Increasing agricultural production in India by area increasing process
is no longer possible as cultivable land left over is only marginal.
Further a considerable cultivable land is being diverted year after
year for industrial purpose and housing etc. Hence self sufficiency
in food lies in increasing the yield per unit area per unit time through
adoption of modern agricultural technology.
It is universally accepted that the use of chemical fertilizers is
an integral part of the package of practices for raising the agricultural
production to a higher place. Studies conducted by the Food and Agricultural
Organization of the United Nations (FAO) have established beyond doubt
that there is a close relationship between the average crop yields and
fertilizer consumption level. More-over the nutritional requirement
of different crops could not be fully met with the use of organic manures
like FYM and other bulky organic manures like Neem cake, Castor cake,
Groundnut cake, etc., for want of their availability in adequate quantities.
Further fertilizers have the advantages of smaller bulk, easy transport,
relatively quick in availability of plant-food constituents and the
facility of their application in proportion suited to the actual requirements
of crops and soils. Hence there is need for an efficient use of fertilizers
as major plant nutrient resource in enhancing the farm productivity.
Other resource of plant nutrients like organic manures, bio-fertilizers
etc., also should be integrated to get the maximum agricultural output
from every kilogram of applied nutrient in the form of fertilizers.
Plants require 16 essential elements for their normal growth and development.
The essential elements exist as structural components of a cell, maintain
cellular organizations, function in energy transformations and in enzyme
reaction.
Carbon, Hydrogen and Oxygen are three naturally occurring nutrients
and form about 94 per cent of the dry weight of plants. These are the
major components of carbohydrates, proteins and fats. Besides their
structural role, they provide energy required for the growth and development
of plants by oxidative breakdown of carbohydrates, proteins and fats
during cellular respiration.
Nitrogen, Phosphorus and Potassium are three major or primary nutrients
which are to be made available in larger quantities.
Nitrogen is an essential constituent of metabolically active compounds
such as aminoacids, proteins, enzymes and some non-proteinous compounds.
When nitrogen is a limiting factor, the rate and extent of protein synthesis
are depressed and as a result plant growth is affected. The plant gets
stunted and develops chlorosis.
Phosphorus is a structural component of all membranes, chloroplasts
and mitochondria and a constituent of sugar phosphates, viz., ADP, ATP,
nucleic acid, Phospholipids and phosphatides. Phosphorus plays an important
role in energy transformations and metabolic processes in plants. It
stimulates root growth.
Potassium plays an important role in the maintenance of cellular organisations
by regulating permeability of cell membranes and keeping the protoplasm
in a proper degree of hydration. It activates the enzymes in protein
and carbohydrate metabolism and translocation of carbohydrates and imparts
resistance to plants against fungal and bacterial disease.
Calcium, magnesium and sulphur are secondary nutrients which are required
in relatively smaller but in appreciable quantities. Calcium, a constituent
of the cell wall, an activator of different plant enzymes and is essential
for the stability of cell membranes.
Magnesium is a constituent of chlorophyll and chromosome. It is known
to play a catalytic role as an activator of a number of enzymes, most
of w.hich are concerned with carbohydrate metabolism.
Sulphur is required to synthesize the sulphur containing amino acids
and proteins, activity of proteolytic enzymes and increases oil content
in oil bearing plants.
Iron, zinc, manganese, copper, boron, molybdenum and chlorine are
required by plants in small quantities for their growth and development.
Hence they are known as micronutrients or trace elements. The very fact
that the micronutrient elements are required by plants in very low concentration
suggests that they all function as catalysts or at least closely linked
with some catalytic processes in plants. Manganese, zinc and copper
are components of certain biological oxidation-reduction systems. Manganese
performs some function in photosynthesis, acts as regulator to the intake
and state of oxidation of certain elements. Zinc is concerned with the
functioning of Sulphydryl compounds such as cystein, in the regulation
of oxidation - reduction potential within the cells. Copper is a constituent
of cytochrome oxidase and component of many enzymes like ascorbic acid
oxidase, phenolase and lactase. Molybdenum is a constituent of nitrate
reductase and nitrogenase enzyme and is associated with nitrogen utilization
and in nitrogen fixation. Chlorine stimulates the activity of some enzymes
and influences carbohydrate metabolism.
