotton or pigeon-pad stalks and stubble are first spread on the farm road and crushed under Vehicles viz. tractors or bullock carts before being piled. Such hard materials should in any case not exceed 10 percent of the total plants residues. Green material which are soft and sufficient and allowed to wilt for 2 or 3 days to remove access moistures before stacking; they tend to pack closely, if they are stacked in the fresh state.  While stacking, each material is spread in layers of about 15cm thickness until the heap is about 1m and 50cm high. The mixture of different kinds of vegetable residuesensures a more efficient decomposition.

The heap is then cut into vertical slices and about 20-25 kg is put under the feet of cattle in the shed as bedding for the night. The next morning the bedding, along with the dung and the urine, and urine earth, is taken to the pits where the composting is to be done.

PIT METHOD

This method includes following steps :

Site and size of pit

The site selected for the compost pit should be near to cattle shed and water source at high level so that no rain water gets in during the mansoon season. A temporary shed amy be constructed over it to protect the compost from heavy raifall. The pit should be about 1 m deep * 1.5-2.0 m wide and of any suitable length.

Filling the pit

The material brought from the cattle shed is spread and on each layer is spread a slurry of dung made with 4.5 kg urine earth and 4.5 kg of inoculum taken from a 15-day-old composting pit. A sufficient quantity of water (nearly 90%) is sprinkled over the material in the pit to the wet it. The pit is filled in this way layer-by-layer and it should not take longer than 1 week to fill. Care should be taken to avoid compacting the material in any way.

Turning

The material is turned 3 times during the whole period of composting (i) after 15 days from filling the pit, (ii) another 15 days , (iii) after another 30 days. At each turning the material is mixed throughly, moistened with water and replaced with the pit.

HEAP METHOD

During rainy seasons or in regions with heavy rainfall the compost may be prepared in heaps above ground. when sufficient nitrogeneous material is not available a green manure or leguminous crop like sunhemp is grown on the fermenting heap by sowing seeds after the first turning. The green mater is then turned in at the second mixing.

Dimensions

The basic

Indore

pile is about 2 m wide at the base, 1.5 m high 2 m long. The sides are tapered so that the top is about 0.5 m narrower in width than the base. A small bund is sometimes built around the pile to protect it from wind which tends to dry the heap.

Forming the heap

The heap isusually commenced with a 20 cm layer of carbonceous material such as leaves, hay-straw, sawdust, wood chips and chopped corn stalks. This is then covered with the 10 cm of nitrogeneous material such as fresh grass, weeds or garden plant residues, garbage, fresh or dry manure or digested sewage sludge. The pattern of 20 cm carbonaceous material and 10 cm nitrogeneous material is followed until the pile is 1.5 m high and they are normally wetted so that they feel damp but not soggy. The pile is sometimes covered with soil or hay to retain heat and is turned at 6- and 12-weeks-interval. In the

republic of korea

, heaps are covered with thin plasic sheets to retain heat and it has also resulted in the death of insects.

If materials are limited, the alternate layres can be added as they become available. Also, all materials may be mixed together in the pile, if one is careful to maintain the proper proportions. Shredding the material speeds up deconposition considerably; most materials can be shredded by running over it several times with a rotary-mower.

Advantages and limitations

Preparation on a large scale can be done through community composting. there is lack of protection from rain and wind. A considerable amount of water is needed ans so the heap method is not suitale in near areas of scanty rainfall.

The intense aerobic decomposition to which the material is subjected no doubt shortens the period of composting but it leads to heavy losses of organic matter and nitrogen. Therefore the C:N ratio should be maintained between 30 and 40 to reduce such losses.

 

BANGALORE METHOD

Preparation of the pit

Trenches or pits 1m deep are dug; the breadth and length of the trenches can be made depending on the availability of land and the type of material to be composted. The selection of site for 1 pit is made as mentioned in the

Indore

method. The trenches should preferably have sloping walls and a floor of 90 cm slope to prevent waterlogging.

Filling the pit

Organic residues and night soil are put in alternate layers and after filling, the pit is covered with a 15-20 cm thick layer of refuse. the materials are allowed to remain in the pit without turning and watering for 90 days. during this period the material settles down due to reduction in volume of the biomass and additional nightsoil and refuse in alternate layers are placed on top and plastered or covered with mud or earth to prevent loss of moisture and breeding of files. the material undergoes anaerobic decomposition at a vey slow rate and it takes about 180-240 days to abtain the finished product.

Advantages and limitations

The recovery of the finished product is greater as compared to aerobic composting but loss of nitrogen is negligible. Labour requirements is less than for the Indore method as turning of material is not done; labour is needed only for digging and filling the pits.

The methods requires along time to produce a finished compost and so takes up more land use. A uniform high temperature is not assured in the biomass. Problems of odour and fly breeding need to be attended too.

SYNTHETIC COMPOST

In the preparation of synthetic compost, the organic nitrogen as dung, required by micro-organism, can be completely substituted by inorganic nitrogen compounds like ammonium sulphate and urea which are utilized equally effectively for decomposition of carbonaceous materials into compost. The Adco process of preparations of synthetic compost developed by Hutuchinson and richards is based on this principle.

This facilitates the utilization of large quantities of various organic waste material where supplies of dung are either short of the requirement or not available at all, as on mechanized farms.

The basic principle of C:N ratio in manure preparation can be applied to add nitrogenous fertilizers in sufficient quantity to decompose. The material to be composted is moistened. This is sprinkled with the fertilizer solution and then with lime. Superphosphate may be added to fortify the phosphorous content of the manure. The treatment is continued layer-wise until the heap or pit is filled to the size and allowed to ferment. The manure becomes ready for application in about 120-180 days and resembles with farmyard manure in its action on soil and plant growth.

LEAF COMPOST

Leaf composting, can be achieved by heap or ditch composting or by windrow composting. windrow are preferred as they allow efficient handling of materials Provide good aeration, allow sufficient of water and are easy to be performed.

It is suggested the formation of uniform-shaped windrow from 2.40 m-3.60 m at the base and 2.40m-3.00m high and of any convenient lenght. Windrow built too high will have excessive compaction at the base resulting in anaerobic conditions. Windrows built too low will not allow sufficient insulation to sustain thermophilic temperatures during cold weather. To ensure proper aeration, it is important to break apart tightly compacted leaves.

Though reduction in size may aid in rapid decomposition, it is not desirable in leaves because it increases the compaction making more frequent aeration necessary. When the incoming leaves are not adequately moist, it is desirable to add water to maintain a proper moisture regime of 40 to 60%.

