Ag - Chem.3.2 Manures, Fertilizersandsoilfertilitymanagement

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COURSE NO.: AG.CHEM.3.2

TITLE: MANURES, FERTILIZERS AND SOIL
FERTILITY MANAGEMENT (2+1)
CONTENTS
Sr.
TITLE
No.
i. Classification and importance of organic manures, properties and methods
of preparation of bulky manures. Green/leaf manuring.
ii. Transformation reactions of organic manures in soil and importance of C:N
ratio in rate of decomposition.
iii. Integrated nutrient management
iv. Chemical fertilizers: classification, composition and properties of major
nitrogenous, phosphatic, potassic fertilizers, secondary & micronutrient
fertilizers, Complex fertilizers, nano-fertilizers, Soil amendments,
v. Fertilizer Storage, Fertilizer Control Order
vi. History of soil fertility and plant nutrition, Criteria of essentiality. Role,
deficiency and toxicity symptoms of essential plant nutrients, Mechanisms
of nutrient transport to plants, factors affecting nutrient availability to plants.
Critical levels of different nutrients in soil. Forms of nutrients in soil.
vii. Chemistry of soil nitrogen, phosphorus, potassium, calcium, magnesium,
sulphur and micronutrients
viii. Soil fertility evaluation, Soil testing, plant analysis, rapid plant tissue tests.
Indicator plants.
ix. Methods of fertilizer recommendations to crops. Factor influencing nutrient
use efficiency (NUE), methods of application under rainfed and irrigated
conditions.
Reference Books
1. Manures and Fertilizes (1992), Seventh Edition by K. S. Yawalkar, J. P.

Agarwal and S. Bokde
2. Soil Fertility, theory and practice (1976) by J. S. Kanwar
3. Soil Fertility and Fertilizers (1985) by S.L. Tisdale, W.L. Nelson and J. D.
Beaton
4. Fundamentals of Soil (1999) by V. N. Sahai
5. Introductory Soil Science (1999) by D. K. Das.
Dr. S. M. Bambhaneeya (Ph.D.- Soil Science)

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CHAPTER- I: ORGANIC MANURES
The manures are organic in nature, plant or animal origin and contain organic
matter in large proportion and plant nutrients in small quantities and used to improve
soil productivity by correcting soil physical, chemical and biological properties.
Manure is organic matter used as organic fertilizer in agriculture. Manures contribute
to the fertility of the soil by adding organic matter and nutrients, such as nitrogen,
that are trapped by bacteria in the soil. Higher organisms then feed on the fungi and
bacteria in a chain of life that comprises the soil food web.
Difference between manures and fertilizers:
Manure Fertilizer
1. Contains O.M. and hence improves 1. Do not contain O.M. and cannot
soil physical properties improve soil physical properties
2. Improves soil fertility as well as 2. Improves soil fertility
productivity
3. Contains all plant nutrients but small 3. Contains one or more plant nutrients
in concentration but in higher concentration
4. Required in large quantity bulky and 4. Required in less quantity
costly concentrated and cheaper
5. Nutrients are slowly available upon 5. Nutrients are readily available.
decomposition
6. Long lasting effect on soil and crop 6. Very less residual effect
7. No salt effect 7. Salt effect is high
8. No adverse effect 8. Adverse effects are observed when
not applied in time and in proper
proportion.
1.1 Bulky Organic Manures:
Bulky organic manures include farm yard manure (FYM) or farm manure, farm
compost, town compost, night soil, sludge, green manures and other bulky sources
of organic matter. All these manures are bulky in nature and supply (i) plant nutrients
in small quantities and (ii) organic matter in large quantities. Of the various bulky
organic manures, farm yard manure, compost and green manure are by far most
important and most widely used.

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Effect of bulky organic manures on soil:
i) Direct effect on plant growth

ii) Increase organic matter content and improve physical properties of soil. Increase
humus content of soil and consequently WHC of sandy soil is increased and the
drainage of clayey soil is improved.
iii) Provide food for soil microorganisms. This increases activity of microbes which in
turn helps in converting unavailable plant nutrients into available forms.
Farm Yard Manure (FYM):
It refers to the decomposed mixture of dung and urine of farm animals along
with litter (bedding material) and left over material from roughages or fodder fed to
the cattle.
On an average well-rotted FYM contains 0.5% Ns 0.2% P205 and 0.5% K20.
FYM is one of the most important agricultural by products. Unfortunately,

however nearly 50 per cent of the cattle dung production in India today is utilized as
fuel and is thus lost to agriculture.
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Average percentage of N, P205 and K2O in the fresh excreta of farm animals:
Excreta of N (%) P2O5 (%) K2O (%)
Cows and bullocks Dung 0.40 0.20 0.10
Urine 1.00 Traces 1.35
Sheep and goat Dung 0.75 0.50 045
Urine 1.35 0.05 2.10
Buffalo Dung 0.26 0.18 0.17
Urine 0.62 Traces 1.61
Poultry - 1.46 1.17 0.62
i) Poultry manure is the richest of all
ii) Urine of all animals contains more percentage of N and K 2O compared to the
dung portion.
Factors Affecting Nutritional Buildup of FYM:
The following factors affect the composition of FYM:
1. Age of animal: Growing animals and cows producing milk retain in their system
nitrogen and phosphorus required for productive purposes like making growth
and producing milk and the excreta do not contain all the ingredients of plant
food given in the feed. Old animals on the downgrade waste their body tissues
and excrete more than what they do ingest.
2. Feed: When the feed is rich in plant food ingredients, the excreta produced is
correspondingly enriched.
3. Nature of Litter Used: Cereal straw and leguminous plant refuse used as litter
enriched the manure with nitrogen.
4. Ageing of Manure: The manure gets richer and less bulky with ageing.
5. Manner of Making and Storage: In making and storage losses are in various
ways. (see ‘Losses in FYM).
Losses during handling and storage of FYM:
(I) Losses during handling:
FYM consists of two original components the solid or dung and liquid or urine.
Both the components contain N, P2O5 and K2O the distribution of these nutrients in
the dung and urine is shown in figure below:

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Approximately half of N and K2O is in the dung and the other half in urine. By
contrast, nearly all of the P2O5 (96%) is in the solid portion. To conserve N, P2O5 and
K2O, it is most essential that both the parts of cattle manure are properly handled
and stored.
i) Loss of liquid portion or urine
Under Indian conditions the floor of the cattle shed is usually un-cemented or
Kachha. As such the urine passed by animals during night gets soaked into the
Kachha floor. When the animals, particularly bullocks, are kept in the fields during
the summer season, urine gets soaked into soil. But during remaining period cattle
are kept in a covered shed and therefore the Kachha floor soaks the urine every day.
Large quantities of nitrogen are thus lost through the formation of gaseous NH 3. The
following reactions take place:
NH2 CO NH2 + 2H2O (NH4)2CO3

Urea in urine Ammonium carbonate
(NH4)2 CO3 + 2H2O 2NH4OH + H2 CO3

NH4OH NH3 + H2O
Gaseous Ammonia
The smell of NH3 in the cattle shed clearly indicates the loss of N.
No special efforts are made in India to collect the liquid portion of the manure.
ii) Loss of solid portion or dung
It is often said that 2/3 of the manure is either utilized for making cakes or is
lost during grazing, the remaining manure is applied to the soil after collecting in
heaps. Firstly, the most serious loss of dung is through cakes for burning or for use
as Fuel-Secondly, when milch animals go out for grazing, no efforts are made to
collect the dung dropped by them, nor is this practicable, unless all milch animals are
allowed to graze only in enclosed small size pastures.
(II) Loss during storage:
Mostly, cattle dung and waste from fodder are collected daily in the morning
by the cultivators and put in manure heaps in an open space outside the village. The
manure remains exposed to the sun and rain. During such type of storage, nutrients
are lost in the following ways:
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i) By leaching:
Losses by leaching will vary with the intensity of rainfall and the slope of land
on which manure is heaped. About half of portion of N and P2O5 of FYM and nearly
90% of K are water soluble. These water soluble nutrients are liable to get washed
off by rain water.
ii) By Volatilization:
During storage considerable amount of NH3 is produced in the manure heap

from
i) the decomposition of urea and other nitrogenous compounds of the urine and
ii) the much slower decomposition of the nitrogenous organic compounds of the
dung. As the rotting proceeds, more and more quantity of ammonia is formed.
This NH3 combines with carbonic acid to form ammonium carbonate and
bicarbonate. These ammonium compounds are unstable and gaseous NH 3 may
be liberated as indicated below:
1. Urea and other nitrogenous microbial
compounds in urine and dung NH3
decomposition
2. 2NH3 + H2CO3 (NH4)2 CO3
3. (NH4)2 CO3+2H2O 2NH4 OH+H2CO3
4. NH4OH NH3 + H2O
Loss of NH3 increases with

i) the increase in the concentration of ammonium carbonate
ii) increase in the temperature and
iii) air movement
Improved Methods of Handling FYM:
It is practically impossible to check completely the losses of plant nutrients
and organic matter during handling and storage of FYM. However, improved
methods could be adopted to reduce such losses considerably.
Among these methods are described here under:
i) Trench method of preparing FYM

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ii) Use of gobar gas-compost plant

iii) Proper field management of FYM
iv) Use of chemical preservatives
ii) Use of gobar gas compost plant:
Methane gas is generated due to anaerobic fermentation of the most common

organic materials such as cattle dung, grass, vegetable waste and human excreta.
Gobar gas and manure both are useful on farms as well as in homes. A few
advantages of this method are given below:
1) The methane gas generated can be used for heating, lighting and motive
power.
2) The methane gas can be used for running oil engines and generators
3) The manure which comes out from the plant after decomposition is quite rich
in nutrients. N -1.5%, P2O5- 0.5%, K2O- 2.0%
4) Gobar gas manure is extremely cheap and is made by locally available
materials.
Superiority of gobar gas compost plant over traditional method:
1000 Kg fresh dung manure obtained by

Sr. Particulars Traditional Gobar gas plant
No. method
1. Loss of OM 500 Kg 270 Kg
2. Loss of N 1.25 Kg Nil
3. Final manure 500 Kg 730 Kg
4. %N 0.5% 1.5%
5. Additional - 2000 C.ft. gas for cooking
advantage
iii) Proper field management of FYM:
Under field conditions, most of the cultivators unload FYM in small piles in the
field before spreading. The manure is left in piles for a month or more before it is
spread. Plant nutrients are lost through heating and drying. To derive maximum
benefit from FYM, it is most essential that it should not be kept in small piles in the
field before spreading, but it should be spread evenly and mixed with the soil
immediately.
iv) Use of Chemical Preservatives:

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Chemical preservatives are added to the FYM to decrease N losses. To be

most effective, the preservatives are applied in the cattle yard to permit direct contact
with the liquid portion of excreta or urine. This has to be done because the loss of N
from urine starts immediately. The commonly used chemical preservatives are I)
Gypsum and ii) Super phosphate. The value of gypsum in preserving the N of
manure has been known and it has been used for many years in foreign countries.
The reaction of gypsum with ammonium carbonate (intermediate product from
decomposition of urea present in urine) is :
(NH4)2 CO3 + CaSO4 CaCO3 + (NH4)2 SO4
As long as the manure is moist, no loss of NH3 will occur, but if the manure
becomes dry, the chemical reaction is reversed and the loss of NH3 may occur. As
such, under Indian conditions, use of gypsum to decrease N losses, does not offer a
practical solution.
Superphosphate has been extensively used as a manure preservative:

2CaSO4 + Ca (H2PO4)2 + 2 (NH4)2 CO3 Ca3(PO4)2 +
2 (NH4)2 SO4 + 2H2O + 2CO2
In this reaction, tricalcium phosphate is formed which does not react with
ammonium sulphate, when manure becomes dry. As such, there is no loss of NH3.
Since FYM becomes dry due to high temperature under Indian conditions, the use of
superphosphate will be safely recommended as a preservative to decrease N losses.
Use of superphosphate as a chemical preservative will have three advantages:
1. It will reduce loss of N as ammonium from FYM.

2. It will increase the percentage of P in manure thus making it a balanced one.
3. Since, tricalcium phosphate produced with the application of superphosphate to
the FYM is in inorganic form, which is readily available to the plants, it will
increase the efficiency of phosphorus.
It is recommended that one or two pounds of SSP should be applied per day
per animal in the cattle shed where animal pass urine.
Supply of plant nutrients through FYM:
On an average, FYM applied to various crops by the cultivators contains the

following nutrients:

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% N : 0.5 % P2O5 : 0.2 % K2O : 0.5
Based on this analysis, an average dressing of 10 tones of FYM supplies

about
50 Kg N 20 Kg P2O5 50 Kg K2O
All of these quantities are not available to crops in the year of application,
particularly N which is very slow acting. Only 1/3 of the N is likely to be useful to
crops in the first year. About 2/3 of the phosphate may be effective and most of the
potash will be available. This effect of FYM application on the yield of first crop is
known as the direct effect of application. The remaining amount of plant food
becomes available to the second, third and to a small extent to the fourth crop raised
on the same piece of land. This phenomenon is known as the residual effect of FYM.
When FYM is applied every year, the crop yield goes on increasing due to
direct plus residual effect on every succeeding crop. The beneficial effect is also
known as cumulative effect.
Compost:
Compost (pronounced /ˈkɒmpɒst/ or /ˈkɒmpoʊst/) is composed of organic materials
derived from plant and animal matter that has been decomposed largely through
aerobic decomposition. The process of composting is simple and practiced by
individuals in their homes, farmers on their land, and industrially by industries and
cities. Composting is largely a bio-chemical process in which microorganisms both
aerobic and anaerobic decompose organic residue and lower the C : N ratio. The
final product of composting is well rotted manure known as compost.
Rural compost: Compost from farm litters, weeds, straw, leaves, husk, crop
stubble, bhusa or straw, litter from cattle shed, waste fodder, etc. is called rural
compost.
Urban compost: Compost from town refuse, night soil and street dustbin refuse,
etc is called urban compost.
Composition of town compost:
Nitrogen Phosphorus Potassium
(%N) (%P2O5) (%K2O)
1.4 1.0 1.4
Compared to FYM, town compost prepared from Katchara and night soil is
richer in fertilizer value.
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Mechanical Composting Plants:
Mechanical composting plants with capacities of 500 – 1000 tonnes per day of
city garbage could be installed in big cities in India and 250 tonnes per day plants in
the small towns. Refined mechanical compost contains generally about 40% mineral
matter and 40% organic materials with organic carbon around 15%. The composition
would vary depending on the feed but typically the nutrient content is about 0.7% N,
0.5% P2O5 and 0.4% K2O. There are trace elements like Mn, B, Zn and Cu and the
material has C : N ratio of nearly 15-17.
Decomposition:
The animal excreta and litter are not suitable for direct use as manure, as
most of its manurial ingredients are present in an unavailable form. However, urine, if
collected separately, can be used directly. The dung and litter have to be fermented
or decomposed before they become fit for use. Hence, the material is usually stored
in heaps or pits, where it is allowed to decompose. Under suitable conditions of
water supply, air, temperature, food supply and reaction, the microorganisms
decompose the material. The decomposition is partly aerobic and partly anaerobic.
During decomposition the usual yellow or green colour of the litter is changed to
brown and ultimately to dark brown or black colour; its structural form is converted
into a colloidal, slimy more or less homogenous material, commonly known as
humus.
Factors controlling process of decomposition:
1) Food supply to micro-organisms and C : N ratio:
The suitable ratio of carbonaceous to nitrogenous materials is 40, if it is wider

than this, the decomposition takes place very slowly and when narrow it is quick. C:N
ratio of the dung of farm animals varies from 20 to 25, urine 1 to 2, poultry manure 5-
10, litters-cereals straw 50, and legume refuse 20.
2) Moisture:
About 60-70 per cent moisture is considered to be the optimum requirement

to start decomposition and with the advance in decomposition, it diminishes
gradually being 30-40 per cent in the final product. Excess of moisture prevents the
temperature form rising high and retards decomposition, resulting in loss of a part of
the soluble plant nutrients through leaching and drainage.
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3) Aeration:
Most of the microbial processes are oxidative and hence a free supply of
oxygen is necessary.
Reasons for poor aeration in pit/heap
i) Excessive watering
ii) Compaction
iii) Use of large quantities of fine and green material as litters
iv) High and big heaps or deep pits.
4) Temperature:
Under the optimum conditions of air moisture and food supply, there is a rapid
increase in the temperature in the manure heap or pit. The temperature usually rises
to 50o –60oC and even to 70oC. The high temperature destroys weed seeds, worms,
pathogenic bacteria, etc, which prevents fly breeding and makes the manure safe
from hygienic point of view.
5) Reaction:
The microorganisms liberate certain organic acids during the course of

decomposition, which, if allowed to accumulate, retards fermentation and sometime
even stop it completely. Hence, it is necessary to control the reaction of the material.
A neutral or slightly alkaline reaction between pH 7.0 and 7.5 is considered

the most suitable. The addition of alkaline substances like lime and wood ashes
neutralized the excess acidity. Since in the preparation of FYM it is a common
practice to add household ashes to the manure pit, it is not necessary to add
additional alkaline substances.
Heap V/S Pit decomposition:

Heap Pit
1. Aerobic 1. Anaerobic
2. Turning is required 2. No turning is required
3. Physical disintegration 3. Very little physical disintegration
4. Quick oxidation 4. Slow rate of decomposition
5. High temp. 60o – 70oC. Kill 5. High temp. is not developed but
weed seeds and pathogenic weed seeds and MO destroyed