Boron helps in cell development by its influence on polysaccharide
formation. It regulates translocation of sugars across membranes and
polyphenolase activity. Iron is a constituent of cytochromes, haem and
non haem enzymes. Perhaps the best known role of iron is its catalytic
role in enzyme activity.
For obtaining maximum crop yields with maximum benefit to the cultivators,
it is most essential that the crop plants should be fed properly with
all nutrients. Soils deficient in particular nutrients must be supplied
with fertilizers containing those plant nutrients.
Thus it is important to know which plant nutrients are lacking in
a soil. Simple and elaborate tests have been developed by the agricultural
scientist to estimate the nutritional requirements of soils and crops.
These methods are known as diagnostic techniques. Fertilizer requirement
is known by different diagnostic techniques and they are as follows
;
By Plant Observation
This is one of the method to know the fertilizer need of plants by
means of the hunger signs of plants which can be detected by the eye.
The basis of the method is the fact that the plant suffering from
severe deficiencies and excess of mineral nutrients usually developed
well-defined and typical sign of disorders in various organs, particularly
in the leaves. Usually, specific abnormal colours are developed in the
leaves due to deficiency of plant nutrients.
Although the hunger signs in plants are easily observed, it is not
easy to recognise the particular nutrient deficiency in nature due to
various field conditions. This requires experience and practice in the
field.
By Plant Analysis
The use of plant analysis as a tool to diagnose fertility status mainly
consists of :
Plant tissue tests or rapid tests,
Total analysis,
Biochemical methods.
The basis of plant analysis for diagnostic purposes is that the amount
of a given nutrient in a plant is an indication of the supply of that
particular nutrient and is directly related to the quantity present
in the soil. The normal growth of a plant is determined by the supply
of the nutrients. However, there is one disadvantage with this method,
that is, while the shortage of one nutrient can limit the growth, other
nutrients may show higher contents in the cell sap irrespective of the
supply.
The use of plant tissue tests as a means to diagnose soil fertility
status has been found to be important. This is a rapid test of the cell
sap of the growing plants. The sap from the ruptured cells is tested
for unassimilated nitrogen, phosphorus, potash and other nutrients.
Tissue tests are getting popular because of the convenience of handling
and the small number of equipment needed for the test. The test can
be made in a few minutes.
Total analysis is used extensively in research work as this gives
a quantitative indication of the level of nutrients in plants. However,
it should be remembered that the determination of total analysis gives
both the assimilated and unassimilated nutrients. Many nutrients such
as N, P, K, Ca, Mg, Mn, Zn, Cu, Fe, Mo and B can be determined by this
method. Usually, the mature plants are selected for this testing.
Biochemical methods to determine the soil fertility require costly
equipments, but offer good opportunities for research work. Two methods
are recognised amongst biological tests. They are, use of higher plants,
Microbiological methods.
By Fertilizer Experiments
In India, simple field experiments on farmers fields as well as complex
field experiments are very popular.
Simple Field Experiments - In well managed state farms, the level
of soil fertility is usually higher than in the farmers fields. This
is due to the use of manures, fertilizers, good management practices,
etc. Many experiments conducted on farmers fields have revealed the
deficiency of nutrients at various levels. These experiment have to
be simple in nature with N, P, K, NP, NK, PK, NPK as the treatments.
These simple field experiments on farmers fields are very educative
and effective for the farmers, as they themselves see the deficiencies
and the response of the nutrients. These trials are useful for advising
the correct type and amount of fertilizer.
Complex Field Experiments
Complex field experiments allow the testing of many factors at a time
and permit a study of interaction among various nutrients. Complex fertilizer
trials helps in determining the correct kinds of fertilizer, amount
and the method of application for each of the soil zone. These experiments
are complicated, expensive and can be done only by experienced people.