The C:N ratio of leaves is relatively high. It can be as high as 80, and needs to be amended with nitrogen. Sewage sludge, urea and grass clippings are good sources of nitrogen. If a nitrogen source is to be added, caution should be exercised to distribute it uniformly throughtout the windrow, lest it may result in undesirable anaerobic conditions and uneven decomposition. Proper aeration can be maintained by periodical mixing of the material.

Under optimum environmental composting conditions, leaf compost will be ready between 180 and 270 days. Leaf mould will have final P^H range of 6-7.

It is suggested the use of finished compost (leaf mould) as converting material (10-15cm) in the subsequent preparation of leaf compost to supply a heavy inoculum of micro-organisms.

ENRICHMENT WITH PHOSPHOROUS

Phosphorous enriched compost is prepared by adding 5% superphosphate at the filling of the compost pits. Other sources of phosphorous for this purpose are powered rock phosphate, preferably of low grade (less than 11% P), can be used with profit. Besides, phosphorous it is a source of calcium and micronutrients. Bonemeal will provide nitrogen as well as phosphorous; it contain 9-11% P and 2-4% N. Steamed bonemeal is more easily ground than the fresh material. It contains a little less nitrogen but more phosphorous than the raw material. Basic slag provides calcium, magnesium and trace nutrients and small amount of phosphorous. Banana residues contains about 1-1.5% phosphorous on an ash basis.

ENRICHMENT WITH POTASSIUM

Granite dust of powdered potassium-containing minerals like feldspars can be added to enrich compost. Potassium and other deficient elements can be added to compost by including plant materials which contain apperciable amounts of those elements. Water hyacinth for example, is a rich source of potassium and of many other elements required by plants. Banana skin and stalks contain 34-42% potassiumon an ash basis, seaweeds are rich in iodine, boron, copper, magnesium, calcium and phosphorous. Leaves are also a good source of trace elements and should form a parta part of every compost heap. Potato peel is rich in trace elements and dry potato vines contain 1% potassium, 4% calcium and 1% magnesium.

VERMI COMPOSTING

VERMI-COMPOSTING is the use of earthworms for composting of organic residues. Earthworms can consume practically all kinds of organic matter. One worm, weighs about 0.5 to 0.6 g, eates wastes as their own body weight perday and produces cast of the same weight per day. It is estimated that 1000 tonnes of moist organic matter can be converted by earthworms into 300 tonnes of compost. Organnic materials undergo comples biochemical changes in the intestines and vermi-composting is an appropriate technique for disposal of non-toxicsolid and liquid organic wastes. It helps in cost effective and efficient recyclicing of animal wastes (poultry, equine,piggery excreta and cattle dung) agriculture residue and industrial wastes using low energy, excreta together with their cocoons and undigested feed make up vermicasting. The castings of earthworms are rich in nutrients (N, P, K, Ca and Mg), and also in bacterial and actinomycetes population. The actinomycetes population in worm cast is over 6 times more than in the original soil (Gaur 1982). A mosist compost heap (30-40% moisture level) of 2.4 m * 1.2 m * 0.6 m high, can support a population of mare than 50,000 worms. The temperature is the culture bed should be within the range of 20⁰-30⁰C. The introduction of worms into compost heap has been found to mix the materials, aerate the heaps and hasten decomposition. turning the heaps is not necessary, if earthworms are present to do the mixing and aeration. Besides rural and urban wastes, effluents from agro-industries viz dairies, tanneries, pulp and paper mills, distilleres etc.can be treated by using earthworms.

Benefits of Earthworms

Earthworms help in the preparation of compost maintaining soil health as follows :
1. Improvement in fertility of soil.
2. Arnelioration of physical condition of soil.
3. Mixing of sub-soil and top soil.
4. Correction of undetermined deficiences in plants.
5. Use of earthworms in recycling of city and rural wastes, sewage waste waters and suldge, and industrial wastes eg. paper, food and wood industries.
6. Supplementing traditional feeds

Species for Vermi-composting
Earthworm can be divided as surface living (epigeic) and burrowing (epianecic) worms. Epigeic or compost worms are found on surface and are reddish brown eg. Lumbricus rubellus (red worms). Of many species of earthworms tested for mass culture all over the world, Eisenia fetida, Eudrilus eugeniae and Perionyx excavatus come in the above order of preference for their ability to compost organic wastes. The shapes of cocoons of Eisenia frtida and Eudrilus eugeniae are dissimilar.

Rearing of earthwormsThe worms are reared and multiplied from a commercially obatined breeder stock in shallow wooden boxes of 45 cm *60 cm, provided with drainage holes and stored on shelves and tiers.
A bedding material is compounded from miscellaneous organic residues saw dust, cereal straw, rice husks, sugarcane trash, bagasse, paper, cardboard, coir waste, grasses etc. and is moistened well with water. The wet mixture is stored for 30 days covered with a damp sack and is throughly mixed several times. When fermentation is complete, chicken manure and green matter eg. Leucaena leaves or water hyacinth is added. The material is placed in the boxes in the ans sufficiently loose for the worms to burrow and should be able to retain moisture. the The proportion of the different materials will vary according to the nature of the material but a final nitrogen content of about 2.4% should be amied at. A pH value as near neutral as possible is necessary and the boxes should be kept at temperatures between 20⁰C and 27⁰C. At higher temperatures the worms will aestivate and at lower temperatures they hibernate. for each 0.1 m² of surface area 100 g of breeder worms are added to the boxes. Inspite of their being able to eat the bedding material, the worm at this stage are regularly fed @ 1 kg of feed a day for every kg of worms. the feed stuffs used are again various types of organic matter and include partially digested cowdung, chicken manure, Leucaena leaves, vegetable waste and water hyacinth. Some form of protection against predators like birds, vats, ants, frogs, leeches and centipeded is provided to the worms.

VERMI-COMPOSTING IN PITS
A number of pits 2m *1m with sloping sides aredug having suitable dimension. Vermi-composting is done in pits and in vitro. Both of these are discussed here.
Bamboo poles are laid in paralled row on the pit's. Its floor is with a lattice of wood strips. Necessary drainage is provided because worms can not survive in a waterlogged condition. Alternatively to this and sand can be placed in the bottom of the pit to facilitate proper drainage. Above this a thick layer (15-20 cm) of good loamy soil should be spread. The pit can now be filled with available organic residues such as animal manure, leaves and green weeds, crop residues etc.