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organisms due to toxic products of

decomposition.
6. Loss of OM is about 50% 6. Loss is about 25%
7. If not properly protected, 7. Moisture loss is minimized. No

moisture loss is high. Watering watering is necessary
is necessary
8. If rainfall is high, leaching takes 8. Protected from leaching but

place anaerobic condition occurs.
Vermicomposting:
Vermicompost is the product of composting utilizing various species of worms,
usually red wigglers, white worms, and earthworms to create a heterogeneous
mixture of decomposing vegetable or food waste, bedding materials, and vermicast.
Vermicast is also known as worm castings, worm humus or worm manure, is the
end-product of the breakdown of organic matter by species of earthworm. The
earthworm species (or composting worms) most often used are Red Wigglers
(Eisenia foetida or Eisenia andrei), though European night crawlers (Eisenia
hortensis) could also be used. Users refer to European night crawlers by a variety of
other names, including dendrobaenas, dendras, and Belgian night crawlers.
Containing water-soluble nutrients, vermicompost is a nutrient-rich organic fertilizer
and soil conditioner.
Vermiculture means artificial rearing or cultivation of worms (Earthworms) and
the technology is the scientific process of using them for the betterment of human
beings. Vermicompost is the excreta of earthworm, which is rich in humus.
Earthworms eat cow dung or farm yard manure along with other farm wastes and
pass it through their body and in the process convert it into vermicompost. The
municipal wastes; non-toxic solid and liquid waste of the industries and household
garbage’s can also be converted into vermicompost in the same manner.
Earthworms not only convert garbage into valuable manure but keep the
environment healthy.
Method of preparation of Vermicompost Large/community Scale:
A thatched roof shed preferably open from all sides with unpaved (katcha)
floor is erected in East-West direction length wise to protect the site from direct
sunlight. A shed area of 12’X12’ is sufficient to accommodate three vermibeds of
10’X3’ each having 1’ space in between for treatment of 9-12 quintals of waste in a

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cycle of 40-45 days. The length of shed can be increased/decreased depending

upon the quantity of waste to be treated and availability of space. The height of
thatched roof is kept at 8 feet from the centre and 6 feet from the sides. The base of
the site is raised at least 6 inches above ground to protect it from flooding during the
rains. The vermibeds are laid over the raised ground as per the procedure given
below. The site marked for vermibeds on the raised ground is watered and a 4”-6”
layer of any slowly biodegradable agricultural residue such as dried
leaves/straw/sugarcane trash etc. is laid over it after soaking with water. This is
followed by 1” layer of Vermicompost or farm yard manure.
Earthworms are released on each vermibed at the following rates:
For treatment of cowdung/agriwaste: 1.0 kg. per
For treatment of household garbage: 1.5 kg. per
The frequency and limits of loading the waste can vary as below depending upon the
convenience of the user
Frequency Loading
Daily 2" /bed/day
In Bulk 12-15"(3-4q/bed/cycle of 45 days)
The loaded waste is finally covered with a Jute Mat to protect earthworms
from birds and insects. Water is sprinkled on the vermibeds daily according to
requirement and season to keep them moist. The waste is turned upside down
fortnightly without disturbing the basal layer (vermibed). The appearance of black
granular crumbly powder on top of vermibeds indicate harvest stage of the compost.
Watering is stopped for atleast 5 days at this stage. The earthworms go down and
the compost is collected from the top without disturbing the lower layers (vermibed).
The first lot of Vermicompost is ready for harvesting after 2-2 ½ months and the
subsequent lots can be harvested after every 6 weeks of loading. The vermibed is
loaded for the next treatment cycle.
Multiplication of worms in large scale:
Prepare a mixture of cow dung and dried leaves in 1:1 proportion. Release
earthworm @ 50 numbers/10 kg. Of mixture and mix dried grass/leaves or husk and
keep it in shade. Sprinkle water over it time to time to maintain moisture level. By this
process, earthworms multiply 300 times within one to two months. These
earthworms can be used to prepare Vermicompost.
Advantages of Vermicomposting:
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 Vermicompost is an ecofriendly natural fertilizer prepared from

biodegradable organic wastes and is free from chemical inputs.
 It does not have any adverse effect on soil, plant and environment.
 It improves soil aeration, texture and tilth thereby reducing soil compaction.
 It improves water retention capacity of soil because of its high organic matter
content.
 It promotes better root growth and nutrient absorption.
 It improves nutrient status of soil-both macro-nutrients and micro-nutrients.
Precautions during vermicomposting:
 Vermicompost pit should be protected from direct sun light.
 To maintain moisture level, spray water on the pit as an when required.
 Protect the worms from ant, rat and bird
Nutrient Profile of Vermicompost and Farm Yard Manure:
Nutrient Vermicompost Farm Yard Manure
N (%) 1.6 0.5
P (%) 0.7 0.2
K (%) 0.8 0.5
Ca (%) 0.5 0.9
Mg (%) 0.2 0.2
Fe (ppm) 175.0 146.5
Mn (ppm) 96.5 69.0
Zn (ppm) 24.5 14.5
Cu (ppm) 5.0 2.8
C:N ratio 15.5 31.3
Night Soil:
Night soil is human excrement i.e. solid and liquid. Night soil is richer in N,
P2O5 and K2O as compared to FYM or compost. On oven dry basis, it has an
average chemical composition of:
N% P2O5% K2O%
5.5. 4.0 2.0
In India it is applied to a limited extent directly to the soil. Pits or trenches of
10 to 12 ft. long, 2 to 3 ft. wide and 9 inches to 1 foot deep are made. In these pits,
night soil is deposited and covered over on top with a layers of earth or Katchara.
This is known as the Poudrette System. Since the material formed in the above
trenches after they become dry, is known as poudrette.
Improved methods of handling night soil:

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Since night soil is an important bulky organic manure, supplying a good deal
of organic matter and plant nutrients to the soil, it is important that night soil is used
by the following improved methods:
1. Night soil should be protected from flies and fly breeding should be controlled.
2. It should be stored in such a way that it does not pollute the supply of drinking
water.
3. Pathogens, protozoa, cysts, worms and eggs should be destroyed before the
night soil is applied to the land.
4. Attempts should be made to compost the night soil with other refuse in urban
centres by municipal or town authorities and in rural areas by the farmer
himself.
Sewage and Sludge:
In the modern system of sanitation adopted in cities, water is used for the
removal of human excreta and other wastes. This is called the sewage system of
sanitation. In this system, there is a considerable dilution of the material in solution
and in dispersion in fact, water is the main constituent of sewage, amounting often to
99.0%.
In general sewage has two components, namely
(i) Solid portion, technically known as sludge and
(ii) Liquid portion, commonly known as sewage water.
Both the components are used in increasing crop production as they contain
plant nutrients. Both components of sewage as separated and are given a
preliminary fermentation and oxidation treatments to reduce the bacterial
contamination, the offensive smell and also to narrow down the C: N ratio of the solid
portion.
(i) Sludges:
In the modern system of sewage utilization, solid portion or sludge is

separated out to a considerable extent and given a preliminary treatment (i.e.
fermentation and oxidation) before its use as manure. Such oxidized sludge is also
called activated sludge which is of inoffensive smell and on dry weight basis
contains up to 3 to 6 per cent N, about 2 per cent P 2O5 and 1 per cent K2O in a form
that can become readily available when applied to soil.
(ii) Sewage irrigation:

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When raw sewage is treated to remove the solid portion or sludge the water,
technically known as treated effluent, is used for irrigation purpose. Such a system
of irrigation is known as sewage irrigation. Thus, both the activated sludge and the
effluent can be used with safely for manuring and irrigating all field crops except the
vegetables which are eaten raw or uncooked.
CONCENTRATED ORGANIC MANURES
Concentrated organic manures are those that are organic in nature and contain
higher percentages of major plant nutrients like N, P 2O5 and K2O compared to bulky
organic manures like FYM and compost. These concentrated manures are made
from raw materials of animal or plant origin. The common concentrated organic
manures are oil cakes, blood meal, fish manure, meat meal and wool waste.
Oil cake:
Oil cake is the residue left after the oil is extracted from oil bearing seeds. It
contains varying quantities of oil depending upon the process of manufacture
employed in treating the oil seed as shown below:
Process of manufacture Oil (per cent)
Country ghani 10-15

Hydraulic press 8-10
Expeller 5-8
Solvent 1-2
Oil cakes are of two types:
1) Edible Oil cake

2) Non Edible Oil cake
Edible oil cakes are valued more as cattle feed and seldom used as manure,
except when it becomes mouldy or rancid and unfit for feeding to cattle. Non edible
oil cakes are used as manure.
Characteristics:
1. Quick acting organic manures as C:N ratio is usually narrow (5-15)

2. Oil prevents rapid conversion of N
3. Nearly 50-80% of its N is made available in 2-3 months and rate of availability
varies with the type of cake and nature of soil.

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4. Castor cake contain Ricin, Mahuva cake contains Saponin and Neem cake
contains Nimbidin which are responsible for slow nitrification of their N due to
effects of alkaloids on soil microorganisms
5. Castor cake has also good vermicidal effect against white ants
6. Groundnut cake has the highest nitrification rate.
7. Mahua cake is very poor in N and takes a long time to nitrify. When used as
manure it has got to be applied to the soil two to three months before
sowing/planting of crop.
Average nutrient contents of principal oil cakes
Name of the oil cake Percentage composition
N P2O5 K2O
Non edible oil cakes
Castor cake 4.3 1.8 1.3
Cotton seed cake [Undecorticated] 3.9 1.8 1.6
Karanj cake 3.9 0.9 1.2
Mahua cake 2.5 0.8 1.8
Neem cake 5.2 1.0 1.4
Safflower cake [Undecorticated] 4.9 1.4 1.2
Edible oil cakes
Coconut cake 3.0 1.9 1.8
Cotton seed cake (decorticated) 6.4 2.9 2.2
Groundnut cake 7.3 1.5 1.3
Linseed cake 4.9 1.4 1.3
Rape seed cake 5.2 1.8 1.2
Safflower cake(decorticated) 7.9 2.2 1.9
Sesame or til cake 6.2 2.0 1.2
Precautions in using oil cakes:

1. It should be powdered before use.
2. Apply during last ploughing in short duration crop.
3. It is best used as a topdressing after the plants have established themselves.
4. Use only when there is sufficient moisture in the soil.
5. If Mahua cake is to be used, apply before 2-3 months before planting or
decompose in a pit and then apply or treat with ammonium sulphate.

18
Blood meal:
Dried blood or blood meal contains 10-12% N and 1-2% P2O5. Blood meal is
prepared from the blood collected from slaughter house treating with copper
sulphate, dried, powdered and bagged and sold as blood meal. Blood meal is a
quick acting manure and is effective for all crops on all soils. It should be applied like
oil cakes.
Meat meal:
Bones and meat are cooked in special type of pan for 2-3 hours. Bones are
separated and meat is dried and powdered. It is quick acting and used like oil cakes.
It contains 10.50% N and 2.5% P2O5.
Fish manure:
Fish and fish waste is dried and powdered. It is quick acting organic manure
and used like oil cakes for all crops on all types of soils. Fish manure or fish meal
contains 4 to 10% N, 3 to 9% P2O5 and 0.3 to 1.5% K2O.
Horn and hoof meal:
Horn and hoof cooked in bone digester, dried and powdered. It contains 13%
N.
Green Manuring:
Practice of incorporating undecomposed green plant tissues into the soil for
the purpose of improving physical structure as well as fertility of the soil.
In agriculture, a green manure is a type of cover crop grown primarily to add
nutrients and organic matter to the soil. Typically, a green manure crop is grown for a
specific period, and then plowed under and incorporated into the soil. Green
manures usually perform multiple functions that include soil improvement and soil
protection:
 Leguminous green manures such as clover and vetch contain nitrogen-fixing
symbiotic bacteria in root nodules that fix atmospheric nitrogen in a form that
plants can use.
 Green manures increase the percentage of organic matter (biomass) in the soil,
thereby improving water retention, aeration, and other soil characteristics.
 The root systems of some varieties of green manure grow deep in the soil and
bring up nutrient resources unavailable to shallower-rooted crops.

19
 Common cover crop functions of weed suppression and prevention of soil

erosion and compaction are often also taken into account when selecting and
using green manures.
 Some green manure crops, when allowed to flower, provide forage for pollinating
insects.
Historically, the practice of green manuring can be traced back to the fallow cycle of
crop rotation, which was used to allow soils to recover.
Types of green manuring:
Broadly two types of green manuring can be differentiated. I) Green manuring

in situ and ii) Green leaf manuring
i) Green manuring in situ:
In this system green manure crops are grown and buried in the same field,
either as a pure crop or as intercrop with the main crop. The most common green
manure crops grown under this system are Sanhemp, Dhaincha and guar.
ii) Green leaf manuring:
Green leaf manuring refers to turning into the soil green leaves and tender
green twigs collected from shrubs and trees grown on bunds, waste lands and
nearby forest areas. The common shrubs and trees used are Glyricidia, Sesbania
(wild dhaincha), Karanj, etc.
The former system is followed in northern India, while the latter is common in
eastern and central India.
Advantages of Green Manuring:

1. It adds organic matter to the soil. This stimulates the activity of soil micro-
organisms.
2. The green manure crops return to the upper top soil, plant nutrients taken up by
the crop from deeper layers.
3. It improves the structure of the soil.
4. It facilitates the penetration of rain water thus decreasing run off and erosion.
5. The green manure crops hold plant nutrients that would otherwise be lost by
leaching.

20
6. When leguminous plants, like sannhemp and dhaincha are used as green
manure crops, they add nitrogen to the soil for the succeeding crop.
7. It increases the availability of certain plant nutrients like phosphorus, calcium,
potassium, magnesium and iron.
Disadvantages of green manuring:
When the proper technique of green manuring is not followed or when
weather conditions become unfavorable, the following disadvantages are likely to
become evident.
1. Under rainfed conditions, it is feared that proper decomposition of the green
manure crop and satisfactory germination of the succeeding crop may not take
place, if sufficient rainfall is not received after burying the green manure crop.
This particularly applies to the wheat regions of India.
2. Since green manuring for wheat means loss of Kharif crop, the practice of green
manuring may not be always economical. This applies to regions where irrigation
facilities are available for raising Kharif crop along with easy availability of
fertilizers.
3. In case the main advantage of green manuring is to be derived from addition of
nitrogen, the cost of growing green manure crops may be more than the cost of
commercial nitrogenous fertilizers.
4. An increase of diseases, insects and nematodes is possible.
5. A risk is involved in obtaining a satisfactory stand and growth of the green
manure crops, if sufficient rainfall is not available.
Green manure crops:
Leguminous Non-leguminous
1. Sannhemp 1. Bhang
2. Dhaincha 2. Jowar
3. Mung 3. Maize
4. Cowpea 4. Sunflower
5. Guar
6. Senji
7. Khesari
8. Berseem
Selection of Green manure crops in situ:
Certain green manure crops are suitable for certain parts of the country.
Suitability and regional distribution of important green manure crops are given below:

21
Sannhemp: This is the most outstanding green manure crop. It is well suited to
almost all parts of the country, provided that the area receives sufficient rainfall or
has an assured irrigation. It is extensively used with sugarcane, potatoes, garden
crops, second crop of paddy in South India and irrigated wheat in Northern India.
Dhaincha: It occupies the second place next to sannhemp for green manuring. It
has the advantage of growing under adverse conditions of drought, water-logging,
salinity and acidity. It is in wide use in Assam, West Bengal, Bihar and Chennai with
sugarcane, Potatoes and paddy.
Guar: It is well suited in areas of low rainfall and poor fertility. It is the most common
green manure crop in Rajasthan, North Gujarat and Punjab.
Technique of Green Manuring in situ:
The maximum benefit from green manuring cannot be obtained without
knowing
(i) When the green manure crops should be grown,

(ii) When they should be buried in the soil and
(iii) How much times should be given between the burying of a green manure crop
and the sowing of the next crop.
(i) Time of sowing:
The normal practice usually adopted is to begin sowing immediately after the
first monsoon rains. Green manure crops usually can be sown/broadcast preferably
giving somewhat higher seed rate.
(ii) Stage of burying green manure crop:

From the results of various experiments conducted on different green manure
crops, it can be generalized that a green manure crop may be turned in soil at the
stage of flowering. The majority of the green manure crops take about six to eight
weeks from the time of sowing to attain the flowering stage. The basic principle
which governs the proper stage of turning in the green manure crops, should aim at
maximum succulent green matter at burying.
(iii) Time interval between burying of green manure crop and sowing of next
crop.
Following two factors which affect the time interval between burring of green
manure crop and sowing of next crop.

22
1. Weather conditions
2. Nature of the buried green material
In paddy tracts the weather is humid due to the high rainfall and high
temperature. These favour rapid decomposition. If the green material to be buried is
succulent, there is no harm in transplanting paddy immediately after turning in the
green manure crop. When the green manure crop is woody, sufficient time should be
allowed for its proper decomposition before planting the paddy.
Regions not suitable for green manuring:
The use of green manures in dry farming areas in arid and semiarid regions
receiving less than 25 inches of annual rainfall is, as a rule, impracticable. In such
areas, only one crop is raised, as soil moisture is limited. Such dry farming areas are
located in Punjab, Maharashtra, Rajasthan, M.P. and Gujarat (Kutch and
Saurashtra).
On very fertile soils in good physical condition, it is not advisable to use green
manures as a part of the regular rotation.
In areas where Rabi crops are raised on conserved soil moisture, due to lack
of irrigation facilities, it is not practicable to adopt green manuring. If green manuring
is followed in this areas, there is danger of incomplete decomposition of the green
matter and as such less moisture for the succeeding crop.
**************
CHAPTER- II: TRANSFORMATION REACTIONS OF

ORGANIC MANURES IN SOIL AND IMPORTANCE OF C: N
RATIO IN RATE OF DECOMPOSITION.