By Soil Testing
Soil testing is one reliable diagnostic tool whose value in evaluating
soil-fertility conditions has been recently recognised in India. Soil
testing is multipurpose in nature. Its purposes are :
To group soils into classes relative to the levels of nutrients for
suggesting fertilizer practices.
To predict the probability of getting a profitable response to the
application of fertilizers.
To help evaluate soil profitability and To determine specific soil
conditions i.e., alkalinity, salinity, acidity, that limit crop yields
and can be improved with soil amendments and other management practices.
Organic fertilizers include both plant and animal bi-products. They
are slow acting. Organic nitrogen fertilizers include oil cakes, fish
manure, dried blood from slaughter houses etc., where as organic phosphorus
from bone meal and organic potassium from cattle dung ash, wood ash,
leaf mould, tobacco stems and water hyacinth.
Organic Manures
Manures are organic or inorganic substances applied to the soil to
supply one or more nutrients to plants to obtain increased yields.
Manures are classified as follows
Manures
Organic manures
Inorganic manures
Bulky
Concentrated
Artificial
Bulky (Slow acting with large quantities of organic
matter) Eg: Cattle, Sheep Poultry, Pig, Goat,, Horse manures, Compost,
Green Manures, Sewage.Sludge.
Concentrated(Quick acting with small quantity of organic
matter.Eg: Groundnut cake, Castor cake, Bonemeal, Blood meal, Horn
meal, Wood ash, Cotton and Linseed Meal.
(Artificial manures,Chemical fertilizers very quick
acting with No organic matter.Eg: Nitrogenous, Ammonium,Phosphatic,
Potassic and Sulphate fertilizers.
Nitrogen is the first fertilizer element of the macronutrients usually
applied in commercial fertilizers. Nitrogen is very important nutrient
for plants and it seems to have the quickest and most pronounced effect.
Role of Nitrogen In Plants
Nitrogen is of special importance in the formation of protein in plants,
It forms a constituent of every living cells in the plants,
It is also present in chlorophyll,
It is involved in photosynthesis, respiration and protein synthesis,
It plays an important role in vegetative growth and it imparts dark
green colour to plants.
If excess nitrogen is applied it delays ripening by encouraging more
vegetative growth. The leaves acquire a dark green colour, become thick
and leathery and in some cases crinkled. The plants become more liable
to attack of pests and diseases. In case of cereal crops, the straw
becomes weak, and the crop very often lodges and straw and grain ratio
is increased. Excess nitrogen deteriorates the quality of some crops
such as potato, barley and sugarcane. It delays reproductive growth
and may adversely affect fruit and grain quality.
The deficiency of Nitrogen leads to formation of yellowish or light
green coloured leaves and plant become stunted. The leaves and young
fruits tend to drop prematurely. The kernels of cereals and the seed
of other crops do not attain their normal size, and become shrivelled
and light in weight.
Phosphorus
Phosphorus is the second fertilizer element and it is an essential
constituent of every living cells and for the nutrition of plant and
animal. It takes active part in all types of metabolism of plant. It
is an essential constituent of majority of enzymes and also structural
component of membrane system of cell, chloroplasts and the mitochondria.
It is intimately associated with the life process.
Phosphorus stimulates root development and growth in the seedling
stage and there by it helps to establish the seedlings quickly. It hastens
leaf development and encourages greater growth of shoots and roots.
It enhances the development of reproductive parts and thus bringing
about early maturity of crops particularly the cereals. It increases
the number of tillers in cereal crops and also strengthen the straw
and thus helps to prevent the lodging. It stimulates the flowering,
fruit setting and seed formation and the development of roots, particularly
of root crops. Phosphorus has a special action on leguminous crops.
It induces nodule formation and rhizobial activity.
Excess phosphorus leads to profuse root growth, particularly of the
lateral and fibrous rootlets. It leads to some trace element deficiencies
particularly iron and zinc.
Deficiency of phosphorus leads to restricted root and shoot growth,
leaves may shed prematurely, flowering and fruiting may be delayed considerably.
In case of potato tubers phosphorus deficiency leads to formation of
rusty brown lessions.