Moisture levels of the contents of pit is maintained through addition of required amount of water. The worms from breeding boxes are introduced in the organic refuse, the worms immediately burrow down into the damp soil.
The compost pit is left for 60 days. It should be shaded from hot sunshine and it must be kept moist. Within 60 days about 10 kg of castinge would have been producer per kg of worms. The pit is then excavated to an extent of about two-thirds to three-quarters and the bulk of the worms removed byhand or by seving. This leaves sufficient worms in the pit for further composting and the pit can be refilled with fresh organic residues and continued.
The compsost can be sun-dried and sieve to give a good quality compost. The average nutrient content of vermi-compost is N 0.6-1.20%, P₂O₅ 1.34-2.20%, K₂O 0.4-0.67%, CaO 0.44% and MgO 0.15%.
The excess worms that have been harvested from the pit can be used in the other pits, sold to other farmers for compost inoculation, and may be used as animal and poultry feed or fish food.

Method of pit vermi-composting
Selection of earthworm : Earthworm which is native to the local soil and vermi-compost may be used.
Size of pit : Any convenient dimensions such as 2m * 1m *1m may be prepared. This can hold 20,000-40,000 worms giving 1 tonne manure/month (30 days).
Preparation of vermibed : a 15-20 cm thick layer of good loamy soil above athin layer (5cm) of broken bricks and sand should be made. This layer is inhabited by earthworms.
Inocluation of earthworms : About 100 earthworms are introduced as an optimum inoculating density into a composit pit of about 2m * 1m * 1m provided with a vernibed.
Organic layering : It is done on the vermibed with fresh cattle dung. The compost pit is then layered to about 5 cm with dry leaves or hay. Moisture content of the pit without flooding is maintained through the addition of water.
Wet organic layering : It is done after 28 days with moist/green organic waste which can be spread over it to a thickness of 5 cm. This practice can be repeated every3-4 days. Mixing of wastes periodically without disturbing the vermibed ensures proper vermi-composting. Wet layering with organic waste can be repeated till the compost pit is nearly full.
Harvesting of vermi-compost : At maturation, the moisture content is brought down by stopping the addition of water for 3-4 days. This ensures drying of compost and migration of worms into the vermibed. The mature compost, a fine loose granular mass is removed out from the pit, dried and packed.
Rate of application : Mature vermi-compost is recommended @ 0.5 tonnes/ha.

To boost vermi-compost production production following suggestions should be followed :
(i) A mixture of cattle, sheep, horse dung with gram and wheat bran and vegetable wastes forms the ideal feed for worms.
(ii) Mixing of gram bran with dung mixture in 3:10 ratio increase the biomass.
(iii) Mixing of wheat bran to dung mixture in 3:10 ratio hastens the growth of worms. Addition of kitchen waste in the same proportion increases the worm population.
(iv) The biogas sludge and poultry dropping in equal quantities enhance the worm population and the biomass.

In-vitro vermi-composting
This is also called as bioconversion in soil. This involves the application of the basal dose (5 tonnes/ha) of vermicastings and covering with 2.5 cm. Layer of organic mater (cowdung or pressmud) followed by 10 cm layer of sugarcane trash, crop residues or city swastes. The worms hatch out within 10 days.

Vermi-composting of agricultural wastes
With the aim of vermi-composting of agricultural wastes an experiment was conducted at the Indian Agricultural Research Institute,

New Delhi

. The usefulness and efficiency of earthworms in composting of agricultural residues was studied.
Two trials were conducted with mixed organic materials. Trial A, had more of green materials like grasses and Leucanena leaves mixed with soil and paper. Experient B had 4 kg of composting materials consisting of 2 kg of paddy straw, 1 kg soil 500 g twigs, and 500 g shredded paper and was laid in layers per pit. The bottom most layer was laid with twigs to allow for percolation of excess moisture. The compost pit was kept moist and care was taken to avoid waterlogging.

 

 

 

 

Source : Indian Agricultural Research Institute,

New Delhi

.
After 10 days of initial decomposition, worms (Eisenia fetida) obtain from M/s Biogenic Ltd., Mumbai were introduced @ 100 worms/pit. Afterthe worms burrowed into the deeper layers, the pit was coveredwith a thin layer of soil.
The results of both of the trials (Table) show that introduction of worms in the organic matter piles was found helpful in composting. Organic carbon was reduced at different intervals of composting. In the inoculated compost, nitrogen content wwas appreciably augmented and the C:N ratio was narrowed to a desirable level. The worms were also active in decomposition of high C:N ratio of compost was brought to 51 only whereas with worms it was narrowed down to 21. The use of worms also increased the available phosphorous content of compost. Conjoint use of cellulolytic fungi and earthworms showed better result then other of them alone.

(3) Town compost. In recent years, large-scale composting of town refuse and night-soil in properly constructed trenches away from human habitations has been taken up successfully by the municipalities of many large and small towns. Trenches, 1 to 1.2 m wide, 75 cm deep and of convenient length, are filled with successive layers of night-soil, town refuse and earth, in this order. The compost gets ready in about three months. The following figures of volume-weight conversion will be found useful in the preperation of town compost.

 

 

Volume		Weight in kg or q
1 cu.m of refuse	=	318 kg or 3.18 q
1 litre of night-soil	=	0.991kg
1 cu. m of compost	=	636 kg or 6.36 q
1 cartload of refuse(0.849 cu. m),/font>	=	95.40 kg

 

Social prejudice against the use of this valuable compost has disappeared and town-composting is almost being rapidly adopted in other localities all over

India

. With a suitable modifications, such as the provision of trench latrines, it can be taken up in villages too. Particulars of the process may may be obtained from the National Extension Service Officers.

(4) Sewage and sludge. The liquid waste, like sulage and sewage contain large quantities of plant nutrients and are used for growing of sugarcane, vegetables and fodder crops near many large towns by operating sewage-farms. In many places, the undiluted sullage has been found to be too strong for healthy plant growth and if it contains readily oxidized organic matter, its use actually reduces nitrates present in the soil. The disadvantages are still greater if sewage is used on land without preliminary treatment. The soil quickly becomes 'sewage sick' owing to the mechanical clogging by colloidal matter in the sewage and the development of anaerobic organisms which not only reduce the nitrates already present in the soil but also produce alkalinity. Bacterial contamination makes the eating of raw vegetables on untreated sewage a real danger to health.