23
Organic matter in the soil comes from the remains of plants and animals. As
new organic matter is formed in the soil, a part of the old becomes mineralized. The
original source of the soil organic matter is plant tissue. Under natural conditions, the
tops and roots of trees, grasses and other plants annually supply large quantities of
organic residues. Thus, higher plant tissue is the primary source of organic matter.
Animals are usually considered secondary sources of organic matter. Various
organic manures, that are added to the soil time to time, further add to the store of
soil organic matter.
Composition of plant residues
Composition of organic residues have un-decomposed soil organic matter

(mainly plant residues together with animal remains, i.e. animal excreta etc.) The
moisture content of plant residues varies from 60 to 90% (average 78%) and 25%
dry matter (solid). Plant tissues (organic residues) may be divided into 91) organic
and (2) inorganic (elemental) composition. The compounds constituting the plant
residues or un-decomposed soil organic matter is shown in the following diagram
Organic Residues
(Un-decomposed organic matter)
Organic Inorganic
(Mineral matter/ elemental
composition or ash)
S, P, Cl, CO3 , Ca, Mg, Na,
K, Fe, Zn, Cu, Mn, etc.
Nitrogenous Non-nitrogenous
Insoluble: protein, peptides, Carbohydrates: Cellulose (insoluble);
Peptones etc. starch, hemicelluloses, pectin, mucilage
etc. (Hydrolysable);
sugars (soluble)
Water-soluble: Nitrates, Ether-soluble: Fats, oils, waxes,
resins
ammonical compounds etc steroids etc.
Miscellaneous: Lignin, tanin, essential oils, organic acids
Transformation Reactions of Organic Manures in Soils:

24
It is found that both bulky and concentrated organic manures contain some
amount of plant nutrients including macro-and micro-nutrients, of which organic
nitrogen content is likely to be dominant. The organic forms of soil nitrogen occur as
consolidated amino acids, proteins, amino sugars etc. When Organic manures like
FYM, composts, oil cakes, green manures etc. are added to the soil, the microbial
attack to these materials takes place and results complete disappearance of the
organic protein with the remainder of the nitrogen being changed into inorganic form
of nitrogen through the process of mineralization.
The organic materials incorporated in the soil do not remain as such very
long. They are at once attacked by a great variety of microorganisms, worms and
insects present in the soil especially if the soil is moist. The microorganism for
obtaining their food, break up the various constituents of which the organic residues
are composed, and convert them into new substances, some of which are very
simple in composition and others highly complex. The whole of the organic residues
is not decomposed all at once or as a whole. Some of the constituents are
decomposed very rapidly, some less readily, and others very slowly.
It is evident that different constituents of organic residues decompose at
different rates. Simple sugars, amino acids, most proteins and certain
polysaccharides decompose very quickly and can be completely utilized within a
very short period. Large macro-molecules which make up the bulk of plant residues
must first be broken down into simpler forms before they can be utilized further for
energy and cell synthesis. This process is carried out by certain specific enzymes
excreted by microorganisms.
Proteins R- NH2 + CO2 + energy + other products
(Present in organic manures)
R - NH2 + HOH NH3 + R - OH + energy + H2O
NH4+ + OH-
(release of ammonium in the soil)
The released ammonium (NH4+) is subject to following changes:

1) It may be converted to nitrites and nitrates through the process of nitrification
carried out by microorganisms,

25
enzymic
2 NH4+ + 3O2 2 NO2- + 2H2O + 4H+ + energy
Oxidation
enzymic
2 NO2- + O2 2 NO3- + energy
oxidation
2) It may be absorbed directly by the plants.

3) It may be utilized by hetero-trophic organisms in further decomposing organic
carbon residues.
4) It may be fixed in the lattice of certain expanding type of clay minerals.
5) It could be slowly released back to the atmosphere as elemental nitrogen.
Mineralization and immobilization of nitrogen or any other nutrient elements
occur continuously in microbial metabolism and the magnitude and direction of
the net effect are greatly influenced by the nature and amount of organic
manures added. Normally organic manures are applied to the soil as a source
of fertilizer nitrogen should contain about 1.5 to 2.0 per cent of the dry weight
of the manures in order to meet the needs of the soil microorganisms,
otherwise little or no nitrogen will be released for the use of plants. The carbon
nitrogen ratio (C : N ratio) in the organic manures remaining in the soil after
consuming by the soil microorganisms is approximately 10:1. Therefore,
different organic manures containing variety of organically bound nutrients like
P, S, and other micro nutrients etc. are subject to transformation in soils
similar to that of mineralization and immobilization processes of nitrogen and
releases inorganic forms of nutrients ion soils which become available to
plants.
Role of Organic Manure:
1. Organic manure binds soil particles into structural units called aggregates.
These aggregates help to maintain a loose, open, granular condition. Water
infiltrates and percolates more readily. The granular condition of soil maintains
favorable condition of aeration and permeability.
2. Water-holding capacity is increased by organic matter. Organic matter
definitely increases the amount of available water in sandy and loamy soils.
3. Surface run off and erosion are reduced by organic matter as there is good
infiltration.
4. Organic matter or organic manure on the soil surface reduces losses of soil by
wind erosion.
26
5. Surface mulching with coarse organic matter lowers soil temperatures in the
summer and keeps soil warmer in winter.
6. The organic matter serves as a source of energy for the growth of soil
microorganisms.
7. Organic matter serves as a reservoir of chemical elements that are essential
for plant growth as well as many hormones and antibiotics.
8. Fresh organic matter has a special function in making soil phosphorus more
readily available in acid soils. Organic acids released from decomposing
organic matter help to reduce alkalinity in soils.
9. Fresh organic matter supplies food for such soil life as earthworms, ants and
rodents. These microorganisms improve drainage and aeration. Earthworms
can flourish only in soils that are well provided with organic matter.
10. Organic matter on decomposition produces organic acids and carbon dioxide
which help to dissolve minerals such as potassium and make them more
available to growing plants.
11. Humus (highly decomposed organic matter) provides a storehouse for the
exchangeable and available cations – potassium, calcium and magnesium.
Ammonium fertilizers are also prevented from leaching because humus holds
ammonium in an exchangeable and available form. It acts as a buffering
agent. Buffering checks rapid chemical changes in pH and in soil reaction.
Importance of C:N ratio in rate of decomposition

The ratio of the weight of organic carbon (C) to the weight of total nitrogen (N)
in a soil (or organic material), is known as C: N ratio. When fresh plant residues are
added to the soil, they are rich in carbon and poor in nitrogen. The content of
carbohydrates is high. This results in wide carbon-nitrogen ratio which may be 40 to
1. Upon decomposition the organic matter of soils changes to humus and have an
approximate C: N ratio of 10:1.
The ratio of carbon to nitrogen in the arable (cultivated) soils commonly
ranges from 8:1 to 15:1. The carbon-nitrogen ratio in plant material is variable,
ranging from 20:1 to 30:1. Low ratios of carbon to nitrogen (10:1) in soil organic
matter generally indicate an average stage of decomposition and resistance to
further microbiological decomposition. A wide ratio of C: N (35:1) indicates little or no
decomposition, susceptibility to further and rapid decomposition and slow
nitrification.
27
► Significance of C:N Ratio

(1) Keen competition for available nitrogen when organic residues (with high C: N
ratio) are added to soils. When organic residues with a wide C/N ratio (50:1) are
incorporated in the soil, decomposition quickly occurs. Carbon dioxide is
produced in large quantities. Under these conditions, nitrate-nitrogen disappears
from the soil because of the instant microbial demand for this element to build up
their tissues. And for the time being, little (or no) nitrogen is an available to plants.
As decomposition occurs, the C/N ratio of the plant material decrease since
carbon is being lost and nitrogen conserved. Nitrates-N again appear in quantity
in the soil, thus, increases plant growth.
(2) Consistency of C: N Ratio. As the decomposition processes continue, both
carbon and nitrogen are now subject to loss the carbon as carbon dioxide and the
nitrogen as nitrates which are leached or absorbed by plants. At a point carbon-
nitrogen ratio, becomes more or less constant, generally stabilizes at 10:1 or
12:1.
**************
CHAPTER- III: INTEGRATED NUTRIENT MANAGEMENT

Modern agricultural production practices have emphasized the wide spread
use of fertilizer and this approach has certainly increased grain yield in many
countries in the last two decades. However, long-term use of chemical fertilizers also
28
led to a decline in crop yields and soil fertility in the intensive cropping system. There
is evidence that over fertilization has increased the concentration of many plant
nutrients in both surface and ground water, which has created a potential health
hazards.
In order to safeguard the environmental from further degradation and to
maintain the purity of air, water and food. We should opt for less use of chemicals
and shift from chemical to ecological agriculture to fertilize our fields. Hence, in
recent years integrated use of inorganic fertilizers and organic manures has become
important for higher agricultural production. No single source of plant nutrients, be it
chemical fertilizer, organic manure, crop residue, green manure or even biofertilizers
can meet the entire nutrient needs of crops in present day agriculture.
Farmyard manure and compost are limited in supply and have low nutrient
content. However, green manure is a potential source of organic manure. The use of
plant residues and biofertilizers is also being advocated in nutrient management.
Organic manure, however, can not be used as a substitute for chemical fertilizer but
only as a component in the whole nutrient management system as the nutrient
needs essential for higher yield goal can not be met exclusively through them
particularly for reasons of insufficiency.
Therefore, to maintain production at high levels, resource has to be made to
the application of fertilizers and organic manure not only provide essential plant
nutrients but also build up the organic carbon and improve soil physical as well as
biological conditions. As “sustainable plant nutrition to increase food production” has
been identified as one of the priorities directly linked to land and water management
resources in relation to environment. Therefore, for the sustained growth, the soil
health is very important to achieve national food security targets. In addition to this,
for maximizing fertilizer use efficiency and ensure a balanced and optimum supply of
essential plant nutrients, INMs has got special emphasizes in present day of
agriculture.
The concept of integrated nutrient management (INM) is the maintenance
of soil fertility and health, sustaining agricultural productivity and improving farmers’
profitability through the judicious and efficient use of mineral fertilizers together with
organic manures industrial/farm wastes and bio fertilizers. Thus, the objectives of
INM are to ensure efficient and judicious use of all the major sources of plant

29
nutrients in an integrated manner so as to get maximum economic yield from a

specific cropping system.
Thus, integrated nutrient management (INM) involving soil resources,
chemical fertilizers, biofertilizers and organic manures is key to the sustained
productivity as it reduces dependence on chemical fertilizers and improve fertilizer
use efficiency by improving physical and biological properties of soil.
Integrated nutrient management has a great potential to offset the growing

heavy nutrient demands, to achieve maximum yields and to sustain the crop
productivity on long-term basis. However, the adoption of green manure technology
in India is limited. Despite the existing constraints in availability and usage of
different organic and biological sources, efforts should be made to synthesise the
available data for developing a agro-ecological specific and practically feasible INM
packages for different crops and cropping system. Therefore, a challenging task
ahead for the researchers is to convert the concept of sustainable productivity into
an operational reality through INMS. It should always be kept in mind that the
development of INMS system is just the beginning and not the end till we make this
system itself self-sustainable.
The various sources of plant nutrients are

1. Soil sources
The nutrient supplying capacity of many soils declined steadily as a result of
continuous and intensive cultivation practices. The low and declining soil fertility are
the main causes of low productivity of most of the cultivated lands. Intensive
cultivation also resulted in the deficiency of certain secondary and micronutrients in
the soils. A scenario of nutrients deficiency shows that N deficiency is universal and
nearly 49, 20 and 47 per cent soils of India are deficient in P, K and Zn, respectively.
Sulphur deficiency is recorded in 125 districts. The Fe, Mn and B have also become
most serious constraints in some agricultural production systems. The long-term
fertilizer experiments in different agro-ecological regions have demonstrated very
clearly that in future K deficiency will become most limiting factor for crop production
under intense cropping. It will also reduce the efficiency of other fertilizer nutrients.
Further, it is estimated that through every year up to 8 m.t. of nutrients are being
depleted through soil erosion.

30
It becomes, therefore, necessary to reduce the nutrient losses through

suitable soil management practices, to ameliorate problems of soils and to use
appropriate crop varieties, cultural practices and cropping system to maximize
utilization of available nutrients.
1. Mineral fertilizers
Mineral fertilizers play an important role in sustaining agricultural production.
However, it is costly input and needs to improve its use efficiency through
optimization of all other crop production factors such as:
a) Making fertilizer recommendations for a cropping system instead of single

crop in the system.
b) Eliminating limiting factors including secondary and micronutrients.
c) Minimizing losses in the field through appropriate time and method of
application and
d) Using appropriate products including super granules and coated urea, direct
use of locally available phosphate rocks in acidic soils, etc.
Thus, to get benefit from fertilizers, they must be applied in the right quantity,
at the right time and placed from the right source and in the right combination.
2. Organic sources
Organic manure acts many ways in augmenting crop growth and soil
productivity. The direct effect of organics relates to uptake of humic substances or its
decomposition products affecting favourably the growth and metabolism of plants.
Indirectly, it augments the beneficial soil microorganisms and their activities and
thus increases the availability of major and minor plant nutrients.
Organic sources are valuable by-products of farming and allied industries

derived from plant and animal matter. Organic sources include farm yard manure,
animal droppings, crop waste residues, sewage, sludge, compost, biofertilizers
human wastes and other various industrial wastes.
The potential annual plant nutrients (N, P and K) generated through organic
sources is about 9.9, 2.7 and 4.4 million tonnes of N, P2O5 and K2O, respectively.
Cattle and buffalo dung contribute to the extent of 3.7, 1.1 and 1.8 million tonnes of
N, P2O5 and K2O, respectively. Most of it is used as fuel. Adoption of biogas
technology can go a long way in saving the much needed nutrients on the one hand

31
and the fuel for which the dung is burnt, on the other. Biogas slurry is richer in plant
nutrients especially in nitrogen than the animal dung. Night soil if properly exploited
can provide about 5 m. t. of N P K nutrients. Estimated current potential availability
of crop residues is 400 million metric tonnes (mmt). In regions where mechanical
harvesting is done, a sizeable quantity of residues is left in the field. These residues
are being burnt in situ causing loss of plant nutrients and organic matter. Rice and
wheat straw account for 70 % of crop residues generated. About one-third of the
crop residues generated get recycled directly on the land and a substantial
proportion get recycled after serving as animal feed where animal dung is used as
FYM.
A few more million tones of NPK nutrients might become available from crop
residues, green manuring, rural and urban wastes, agro- industrial wastes, fisheries,
bone meal, etc. Careful collection, conservation and recycling of those manures
would enable India to meet its nutrient requirement and develop its agriculture on a
sustainable basis. The organic manures also contain sufficient quantity of
micronutrients. Hence, the combined use of organic, biological and inorganic
fertilizers assumes special significance as complementary and supplementary to
each other in agricultural production and soil productivity.
Thus, all the major sources of plant nutrients such as soil mineral, organic
and biological should be utilized in an efficient and judicious manner in sustainable
crop production. Also, integrated nutrient supply is important as a soil ameliorant in
alleviating the adverse soil ecological conditions and improving soil productivity.
3. Organic cycling
(A) Green manuring
Green manuring has a long history with the farmers. However, in the
intensive farming, a farmer may not be able to practice green manuring in a
traditional manner by devoting an entire season to a green manure crop. But, green
manuring is one of the most effective and environmentally sound method of organic
manuring that offers an opportunity to cut down the use of chemical fertilizers. Green
manuring of soils for the benefit of crop is an old practice but it has gone into
background in late 1960. In the present context of integrated nutrient supply system,
it needs adequate attention being the cheapest source of input for building up the
soil fertility and supplementing plant nutrients especially nitrogen.
32
The green manuring helps to increase crop yield through following processes
a) The nodulated legumes fix atmospheric N to enrich soil N.

b) The decomposing organic matter has a solubilizing effect on N, P, K and
micronutrients present in the soil.
c) It reduces leaching and gaseous losses of N to increase the use efficiency of
plant nutrients, and
d) It improves physical, chemical and biological environs of the soil.
Where farmers are not willing to spare their merge land resources and inputs
for growing a green manure crop, fresh lopping of some perennial leguminous trees
like Glyricidia grown in hedge rows and field bunds may be used for incorporation
into soil as a source of N. This practice is common in southern parts of the country.
4. Biological sources
With the discovery of Hellrigel and Wilfarth a century ago (1886) that the
nodules of legume roots contain colonies of symbiotic bacteria able to capture
atmospheric nitrogen molecules to the benefit of the host plants heralded a growing
realization of the importance of soil biota in fertility studies. Biofertilizers are the
fertilizers of biological origin. Recent use of the term encompasses all the organic
manure including green manure. However, in restricted scope, biofertilizers are the
preparations of living microorganisms used to improve plant nourishment and soil
fertility and thereby achieving more sustainable crop production. Biofertilizers are
considered to be cost effective ecofriendly and renewable sources of non-bulky, low
cost plant nutrients supplemental to chemical fertilizers in sustainable agricultural
systems in India.
1. Rhizobium Inoculants: Rhizobium fixes nitrogen symbiotically with legumes.

Rhizobium cultures are recommended for inoculation of seeds of various pulses and
legume crops for meeting about 80% of the nitrogen requirement of such crops. In
case of legumes, about 10-20 kg inorganic N\ha is recommended for application to
soils for initial growth and establishment of the seedlings. Introduction of leguminous
crops in crop rotation has shown to maintain soil fertility. Normally inoculation with
Rhizobium in traditional pulses results in increase of grain yield by 2-3 q\ha.
Rhizobium inoculations now become a practice for introduced legume crops.
2. Azotobacter inoculants: Azotobacter fixes nitrogen non-symbiotically and

benefits the plants by growing in the rhizosphere of plants. Several workers have
33
tested azotobacter chrococcum inoculants in field trials. It is estimated that

Azotobacter inoculation could save about 15-20kg N\ha and increase grain yield by
about 10 per cent. They also produce growth hormones, which improve the
germination of seeds, development of better root system and better stand of plants.
3. Azospirillum inoculants: The group of gram-negative nitrogen fixing spirilla,

which was originally named as spirillum lipoferum, has been reclassified into at least
two species in the genus Azosperillum, A. brasilense and A. lipoferum. Field trials
showed that sorghum and pearl millet usually responded to inoculation with A.
brasilense cultures and could save about 20-40 kg N\ha. Similarly, wheat showed
significant response to A. lipoferum.
4. Blue green algae inoculants: Wetland rice field is an ideal ecosystem for algal
nitrogen fixation values ranging from 40-80 kg N/ha/year. Algal inoculation can
increase grain yield by about 10-20 %. BGA is also reported to produce growth
promoting substances.
5. Azolla: The water fern Azolla fixes atmospheric N due to the presence of
heterocystons blue green algal Anabeana azolla in its dorsal leaves. A. pinnata is
found in India. The chemical composition of Azolla (dry basis) is 4-6% N, 0.5-0.6%
P, 2-6% K, 9-10% ash, 5 % crude fat, 9 % crude fiber and 20-30 % crude protein. It
is thus a good source of organic N and can also be used as a green manure.
6. Phosphatic biofertilizer: Several soil bacteria (Pseudomonas striata, Bacillus

polymixa) and fungi (Aspergillus awamori) posses the ability to bring insoluble
phosphate in to soluble forms through secretion of organic acids. These acids lower
the pH and bring about dissolution of immobilized forms of phosphates. Besides,
some of the hydroxy acids may chelate with calcium and iron resulting in effective
solubilization and thereby higher utilization of soil phosphate by plants. Application of
organic manure along with PSM can enhance the availability of P from rock
phosphate. VAM can play an important role in enhancing P availability to plants on P
deficient soils. They can also increase the transport of other mineral elements such
as zinc and copper.
**************
CHAPTER- IV: CHEMICAL FERTILIZERS

34
Fertilizer is any material dry or liquid added to the soil in order to supply one
or more plant nutrients. The term fertilizer is generally applied to commercially
manufactured materials other than lime and gypsum.
NITROGEN FERTILIZERS
Nitrogen is present in soil as (i) Organic form and (ii) inorganic form. Inorganic
form includes ammonical (NH4+), Nitrite (NO2-) and Nitrate (NO3-). Plant absorbs N in
the form of NO-3 and NH+4 forms by paddy in early stages. Nitrogen in NH+4 form
goes on exchange complex on clay and organic colloids and hence, this part is not
lost due to leaching, while NO-3 is lost due to leaching as it does not go on exchange
complex under neutral to higher pH values of soil. But it goes on exchange under
highly acidic conditions. The nitrate fertilizers are hygroscopic in nature, it is for this
reason, nitrate fertilizers are not commonly used even though plant absorbs N as
NO-3. Therefore, organic form (urea) and fertilizers of NH4 form like ammonium
sulphate are widely used.
Most of Indian soils are low in N and the requirement of N by crop is
throughout its growing period, therefore N should be applied in such a way that plant
gets it throughout its life period. It becomes absolutely necessary to apply
nitrogenous fertilizers to every soil and crop. For this, the total quantity of
nitrogenous fertilizers requirement is more compared to fertilizers of other nutrients.
COMMERCIAL NITROGENOUS FERTILIZERS
Commercial nitrogenous fertilizers are those fertilizers that are sold for their
nitrogen content and are manufactured on a commercial scale.
Nitrogenous Fertilizers:
Nitrogenous fertilizers may be classified into four groups on the basis of the
chemical form in which nitrogen is combined with other elements with a fertilizer.
Nitrogenous Fertilizers
Nitrate Ammonical Nitrate and Amide

Fertilizers Fertilizers Ammonical Fertilizers
Fertilizers
1) Nitrate Fertilizers:
Nitrogen is combined as NO3- with other elements. Such fertilizers are
i) Sodium nitrate or Chilean nitrate (NaNO3) – 16% N
ii) Calcium nitrate [Ca (NO3)2] – 15.5% N.