Potassium
Potassium is the third fertilizer element. Potassium acts as a chemical
traffic policeman, root booster, stalk strengthener, food former, sugar
and starch transporter, protein builder, breathing regulator, water
stretcher and as a disease retarder but it is not effective without
its co-nutrients such as nitrogen and phosphorus.
Potassium is an essential element for the development of chlorophyll.
It plays an important role in photosynthesis, i.e., converting carbon-dioxide
and hydrogen into sugars, for translocation of sugars, and in starch
formation. It improves the health and vigour of the plant, enabling
it to withstand adverse climatic condition. It increases the crop resistance
to certain diseases. Potash plays a key role in production of quality
vegetables. Potassium is an enzyme activator and increases the plumpness
and boldness of grains and seeds. It improves the water balance. Promotes
metabolism and increases the production of carbohydrates.
Potassium deficiency causes stunting in growth with shortening of
internodes and bushy in appearance, brings about chlorosis, i.e., yellowing
of leaves and leaf scorch in case of fruit trees. It is also responsible
for the 'dying back tips' of shoots. Its deficiency leads to reduction
in photosynthesis, blackening of tubers in case of potato, tips or margin
of lower leaves of legumes, maize, cotton, tobacco and small grains
are either scorched or burnt.
Secondary Nutrients
Secondary nutrients include calcium, magnesium and sulphur, which
play an important role in plant growth and development. The details
of these nutrients are given below.
Calcium
Calcium as calcium pectate is an important constituent of cell wall
and required for cell division. It is a structural component of chromosomes.
It includes stiffness to straw and there by tends to prevent lodging.
It enhances the nodule formation in legumes, helps in translocation
of sugars, neutralizes organic acids which may become poisonous to plants.
It is an essential co-factor or an activator of number of enzymes. It
improves the intake of other plant nutrients, specially nitrogen and
trace elements by correcting soil pH. Excessive amounts of calcium can
decrease the availability of many micronutrients.
Deficiency of calcium lead to 'Die back' at the tips and margins of
young leaves. Normal growth of plants is arrested i.e., roots may become
short, stubby and bushy, leaves become wrinkled and the young leaves
of cereal crops remain folded. The acidity of cell sap increases abnormally
and it hampers the physiological function of plant. As a result of which
plant suffers and causes the death of plant at last.
Magnesium
Magnesium is an essential constituent of chlorophyll. Several photosynthetic
enzymes present in chlorophyll requires magnesium as an activator. It
is usually needed by plants for formation of oils and fats. It regulates
the uptake of nitrogen and phosphorus from the soil. Magnesium may increase
crop resistance to drought and disease.
Deficiency of magnesium leads to yellowing of the older leaves known
as chlorosis. Acute deficiency of magnesium also causes premature defoliation.
In case of maize the leaves develop interveinal white strips, in cotton
they change to purplish red, veins remain dark green, in soybean they
turn yellowish and in apple trees, brown patches (blotches) appear on
the leaves.
Sulphur
Sulphur has specified role in initiating synthesis of proteins. Sulphur
is an important nutrient for oil seeds, crucifers, sugar and pulse crops.
It is an essential constituent of many proteins, enzymes and certain
volatile compounds such as mustard oil. It hastens root growth and stimulates
seed formation. It is essential for the synthesis of certain aminoacids
and oils. It can be called as master nutrient for oilseed production.
The deficiency of sulphur leads to slow growth with slender stalks,
nodulation in legumes may be poor and nitrogen fixation is reduced.
The young leaves turn yellow and the root and stems become abnormally
long and develop woodiness. In case of fruit trees, the fruits become
light green, thick skinned and less juicy. Sulphur deficient plant produces
less protein and oil.
Micronutrients
Micronutrient elements are required by plants in very low concentration
suggests that they all function as catalyst or atleast closely linked
with some catalytic process in plants. Micronutrient elements include
boron, copper, zinc, iron, manganese, molybdenum and chlorine.
Boron helps in cell development by its influence on polysaccharide
formation. It regulates translocation of sugars across membranes and
polyphenolase activity. Iron is a constituent of cytochrome, haem and
non-haem enzymes. Perhaps the best known role of iron is its catalytic
role in enzyme activity.