For these reasons, it is now usual to construct a setting or a septic tank in which sewage is stand allowed to relieve it of the heavier portion of the solid matter in it, or to undergo a preliminary fermentation. The effluent from the settling-tank, however, still carries a large amount of objectionable colloidal matter, and the deposit of sludge that settles in the tank is of small manurial value and is often offensive. These defects can be removed by thoroughly aerating the sewage in the settling-tank by blowing air through it. The sludge that settles at the bottom in this process is called 'activated sludge' It has the remarkable property of bringing about the rapid oxidation of the organic matter present in fresh sewage. It is also in offensive and on dry-weight basis, contains 3 to 6 per cent N, about 2 percent P₂O₅ and 1 per cent K₂O in forms that can become readily available when applied to the soil. Similarly, the effluent is a clear, odourless liquid containing nitrates in solution, from shich most of the pathogenic bacteria originally present have been removed. Both the activated slidge and the effluent can be used with safety for manuring and irrigating crops. However, under no circumstances should any produce grown on a sewage-farm be eaten uncooked

 

 

5) Night-soil or poudrette.Very few towns

India

are equipped with complete sewage. The sanitory disposal of night-soil with an effective control of foul smell and fly nuisance is, therefore, a serious problem all over the country. Since human excrements are a potential source4 of soil improvement, public health authorities in many towns make the necessary arrangements for its conservation and conversion into a form in which it can be safely used as a manure. The dehydration of night_soil, as such, or after admixture with absorbing materials,e.g. soil, ash. charcoal and sawdust, produces a poudrette that can be easily used as a manure. The mixing of night-soil with an equal volume of ash and 10 per cent powdered charcoal produces an odourless material,containg 1.32 per cent potash and 24.2 per cent time. The addition of 40 to 50 per cent of sawdust to the night-soil yields straightway a dry, acidic poudrette which may contain 2 or 3 per cent nitrogen. The annual potential quantity of manurial ingredients in the night-soil from India's present population of 600 millions is estimated at appromimately 8.1 million tonnes of dry matter containing almost 0.4 million tonnes of nitrogen, 0.25 million tonnes of phosphoric acid and 0.17 million tonnes of potash.

(5) Green manures.Despite special efforts at increasing the supplies of farmyard manure and compost, the supply of farm and other organic manures is scarce and ever becoming more costly. Green-manuring, wherever feasible, is the principal supplementary means of adding organic matter to the soil. It consists in the growing of a quick-growing crop and ploughing it under to incorporate it into the soil. The green-manure crop supplies organic matter as well as additional nitrogen particularly if it is a legume crop, which has the ability to acquire nitrogen from the air with the help of its root-nodule bacteria. A leguminous crop producing 8 to 25 tonnes of green matter per hectare will add about 60 to 90 kg of nitrogen when ploughed under. Rhis amount would equal an application of three to ten tonnes of farmyard manure on the basis of organic matter and its nitrogen contribution. The green manure crops also exercise a protective action against erosion and leaching.

The crops most commonly used for green-manuring in this country are the following:

Sunnhemp (Orotalaria juncea), dhaincha(Sesbania aculeata), cluster-bean(Cyamopsis tetragonoloba), senji(Melilotus parviflora), cowpea(Vigna catjang, V. sinensis), horse-gram(Dolichos biflorus), pillipesara(Phaseolus trilobus), berseem or Egyptian clover(Trifolium alexandrinum).Lentil(Lens esculenta) is recommended in

Kashmir

for green-manuring paddy. Sown in late autumn, it is said to provide a winter cover and make new growth in early spring for ploughing under before the sowing of paddy. Sunnhemp is the most outstanding green-manure crop. It is well suited to almost all parts of the country and fits in well with sugarcane, potatoes, garden crops and the second-season paddy in southern

India

and with irrigated wheat in the north. Dhainchais in wide use in

Assam

,

Bengal

and Tamil Nadu. It does well on alkaline and water-logged soils. Cluster-bean, berseem and senji do well in Punjab, Uttar Pradesh, Rajas than,

Delhi

and some parts of Madhya Pradesh. Berseem is well suited for orchards and the irrigated crops of cotton and sugacane sown in spring or early summer, as in

Punjab

and Uttar Pradesh. Cowpea and horse-gram are used for green locality is naturally the one most suited to its soil and climatic conditions.

Very often, berseem, senji and lucerne (Medicago sativa), and sometimes sunnhemp are grown partly for fodder and partly for fodder and partly for green_manuring. In the case of annual crops of senji and berseem one or more cuttings are taken for use as green-foedder.

Lucerne

which is allowed to grow for two or three years, is cut seven to eight times for the same purpose. In the case of sunnhemp, the tops are fed to the cattle. In all these instances, the residues (roots and stumps) are incorporated into the soil. These crop residues contain considerable amounts of nitrogen, phosphorus, potassium and other mineral nutrients, besides organic matter. In the case of orchards, the annual green manure-cum-forage crop should be grown at such a time as to interface the least with tree growth and fruit development.

Pulses form an essential part of the

India

diet, and are grown commonly as pure crops in rotation or mixed with cereals, oilseeds, and fibre crops. Roots and stubble of these pulse legumes return to the soil small quantities of organic matter rich in nitrogen. The inclusion of groundnut on the cotton-jawar rotation of centra, southern and western India, the growing of a quick-maturing variety of ming(Phaseolus aureus) before wheat in Uttar Pradesh, and wheat and rabi jowar in Marathwada Division of Bombay the sowing of peas in the standing crop of irrigated cotton in Uttar Pradesh, and the sowing of sunnhemp in the standing paddy crop in Andhra Pradesh, Tamil Nadu and Karnataka states, or of val IDolichos lablab) in the coastal paddy areas of Maharashtra, are valuable practices for soil improvement. All these leguminous crops leave the soil in a better physical conditions and richer in nitrogen. The growing of pulses mixed with cereals all over India, the intercropping of cotton with groundnut of with tur(Cajanus indicus) in central and southern parts of the country, or with cluster-bean, mung and moth(Phaseolus aconitifolus) in Punjab and adjoing states; the growing of wheat mixed with peas and gram in northern and central India; and the growing of fodder sorghum mixed with Dolichos lablab in some parts of Tamil Nadu also enrich the soil.

In localities near forests in Tamil Nadu, Karnataka and Andhra Pradesh, the paddy crop is often manured with green forests leaves. These are incorprated into the soil at the time of puddling. In recent years, extensive efforts have been made in these states to plant Glyricidia maculata and Sesbania speciosa on the borders of paddy fields or in other vacant spaces to provide green leaf for manuring the paddy crop. Grown from seedlings or rooted stumps, planted 2 m apart, each Glyricidia plant is said to give annually tow cuttings each of about 6 to 12 kg of green leaf. It does well in both red black soils. Similarly Sesbania speciosa seedlings planted 10 cm apart on paddy borders produce 1,000 to 2,500 kg of green leaf for manuring 0.4 ha of paddy. Only 115 g of seed is needed to provide seedlings sufficient for border-planting ot two hectares of paddy. In certain other paddy-growing areas, Pongamia pinnata(karanji), Tephrosia, Terminalia and other trees yielding large quantities of leaves are planted for use as a green manure. In the Malabar districts of Tamil Nadu, Indigofera teysmanni is grown to pfovide green leafy twigs for manuring paddy.