35
Out of these, sodium nitrate is an imported commercial fertilizer.

2) Ammonical Fertilizers :-
In these fertilizers, nitrogen is combined in ammonical (NH4) form with other
elements. Such fertilizers are
i) Ammonium sulphate [(NH4)2 SO4] – 20% N
ii) Ammonium Chloride (NH4Cl) 24 to 26% N
iii) Anhydrous ammonia - 82% N
3) Nitrate and ammonical Fertilizers:
These fertilizers contain nitrogen in the form of both nitrate and ammonical. Such
fertilizers are
i) Ammonium nitrate (NH4 NO3) - 33 to 34% N
ii) Calcium ammonium nitrate -- 26% N
iii) Ammonium sulphate nitrate – 26% N
4) Amide fertilizers:
These fertilizers contain nitrogen in amide or cynamide form. Such fertilizers are
i) Urea [CO (NH2)2 ]– 46% N
ii) Calcium cynamide (Ca CN2) – 21% N
General characteristics of four groups:

1) Nitrate fertilizers:
Most of the field crops except paddy in early stages of their growth, take up
nitrogen in nitrate form as such,
i) Nitrate fertilizers are readily absorbed and utilized by these crops. Nitrate
fertilizers are very often used as top and side dressings.
ii) The great mobility of the nitrate ion in the soil has the advantage that, even by
broadcasting the fertilizer on the surface of the soil, the nitrogen reaches the root
zone quickly.
iii) On the other hand, there is also the increased danger of leaching of these
fertilizers. On dry soils, nitrate fertilizers are superior to the other forms of
nitrogenous fertilizers.
iv) All nitrate fertilizers are basic in their residual effect on the soils and their
continued use may play a significant role in reducing soil acidity. Sodium nitrate,
for example, has a potential basicity of 29 pounds of calcium carbonate per 100
pounds of fertilizer material.

36
2) Ammonical Fertilizers:
i) Ammonical fertilizers are water soluble.
ii) It is less rapidly used by plant than NO-3, as it is to be changed to NO-3 before
use by crop.
iii) It is resistant to lost due to leaching as being cation goes on exchange
complex.
iv) Any fertilizers which contain N as NH+4 or which is changed as NH+4 produced
acidity in soil due to production of HNO3.
v) Ammonium (NH+4) of fertilizer goes on exchange complex, used by crop like
paddy.
vi) Used by microorganisms nitrified to NO3 and lost due to volatilization from soil.
3) Nitrate and Ammonical Fertilizers:
i) Fertilizers of this group are soluble in water.
ii) Nitrate part can readily be used by crop.
iii) NH+4 can go on exchange and hence, this is best type but did not over take
ammonium sulphate and urea, as they are hygroscopic in nature.
iv) They are acidic in their residual effect on soil
4) Amide Fertilizes:
i) Fertilizers of this group are readily soluble in water. They are easily
decomposed by microorganisms due to presence of oxidisable carbon.
ii) They are quickly changed to NH+4 then in to NO-3.
Manufacturing process of ammonium sulphate and urea:
Most of the nitrogenous fertilizes like ammonium sulphate, urea, ammonium
nitrate, ammonium sulphate nitrate and even DAP are manufactured by using NH -3
as one of the important compound. Most of the commercial NH-3 is prepared by
Haber’s process by the fixation of atmospheric N by means of H2.
The reaction is:
200 atm. Pressure
N2+3H2 2NH3 + 24.4 KCal
at 550oC
temp
Fe and Mo as catalysts
Ammonia can also be obtained from natural gas, coal gas and naphtha.
Therefore, cost of fertilizer production in fertilizer factory installed near a
petrochemical will be low.

37
The NH3 gives ammonium sulphate with sulphuric acid, NH4Cl with HCI; NH4
NO3 with HNO3; urea with CO2; MAP and DAP with H3PO4. Thus, NH3 is chief
compound for most of the nitrogenous fertilizers.
i) Preparation of Ammonium sulphate (A/S) :-
It is prepared by
(a) reacting NH3 with H2SO4
(b) gypsum process
(c) by-product of coal and steel industries.
a) NH3 with H2SO4 :- NH3 is reacted with H2SO4 giving A/S. The liquid is crystallized
and crystals of A/S are obtained.
2NH3 + H2SO4 = (NH4)2 SO4
Since the sulphur used in sulphuric acid is to be imported, the source of H 2SO4
becomes costlier and hence, gypsum a cheaper source of sulphur is used in gypsum
process.
b) Gypsum process: The main raw materials required in gypsum process is NH3,
pulverized gypsum, CO2 and water. NH3 is obtained by Haber’s process. This NH3
when reacts with CO2, gives (NH4)2 CO3. The ground gypsum when reacts with
(NH4)2 CO3 solution gives (NH4)2 SO4 and CaCO3. The reactions are :
N2 + 3H2 ----- 2NH3
2NH3 + H2O + CO2 = (NH4)2 CO3
(NH4)2 CO3 + CaSO4 = (NH4)2 SO4 + CaCO3
ii) Preparation of Urea :-
Urea is manufactured by reacting anhydrous ammonia with CO2 under higher
pressure in presence of suitable catalyst. The intermediate unstable product
ammonium carbamate is decomposed to urea :
N2+3H2 = 2NH3
2NH3+CO2 NH2COONH4
30 atm (Amm. Carbomate)
NH2COONH4 NH2 CONH2 + H2O
Urea
During the preparation of urea, biuret is formed which is harmful. This biuret is
formed when two molecules of urea are reacted eliminating NH3.
NH2.CO.N (H2 + H.N) HCO.NH2 = NH2 CO. NH.CO NH2 + NH3
Urea Urea Biuret

38
In urea biuret should not be more than 1.5%.

Now a days urea is used as fertilizer more compared to other nitrogenous
fertilizers due to the following reasons:
a) Higher N content (44 to 46 per cent).
b) Good physical conditions.
c) Less acidic in residual effect compared to A/S.
d) Less cost per unit of N in production, storage and transport.
e) Lack of corrosiveness.
f) Suitable for foliar application, and
g) It is having of equal agronomical value compared to other nitrogenous fertilizers.
Ease of storage, handling and residual effect of nitrogenous fertilizers in soil:
The nitrogenous fertilizers differ in their ability to become moist or hygroscopic
and as such they have to handle carefully in rainy season. The main features of
nitrogenous fertilizers from storage view point are as follows:
(A) Ease of storage and handling:
Sr.No. Fertilizer Ease of storage and handling
i. A/S Storage property good, no difficulty in handling
and storage.
ii. Ammonium chloride Storage property excellent, no difficulty in
handling and storage.
iii Ammonium Nitrate Storage property satisfactory but it is
hygroscopic, so the bag should be firmly tied.
As it is fire hazardous, handle carefully.
iv. Sodium nitrate Storage property good, no difficulty in handling
and storage.
v. Ammonium sulphate Storage property satisfactory, slightly
nitrate hygroscopic, store in dry condition.
Sr. No. Fertilizer Ease of storage and handling
vi. Calcium ammonium Storage property satisfactory but it is
nitrate hygroscopic. Use entire bag in one lot. Store
bags in dry place. Tie half way used bag firmly
when it is to be used.
vii Urea Storage property satisfactory. It is hygroscopic.
Use entire bag in one lot and store in a dry
place.
(B) Residual effect of nitrogenous fertilizers in soil:

(On lime basis) – Nitrogenous fertilizers differ in their residual effect.
Fertilizers which contain NH+4 ions or which produce NH+4 ion in soil, produce acidity
in soil or cause loss of lime. While other fertilizers being basic in reaction save lime.
Among several nitrogenous fertilizes, except NaNO3 and calcium ammonium nitrate

39
are acid producing. Sodium Nitrate is basic in residual effect as it save lime, while
CAN is neutral.
The amount of lime lost or saved when nitrogenous fertilizers are added to
soil is as under:
S.No. Fertilizer Pounds of CaCO3/100 lbs of fertilizers
when added to soil for
Equivalent acidity Equivalent basicity
(lime lost) (lime saved)
1. Ammonium Sulphate 110 --
2. Ammonium chloride 128 --
3. Ammonium Nitrate 60 --
4. Ammonium Sulphate Nitrate 93 --
5. Urea 80 --
6. Sodium nitrate - 29
7. Potassium Nitrate -- 26
8. Calcium Nitrate -- 21
9. Calcium Cynamide -- 63
10. CAN ( Neutral) ( Neutral)
SLOWLY AVAILABLE NITROGENOUS COMPOUNDS AND NITRIFICATION

INHIBITORS
Firstly, the N requirement of growing plant is less in early stages of growth,
maximum during its grand growth period and very low at the subsequent stages up
to harvest. It is thus, seen that N is required through out the growth period.
Secondly, the nitrogenous fertilizers in general, and high analysis nitrogenous
fertilizer in particular, give out the entire amount of added N through fertilizer in
available form in very short period. The crop is unable to use the entire available
amount in such a short period.
Thirdly, the N not used by a crop is either lost due to leaching and
volatilization or fixed as NH3 by clay particles and immobilization by micro-
organisms.
In general, the crop recoveries of N seldom exceeds 60 to 70% of that added
as fertilizers. Under the circumstances, one should be careful for the use of
nitrogenous fertilizers. Therefore, the nitrogenous fertilizers should be used or
manufactured or made to act in soil in such a way that there should be minimum
loss, maximum recovery and availability should be through out the growth period as
per requirement of crop.
Attempts have been made in this direction to overcome the problem by four
ways:
40
I. Proper agronomic practices

II. Preparing large size granules
III. Preparing slow release nitrogenous compounds
IV. Use of nitrification inhibitors
i) Proper Agronomic Practices:

There are two established agronomic practices (a) application of fertilizers N
to a crop in two or more splits to coincide with the important growth stages (b)
Placement of N 3 to 5 cms below soil surface at the time of sowing/planting, which
permits better contact with soil particles to retain NH4-N and also prevent losses due
to volatilization.
ii) Preparing large size granules and briquettes:
By preparing large size granules like urea super granules and briquettes of
varying in weight from 1 to 3 gram, increase efficiency of fertilizers, by slower rate of
hydrolysis, increase in the rate of downward diffusion and low volatilization loss as
NH3.
iii) Preparing slow release nitrogenous compounds:
By the formation of slow release compounds which are ranging from quite
soluble to completely insoluble but slowly available form Nitrogenous fertilizers which
have few dissolving rates and release their nitrogen slowly are known as slow
release nitrogenous fertilizers. These fertilizers are classified into two groups: a)
Chemical compounds with inherently slow rate of dissolution. Eg. Urea formaldehyde
compound, Isobutylidene Diured (IBDU), Crotonylidene Diurea (CDU), Oxamide
(CONH2)2, and
(b) Material formed by coating to conventional N fertilizers, Eg. sulphur coated urea,
lac coated urea, neem cake coated urea, plastic coated urea.
iv) Nitrification Inhibitors:
These materials decrease the activity of nitrifying bacteria (organisms) and
slow rate of nitrification. These compounds are :
a) AM (2 amino chloro-6-methyl pyrimidins)
b) N-serve or Nitrapyrin (2-chloro-6trichloromethyl pyridine)
c) Thiourea
PHOSPHATIC FERTILIZERS

41
The phosphorus (P) nutrient of all phosphatic fertilizers is expressed as P2O5. In soil,
P is present as (i) Organic P (ii) Inorganic P. The forms of inorganic P are H2PO-4;
HPO-24; and PO-34; Out of which, H2PO4 and HPO4 ions are available to plant. In soil,
water in is changed to HPO-24 and PO-34 ions with increase in pH.
-H+ -H+
H2PO-4 HPO-24 PO-34
Firstly, the P in soil is immobile or slightly mobile around one cm diameter and
therefore, they should be applied in root zone.
Secondly, the requirement of P is maximum in the initial stages. The crop
takes up 2/3 of total P when the crop gains 1/3 of total dry matter and hence, the
entire quantity should be applied at one time that is at the time of sowing as a basal
dose.
Thirdly, water soluble-P is changed to insoluble form as Fe and Al –PO4
(Phosphate) under acidic and calcium phosphate in calcareous or high Ca content or
in higher pH soils and hence, there is no danger for the loss due to leaching and
volatilization.
Classification of phosphatic fertilizers:
The phosphatic fertilizers are classified into three classes depending on the
form in which H3PO4 combined with Ca.
Phosphatic fertilizers
I II III
Water soluble P Citric acid soluble P Citrate and water
containing containing insoluble-P containing
Super phosphate (SSP) Basic slags Rock phosphate
(16 to18% P2O5) (14 to 18% P2O5) (20 to 40% P2O5)
Double Super phosphate Dicalcium phosphate Raw bone meal
(DSP) (34 to 39% P2O5) (20 to 25% P2O5 and 3 to
(32 to 36% P2O5) 4% N)
Triple Super phosphate Rhenania phosphate
(TSP) (23 to 26% P2O5)
(46 to 48% P2O5)
Mono ammonium phosphate Steamed bone meal
(20% N and 20% P2O5) (22% P2O5)
Diammonium phosphate (Part of P2O5 soluble in
(18% N and 46% P2O5) citric acid)

42
i) Characteristics and conditions for the use of water soluble P containing

fertilizer:
a) They contain water soluble-P as H2PO4 ion which can be absorbed quickly
and available to plants when root system is not fully developed.
b) Water soluble-P is rapidly transformed into water insoluble form in soil and
hence there is no danger of loss due to leaching.
c) These fertilizers should be used on slightly acidic, neutral to alkaline soils but
not on acidic soils as the water soluble-P is changed to unavailable Fe and
A1-PO4.
d) These fertilizers are applied when a crop requires quick start and for short
duration crops.
ii) Characteristics and conditions for the use of citric acid (1%) soluble P
containing fertilizers:
a) They contain citrate soluble-P and hence this P is less available than water
soluble-P.
b) They are suitable for moderately acid soils because it gets converted into
water soluble form. They are basic in reaction and Ca content.
c) There are less chances of getting fixed by Fe and Al.
d) They are suitable for long term crops and where immediate and quick start to
crops is not important.
iii) Characteristics and conditions for the use of citrate and water insoluble P
fertilizers :
a) They are suitable for strongly acidic soils

b) They contain insoluble P and hence not available to crops
c) The P is available when ploughed with green manuring crop or organic
residues.
d) They are used for long duration crops and in large quantity 500 to 1000 kg/ha
e) They are used where immediate effects are not important
POTASSIC FERTILIZERS
Potassium (K) is present in soil as:

43
i) Readily available forms as in soil solution and as exchangeable. These forms are
available and plant absorbs these K forms as K+ ion.
ii) Slowly available form as non-exchangeable i.e. fixed
iii) Relatively unavailable in the form of minerals (feldspars and micas etc.)
Firstly, the potash behaves partly like N and partly like P. From view point of the
rate of absorption, it is required (absorbed) up to harvesting stage like N and like P, it
becomes slowly available. Therefore, the entire quantity is applied at sowing time.
Secondly, potash being cation adsorbed on clay complex and hence leaching
loss reduces. Leaching is greater in light soils than heavy textured soils. Therefore,
like N, some time split application of K is desirable in sandy soil.
Thirdly, even though the soil contains enough potash or does not give response
to crops, it becomes necessary to apply for the following reasons:
a) Maintaining K status of soil
b) For improving burning quality of tobacco
c) For neutralizing harmful effects of chloride in plant
d) For sugars or starch producing crops like potato, sweet potato, sugar cane,
sugar beet, banana etc. for formation of sugar and starch.
e) For fibrous crops like sann, flex etc. to give strength to fibre and
f) For the formation of pigments in crops like tomato, brinjal etc. for quality
purpose and it improves the luster and gives more colouration to the fruits of
these crops by which more price can be have of the said products.
Classification of potassic fertilizers :
Potassic fertilizer
Fertilizer containing Chlorine . Fertilizer containing other than

chlorine.
Eg. KCl (Muriate of potash 58% K2O). Eg. Sulphate of potash (K2SO4 48% K2O)
This is cheaper fertilizer and used
extensively by cultivators for all crops Potassium Nitrate (KNO3 44% K2O, 13%
except where chlorine is not desired in N)
fertilizer Sulphate of potash and magnesium
(double salt of K and Mg, (Schoenite)