Copper, zinc and manganese are components of certain biological oxidation-reduction
systems. Manganese performs some function in photosynthesis, acts as
regulator to the intake and state of oxidation of certain elements.
Zinc is concerned with the formation of Sulphydryl compounds such
as cystein in the regulation of oxidation-reduction potential within
the cells. Molybdenum is a constituent of nitrate reductase and nitrogenase
enzyme and is associated with nitrogen utilization and in nitrogen fixation.
Chlorine stimulates the activity of some enzymes and influences carbohydrate
metabolism.
Inserting or drilling or placing the fertilizer below the soil surface
by means of any tool or implement at desired depth to supply plant nutrients
to crop before sowing or in the standing crop is called placement.
With placement methods, fertilizers are placed in the soil irrespective
of the position of seed, seedling or growing plants before sowing or
after sowing the crops. The following methods are most common in this
category.
Plough - Sole Placement
In this method, the fertilizer is placed in a continuous band on the
bottom of the furrow during the process of ploughing. Each band is covered
as the next furrow is turned. No attempt is usually made to sow the
crop in any particular location with regard to the plough sole bands.
This method has been recommended in areas where the soil becomes quite
dry up to a few inches below the soil surface during the growing season,
and especially with soils having a heavy clay pan a little below the
plough-sole. By this method, fertilizer is placed in moist soil where
it can become more available to growing plants during dry seasons.
Deep Placement of Nitrogenous Fertilizers
This method of application of nitrogenous and phosphatic fertilizers
is adopted in paddy fields on a large scale in Japan and is also recommended
in India. In this method, ammonical nitrogenous fertilizer like ammonium
sulphate or ammonium forming nitrogenous fertilizer like urea, is placed
in the reduction zone, where it remains in ammonia form and is available
to the crop during the active vegetative period.
Deep or sub-surface placement of the fertilizer also ensures better
distribution in the root zone and prevents any loss by surface drain-off.
Deep placement is done in different ways, depending upon the local cultivation
practices. In irrigated tracts, where the water supply is assured, the
fertilizer is applied under the plough furrow in the dry soil before
flooding the land and making it ready for transplanting. In areas where
there is not too much of water in the field, it is broadcast before
puddling. Puddling places the fertilizer deep into the root zone.
Sub - Soil Placement
This refers to the placement of fertilizers in the sub-soil with the
help of heavy power machinery.
This method is recommended in humid and sub-humid regions where many
sub-soils are strongly acidic. Due to acidic conditions the level of
available plant nutrients is extremely low. Under these conditions,
fertilizers, especially phosphatic and potassic are placed in the sub-soil
for better root development.
Localised Placement
This method refers to the application of fertilizers into the soil
close to the seed or plant.
Localised placement is usually employed when relatively small quantities
of fertilizers are to be applied. Localised placement reduces fixation
of phosphorus and potassium.
Bulk Blending
It is the process of mixing two or more different fertilizers varying
in physical and chemical composition without any adverse effects.
For this formulation certain additional materials called 'Fillers'
and 'Conditioners' are used to improve the physical condition of the
mixed fertilizer. This mixed fertilizer should be applied as top dressing.
Liquid Fertilization
The use of liquid fertilizers as a means of fertilization has assumed
considerable importance in foreign countries. Solutions of fertilizers,
generally consisting of N, P2O5, K2O in the ratio of 1 : 2 : 1 and 1
: 1 : 2 are applied to young vegetable plants at the time of transplanting.
These solutions are known as 'Starter Solutions'.
They are used in place of the watering that is usually given to help
the plants to establish. Only a small amount of fertilizer is applied
as a starter solution. The starter solution has two advantages.
The nutrients reach the plant roots immediately,
The solution is sufficiently diluted so that it does not inhibit
growth.
As such a starter solution helps rapid establishment and quick early
growth. There are two disadvantages of starter solution, if watering
is not a part of the regular operation-extra labour is necessary and
the fixation of phosphate may be greater.