For the proper rotting of the green manure, it is necessary that the green material should be succulent and there should be adequate moisture in the soil. Plant at the flowering stage, contain the greatest bulk of succulent organic matter with a low carbon/nitrogen ratio. The incorporation of the green-manure crop into the soil at this stage allows a quick liberation of nitrogen in the available form. With advancing age, the percentage of carbonaceous matter in the plants increases and that of nitrogen decreases. if the material with a side carbon/nitrogen ratio isploughed under, micro-organisms bring about its decomposition, draw upon the released nitrogen and mineral nutrients and cause a temporary nutirient deficiency.

Sometimes methi or dhaincha is sown in-between the rows of the newly planted sugarcane crop, or cluster-bean is planted between the rows of irrigated American cotton. When the leguminous plants are five to six weeks old, they are incorporated into the soil. Sugarcane and cotton are claimed to benefit from the legumes. The decay of green matter in this case seems to occur when it best serves as a fertilizer for the beneficiary crop.

The increase of yield after green-manuring is usually of the order of 30 to 50 per cent. The fertilizing value of the legume crop can be increased a great deal by manuring it with superphosphate. This practice not only increases the phosphorous content of the green-manure plants, but also encourages their plant growth on the whole, thus converting an inorganic fertilizer into an organic manure. Green manures have a marked residual effect also.

Fertilizers.Despite the special steps taken in recent years to increase the supply of farmyard and other bulky organic manures, the available quantities are insufficient to meet the existing and prospective needs. Fertilizers have also the dvantage of smaller bulk, the resultant easy transport, relatively quick availability of their plant-food constituents and the possibility of their application in proportions suited to the actual requirements of different crops and soils. Fertilizers are usually classified according to the three principal elements and may, therefore, be included in more than one group. The progress of imports and local production of fertilizers is shown in Table 4.

Nitrogeneous Fertilizers.According to the manner in which their nitrogen is combined with other elements, the nitrogenous fertilizers are divided into four groups; nitrare, ammonia and ammonium salts, chemical compunds containing nitrogen in the amide form, and plant and animal by-products.

Table 4. Production, import and consumption of nitrogenous(N), phosphate (P₂O₅) and potassic fertilizers in

India^*

 

India

 

^*Indian Agric. in brief - 14^th Edn. and FAI annual Review - 1975 - 76 and Department of Agriculture.

Table 5. Types and composition of fertilizers in use in India

(a) Straight - N fertilizers

 

(b) Straight phosphatic fetilizers

 

(c) Straight potassic fetilizers

 

(d) N-P fertilizers

 

(e) N - P - K - fertilizers

 

 

 (f) Micronutrients

 

 

SODIUM NITRATES : It is also known as 'Chilean' nitrate. It owes its importance as a pioneer nitrogenous fertilizer. It occurs in natural deposits in northern

Chile

and is refined before shipping. The refined product contains about 16 per cent nitrogen in the nitrate form, which renders it directly available tp plants. For this reason, it is highly valued as a source of nitrogen when applied as top-and side-dressings, especially to young plants and garden vegetables, which need readily available nitrogen for quick growth leached out from the soil. for wheat, maize, barley, cotton, sugarcane, etc., it is as benefecial as ammonium sulphate.

Sodium nitrate is particularly useful for acidic soils. Its continued and abundant use in soils is said to cause deflocculation and develop a bad physical condition in regions of low rainfall. It should be stored in a dry ware-house

AMMONIUM SULPHATE : It is the most widely used fertilizer in the country. It is a white crystalline salt, containing 20 to 21 percent aoomniacal nitrogen. It is easy to handle and it stores well under dry conditions. During the rainy season, it sometimes, forms lumps. These lumps should be powedered before use. Being soluble in water, it acts quickly, but despite its high solubility, its nitrogen is not readily lost in drainage, because the ammonium ion is retained by the soil particles. it is, therefore, very suitable for wet-land crops, e.g. paddy and jute. It has also been found useful on wheat, cotton, sugarcane, potatoes and many other crops grown on a wide variety of soils. It has, however, an acid effects on the soils. Its long-continued use increases soil acidity and lowers the yield. The application of this fertilizer to acid soils improved the yield of tea plants considerably. It is advisable to use this fertilizer in conjunction with bulky organic manures to safeguard against the ill effects of continued application of ammonium sulphate to field and horticultural crops.

Ammonium sulphate can be applied before sowing, at sowing time, or as a top-dressing to the growing crop. it should not be applied along with, or too close to, the seed, because in concentrated form, it affects seed germination very adversely.

AMMONIUM NITRATE : It is a white crystalline salts, containing 33 to 35 per cent nitrogen, half as nitrate nitrogen and half in the ammonium form. in the ammonium form, it cannot be easily leached from the soil. This fertilizer is quick-acting, but highly hygroscopic and not fit for storage. Granulation of the material and a light coating of the granules with oil reduce hygroscopicity to some extent. It has an acidulating effect on the soil. Under certian conditions, it is explosive, and, therefore, it should be handled cautiously.

'Nitro Chalk' is the trade name of a product formed by mixing ammonium nitrate with about 40 per cent lime-stone or dolomite. It is granulated, non-hazardous and less hygroscopic. it contains 20.5 per cent nitrogen, half in the form form of ammonia and half as nitrate. The presence of lime in it makes it particularly useful for acid soils.

AMMONIUM SULPHATE NITRATE : It is a mixture of ammonium nitrate and ammonium sulphate. it is available in a white crystalline form or as dirty-white granules. This fertilizer contains 26 per cent nitrogen, three-fourths of it in the ammoniacal form and the rest(6.5 per cent) as nitrate nitrogen. It is non-explosive and not as deliquescent as ammonium nitrate. It is readily soluble in water and is very quick-acting. its keeping quality is good and it is useful for all crops. Its keeping quality is good and it is useful for all crops. Its acid effect on the soils is only one-half of that of ammonium sulphate. It can be applied before sowing, at sowing time or as a top-dressing, but it should not be applied along the seed.

AMMONIUM CHLORIDE : It is a white crystalline compound, possessing a good physical condition and containing 26 per cent ammoniacal nitrogen. It is extensively used on paddy in Japan , In India, it is used largely in industries. In general, it is similar to ammonium sulphate in action. It is usually not recommended for tomatoes, tobacco and such other crops as may be injured by chlorine.

UREA : It is a white, crystalline, organic chemical. It is a highly concentrated nitrogenous fertilizer, containing 45 to 46 per cent of non-proteined organic nitrogen. it is fairly hygroscopic and presents considerable difficulty, it 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. When applied to the soil, its nitrogen is rapidly changed into ammonia. Like ammonium nitrate, urea supplies nothing but nitrogen.