44
K2SO4, MgSO4
(25 to 30% K2O)
Chemistry of K compounds:
Potassium is not found in free state in soil. As metal, it reacts with CO 2

forming K2O and K2O with H2O gives KOH. For this reason, K in elemental form is
not used as fertilizer. It must be combined with other element like chlorine or group
of elements.
Properties of Potasic fertilizers:
Muriate of Potash (KCl):
It is commonly marketed as a commercial fertilizer in granular form. However,

it is also available in powder form. It is easily soluble in water. On application to the
soil, it ionizes to dissociate into K+ and Cl ions. K+ like NH4+ gets attached or
absorbed on the soil complex. As such, though muriate of potash is readily soluble in
water, it is not leached.
Potassium sulphate (K2SO4) :
It is water soluble. On application to the soil, it separates into K + and SO4-2

ions. K+ is absorbed by growing plants or is absorbed on the soil complex. As such,
though potassium sulphate is readily soluble in water, it is not lost by leaching.
SECONDARY AND MICRONUTRIENT FERTILIZERS
The secondary nutrients fertilizers: The secondary plant nutrients are Ca, Mg
and S. Out of these, three nutrients, Ca and Mg are added indirectly in soil through
fertilizes and soil amendments. Soil contains Ca and Mg as exchangeable and as
CaCO3 and dolomite. Normally, it is not necessary apply Ca and Mg fertilizers in
soils of India.
Formerly, the use of FYM, A/S and superphosphate sources of S were used
and now their use is either restricted or their replacement by other fertilizers which
are devoid of S. Therefore, sulphur now becomes necessary to apply in soil because
of the following reasons:
i) A/S a source of S is replaced by urea

45
ii) Another source of S, superphosphate is replaced by DAP

iii) Use of KCl instead of K2SO4
iv) Decrease in the use of FYM and
v) Use of high yielding varieties which absorb more quantity of nutrients.
The soils deficient in sulphur are supplied with the sources of S like elemental
S. Elemental S when applied to soil, it is changed to SO 2 SO3 and H2SO4. This
H2SO4 with basic material of soil gives its sulphate salt. Plant absorbs S as SO -24.
Micronutrients or Trace Elements:
The micro-nutrients are zinc (Zn), iron (Fe), copper (Cu), Manganese (Mn),
Boron (B), Molybdenum (Mo) and Chlorine (Cl). These nutrients are present in
available forms in soil in very small quantity and the requirement by crops is also
less. Application of micronutrient fertilizers now become necessary as their
deficiencies are observed in soil. The deficiency of micronutrients was observed in
soil because of the following reasons.
I. Due to increase in irrigation facility, the number of crops taken in an year are
increased.
II. Use of hybrid varieties which absorb more nutrients
III. Intensive cultivation
IV. Reduction in the use of organic manures like FYM, which supply these
nutrients,
V. Use of high analysis fertilizers which are devoid of these nutrients.
Out of these micronutrients, chlorine is not applied as its fertilizer because it is
indirectly applied through irrigation water. Mo is required in very small quantity and is
also present in sufficient in some of seeds and soils and hence generally its
fertilizers are not used. Boron is found to be deficient in calcareous soil as it is
changed to calcium borate which is insoluble and hence boron is applied as its
fertilizers. All these nutrients are present as anions. These four micronutrients are
generally applied both soil and foliar as their sulphates at the time of deficiency. The
micronutrient limits of the deficiency in soil, quantity and type of fertilizers added by
soil and foliar application is given below:

46
SN Element Rating (ppm) Soil application Foliar

Low Medium High application
(200 to 300
lit/ha)
1. Iron <2 2 to 5 >5 10 ppm Fe as Mix.0.4% FesO4
FeSO4 i.e. solution with
100 Kg FeSO4/ha 0.2% lime
solution
2. Managanese <3 3 to 5 >5 10ppm Mn as Mix.0.6%
Exchange <10 100 to 200 >200 MnSO4 i.e. 80Kg MnSO4
Reducible 0 MnSO4/ha Solution with
0.3% lime
solution
3. Zinc <0.5 0.5 to 1.0 >1.0 5 ppm Zn as Mix 0.6%
ZnSO4 ZnSO4 with
i.e. 45 kg ZnSO4/ha 0.3% lime
solution
4. Copper <0.2 0.2to 0.5 >0.5 5 ppm Cu as Mix 0.4%
CuSO4 CuSO4
i.e. 40 Kg solution with
CuSO4/ha 0.2% lime
solution
5. Boron <0.1 0.1 to 0.5 >0.5 0.2 ppm B as Borax 0.2% Borax
i.e.15 Kg Borax/ha solution
6. Molybdenum <0.0 0.05 to 0.1 >0.1 0.05 ppm Mo as 0.05%
5 ammonium ammonium
molybdate i.e. 1.8 molybdate
kg/ha solution.
The micronutrients are soon changed to insoluble forms when they are added to
soil and hence chelates are used as one of the sources. Chelates (meaning “Claw") is a
compound in which metallic cation is bounded to an organic molecule.
The common chelating agents are:
EDTA : Ethylene Diamine Tetra Acetic Acid
DTPA : Diethylene Triamine Penta Acetic Acid
HEDTA : Hydroxy Ethylenthylene diamine Triacetic Acid
NTA : Nitricotriacetic acid
FERTILIZER MIXTURES (MIXED FERTILIZERS)

For application of individual nutrient, fertilizers of the nutrients were also
applied separately which increased labour cost, transport and storage cost. In order
to avoid the said difficulty, the fertilizer mixtures were used.

47
Fertilizers Mixtures: A mixture of two or more straight fertilizer materials is referred

to as fertilizer mixture. The term complete fertilizer refers to these fertilizers that
contains three major (N, P and K) nutrients.
Advantages of fertilizer mixtures :
1) Less labour is required to apply a mixture than to apply its components
separately.
2) Use of fertilizer mixture leads to balanced manuring.
3) The residual acidity of fertilizers can be effectively controlled by the use of proper
quantity of lime in fertilizer mixture.
4) Micronutrients can be incorporated in fertilizer mixture.
5) Mixture have better physical condition.
Disadvantages of fertilizer mixtures:
1) Use does not permit individual nutrient application which oat specific growth
stage of crop.
2) Unit cost of plant nutrients in mixtures is usually higher than those of straight
fertilizers.
3) Farmers use mixtures without careful study of their needs.
Materials and methods of preparing fertilizer mixtures:
The type of grade of fertilizer mixture to be prepared should be decided. The
straight fertilizers are chosen according to compatibility in mixture. The quantity of
each fertilizer is calculated for the preparation of desired quantity of preparing
fertilizer mixture. It happens that there is a gap in weight of fertilizers taken on the
basis of nutrient content and the total weight of fertilizer mixture. The gap is filled by
using filler. A filler is the make weight material added to a fertilizer mixture. The
common fillers used are: sand, soil, ground coal, ash and other waste products. It is
also necessary to add the conditioners to avoid caking. For this low grade organic
materials like tobacco stem, peat, groundnut and paddy hulls are added at the rate of
100 lbs/ton of mixture. If the fertilizers used leave acidic residual effect when it is
added in soil then liming materials like lime stone, dolomite etc. are added.
Incompatibility in fertilizer mixtures:
1. Fertilizers containing NH3 should not be mixed with basically reactive
fertilizers, otherwise there will be loss of N as NH3.

48
2. All water soluble phosphatic fertilizers should not be mixed with those
fertilizers that contain free lime, otherwise a portion of soluble phosphate is
converted into an insoluble form.
3. Easily soluble and hygroscopic fertilizers tend to cake or form slums after
mixing. Such fertilizers should be mixed shortly before use.
Considering the incompatibility, the chart is given below which can be used
while preparing fertilizer mixture.
1 2 3 4 5 6 7 8 9 10 11
  X X *    X   1. Muriate of Potash
  X X *   X X   2.Sulphate of potash
X X   * X * *    3.Sulphate of
ammonia
X X   * X * *    4.Calcium
amm.nitrate
* * * * * * * * * * * 5.Sodium nitrate
  X X *  * X X X * 6.Calcium cynamide
  * * * *    * * 7.Urea
 X * * * X *   * * 8.Superphosphate
single or triple
X X   * X *     9.Ammon.Phosphate
    *  * *    10.Basic slag
    * * * *    11.Calcium
carbonate
Guide for mixing fertilizers

 Fertilizer which can be mixed
* Fertilizer which may be mixed shortly before use
X Fertilizer which can not be mixed

49
Calculation of quantity of fertilizers to be used in mixture :

Example :- Prepare 600 kg of a 4-8-10 fertilizers mixture in which half the nitrogen
is in ammonium sulphate (20 per cent N) and the other half divided between nitrate
of soda (16 per cent N) and tankage (6 per cent N and 6 per cent P 2O5). P2O5 and
K2O are to be added in the form of superphosphate (16 per cent P 2O5) and muriate
of potash (60 per cent K2O) respectively.
In the present example, 4 Kg of nitrogen in every 100 Kg of mixture is supplied with 2
Kg N as ammonium sulphate
1 Kg N as nitrate of soda
1 Kg N as tankage
2x100
For N = = 10 Kg of ammonium sulphate
20
1 x 100
N = = 6.25 kg of nitrate of soda
16
1 x 100
N = = 16.66 kg of tankage
6
Since, tankage contains nitrogen and phsophoric acid, 16.66 kg of tankage,
mixed in every 100 Kg of fertilizer.
Mixture wil also add 16.66 x 6 = 1 Kg of P2O5.

100
This means that out of 8 Kg of P2O5, 1 Kg is supplied through tankage and the
remaining 7 Kg comes from superphosphate.
For P2O5 = 7x100 = 43.75 Kg of superphosphate

16
K2O = 10x100 = 16.66 Kg of muriate of potash
60
Thus, the total quantity of various fertilizers required to prepare 100 kg of a 4-8-10
fertilizer mixture will be
Ammonium sulphate……. 10.00 Kg
Nitrate of soda 6.25 Kg
Tankage 16.66 Kg
Superphosphate 43.75 Kg
Muriate of potash 16.66 Kg
Total quantity of straight fertilizer 93.32 Kg
Filler 6.68 Kg
50
Mixed fertilizer 100.00 Kg
For preparing 600 kg of the fertilizer mixture of the 4-8-10 grade, the following
quantities of fertilizers and filler will be required:
Ammonium sulphate : 10x6 = 60.0 kg

Nitrate of soda : 6.25x6 = 37.5 Kg
Tankage : 16.66x6 = 100.00 Kg
Superpohosphate : 47.75x6 = 262.5 Kg
Muriate of potash : 6.68x6 = 40.0Kg
Total : 600.00 Kg
Fertiliser mixtures available in the market:
1. Sufla (15:15:15)
2. Sufla (20:20:0)
3. Lakshmi (12:12:12)
4. Lakshmi (8:8:8)
5. IFFCO-1 (10:26:26)
6. IFFCO-2 (12:32:16)
COMPLEX FERTILIZERS
Due to uneconomical and labour cost of using individual fertilizer, the fertilizer
mixtures were prepared and they were used. These fertilizer mixtures were not
homogenous, containing less quantity of N, P, K and many times inferior quality of
material were used. For these difficulties, complex fertilizers have been prepared.
These complex fertilizers contain the nutrients of grade mentioned, homogenous,
granular and good physical conditions.
Complex Fertilizers:
Commercial complex fertilizers are those fertilizers which contain at least two or
three or more of the primary essential nutrients. When it contains only two of the
primary nutrients, it is designated as incomplete complex fertilizer. While those
contain three nutrients are designated as complete complex fertilizers. At present,
the complex fertilizers obtained by chemical reaction are more important than
fertilizer mixtures. Complex fertilizers being manufactured in India are
Nitrophosphate DAP and Ammonium phosphate sulphate Characteristics of
complex fertilizers:

51
1. They usually have high content of plant nutrients more than 30 kg/100 kg of
fertilizer. As such they are called high analysis fertilizers.
2. They usually have uniform grain size and good physical condition.
3. They supply N and P in available form in one operation. Nitrogen is present as
NO-3 and NH+4 forms and P as water soluble form upto 50 to 90% of total P 2O5.
4. They are cheaper compared to individual fertilizer on the basis of per Kg of
nutrient.
5. Transport and distribution cost is reduced on the basis of per kg of nutrients.
Fertilizers grades: The grades of complex fertilizers are given below:
Sr. No. N P K
1 10 26 26
2 12 32 16
3 14 36 12
4 22 22 11
5 14 35 14
6 17 17 17
7 14 28 14
8 11 22 22
9 19 19 19
10 14 14 14
11 11 11 11
12 17 17 16
13 20 10 10
14 13 13 20
TIME AND METHOD OF FERTILIZER APPLICATION AND BLANCED

FERTILIZETION
To obtain the maximum benefit from fertilizers, it is most essential that
fertilizes to be applied at the proper time and at the proper place. The fertilizers to be
applied, possess different qualities with regard to solubility in water and movement in
to the soil solution. Similarly, soils are of different nature, sandy to clayey. The nature
of the soil governs the movement of applied fertilizers. Again, the requirement of
plants for different plant nutrients varies to their stage of growth. For example,
nitrogen is absorbed by the plants throughout the growth period. While phosphorus
is absorbed at a faster rate during the early growth period. Thus, the time and
method of fertilizers application will vary in relation to :
1) The nature of fertilizer
2) The soil type and
3) The difference in nutrient requirement and nature of field crops.
Principles governing selection of proper time for application of fertilizers :
52
1) Nitrogen is required throughout the crop growth. As such, it is absorbed by the

plant at the same rate as that of its growth. All plants grow at a slow rate in
the beginning. Then follows a rapid increase in the growth rate. Near the
harvest time, the rate of growth again slows down. Accordingly, nitrogen is
taken up by the plant slowly in the beginning, rapidly during the grand growth
period, and again slowly as it nears maturity. In other words, the nitrogen
requirement of a growing plant is less in the early stages of growth, maximum
during its grand growth period, and very low at the subsequent stages upto
harvest. It is thus seen that nitrogen is required throughout the growth period.
2) Nitrogenous fertilizers are soluble in water. They are mobile and move rapidly
in all directions within the soil. As such nitrogen is easily lost through leaching.
Since nitrogen is required throughout the growth period and nitrogenous
fertilizers are lost through leaching, it is better not to apply too much
nitrogenous fertilizers at one time, but to apply in split doses throughout the
growth period. This will supply nitrogen to growing plants during the entire
growth period and the plants will not suffer from nitrogen deficiency.
3) Phosphorus is required during the early root development and early plant
growth. As such, crop plants utilize 2/3 of the total requirement of phosphorus
when the plants accumulate 1/3 of their dry weight. In other words, plants
require more of phosphorus during the early growth period.
4) All phosphatic fertilizers release phosphorus for plant growth slowly. This is
true even for super phosphate which contains monocalcium phosphate or
water soluble P2O5. On application of super phosphate to the soil watersoluble
P2O5 becomes immediately slightly insoluble or is converted into dicalcium
phosphate or citrate soluble P2O5.In this form, phosphorus becomes available
to plants slowly.
5) On the one hand, phosphorus is required in greater quantities during the early
growth period; while on the other, all phosphatic fertilizers become available
to the growing plants slowly. As such, it is always recommended that the
entire quantity of phosphatic fertilizers should be applied before sowing or
planting.
6) Potash behaves partly like nitrogen and partly like phosphorus. From the point
of view of the rate of absorption, it is like nitrogen, being absorbed up to the
harvesting stage. But potassic fertilizers, like phosphatic fertilizers, become

53
available slowly. As such, it is always advisable to apply the entire quantity of

the potash at sowing time.
7) Leaching is greater from sandy soils than from heavy textured soils. This
means that more frequent applications or split application of nitrogenous
fertilizers, and sometimes of potassic fertilizers, is desirable on sandy soils.
Practical recommendations based on the principles guiding the time of
application of fertilizers can be summed up as follows :
1. Nitrogenous fertilizers should be applied in two split doses to crops of four to five
months duration, in three splits to crops of 9 to 12 months duration, and in four to
five splits when crops are of still longer duration, like adsali crop of sugarcane.
2. On sandy soils or light textured soils more frequent or split application of
nitrogenous fertilizers is desirable, compared to heavy textured soils, like clayey
soils. This is important for reducing losses due to leaching.
3. The entire quantity of water soluble phosphatic fertilizers should be applied in
one dose at sowing time. In acid soils, it is advisable to apply bone meal or rock
phosphate a week or fortnight prior to sowing.
4. Potassic fertilizers also should be applied in one dose at planting time.
Principles involved in selecting the correct methods of fertilizer application:
1. Nitrogenous fertilizers are easily soluble in water and move rapidly in all
directions from the place of application. In other words, nitrogenous fertilizers
applied on the soil surface reach the plant roots easily and rapidly. As such,
these fertilizers are broadcasted on the soil surface just before sowing.
2. Since nitrogen is liable to be lost by leaching, it is applied at different stages of
plant growth. Since nitrogenous fertilizers move rapidly in moist soil, application
of nitrogenous fertilizers on the soil surface followed by irrigation is good enough
to meet the nitrogen requirement at the critical stage of plant growth. In other
words, nitrogenous fertilizers are suitable for topdressing and side dressing.
3. Since phosphorus moves slowly from the point of placement it should be placed
where it will be readily accessible to the plant roots.
4. Progressive fixation of phosphates by soil clays continues to diminish their
efficiency for a considerable period following application. Fixation refers to any
chemical or physical interaction between the applied plant nutrients and the soil
whereby the nutrients become less available to crops. To reduce the fixation of

54
phosphate, phosphatic fertilizers should be so placed that they come into

minimum contact with the soil particles and are closer to the plant roots. In other
words, localized placement of phosphatic fertilizers near the seeds or seedling
roots should be practiced.
5. Since potassic fertilizers move slowly in the soil, they should also be placed near
the root zone.
Balanced Fertilization:
Plants contain 90 or more elements, only 16 of which are currently known to
be essential. The elements essential for plant growth are carbon, hydrogen, oxygen,
phosphorus, potassium, nitrogen, sulphur, calcium, iron, magnesium, boron,
manganese, copper, zinc, molybdenum and chlorine. On practical point of view,
generally application of nitrogenous, phosphatic and potassic fertilizers are
considered as balanced fertilization.
Unbalanced fertilization has led to decrease in the yield of crops and also
deteriorate the physical condition of the soil. the growing of crops by using only
nitrogen fertilizer have depleted the reserve of available phosphoric acid, potash,
and other nutrients in the soil. The result is that subsequent additions of nitrogen
fertilizer do not result in increased yields because some other essential elements
such as phosphorus and potash are now a limiting factor.
Balanced application of fertilizers enhances the efficiency of nutrients. For
example, the efficiency of a nutrient like nitrogen is greatly enhanced when it is used
in conjunction with phosphorus. For instance, when a dose of 30 Kg of nitrogen was
applied in the field, only 14 to 30% of nitrogen is utilized by the crops. On the other
hand, when 30 Kg of nitrogen was applied along with 30 Kg of phosphoric acid, the
recovery of added nitrogen varied from 23 to 50%. This clearly shows that
phosphoric acid contributed to the better utilization of the nitrogen. Just as
phosphoric acid helps in the better utilization of nitrogen, potash also helps in the
better assimilation of nitrogen and phosphoric acid. Balanced fertilizer application,
particularly, phosphorus and potash makes plants more drought resistant and winter
hardy.
Soil amendments
Soil amendments are substances which when added to the soil help plant
growth indirectly by augmenting physical, chemical or biological changes in the soil.
Soil amendment usually contains plant nutrient. But they cannot be classified along