Direct application of liquid fertilizers to the soil need special
equipment. Anhydrous ammonia (a liquid under high pressure upto 14 kg
per square cm. Or more) and nitrogen solutions are directly applied
to the soil. This practice is very popular in the United States of America.
Plant injury or wastage of ammonia is very little if the material is
applied about 10 cm below the seed. If the application is shallow, nitrogen
from ammonia will be lost. This method allows direct utilisation of
the cheapest nitrogen source.
Straight and mixed fertilizer containing N, P and K easily soluble
in water, are allowed to dissolve in the irrigation stream. The nutrients
are thus carried into the soil in solution. This practice of fertilization
is called "Fertigation". This saves the application cost and allows
the utilization of relatively in expensive water-soluble fertilizers.
Usually nitrogenous fertilizers are most commonly applied through irrigation
water.
Foliar Application
This refers to the spraying on leaves of growing plants with suitable
fertilizer solutions. These solutions may be prepared in a low concentration
to supply any one plant nutrient or a combination of nutrients.
It has been well established that all plant nutrients are absorbed
through the leaves of plants and this absorption is remarkable rapid
for some nutrients. Foliar application does not result in a great saving
of fertilizer but it may be preferred under the following conditions.
When visual symptoms of nutrient deficiencies observed during early
stages of deficiency.
When unfavourable soil physical and chemical conditions, which reduce
fertilizer use efficiency (FUE).
During drought period where in the soil application could not be done
for want of soil moisture.
There are certain difficulties associated with the foliar application
of nutrients as detailed below,
Marginal leaf burn or scorching may occur if strong solutions
are used.
As solutions of low concentrations (usually three to
six per cent) are to be used, only small quantities of nutrients can
be applied in single spray.
Several applications are needed for moderate to high
fertilizer rates, and hence
Foliar spraying of fertilizers is costly compared to
soil application, unless combined with other spraying operations taken
up for insect or disease control.
Soil fertility may be defined as the inherent capacity of soil to
supply plant nutrients in adequate amount and in suitable proportion
and free from toxic substances. There are two types of soil fertility
viz.,
Inherent or Natural Fertility
The soil, as a nature contain some nutrients, which is known as inherent
fertility. Among plant nutrients nitrogen, phosphorus and potassium
is essential for the normal growth and yield of crop. The inherent fertility
has a limiting factor from which the fertility is not decreased.
Acquired Fertility
The fertility develops by application of manures and fertilizers,
tillage, irrigation, etc., is known as acquired fertility.
The acquired fertility has also a limiting factor. It is found by
experiment that the yield does not increase remarkably by application
of additional quantity of fertilizers.
Factors Effecting Soil Fertility
The factors that are effecting soil fertility may be of two types,
i.e.,
Natural factors and
Artificial factors
The natural factors are those which influences the soil formation
and the artificial factors are related to the proper use of land.
The factors effecting the fertility of soil are parent material, climate
and vegetation, topography, inherent capacity of soil to supply nutrient,
physical condition of soil, soil age, micro-organisms, availability
of plant nutrients, soil composition, organic matter, soil erosion,
cropping system and favourable environment for root growth.
Maintenance of Soil Fertility
Maintenance of soil fertility is a great problem of our farmers. Cultivation
of particular crop year after year in the same field decreases the soil
fertility. To increase the soil fertility, it is necessary to check
the loss of nutrient and to increase the nutrient content of soil.
The following things must be properly followed for increasing the
fertility of soil.
It is well known fact that in high rainfall areas, due to the leaching
of bases, acids soils are formed, while in low rainfall regions, on
account of arid and semi arid conditions, saline and alkali soils occur.
Thus soil vary in acidity or alkalinity. The soil reaction is indicated
by pH scale. When Ca(OH)2 or lime is added to the soil, it will become
alkaline.
Liming of Acidic Soils
Liming means addition of any compound containing Calcium alone or
both calcium and magnesium, that is capable of reducing the acidity
of the soil. Lime correctly refers only to Calcium oxide (CaO), but
the term as applied in agriculture is universally used to include various
other materials also, like Calcium carbonate, Calcium hydroxide, Calcium
- magnesium carbonate (marl) and Calcium silicate slags.