It may be applied at sowing time or as a top-dressing, but should not be allowed to come into contact with the seed. It is suitable for most frops and can be applied to all soils

 

AMMONIA. It is a gas containing about 80 percent of nitrogen. Under suitable conditions of temperatures and pressure, it becomes liquid(anhydrous ammonia). Another form, 'aqueous ammonia', results from the absorption of ammonia gas into water, in which it is soluble. Ammonia is used as a fertilizer in both these forms. Anhydrous ammonia can be applied by introducing it into irrigation water, or directly into the soil from special containers, which makes its use rather expensive. Its possibilities as manure for paddy, sugarcane and cotton are being onvestigated at Bangalore in the Karnataka state. In manurial experiments on cotton in Maharashtra , aqueous ammonia has been found to be as efficient as ammonium sulphate.

CALCIUM AMMONIUM NITRATE :Calcium ammonium nitrate is a fine free-flowing, light brown or grey granular fertilzer. It is commercially prepared from ammonium nitrate and ground limestone. It is almost neutral and can be safely applied even to acid soils. Its total nitrogen content may vary from 25 to 28 per cent. Half of this total nitrogenis in the ammoniacal form and half is in nitrate form. According to the prescribed standards, its moisture content should not be more than 0.5% by weight. As regards the particle size, 90 per cent of the material should pass through 4 mm IS sieve and be retained on a 1-mm IS sieve but not more than g per cent shall be below 1 mm.

ORGANIC NITROGENOUS FERTILIZERS :These fertilizers include plant and animal by-products, such as oil cakes, fish manure and dried blood from slaughter houses. Before their organic notrogen can be used by the crops, it is converted through bacterial action into readily usable ammonia-nitrogen and nitrate nitrogen. These fertilizers are, therefore, relatively slow-acting, but they supply available nitrogen for a longer perios. Furthermore, they may also small amounts of organic stimulants that they may contain, or of some of the minor elements needed by plant.

Oil-cakes of different kinds are produced in India to the tune of about two million tonnes anually. They contain not only nitrogen but also some phosphoric and potash, besides a large quantity of organic matter. The chemical composition of the principal oil-cakes available in the country is given in Table 6. In addition to the three fertilizing constituents (N, P₂O₅ and K₂O), the oil-cakes invariably contain2 to 15 per cent of oil, depending on whether the oil is extracted by using solvent process or with expelers, hydraulic presses or indigeneous ghanis. This residual oil, however, dous not, in practice, affect their manurial value. Owing to the great importance of using edible oil-cakes as a cattle feed, their utilization as fertilizers is undesirable. They should be fed to cattle and the excrements may be used as manure. Inedible cakes, like castor cake, neem, mahua cake and karanj cake can, however, be recemmended for use in conjunction with quicker-acting chemical fertilizers.

Dried blood or blood_meal contains 10 to 12 per cent highly available nitrogen and 1 to 2 per cent phosphoric acid. It is a very quick-acting manure and effective on all crops and all types of soils. It should be used in the same way as oil cakes.

Fish manure is available either as dried fish or as fish-meal or powder. In regions where fish oil is extracted, the residue can be used as a manure. Depending on the type of fish, its manurial constituents vary from 5 to 8 per cent of organic nitrogen and from 4 to 6 per cent of phosphoric acid. It is quick-acting and suitable for all crops and soils. It should preferably be powdered before use.

Phosphate fertilizers.These are classified as natural phosphates, treated or processed phosphates, and by-product phosphates anc chemical phosphates.

Rock Phosphate.It occurs as natural deposits of rock in Morocco , the United States of America , Poland , Russia , Tunisia , Algeria , Algeria , Brazil , Egypt , Nehru and some islands in the Pacific Ocean and the Indian Ocean . It contains 25 to 35 per cent phosphoric acid, but this phosphorus is insoluble in water. Practically no rock phosphate, as such, is used as a fertilizer in this country, except some quantity in southern India . In other countries, finely pulverized phosphate rock has been found to give satisfactory results in soils which are very deficient in phosphprus and are acidic. Adequate rainfall and a long growing period of the crop enhance the response. All the same, very little rock phosphate is used is directly as a fertilizer even in these countries. Much more of it is used to manufacture superphosphate, the phosphoric acid of which is water-soluble and is in an available form.

SUPERPHOSPHATE :It is the most widely used fertilizer in India . Prepared formerly by treating bones with sulphuric acid, it is now manufactured largely by treating ground phosphate rock with almost an equalquantity by weight of sulphuric acid. This treatment produces a brownish-grey mixture containing monocalcium phosphate and calcium sulphate(gypsum) in practically equal quantites. This fertilizer is manufactured in three grades : single superphosphate containing 16 to 20 per cent phosphoric acid; dicalcium phosphate, 35 to 38 per cent; and triple superphosphate ,44 to 49 per cent. Single superphosphate is the most commonly available grade in the Indian market. Triple superphosphate in the prodiction of which liquid phosphoric acid is used instead of sulphuric acid, contains very little calcium sulphate. Tripple superphosphate is used mostly in the manufacture of concentrated mixed fertilizers.

The phosphoric acid in superphosphate is wholly water-soluble but when applied to the soil, it is immediately converted into insoluble phosphate owing to precipitation as calcium, iron or aluminium phosphate, according as the soil is alkaline or acid. Thus athe fertilizer is not leached, but is slowly dissolved in the soil solution. Fixation losses can be reduced by applying the fertilizer in bands on both sides of the row of seeds at a depth of 10 to 15 cm with a drill. By this means, at least some of the phosphate does not come into direct contact with the soil and thus the available phosphorous is readily released for absorption by the plant roots.

The fertilizer is suitable for all crops and can be applied to all soils. In acid soils, it should properly be used in conjunction with organic manure. It should be applied before or at sowing or transplanting.

Basic-slag.This is a by-product of steel factories. Depending on the phosphorous content of the iron ore, it contains from 6 to 20 per cent of phosphoric acid (P₂O₅). Slag from Indian steel-mills is poor in P₂O₅ and is not used as a fertilizer. The high-grade European slag containing 15 to 18 per cent P₂O₅ is a popular phosphatic fertilizer in central Europe . It is not as soluble as superphosphate, but unlike the latter, it is alkaline in reaction and good for acid soils. For effective use, it must be pulverized before application.