55
with fertilizers as their main aim is not to supply the nutrient directly, but they are
very helpful for plant growth (Rai, 1965).
The organic amendments: The organic amendments as such do not help in
replacing the exchangeable Na as against the gypsum or other amendments.
Primarily, they improves the physical condition of the soil by improving the
aggregation in the soil. The most common organic amendment is the FYM which is
added in the first year of reclamation @ 50 tones/ha and is reduced to half in
succeeding years. The efficiency of gypsum has been found to increase when it is
applied along with FYM. Molasses and pressmud, which are sugar factory waste,
have also been used. Pressmud, a byproduct from sugar factories, contains CaCO 3.
Since Ca is present as CaCO3, it is slow acting amendment requiring acid or acid
formers. As against carbonation process, pressmud from sugar factories employing
sulphitation process has superior reclamation value, as it contains sulphate of lime
instead of its carbonate.
Green manuring with Dhaincha (Sesbania aculeata) has been found most
successful. The juice of green plants can neutralize high alkalinity, its initial pH being
4.01, with only slight rise even within a month. In black cotton soil, it thrives well
under moderately saline conditions and can with stand high alkalinity, water logging
or drought so that it is remarkably suited in that region to alkali soils, characterized
by such adverse conditions. Sulphurated hydrogen is generated by the
decomposition of Dhaincha.
Paddy straw or rice husk have also been used at a rate varying between 15 to
30 tones/ha. Weeds like Argemone mexicana has been found very suitable for alkali
soils. The other weeds found suitable for the purpose of green manuring are Ipomea
grandiflora and Pongamia glabra. The Russian workers have suggested the addition
of cellulose with sufficient addition of nitrogen for easy decomposition.
A. Different types of chemical amendments:
1. Soluble calcium salts e.g.
(i) Calcium chloride (CaCl2.2H2O)
(ii) Gypsum (CaSO4.2H2O)
(iii) Calcium sulphate (CaSO4)
2. Acid or acid formers e.g.
(i) Sulphur (S)
(ii) Sulphuric acid (H2SO4)
(iii) Iron sulphate (FeSO4.7H2O)
(iv) Aluminium sulphate (Al2(SO4)3.18H2O)
(v) Lime sulphur (calcium poly sulphide) (CaS5)
56
(vi) Pyrites (FeS2)

The kind and amount of chemical amendment to be used for the
replacement of exchangeable Na in soils depend upon the soil characteristics,
the desired rate of replacement and economic considerations. Soluble calcium
salts are preferred when soil does not contain alkaline earth carbonates or
calcium carbonate. Acid or acid formers are preferred when soil contains
alkaline earth carbonates or CaCO3. Acid or acid formers are also used along
with calcium salt of low solubility but the rate of reaction is very low.
B. Advantages and disadvantages of amendments:
The CaCl2 is highly soluble and Ca is readily available but its cost is a
prohibitive factor. Iron and aluminum sulphates also hydrolyze readily in the soil
to form H2SO4 but here also the cost is acting. Amendment, which can be used
in calcareous soils but it requires special equipments and is hazardous in
handling. Sulphur is a slow acting amendment and large applications are
needed. It requires more time for complete oxidation. In cool winter season, the
oxidation rate is too slow to give satisfactory results. Since the oxidation process
is fully microbial, an optimum amount of moisture has to be maintained
continuously in the soil. The soil should not be leached until sufficient time has
been allowed for most of the sulphur to oxidize. Limestone is a low cost
amendment but the solubility is affected by pH of the soil and particle size of the
amendment. Like S, pyrite has to be oxidized first which is a slow process and
the rate of reaction depends on particle size. Again the application of pyrites at
higher rate markedly decreases its oxidation rate. It is a cheap amendment.
Gypsum is the most common amendment used for reclaiming saline-
sodic as well as non-saline sodic soils. It is a low cost amendment and the rate
of reaction in replacing Na is limited on its solubility in water, which is about 0.25
% at ordinary temperature. While applying gypsum, mixing it in shallow depth
(upper 10 cm depth) is more effective. It is applied by broadcast method or
incorporated by disc plough. Gypsum is applied at the time of ponding or
leaching. Gypsum directly prevents crust formation, swelling, dispersion and
acts as mulch in case of surface application and indirectly increases porosity,
structural stability, infiltration and hydraulic properties, soil tilth, drainage and
leaching and reduces dry soil strength.
C. Chemical reactions of amendments in soil: The following chemical reactions
illustrate the manner in which various amendments react in the different classes
57
of alkali soils. In these equations the letter X represents the soil exchange
complex.
Reclamation of saline-alkali soils
Class 1. Soils Containing Alkaline-Earth Carbonates
GYPSUM: 2NaX + CaSO4 ↔ CaX2 + Na2SO4
SULPHUR: (1) 2S + 3O2 ↔ 2SO3 (microbiological oxidation)

(2) SO3 + H2O ↔ H2SO4
(3) H2SO4 + CaCO3 ↔ CaSO4 + CO2 + H2O*
(4) 2NaX + CaSO4 ↔ CaX2 + Na2SO4
LIME-SULPHUR (CALCIUM POLYPHOSPHATE):
(1) CaS5 +8O2 + 4H2O ↔ CaSO4 + 4H2SO4
IRON SULPHATE:
(1) FeSO4 + H2O ↔H2SO4 + FeO
D. Quantity of amendments to be added: These are evidences to show that

even 50 % of the theoretical gypsum requirement for replacement of
exchangeable Na in alkali soils has improved their physical properties and
assisted response to management practices. Generally, 50 to 75 % of GR (as
determined by Schoonover’s method) has been found most satisfactory in many
types of soils.
The equivalent proportion of different amendments in relation to 1 ton of
gypsum is as follows:
Amendments Weight in tones equivalent to 1 tone
gypsum
Gypsum 1.000
Sulphuric acid 0.570
Sulphur 0.186
FeSO4.7H2O 1.620
Aluminium sulphate 1.290
Limestone (CaCO3) 0.580
Lime sulphur (Calcium polysulfide containing 0.756
24 % S)
Among all the amendments, gypsum is the most common amendment that is
used for the purpose of reclamation. The rate of addition of gypsum can be
58
determined by estimating the gypsum requirement (GR) of a soil. Alternatively,

the GR can also be determined by knowing the exchangeable Na in soil and
working out the extent of reduction of Na on equivalent basis. The gypsum
requirement for replacing 1 me of Na upto a soil depth of 15 cm comes to about
1.92 tones/ha. Since an ESP of 10 and below is considering safe for tolerable
physical condition of the soil, replacement by calcium to this level is all that is
attempted in practice.
E. The organic amendments: The organic amendments as such do not help in
replacing the exchangeable Na as against the gypsum or other amendments.
Primarily, they improve the physical condition of the soil by improving the
aggregation in the soil. The most common organic amendment is the FYM which
is added in the first year of reclamation @ 50 tones/ha and is reduced to half in
succeeding years. The efficiency of gypsum has been found to increase when it
is applied along with FYM. Molasses and pressmud, which are sugar factory
waste, have also been used. Pressmud, a byproduct from sugar factories,
contains CaCO3. Since Ca is present as CaCO3, it is slow acting amendment
requiring acid or acid formers. As against carbonation process, pressmud from
sugar factories employing sulphitation process has superior reclamation value, as
it contains sulphate of lime instead of its carbonate.
Green manuring with Dhaincha (Sesbania aculeata) has been found
most successful. The juice of green plants can neutralize high alkalinity, its initial
pH being 4.01, with only slight rise even within a month. In black cotton soil, it
thrives well under moderately saline conditions and can with stand high alkalinity,
water logging or drought so that it is remarkably suited in that region to alkali
soils, characterized by such adverse conditions. Sulphurated hydrogen is
generated by the decomposition of Dhaincha.
Paddy straw or rice husk have also been used at a rate varying
between 15 to 30 tones/ha. Weeds like Argemone mexicana has been found very
suitable for alkali soils. The other weeds found suitable for the purpose of green
manuring are Ipomea grandiflora and Pongamia glabra. The Russian workers
have suggested the addition of cellulose with sufficient addition of nitrogen for
easy decomposition.

59
Reclamation of Acidic Soils

Principles of Liming Reactions: The reclamation of acidic soils is done by
addition of liming material which may be calcitic limestone (CaCO3) or dolomitic
limestone [CaMg(CO3)2]. The rate of lime requirement is determined in the
laboratory by method of Shoemaker (1961). The particle size of liming material
affects the rate of neutralization reaction. Both these limestones are sparingly
soluble in pure water but do become soluble in water containing CO 2. The greater
the partial pressure of CO2 in the system, the more soluble the limestone
becomes. Dolomite is somewhat less soluble than calcite. The reaction of
limestone (CaCO3) can be written as:
CaCO3 + H2O + CO2 → Ca(HCO3)2
Ca(HCO3)2 → Ca2+ ↓ + 2HCO3-
(Takes part in cation exchange reactions)
H+ + CO32- → H2CO3- ↔ H2O + CO2
(From soil solution) (from lime)
In this way hydrogen ions (H+) in the soil solution react to form
weakly dissociated water, and the calcium (Ca2+) ion from limestones is left to
undergo cation exchange reactions. The acidity of the soil is, therefore,
neutralized and the per cent base saturation of the colloidal material is increased.
Why Gypsum is not considered as a Liming Material?
Gypsum is not considered as liming materials because on its
application to an acid it dissociates into (Ca2+) and sulphate (SO42-) ions:
CaSO4 ↔ Ca2+ + SO42-
The accompanying anion is sulphate and it reacts with soil moisture
produces mineral acid (H2SO4) which also increases soil acidity instead of reducing
soil acidity.
Beneficial effect of lime
1. Lime makes P2O5 more available.
2. Lime increase availability of N, increase nitrification and nitrogen fixation.
3. Increase soil pH favours the microbial activity and increase organic matter
decomposition and nutrient transformation for root growth.
4. Mo an essential element to rhizobium in N fixation process increases with
increase in soil pH following lime.
5. Reduce toxicity of Al, Fe and Mn.

60
6. Lime is essential source of essential Ca as well as Mg if dolomitic lime stone

has been applied as liming material.
7. It causes an increase in CEC, which reduces the leaching of base cations,
particularly K.
(Source: Soil Fertility and Nutrient Management. S. S. Singh)
SOLVED EXAMPLES:
Example 1: A soil contains 12 me Na/100 g soil. The CEC of the soil is 20.
Exchangeable Na percentage is to be reduced to 10. Workout the gypsum
requirement.
ESP = Exch. Na/CEC x 100 = 12/20 x 100 = 60 %

Initial ESP – Final ESP = 60 – 10 = 50 % ESP to be reduced
Exch. Na = 12 x 50/60 = 10 me exch. Na/100 g to be replaced
GR = 1 me exch. Na/100 g = 86 mg gypsum/100 g
= 860 mg/1000 g
= 860 ppm
= 860 x 2.24 = 1926.4 kg/ha
10 me exch. Na = 10 x 1926.4 = 19264 kg/ha = 19.2 t/ha
If purity is 80 then,
GR = 19.2 x 100/80 = 24 t/ha
The GR in this example is 19.2 tones/ha. To get the net value of weight
of gypsum, the value has to be multiplied by purity percentage i.e. if the purity of the
commercial gypsum is 80 %, then the exact weight in the above example would be
24 tones/ha.
Example 2: Calculate GR of alkali soils containing CEC 20 me/100 g [cmol(p+)kg-1]

and 10 me exch. Na/100 g soil, ESP reduced to 10.
CEC = 20 me/100 g
Exch. Na = 10 me/100 g
ESP reduced to = 10 %
ESP = [Exch. Na/CEC] x 100
= [10/20] x 100
= 50
Initial ESP – Final ESP = 50 – 10 = 40 ESP to be reduced
ESP 50 = Exch. Na 10
So ESP 40 =10 x 40/50 = 8 Exch. Na me/100 g to be reduced
1 me Exch. Na/100 g = 86 mg Gypsum/100 g
= 860 mg Gypsum/1000 g
= 860 ppm Gypsum
= 860 x 2.24 = 1926 kg/ha Gypsum
= 1.926 t/ha Gypsum
So 8 me Exch. Na/100 g = 8 x 1.926 = 15.41 t/ha
61
Example 3: Soil having CEC 40 me/100 g. It has Na 20 me/100 g in exch. form.

Bring down exch. Na to 10 %. Calculate % Na. How much Na to be replaced as to
bring its saturation to 10 % and calculate GR in kg/ha. Gypsum purity is 80 %.
(1) ESP = (Exch. Na/CEC) x 100 = (20/40) x 100 = 50 ESP

Initial ESP – Final ESP = 50 – 10 = 40 ESP to be reduced
(2) Exch. Na = (ESP x CEC)/100 = (40 x 40)/100 = 16 me Na/100 g to be replaced
(3) GR = 1 me Na/100 g = 86 mg gypsum/100 g
= 860 ppm
= 860 x 2.24 kg/ha
16 me Na/100 g = 16 x 860 x 2.24 = 30822 kg/ha
(4) 80 % purity = 30822 x 100/80 = 38528 kg/ha
Example 4: A soil have CEC = 25 me/100 g soil which possesses 5, 8 and 3 me/100
g of Ca, Mg and K, respectively. Calculate quantity of Na in me/100g and kg/ha and
K2O kg/ha.
(1) Na me/100 g = CEC – (Ca + Mg + K)

= 25 – (5 + 8 + 3) = 9 me/100 g
= 9 x 23 mg/100 g = 207 mg/100 g
= 2070 mg/1000 g = 2070 ppm
(2) Na (kg/ha) = 2070 x 2.24 = 4636.8 kg/ha
K = 3 me/100 g
= 3 x 39 mg/100 g = 117 mg/100 g
= 1170 mg/1000 g = 1170 ppm
= 1170 x 2.24 = 2620.8 kg/ha
(3) K2O (kg/ha) = 2620.8 x 1.20 = 3144.96 kg/ha
Example 5: Workout the GR from following observations

(1) Weight of alkali soil =5g
(2) Sat. gypsum soln. = 100 ml
(3) Aliquate taken = 5 ml
(4) Difference of 0.02 N EDTA reading between blank and sample = 0.4
GR t/ha = Z x (1.72/1000) x (100/5) x (100/5) x 10,000 x 2.24/1000

= 0.4 x 15.411 = 6.16 t/ha
Soil Conditioner
These are material, which are used to bring about required physical properties
of soil or it is used to improve and maintain the physical conditions of the soils. Crop
residues, organic manures and other organic materials are the organic soil
conditioners. Other synthetic organic materials which are used as soil conditioners
are Polyvinyl alcohol (PVA), Carboxymethyl cellulose (CMC) and Krillium
conditioners. These materials use to form soil aggregates or they use to stabilize soil
aggregate formed by mechanical manipulations. However, its application is found
62
restricted to green house, glass house or in growing high value crops like
vegetables, ornamental plants or spices and condiments etc.
(Source: Soil Fertility and Nutrient Management. S. S. Singh)
Nano-Fertilizers:
Nanotechnology has progressively moved away from the experimental into the
practical areas, like the development of slow/controlled release fertilizers, conditional
release of pesticides and herbicides, on the basis of nanotechnology has become
critically important for promoting the development of environment friendly and
sustainable agriculture.
Indeed, nanotechnology has provided the feasibility of exploiting nanoscale or
nanostructured materials as fertilizer carriers or controlled release vectors for
building of so-called “smart fertilizer” as new facilities to enhance nutrient use
efficiency and reduce costs of environmental protection. Encapsulation of fertilizers
within a nanoparticle is one of these new facilities which are done in three ways
a) the nutrient can be encapsulated inside nanoporous materials,
b) coated with thin polymer film and
c) delivered as particle or emulsions of nanoscales dimensions.
In addition, nanofertilizers will combine nanodevices in order to synchronize the
release of fertilizer-N and -P with their uptake by crops, so preventing undesirable
nutrient losses to soil, water and air via direct internalization by crops, and avoiding
the interaction of nutrients with soil, microorganisms, water, and air. Among the
latest line of technological innovations, nanotechnology occupies a prominent
position in transforming agriculture and food production.
Some of the major evident benefits of nano fertilizer are as under:
 The quantity required for nano fertilizer application is considerably reduced as
compared to conventional fertilizers.
 Nano fertilizer will help to boost the crop production efficiently besides
reducing nutrient losses into the surrounding water bodies (Eutrophication).
 Nano-structured formulation might increase fertilizer efficiency and uptake
ratio of the soil nutrients in crop production, and save fertilizer resource.
 Nano-structured formulation can reduce loss rate of fertilizer nutrients into soil
by leaching and/or leaking.
**************
63
CHAPTER- V: FERTILIZER STORAGE AND FERTILIZER CONTROL

ORDER
Warehousing and storage of fertilizers is a very important and massive

activity. Ideally a marketer would like the fertilizer to spend minimum time in a
godown because storage costs money, blocks money, occupies space, needs
supervision and inspite of precautions, some fertilizer can be stolen or damaged.
Storage can be called a necessary evil. People who pay for storage, often think
whether it is better to spend on this item or to give off- season rebate to the farmer
and let him do the storage.
The principles of good storage at the field level are:
(i) The fertilizers should be stored in a cool, dry and damp proof godown. The rain
water must not get entered in the godwon and there is no need to have windows
in the godown. But they should have proper ventilation for regulating for exit of
gases from the store. The ventilators should be sealed in rainy season.
(ii) The bags should not be piled up directly on the floor as moisture of the floor
causes the damage to the fertilizer. The wooden racks should be used for pilling
the fertilizer bags.
(iii) The bags should not be piled together in a row of 8-10 bags.
(iv) The bags should not touch the wall of the godwon.
(v) Proper space should be allowed between two of piled fertilizers for convenience
of lifting the fertilizers.
(vi) The fertilizer that are hygroscopic in nature such as Urea, Ammonium Nitrate,
Ammonium Sulphate Nitrate, Calcium Ammonium Nitrate must be stored in
water proof bag and the entire bag should be used in one lot. Otherwise, the
bag should be tied tightly and stored in a dry and damp proof godwon after
taking required fertilizers.
(vii) The fertilizers that are fire hazardous such as Ammonium Sulphate must be
handled very carefully.
(viii) All types of fertilizers such as Nitrogenous, Phosphatic and Potassic fertilizers
should not be piled together. But they should be piled separately so that their
handling is easy and gas fumes release from one group may not affect the
quality of others.