The effects of liming on the soil and plants are as follows :
Lime neutralizes soil acidity,
Beneficial soil bacteria are encouraged by adequate supplies of lime
in the soil,
Lime makes phosphorus more available,
Liming helps the availability of potash and molybdenum,
Lime furnishes two essential elements, namely calcium and magnesium
(if lime is dolamitic) for plant nutrition,
Fertilizers are relatively safer than pesticides which exhibit toxic
properties on living systems. However, all the quantities of fertilizers
applied to the soil are not fully utilized by plants. About 50 per cent
of fertilizers applied to crops are left behind as residues. Though,
inorganic fertilizers are not directly toxic to man and other life forms,
they have been found to upset the existing ecological balance. The nutrients
escape from the fields and are found in excessive quantities in rivers,
lakes and coastal waters.
Algae blooms occur when the nutrient load is high, and these smother
other aquatic vegetation and also interfere with the oxygen regulation
in the water bodies. This phenomena may lead to loss of fish. Among
the major synthetic plant nutrients, nitrogenous fertilizers cause most
harm. Contamination of the environment arises because not all the fertilizer
applied is taken up by the crop and removed at harvest. In tropical
climate the maximum recovery in dry land crops is 50 to 60 per cent
and 40 per cent in rice because much of nitrogen is lost as ammonia
into the atmosphere.
Eutrophication of water bodies due to higher nitrate and phosphate
concentrations, increasing levels of nitrates in drinking water sources,
accumulation of heavy metals such as lead and cadmium in soils and water
resources are the principal causes of environmental concerns due to
fertilizer use in agriculture. In the a national wide survey it was
found that many streams and more than 20 % of wells contain 10 to 50
mg or even more of nitrates per litre of water. The contamination is
caused by domestic sewage leaking to the ground water. The nitrates
in drinking water can lead to several ailments. Blue - baby syndrome
in infants and gastric and other forms of cancer have been related with
nitrates in drinking water or diet.
Another hazard associated with excessive use of fertilizers is the
gaseous loss of nitrogen, into the atmosphere. High doses of carbon
dioxide and ammonia that escape into the atmosphere both from fertilizer
manufacturing plants and soils affect human health. Further the oxides
of nitrogen have been reported to adversely affect the ozone layer,
which protects the earth from UV radiation and heating up of earth.
The oxides of nitrogen cause respiratory diseases like asthma, lung
cancer and bronchitis. Arsenic, ammonia are waste stream components
of nitrogen manufacturing plants while fluoride, cadmium, chromium,
copper, lead and manganese are waste stream components of phosphatic
fertilizer industry. If these waste stream of components are not properly
disposed they cause harm to human beings and animals with contamination
of air and water.
The keeping quality of perishables like vegetables and fruits get
declined with excess use of fertilizers particularly nitrogenous fertilizers.
Use of fertilizer by the farmer for increased crop production depends
almost entirely on its economics. This is usually done by reporting
response per unit area or per unit nutrient applied. With a view to
convince the farmer about the profitability of fertilizer use, cost
benefit ratio is also worked out.
Almost all such calculations are based on evaluating the extra produce
at the support/market price and deducting the cost of fertilizer only
at the statutory prevailing rates.
Due to high cost of commercial fertilizer marketed in India, the question
of economics of fertilizer use has assumed great importance. The fertilizer
association of India, New Delhi, therefore, organised series of group
discussions on "Economics of Fertilizer use" during 1975. The recommendations
of these group discussions are listed below,
Uniformity of approach in studying the economics of fertilizer is
essential.
The fertilizer recommendations should be based on soil test values.
Balanced use of fertilizer should be advocated for better economic
returns.
Use of nitrogenous fertilizer in split doses economises fertilizer
use.
Micronutrient deficiencies should be corrected as and when needed.
Fertilizer schedule should be adopted for the whole crop sequence
instead of a single crop.
To get the maximum benefit from the applied fertilizers, crops should
be irrigated at the critical growth stages.