Bone-meal.The use of raw bones as amanure for fruit_trees is an age-old practice in this country. Burying the skeleton of an animal under a fruit-tree is known to benefit its growth and bearing. Large quantities of bones used to be exported until a few years ago. Exports have since declined and bone-meal(i.e. ground bone) is now a widely used phosphate fertilizer. It is available in two forms : (i) raw bone-mel, and (ii) steamed bone-meal. The steaming of bones under pressure removes fats, greases, nitrogen and glue-making substances. Thus, while raw bone-meal contains about 4 per cent slow-acting organic nitrogen and 20 to 25 per cent insoluble phosphoric acid. Steamed bones are more brittle and can be readily ground. This is an advantage, as the rate of availability of phosphoric acid. Steamed bones are more brittle and can be readily ground. This is an advantage, as the rate of availability of phosphoric acid in bones depends largely on their degree of pulverization. Bone-meal contains only 1 to 2 per cent nitrogen but 25 to 30 per cent phosphoric acid. Steamed bones are more brittle and can be readily ground. This is an advantage, as the rate of availability of phosphoric acid. in bones depends largely on their degree of pulverization. Bone-meal, having particles not larger than3/32 inch, considered suitable for use as a fertilizer, but the more finely powedered it is, the quicker its P₂O₅ becomes available in the soil.

Being relatively slow-acting, bone-meal should not be used as a top-dressing; it must be incorporated into the soil in order to become available. It may be applied either at sowing time or a few days before sowing and should be broadcast. It is particularly suitable for acid soils. It is considered a safe manure for all crops.

In some parts of the country, charred and powedered bones are used as a manure. Charring destroys about half the nitrogen, but leaves intact practically the whole of P₂O₅ in a quickly available form. In the absence of arrangements for steaming and grinding, charring can be easily carried out even in remote villages.

Potassic fertilizers. Most of the Indian fertilizers soils contain a sufficient amount of potash. Potassic fertilizers should, therefore, be applied only to such soils as are definitely known to be defecient in potash or to those which respond to their application, such as sandy soils. They can also be applied to certain crops, such as tobacco, potato, onion, tomato and fruit-trees, to improve the quality and appearance of their produce.

Potassic fertilizers in common use are : (i) muriate of potash(potassium chloride), and (ii) sulphate of potash (potassium sulphate). These salts are important constituents of the waters of oceans and inland seas and of saline deposits derived thereform. The largest known deposits of these salts are at Stassfurt in Germany , in the Caspian Sea region in Russia , in the Dead Sea in Palestine and at some places in California , New Mexico , france and Spain .

MURIATE OF POTASH : It is a gray crystalline material containing 50 to 63 per cent potash (K₂O), the whole of which is readily available. Though highly soluble in water, it is not lost from the soil, as it is absorbed on the colloidal surfaces. it can be applied at sowing time or before sowing.

SULPHATE OF POTASH : It is made by treating potassium chloride with magnesium sulphate and is, therefore, more costly. it contains 48 to 52 per cent K₂O. It dissolves readily in water and becomes available to the crop almost immediately. It can be applied at any time up to sowing, but should not be drilled with the seed. It is considered better than muriate of potash for crops, such as tobacco, chillies, potato and fruit-tree, where quality is of prime importance.

Other sources. Wood ashes, cattle-dung ash, leaf-mould, tobacco stems and water hyacinth are the available indigenous sources of potash. Unleached wood ash contains 5 to 6 per cent of potash in the form of potassium carbonate (which is alkaline), 1 to 2 per cent phosphoric acid and 25 to 30 per cent lime (Cao). Both potassium carbonate and lime in the wood ashes counteract the acidity in the soil. Groundnut shell, paddy husk and bagasse ashes are available near decorticating factories and rice and sugar-mills. These also contain a fair amount of potash and some phosphoric acid. Ground tobacco stems contain 2 to 3 per cent of nitrogen and 6 to 10 per cent of potash in quickly available forms. Hyacinth abounds as a weed in fresh-water ponds in Bengal, Assam , Tripura and Malabar in Kerala. When dry, it contains 1 per cent nitrogen, 4 per cent potassium and a small quantity of phosphorous.

Soil amendments. Lime is generally used for correcting soil acidity, for improving the physical condition of the soil and encouraging bacterial activity. Similarly, gypsum is used for reclaiming 'alkali' soils or land from the sea and improving the structure of heavy black clay soils. Hence, these are called soil amendments.

Compund fertilizers. These fertilizers are multiple nutrient materials, supplying two or three plant nutrients simultaneously. When both nitrogen and phosphorous are deficient in a soil, a compound fertilizer, e.g. ammophos, can be used. It contains 16 per cent N and 20 per cent P₂O₅. Its use does away with the necessity of purchasing two different fertilizers and mixing them in correct proportion before use. The nutrient contents of some of the other compound fertilizers are shown below :

 

	N	P2O5	K2O
Monoammonium phosphate	11.0	48.0	-
Diammonium phosphate Ammoniated superphosphate(4 - 7 per cent)	2.0 - 4.0	14.0 - 20.0	-
Potassium nitrate	13.0	-	44.0

Mixed fertilizers. Compound fertilizers contain plant food elements in fixed propertions and are, therefore, not always best adapted ti different kinds of soils. Accordingly, the needs of different soils can generally be met most economically by the use of fertilizer mixtures containing two or more materials in suitable propertions. Mixtures usually meet nutrient deficiences in a more balanced manner and require less labour to apply than straight fertilizers used seperately. Mixtures containing all the three principal used seperately. Mixtures containing all the three principal nutrients (N, P and K) are termed complete fertilizers.

Some manufacturers prepare special mixtures for different crops, such as wheat, sugarcane, pady, potatoes, tabacco, fruit-trees and vegetables. Trade names like Ammophos, Niciphos and Nitrochalk are employed for other proprietary products, In foreign countries, even insecticides, fungicides and weed-killers, such as DDT, BHC and mercury or copper salts and 2, 4-D are sometimes incorporated into fertilizers mixtures.

When a required mixture is not available of the cost of the mixture sold in the market is high in relation to the cost of its individual components, it may be made at home by mixing the constituent fertilizers in correct proportion. The preparation of mixed fertilizers requires a good knowledge of the properties and mutual reactionof the component straight fertilizers under different climatic and storage conditions. Therefore in preparing such mixtures at the farm or at home, care should be taken to avoid the uneven mixing of incompatible fertilizers, or the mixing which leads to a loss of some of the fertilizing nutrients in the form of gas, converts soluble nutrients into insoluble ones or induces caking. It is unwise to mix the following:

 

1.	Ammonium sulphate, ammonium chloride, other ammoniacal fertilizers and nitrogenous organic manures with lime.
2.	Sodium nitrate or potassium nitrate with superphosphate.
3.	Nitrochalk with superphosphate or lime.
4.	Ammonium sulphate-nitrate with lime.
5.	Urea with superphosphate.
2.	Superphosphate with lime or calcium carbonate or wood ashes.