64
(ix) The bag should not be kept open at any time to avoid the formation of cakes or
lumps.
(x) The home mixed fertilizer should not be stored. Rather it should be used
immediately after mixing of different fertilizers.
(xi) Prolonged storage of fertilizer should be avoided.
Fertilizer Control Order:

The history of the Indian fertilizer industry dates back to 1906, when the first
fertilizer factory opened at Ranipet (Tamil Nadu). Since then, there have been major
developments in terms of both the quantity and the types of fertilizers produced, the
technologies used and the feedstocks employed. The fertilizer industry in India is in
the core sector and second to steel in terms of investment.
Prior to 1960/61, India produced only straight nitrogenous fertilizers [ammonium
sulphate (AS), urea, calcium ammonium nitrate (CAN), ammonium chloride and
single superphosphate (SSP)]. The production of NP complex fertilizers commenced
in 1960/61. Currently, India produces a large number of grades of NP / NPK complex
fertilizer. These include 16–20–20, 20–20–0, 28–28–0, 15–15–15, 17–17–17, 19–
19–19, 10–26–26, 12–32–16, 14–28–14, 14–35–14 and 19–19–19. In addition, India
produces various grades of simple and granulated mixtures.
The fertilizer was declared as an Essential Commodity in 1957 in India. To
control the trade, price, quality of fertilizers and their distribution, “The fertilizers
(Control) Order” came in to force in 1957. Since then the The Fertilizer (Control)
order (FCO) has been amended periodically. It is useful for the personnels engaged
in: Fertilizer manufacture, fertilizer business, fertilizer analysis and fertilizer
inspection.
FERTILIZER CONTROL ACT
The Union Government of India promulgated the fertilizer Control Act (F.C.O)
in 1957 under the Essential Commodities Act, 1955 (section 3) with a view to
regulate fertilizer business in India.
The F.C.O. keeps a strict watch on quality control of fertilizers, provides for
the registration of dealers and statutory control of fertilizer prices by Government.
Therefore, everybody involved in fertilizer business as a manufacturer, dealer or a
salesperson, must have proper understanding of the F.C.O. in order to avoid
infringement of Government regulations.

65
The provisions given in the Order will also help the consumers/ farmers to
know their rights and privileges in respect of fertilizer quality and Authorities to be
approached for their grievances regarding supply of substandard materials,
overcharging or containers of underweight supplies.
The F.C.O. is published by the Fertilizer Association of India (F.A.I.), updated
when ever felt necessary. The Order has provisions on quality for each consumed
fertilizer product and F.C.O. should be consulted under infringement of any of them.
Control of Quality of Fertilizers
The F.C.O. has provisions to penalize manufactures, distributors, and dealers
for supply of spurious or adulterated fertilizers to consumers or farmers. The F.C.O.
has fixed specifications for various fertilizers, which must be present in them failing
which the legislation comes in force, and guilty is punished.
Specifications of fertilizers
To control the quality of fertilizers “The Fertilizer Control Order, 1985” has laid
down specifications for the fertilizers. The parameters of the specifications are as
follows:
i. Moisture, per cent by weight maximum
ii. Total nutrient content, percent by weight
iii. Forms of nutrient, per cent by weight
iv. Impurities, per cent by weight
v. Particle size.
1. Ammonium Sulphate
(i) Moisture per cent by weight, maximum 1.0
(ii) Ammoniacal nitrogen per cent by weight, minimum 20.6
(iii) Free acidity (as H2SO4.) per cent by weight, maximum (0.04 for material 0.025
obtained from by product ammonia and by-product gypsum)
(iv) Arsenic as (As2O3) per cent by weight, maximum 0.01
(v) Sulphur (as S) ,per cent by weight, minimum 23.0
2. Urea (46% N) (While free flowing)
(ii) Total nitrogen, per cent by weight, (on dry basis) minimum 46.00
(iii) Biuret per cent by weight, maximum 1.5
(iv) Particle size—Not less than 90 per cent of the material shall pass
through 2.8 mm IS sieve and not less than 80 per cent by weight shall be
retained on 1 mm IS sieve

66
3. Potassium Chloride (Muriate of Potash)

(ii) Water soluble potash content (as K2O) per cent by weight, minimum 60.0
(iii) Sodium as NaCI per cent by weight (on dry basis) maximum 3.5
(iv) Particle size -—minimum 65 cent of the material shall pass through 1.7
mm IS sieve and be retained on 0.25 mm IS sieve.
4. Diammonium Phosphate (18-46-0)

(ii) Total nitrogen per cent by weight, minimum 18.0
(iii) Ammonical nitrogen form per cent by weight, minimum 15.5
(iv) Total nitrogen in the form of urea per cent by weight, maximum 2.5
(v) Neutral ammonium citrate soluble phosphates (as P2O5) per cent by 46.0
weight, minimum
(vi) Water soluble phosphates (as P2O5) per cent by weight, minimum 41.0
(vii) Particle size -– not less than 90 per cent of the material shall pass
through 4 mm IS sieve and be retained on 1 mm IS sieve. Not more than 5
per cent shall be below than 1 mm size.
5. Zinc Sulphate Heptahydrate (ZnSO4.7H2O)

(ii) Matter insoluble in water per cent. by weight, maximum 1.0
(iii) Zinc (as Zn) per cent. by weight, minimum 21.0
(iv) Lead (as Pb) per cent by weight, maximum 0.003
(v) Copper (as Cu) per cent by weight, maximum 0.1
(vi) Magnesium (as Mg) per cent by weight, maximum 0.5
(vii) pH not less than 4.0
(viii) Sulphur (as S),percent by weight, minimum 10.0
(ix) Cadmium (as Cd), percent by weight, maximum 0.0025
(x) Arsenic (as As),percent by weight, maximum 0.01
SPECIFICATIONS OF MANURE
Example: Vermicompost :
(i) Moisture, per cent by weight 15.0-25.0
(ii) Colour Dark brown to black
(iii) Odour Absence of foul odour
(iv) Particle size Minimum material should pass through 90%
4.0 mm IS sieve
(v) Bulk density (g/cm3) 0.7-0.9
(vi) Total organic carbon, per cent by weight, minimum 18.0
(vii) Total Nitrogen (as N), per cent by weight,minimum 1.0
(viii) Total Phosphates (as P2O5), per cent by weight, 0.8
minimum
(ix) Total Potash (as K2O), per cent by weight, minimum 0.8
(x) C:N ratio <20
(xi) pH 6.5-7.5
67
(xii) Pathogens Nil

(xiii) Conductivity (as dsm-1),not more than 4.0
(xiv) Heavy metal content, (as mg/kg), maximum
Cadmium (as Cd) 5.0
Chromium (as Cr) 50.00
Nickel (as Ni) 50.00
Lead (as Pb) 100.00
Fertilizer Movement Control Order

The Fertilizer Movement Order (F.M.O.) was promulgated by Government of
India in April 1973 to ensure an equitable distribution of fertilizers in various States.
According to the fertilizer movement order, no person or agency can export chemical
fertilizers from any State. However, Food Corporation of India, Warehousing
Corporation of India and Indian Potash Limited; materials like Rock phosphate, bone
meal (both raw and steamed) and zinc sulphate are exempted from the movement
restriction.
Agency responsible for Enforcement of F.C.O

The Controller of Fertilizers for India, usually a Joint Secretary to the
Government of India (Ministry of Agriculture) is responsible for the enforcement of
F.C.O. throughout the country.
**************

68
CHAPTER- VI: SOIL FERTILITY AND PLANT NUTRITION

The word 'fertile' means bearing abundantly and a fertile soil is considered to
be one that produces abundant crops under suitable environmental condition. Soil
fertility is vital to a productive soil. But a fertile soil is not necessarily a productive
soil. All fertile soils may or may not be productive. Poor drainage, insects, drought
and other factors can limit production, even when fertility is adequate. To fully
understand soil fertility, one must know other factors which support or limit
productivity.
SOIL FERTILITY:
It refers to the inherent capacity of soil to supply all the essential nutrients to
plant in suitable quantity and in the right proportion.
SOIL PRODUCTIVITY:
Soil productivity is the ability of a soil for producing a specified plant or
sequence of plants under a specified system of management. It is usually expressed
in terms of crop yield.
The soil is said to be productive when good yields are obtained. Productive
soils are those, which contain adequate amounts of all essential nutrients in readily
forms to plants are in good physical condition to support plants and contain just the
right amount of water and air for desirable root growth. Thus, soil fertility, good
management practices, availability of water supply and a suitable climate contribute
towards soil productivity. Soil fertility denotes the status of plant nutrients in the soil
while soil productivity denotes the resultant of various factors influencing crop
production both within and beyond the soil. Thus, soil productivity is a function of
environmental factors combined with soil fertility or more correctly, in combination
with environmental factors and management practices constituents soil productivity.
“All the productive soils are fertile but all the fertile soils may not be
productive”
History of development of soil fertility
Francis Bacon (1591- 1624) suggested that the principle nourishment of plants was
water and the main purpose of the soil was to keep plants erect and to protect from
heat and cold.
Jan Baptiste Van Helmont (1577 – 1644) was reported that water was sole nutrient
of plants.

69
Robert Boyle (1627 – 1691) an England scientist confirmed the findings of Van
Helmont and proved that plant synthesis salts, spirits and oil etc from H2O.
Anthur Young (1741 – 1820) an English agriculturist conducted pot experiment
using Barley as a test crop under sand culture condition. He added charcoal, train
oil, poultry dung, spirits of wine, oster shells and numerous other materials and he
conduced that some of the materials were produced higher plant growth.
Priestly (1800) established the essentiality of O2 for the plant growth.
J. B. Boussingault (1802-1882) French chemist conducted field experiment and
maintained balance sheet. He was first scientist to conduct field experiment. He is
considered as father of field experiments.
Justus Von Liebig (1835) suggested that
a) Most of the carbon in plants comes from the CO2 of the atmosphere.
b) Hydrogen and O2 comes from H2O.
c) Alkaline metals are needed for neutralization of acids formed by plants as a
result of their metabolic activities.
d) Phosphorus is necessary for seed formation.
e) Plant absorb everything from the soil but excrete from their roots those
materials that are not essential.
The field may contain some nutrient in excess, some in optimum and some in
least, but the limiting factor for growth is the least available nutrient. The Law of
Minimum, stated by Liebig in 1862, is a simple but logical guide for predicting crop
response to fertilization. This law states that, “the level of plant production cannot be
greater than that allowed by the most limiting of the essential plant growth factors”.
The contributions made by Liebig to the advancement of agriculture were
monumental and he is recognized as the father of agricultural chemistry.
Crops depend on extrinsic and intrinsic factors for their growth and environment
to provide them with basic necessities for photosynthesis. These essential plant
growth factors include: • light, heat, air, water, nutrients & physical support
If any one factor, or combination of factors, is in limited supply, plant growth

will be adversely affected. The importance of each of the plant growth factors and
the proper combination of these factors for normal plant growth is best described by
the principle of limiting factors. This principle states: "The level of crop production
can be no greater than that allowed by the most limiting of the essential plant growth

70
factors." The principle of limiting factors can be compared to that of a barrel having
staves of different lengths with each stave representing a plant growth factor.
J.B. Lawes and J. H. Gilbert (1843) established permanent manurial experiment at

Rothemsted Agricultural experiment station at England. They conducted field
experiments for twelve years and their findings were
S. N. Winogradsky discovered the autotrophic mode of life among bacteria and
established the microbiological transformation of nitrogen and sulphur. Isolated for
the first time nitrifying bacteria and demonstrated role of these bacteria in nitrification
(l890), further he demonstrated that free-living Clostridium pasteuriamum could fix
atmospheric nitrogen (1893). Therefore, he is considered as "Father of soil
microbiology".
Robert Warrington England showed that the nitrification could be supported by
carbon disulphide and chloroform and that it would be stopped by adding a small
amount of unsterilized soil. He demonstrated that the reaction was two step
phenomenon. First NH3 being converted to nitrites and the nitrites to nitrites.
6.1 The soil as a Nutrient Source for Plants
Mineral Nutrients in the Soil: Mineral nutrients occur in the soil in both dissolved
and bound form. Only a small fraction (less than 0.2%) of the mineral nutrient supply
is dissolved in soil water. Most of the remainder, i.e., almost 98% is either bound in
organic detritus, humus and relatively insoluble inorganic compounds or incorporated
in minerals. These constitute a nutrient reserve, which becomes available very
slowly as a result of weathering and mineralization of humus. The remaining 2% is
adsorbed on soil colloids. The soil solution, the soil colloids and the reserves of
71
mineral substances in the soil are in a state of dynamic equilibrium, which ensures
continued replenishment of supplies of nutrient elements.
Adsorption and Exchange of ions in the soil: Both clay minerals and humic
colloids have a negative net charge so that they attract and adsorb primarily cations.
There are also some positively charged sites where anions can accumulate. How
tightly a cation is held depends on its charge and degree of hydration. In general,
ions with high valences are attracted more strongly for example, Ca2+ is more
strongly attracted than K+. Among ions with the same valence those with little
hydration are retained more firmly than those that are strongly hydrated. The
tendency for cations adsorption decreases in the order Al3+, Ca2+, Mg2+, NH4+, K+
and Na+
The swarm of ions around particles of clay and humus as an intermediary
between the solid soil phase and the soil solution. If ions are added to or withdrawn
from the soil solution, exchange takes place between solid and liquid phases.
Adsorptive binding of nutrient ions offers a number of advantages nutrients liberated
by weathering and the decomposition of humus are captured and protected from
leaching the concentration of the soil solution is kept low and relatively constant; so
that the plant roots and soil organisms are not exposed to extreme osmotic
conditions; when required by the plant, however, the adsorbed nutrients are readily
available.
Solid phase
non adsorbed
(Organic matter or M (In shoot) Transpiration M (In xylems)
minerals)
M
M (R)
M
M M M
(Root absorbing
(Adsorbed) (Soil solution) (Accumulation in
surface)
Solid phase root)
Nutrient release and path for absorption
ESSENTIAL AND BENEFICIAL ELEMENTS

72
► The criteria of essentiality: In order to distinguish elements, which are essential

from those which may be taken up by the plant but are not essential, Arnon (1954)
has laid down the following criteria:
(1) The plant must be unable to grow normally or complete its life-cycle in the
absence of the element;
(2) The element is specific and can not be replaced by another; and
(3) The element plays a direct role in metabolism.
Table 1: Essentiality of nutrients discovered by scientists. Source: Tisdale et al.
(1997)
Nutrient Essentiality discovered authors Year of
(Discoverer) discovery
H&O Since time immemorial
C Priestley et al. 1800
N Theodore de Saussure 1804
K, Ca, Mg & P C. Sprengel 1839
S Sachs and Knop 1860
CI T.C. Broyer, A.B. Carlton, CM. Johnson and 1954
P.R. Stout
Fe E Gris 1843
B K. Warington 1923
Mn J.S. McHargue 1922
Zn A.L. Sommer and CP. Lipman 1926
Cu A.L. Sommer, CP. Lipman and G. McKinney 1931
Mo D.I. Arnon and P.R. Stout 1939
Ni P.H. Brown, R.M. Welch and E.E. Cary 1987
► Essential nutrients so far recognized: Carbon, hydrogen and oxygen, nitrogen,

phosphorus, potassium, calcium, magnesium, sulphur, iron, manganese, zinc,
copper, boron, molybdenum and chlorine are recognized as universally essential.
There is convincing evidence that these mineral elements are essential requirements
for diverse groups of plants algae, bacteria, fungi and the green plants.
CLASSIFICATION OF ESSENTIAL PLANT NUTRIENTS:

(i) On the basis of amount of nutrients present in plants, they can be classified
in to three groups:
73
Nutrients Average concentration Function in plant Nutrient category

in plant tissue
N 1.5% Proteins, amino acids
Primary
P 0.2% Nucleic acids, ATP
Macronutrients
K 1.0% Catalyst, ion transport
Ca 0.5% Cell wall component
Mg 0.2% Part of chlorophyll Secondary
S 0.1% Amino acids
Fe 100 mg/kg Chlorophyll synthesis
Cu 6 mg/kg Component of enzymes
Mn 20 mg/kg Activates enzymes
Zn 20 mg/kg Activates enzymes
Micronutrients
B 20 mg/kg Cell wall component
Mo 0.1 mg/kg Involve in N fixation
Cl 100 mg/kg Photosynthesis
reactions
(ii) According to mobility:

(a) In soil:
1. Mobile: NO3-, SO42-, BO33-, Cl- and Mn2-
2. Less mobile: NH42-, K+, Ca2+, Mg2+ and Cu2+
3. Immobile: H2PO4-, HPO42- and Zn2+
(b) In plant:
1. Highly mobile: N, P and K
2. Moderately mobile: Zn
3. Less mobile: S, Fe, Mn, Cu, Mo and Cl
4. Immobile: Ca and B
(iii) According to metal and non metal
1. Metal: K, Ca, Mg, Fe, Mn, Zn and Cu
2. Non metal: N, P, S, B, Mo and Cl
(iv) According to cation and anion
1. Cation: K, Ca, Mg, Fe, Mn, Zn and Cu
2. Anion: NO3, H3PO4 and SO4
6.3 Beneficial elements: Apart from vanadium, silicon, aluminum, iodine, selenium
and gallium, which have been shown to be essential for particular species of plants,
there are several other elements, like rubidium, strontium, nickel, chromium and
arsenic, which at very low concentrations and often under specific conditions have
74
been shown to stimulate the growth of certain plants or to have other beneficial
effects. These elements, the essentiality of which for growth and metabolism has not
been unequivocally established but which are shown to exert beneficial effects at
very low concentrations are often referred to as 'beneficial elements',
6.4 Forms of nutrients in soil
In soil, Nutrient present in different forms are as under
Sr. Nutrient Forms
No.
1. Nitrogen Organic N (97%) and Mineral N NH4+, NO3-
2. Phosphorus Solution P, Calcium, Iron, Aluminium and Occluded P,
Organic P (25%-90%) and Mineral P
3. Potassium Water soluble K, Exchangeable K, Fixed K and Mineral K (90-
98%),
4. Sulphur Sulphate S, Non sulphate S, Adsorbed S, Organic S(95%)
and Total S,
5. Micronutrients Water soluble ion, Exchangeable, Adsorbed, chelated or
complexed ion, Cation held in secondary clay mineral and
insoluble metal oxides and cation held in primary mineral
6.5 Mechanisms of nutrient transport to plants