Ammonium nitrate is an explosive chemical and, therefore, dangerous should be mixing at home. Mixtures containing other nitrates should be made in only such quantities as are to be used immediately, because they absorb water quickly and are not suitable for storage. Bone meal, sulphate of potash and muriate of potash can be mixed with all fertilizers. For further guidance or information on the method of mixing fertilizers, the State Agricultural Chemist or the nearest officer of the Government Agricultural Department should be contacted.

MODE AND TIME OF APPLICATION OF FERTILIZERS AND MANURES

Bulky organic manures should be applied well ahead of sowing, so that the preliminary decomposition takes place before the seeds germinate. Failing presowing application, they may be applied any time after the seedlings have established themselves. They are best applied in the powedered form. A sufficient supply of moisture in the soil is essential for their rapid decomposition. In the case of inorganic fertilizers, potassic and phosphatic fertilizers are best applied just before sowing or transplanting. Nitrogenous fertilizers may be applied either at planting and partly later.

Split

application is particularly desirable for nitrogen when applied to irrigated crops or to crops in heavy-rainfall areas.

Fertilizers applied before sowing should be broadcast uniformly and harrowed in. In the case of fertilizers containing soluble phosphate, the desirability of applying them in 2.5 to 5 cm wide bands on each side of the row of seeds at a depth of 10 to 15 cm with a drill has already been pointed out. This operation reduces the fixation of soluble phosphate in the soil. It is also a good practice to mix superphosphate with farmyard manure at 18 to 22 kg to a tonne before applying the organic manure, particularly of dairy farms land. Sulphate of ammonia used as a top-dressing should not be applied when plant leaves are wet. In the case of irrigated crops, the application of fertilizer should invariably be followed by a watering. In the case of fruit-trees, the fertilizer should be applied to the soil under the crown, a few metres away from the trunk. The area of application should be progressively extended as the trees grow bigger.

In advanced countries, fertilizers are usually applied with the help of machinery of diverse kinds and sometimes with an aeroplane or a helicopter. Combined-planters and fertilizer-distributors are employed when row crops are fertilized at sowing time.

Diagnosing the fertilizer needs of soils.There are four methods of determining the fertilizer requirements of soil :
(i) field experiments, (ii) pot tests, (iii) biological tests, and (iv) chemical test.

Field experiments contribute the more relaible method, but being time-consuming and expensive, they are conducted mainly by the research farms and research organisations. Farmers wishing to use field experiments as a Valid means of determining the fertility status of their soils should seek the advice of the state agronomist. Improperly conducted field experiments not only mean economic fertilizer practices.

Pot experiments permit test witha alarge number of manurial treatments within a limited space and in a relatively short time. However, as the conditions of such tests are different from those in the field, the results are not always directly applicable to large-scale farming.

Biological tests involve the growth of seedlings or of lower forms of plants, such as fungi and bacteria, under specified conditions and the study of their relative growth or the content of needed nutrients. A peridic testing of plant tissues for nitrates and other nutrients indicates the changing needs of crops for different food elements. But these are slow and costly processes and hence not always practicable

The chemical analysis of soils or of plants growing on them constituents the modern method of determining the fertility status of a soil. Such analysis give information on the relative abundance or scarcity of the different nutrients required by crops from the soil, but they give no indication regarding the exact quantity, of fertilizer that may be applied to make good the deficiency. The dependability of this, method can, however, be increased a great deal by co-ordinating its results with those obtained from field experiments.

Facilities for rapid soil-testing have been made available in almost all states and can be availed of. At the same time, a very large number of fertilizer experiments with different crops on a variety of soils are conducted annually in all parts of the country under a comprehensive scheme. The results of these field experiments, when calibrated against those of rapid soil tests, will make the latter purely dependable. This will then be a valuable aid in the hands of extension workers in furnishing advice to farmers regarding fertilizer practices.

It is also sometimes possible to obtain a clue to the nutrient deficiences of soil with the help of deficiency symptoms in plants, as described already. However, a correct deagnosis of deficiency symptoms needs extensive experience. Furthermore, such symptoms in plants appear long after the actual occurance of nutrient deficiency in the soil. Therefore, such soil deficiencies must be diagnosed and remedied much earlier by adopting other means.

How much fertilizer to apply.In a vast country, such as India, possessing a wide variety of climatic and soil conditions, no definite quantity of any fertilizer can be prescribed as an optimum dose even for one and the same crop for all regions. each state in the country has conducted fertilizer investigations for the last 50 years and accumulated information on the manurial requirements of principal crops under local conditions. Therefore, for specific fertilizer practices in relation to particular crops and soils, the state agricultural department should always be consulted.

For determining the quantities of fertilizers from the recemmended rates of application N,P or K, or vice versa, the following conversion factors may be used :

Conversion factors determining quantities of fertilizers

Considerations governing the use of fertilizers.It may be stressed that in order to secure the maximum response to fertilizers, the crop should be irrigated immediately, following their application and at suitable intervals thereafter. The response of a crop under arid and semi-arid conditions is usually uncertain and relatively small. It is, therefore, advantageous to restrict the use of chemical fertilizers mainly ti irrigated lands and areas of assured rainfall.

It must also be borne in mind that the maximum profit from the use of fertilizers depends on many factors, such as the nature of soil, the kinds of crop grown, the climate (in relation to soil, the kinds of crops growth), the prices of fertilizers, the market price of the agricultural produce and so no. All these factors must be given due consideration to secure the most economic results. Changes in one or more of them are bound to influence the economic results. changes in one or more of them are bound to influence the economics of fertilizer use. The use of fertilizers is also subject to the 'law of diminishing returns'. This means that the rate of increase in the crop yield decreases after a certain point is reached regarding the quantity of fertilizer used, and consequently the value of the additional yield finally becomes less than the cost of the fertilizer. Usually, the smaller applications of fertilizers produce greater percentage increase of yield than larger applications.

It should also be exphasized that an adequate supply of nutrients is only one of the factors that determine crop yield and that the application of fertilizers is not the sole means of making good the nutrient deficiencies in soils and plants. Equal attention must be paid to the other soil and crop-management practices to ensure good tilt, proper drainage, the required soil reaction, soil conversion, good land use, a suitable crop rotation, adequate organic matter in the soil and satisfactory soil micro-organism activity. Each one of these plays a vital role in determining the eventual productioin. the neglecting of one or more or these factors leads to a reduction in yield and created the need for still heavier manuring. Finally, manuring should not only be balanced in itself, but should also be designed to supplement the good effects of proper land use and beneficial soil management.