Two important theories, namely, soil solution theory and contact exchange
theory explain nutrient availability to plants.
(i) Soil solution theory:

(a) Mass flow: Movement of nutrient ions and salts along with moving water.
(b) Diffusion: Occurs when there is concentration gradient of nutrients
between root surface and surrounding soil solution. Ions move from the
region of high concentration to the region of low concentration.
(ii) Contact exchange theory: The important of contact exchange in nutrient
transport is less than with soil solution movement. A close contact between root
surface and soil colloids allows a direct exchange of ions.
6.6 Factors Influencing Nutrient Availability

Several factors influence nutrient availability:
(1) Natural supply of nutrients in the soil which is closely tied up to parent material
of that soil and vegetation under which it is developed.
(2) Soil pH as it affects nutrient release,

75
(3) Relative activity of microorganisms which play a vital role in nutrient release
and may as in the case of mycorrhizae directly function in nutrient uptake
(4) Fertility addition in the form of commercial fertilizer, animal manure and green
manure, and Soil temperature, moisture and aeration.
6.7 Nutrient deficiency
Generalized symptoms of plant nutrient deficiency
Nutrients Visual deficiency symptoms
N : Light green to yellow appearance of leaves, especially older leaves,
stunted growth, poor fruit development
P : Leaves may develop purple colouration, stunted plant growth and
delay in plant development
K : Marginal burning of leaves, irregular fruit development
Ca : Reduced growth or death of growing tips, poor fruit development and
appearance
Mg : Initial yellowing of older leaves between leaf veins spreading to
younger leaves, poor fruit development and production
S : Initial yellowing of young leaves spreading to whole plant, similar
symptoms to N deficiency but occurs on new growth
Fe : Initial distinct yellow or white areas between veins of young leaves
leading to spots of dead leaf tissue
Mn : Interveinal yellowing or mottling of young leaves
Zn : Interveinal yellowing on young leaves, reduce leaf size, brown leaf
spot on paddy
Cu : Stunted growth, terminal leaf buds die, leaf tips become white and
leaves are narrowed and twisted.
B : Terminal buds die, breakdown of internal tissues in root crops, internal
cork of apple, impairment of flowering and fruit development
Mo : Resemble N deficiency symptoms, whiptail diseases of qualiflower,
leaves show scorching and whithering
Cl : Chlorotic leaves, some leaf necrosis
Nutrient deficiency may not be apparent as striking symptoms such as

chlorosis on the plant, especially when mild deficiency is occurring. However,
significant reduction in crop yields can occur with such deficiencies. This situation is
termed hidden hunger and can only be detected with plant tissue analysis or yield
decline
6.8 Management:
1. Addition of nutrient through fertilizer in soil as well as foliar application
2. Addition of organic manure
3. Correction of soil problems i.e. salinity, sodicity, acidity etc.

76
6.9 Nutrient toxicity and management

Nutrient toxicities in crops are more frequent for manganese (Mn) and boron
(B) than for other nutrients. Manganese toxicity is found on acid soils in many parts
of the world. Boron toxicities occur in irrigated regions where the well or irrigation
waters are exceptionally high in B. Most other nutrient toxicities occur when large
amounts of nutrients in question have been added in waste, e.g., sewage sludge.
Crops grown near mines and smelters are prone to nutrient toxicities. Generally, the
symptoms of toxicity in crops occur as burning, Chlorosis and yellowing of leaves.
Toxicities can result in decreased yield and/or impaired crop quality.
Prevention of toxicity
(1) With the exception of Mo, toxicity of other nutrients can be reduced by liming.
(2) Following recommended rates of fertilizers and the safe and controlled use
of waste materials, such as sewage sludge and coal fly ash, should reduce
metal loading and nutrient toxicity in crops.
(3) Use of crop species and genotypes less susceptible to toxicity are
recommended where toxicity is suspected.
(4) Provided sufficient drainage because availability of nutrients like Fe and Mn
is increases up to toxicity level under water logged condition.
(5) Ground water must be monitored regularly, if content of B and Cl is too high
stop to applied water or applied with dilution.
(6) Addition of sufficient amount of organic matter, that bind the some of the
toxic elements.
(7) Ploughing in dry soil so increase the infiltration rate and leach the toxic
element with rain water.
**************

77
CHAPTER VII: CHEMISTRY OF SOIL NITROGEN, PHOSPHORUS,

POTASSIUM, CALCIUM, MAGNESIUM, SULPHUR AND
MICRONUTRIENTS
The changes undergone by common fertilizers after these are taken out of the
bag and added to soils are discussed. By understanding the fate of fertilizers,
measures for increasing their efficiency can be suggested and adopted. When
fertilizers react with soils, the compounds produced are by and large similar to the
ones which are present in soils and which are produced by the breakdown of
minerals and organic matter. That is why soils accept fertilizers without any fuss.
7.1 Nitrogen:
Nitrogen occurs in soil in both cationic (NH4+) and anionic (NO3-, NO2-) forms,
the greater parts occurs in organic forms. NH4+ fixed on the cation exchange sites,
are tightly bound by clay and is slowly available to plants. The available nitrates and
ammonium form is only 1-2% of the total soil nitrogen. Nitrate is highly mobile.
Nitrogen availability depends upon the rate at which organic nitrogen is converted to
inorganic nitrogen (mineralization). Most soil nitrogen is unavailable to plants. The
amount in available forms is small and crops withdraw a large amount of nitrogen.
Two forms of nitrogen available to plants are nitrate (NO3-) and ammonium (NH4+).
Nitrogen transformation in Soils
The cycling of N in the soil-plant-atmosphere system involves many
transformations of N between inorganic and organic forms. Nitrogen is subjected to
amino compounds (R-NH2, R represents the part of the organic molecules with
which amino group (NH2) is associated), then to ammonium (NH4+) ion and nitrate
(NO3-). Ammonium nitrogen is often converted to nitrate-nitrogen by micro-organisms
before absorption through a process called nitrification.
Nitrogen Mineralization
The conversion of organic N to NH4+ and NO3- is known as nitrogen
mineralization. Mineralization of organic N involves two reactions, aminisation and
ammonification, which occur through the activity of heterotrophic micro-organisms.
The enzymatic process may be indicated as follows:
+H2O Mineralization +O2 +O
RNH2 ROH + NH4 NO2- + 4H NO3-
-H2O -O2 O
Immobilization

78
Aminisation:
The decomposition of protein into amines, amino acids and urea is known as
aminisation.
NH2 O O
Proteins H2O R - C - COOH + R-NH2 + H2N - C - NH2 + CO2 + Energy

Bacteria, H
Fungi Amino acids Amines Urea
Ammonification
The step, in which, the amines and amino acids produced by aminisation of
organic N are decomposed by other heterotrophs, with the release of NH 4+, is
termed as ammonification.
R -NH2 + H2O NH3+ R - OH + Energy
H2O
NH4+ + OH-
Nitrogen immobilization
Immobilisation is the process in which available forms of inorganic nitrogen
(NO3- NH4+) are converted to unavailable organic nitrogen. Immobilisation includes
assimilation and protein production so those inorganic ions are made into building
block of large organic molecules.
Nitrification
Nitrification is a process in which NH4+ released during mineralization of
organic N is converted to NO3-. it is a two step process in which NH4+ is converted
first to NO2- and then to NO3-. Biological oxidation of NH4+to NO2- is represented by:
Nitrosomonas
2NH4+ + 3O2 2NO2- + 2H2O + 4H+
NO2- is further oxidized to NO3- be bacteria

Nitrobactor
-
2NO2 + O2 2 NO3-
7.2 Phosphorus
Organic and inorganic forms of phosphorus occur in soils and both the forms
are important to plants as source of phosphorus. The relative amounts of
phosphorus in organic and inorganic forms vary greatly from soil to soil.

79
Organic phosphorus compounds

Organic phosphorus represents about 50% of the total P in soils (Varies between 15
and 80% in most soil. Most organic P compounds are esters of orthophosphoric acid
and have been identifies primarily as (a) inositol phosphates, (b) phospholipids and
(c) nucleic acids.
Inorganic phosphorus compounds
Most inorganic phosphorus compounds in soil fall into one of the two group:
(a) those in which calcium is the dominant controlling cation (calcium phosphate) and
(b) those in which iron and aluminum are the controlling cations (iron and aluminum
phosphates).
Phosphate Retention and Fixation
Phosphate anions can be attracted to soil constituents with such a bond that
they become insoluble and not easily available to plants. This process is called
phosphate fixation or retention.
Phosphate retention
Acid soils usually contain significant amounts of soluble and exchangeable
Al3+, Fe3+ and Mn2+ ions. Phosphate, when present, may be adsorbed to the colloid
surface with these ions serving as a bridge. This phenomenon is called co-
adsorption. The phosphate retained in this way is still available to plants. Such a
reaction can also take place with Ca-saturated clays.
Ca clay adsorbs large amounts of phosphate. The Ca2+ ions forms the linkage
between he clay and phosphate ions as : Clay-Ca-H2PO4.
The phosphate ions can also enter into a chemical reaction with the foregoing
free metal ions as: Al3++3H2PO4- Al(H2PO4)3. The product formed is not
soluble in water and precipitates from solution. With the passage of time the Al
phosphate precipitates, become less soluble and less available to plants. The lower
the soil pH, the greater the concentration of soluble Fe, Al, and Mn: consequently,
larger the amount of phosphorus retention in this way.
Phosphate fixation in acidic soils:

Many acidic soils contain high amounts of free Fe and Al and Fe and Al
hydrous oxide clays. The free Fe, Al and the sesquioxide clays react rapidly with
phosphate, forming a series of not easily soluble hydroxyl phosphates.

80
Fe-OH Fe-O O
O + PO43- O P
Fe-OH Fe-O O
The amount of phosphate fixed by this reaction usually exceeds
that fixed by phosphate retention. Generally, clays with low sesquioxide ratios
(SiO2/R2O3) have a higher P-fixing capacity.
Phosphate fixation in alkaline soils:
Many alkaline soils contain high amounts of soluble and exchangeable Ca2+
and, frequently, CaCO3. Phosphate react with both the ionic and carbonate form of
Ca.
3Ca2+ + 2PO43 Ca3(PO4)2 (Insoluble)
3CaCO3 + 2PO43- Ca3(PO4)2 + 3CO2 (Insoluble)
Phosphate fixation cannot be avoided entirely, but it may be
reduced by addition of competing ions for fixing sites. Organic anions from stable
manure and silicates are reported to be very useful in reducing P fixation.
7.3 Potassium
Forms and availability of potassium in soils
Potassium in soil occurs in four phases namely soil solution phase,
exchangeable phase, non-exchangeable phase and mineral phase. The different
forms are in dynamic equilibrium with one another.
The forms of potassium in soils were positively and significantly correlated
with K content in silt and clay.(Venkatesh and Satyanarayan, 1994).
Water soluble K:
The water soluble K is the fraction of soil potassium that can be readily
adsorbed by the growing plants. However this is a very small fraction of total K. The
dilution of the soil incrases the concentration of water-soluble K and drying
decreases it further. It is about 1 to 10 mg kg-1 of total K.
Exchangeable K:
Exchangeable K is held around negatively charged soil colloids by
electrostatic attraction. Thus, exchangeable potassium represents that fraction of K,
which is adsorbed on external and accessible internal surfaces. It is about 40 to 60
mg kg-1 of total K.
Non-exchangeable (fixed) K:

81
Potassium held at inter lattice position is generally non-exchangeable. Non-

exchangeable K is distinct from mineral K in that it is not bonded covalently within
the crystal structures of soils mineral particles. Instead, it is held between adjacent
tetrahedral layers of dioctahedral and trioctahedral micas, vermiculites and
intergrade clay minerals. It is about 50 to 750 mg kg-1 of total K.
Mineral (lattice) K:
Lattice K is a part of the mineral structure and is available to the plants very
slowly. (As compared to the non-exchangeable K). Both the rate and amount of
lattice K released to plants depend on the quantity of clay, especially the smaller clay
particles, and its mineralogy. It is about 5,000 to 25,000mg kg-1.
For convenience, the various forms of potassium in soils can be classified on
the basis of availability in three general groups: (a) unavailable (b) readily available
and (c) slowly available.
A dynamic equilibrium of various forms of K in the soil may be shown as :
K(lattice) K(exchangeable) K (solution)
Relatively Unavailable Forms
The greatest part (90-98%) of all soil potassium in a mineral soil is in relatively
unavailable forms. The compounds containing most of this form of potassium are the
feldspars and micas. These minerals are quite resistant to weathering and probably
supply relatively insignificant quantities of potassium during a given growing season.
Readily Available Forms
The readily available potassium constitutes only about 1-2% of the total
amount of this element in an average mineral soil. It exists in soils in two forms; (i)
potassium in soil solution and (ii) exchangeable potassium adsorbed on soil colloidal
surfaces. Most of this available potassium is in the exchangeable form
(approximately 90%). Soil solution potassium is most readily adsorbed by higher
plant and is, of course, subject to considerable leaching loss.
Slowly Available Forms
In the presence of vermiculite, smectite, and other 2:1- type minerals the
potassium of such fertilizers as muriate of potash not only becomes adsorbed but
may become definitely 'fixed' by the soil colloids. The potassium as well as
ammonium ions fit in between layers in the crystals of these normally expanding
clays and become an integral part of the crystal. Potassium in this form cannot be

82
replaced by ordinary exchange methods and consequently is referred to as non-

exchangeable potassium. As such this element is not readily available to higher
plants. This form is in equilibrium, however, with the available forms and
consequently acts as an extremely important reservoir of slowly available potassium.
7.4 Sulphur Transformation in Soil
Sergei Nikolaievich Winogradsky (1856 – 1953) was microbiologist, ecologist
and soil scientist who pioneer for his notable work on bacterial sulfate reduction. The
transformation of sulphur are important indicators of its availability to plants.
Availability of sulphur from organic sulphur reserves in soils depends on its
mineralization through microbial activity.
Sulphur Oxidation:
Sulphur oxidation ocuuring in soils is mostly biochemical in nature. Sulphur
oxidation is accomplished by number of autotrophic bacteria including those of
genus Thiobacillus, five species of which have been characterized:
(a) Thiobacillus thioxidans (b) T. thiparus (c) T. nonellus (d) T. denitrificans (e) T.
ferooxidans
In soils, sulfides, elemental sulphur, thiosulphates and polythionates are
oxidized.
Oxidation reactions:
H2S + 2O2 H2SO4 2H+ + SO42-
2S + 3O2 + 2H2O 2H2SO4 4H+ + 2SO42-
Thus S-oxidation is an acidifying process.
Sulphur reduction:
Sulphate tend to be unstable in anaerobic environments so they are reduced
sulfides by a number of bacteria of two genera, Desulfovibro (five species) and
Desulfotomaculum (three species).
The organisms use the combined oxygen in sulfate to oxidize organic materials.
Reduction reactions:
2R-CH2OH + SO42- 2R-COOH + 2H2O + S2-
(Organic alcohol) (Sulfate) (Organic acid) (Sulfide)
Also, sulfites (SO32-), thiosulfates (S2O32-) and elemental sulphur (S) are
rather easily reduced to the sulfides form by bacteria and other organisms.
The oxidation and reduction of inorganic sulphur compounds are of great
importance to growing plants. These reactions determine the quantity of sulfate

83
present in soils at any one time. Also, the state of sulphur oxidation determines to a
marked degree the soil acidity as S-oxidation is an acidifying process.
7.5 Calcium and Magnesium Transformations in Soil
Calcium is an important amendment element in saline and alkali soils.
Calcium application helps in correcting the toxicity and deficiency of several other
nutrients. The main transformations of Ca and Mg in soils are (i) solubilization and
leaching and (ii) conversion into less soluble fractions by adsorption.
Solubilization and leaching of calcium and magnesium: It is affected by following:
Soil texture: Losses are more in light textured soils because of high permeability
and percolation of rain and irrigation water.
Rainfall: As the rainfall increases the loss of Mg and Ca also increases.
Organic matter: Application of organic matter leads to net loss of Ca and Mg from the
soil.
Ferrolysis: High amounts of bases such as Ca2+ and Mg2+ may be lost from the
exchange complex and laeached by high amounts of cations such as Fe2+ and
Mn2+ which are released following reduction of soil. This is called ferrolysis.
Conversion of calcium and magnesium into less soluble form by adsorption: Clacium
and magnesium in soil solution and in exchange complex are in a state of dynamic
equilibrium. When their concentration in solution decreases, Ca and Mg coming from
the exchange complex replenish this. On the other hand if their concentration in soil
solution is high, there is tendency towards their being adsorbed on the exchange
complex.
7.6 Fe and Zn Transformations in Soil:
Iron
The most important chemical change that takes place when a soil is
submerged is the reduction of iron and the accompanying increase in its solubility.
The intensity of reduction depends upon time of submergence, amount of organic
matter, active iron, active manganese, nitrate etc.
Due to reduction of Fe3+ to Fe2+ on submergence, the colour of soil changes
from brown to grey and large amounts of Fe2- enter into the soil solution. It is evident
that the concentration of ferrous iron (Fe2+) increases initially to some peak value the
thereafter decreases slowly with the period of soil submergence. Organic matter also
enhances the rate of reduction of iron in submerged soils. The initial increase in the

84
concentration of ferrous iron (Fe2+) on soil submergence is caused by the reduction

that are shown below:
The decrease in the concentration of Fe2+ following the peak rise is caused by the
precipitation of Fe2+ as FeC03 in the early stages where high partial pressure of C02
prevails and as Fe3(OH)8 due to decrease in the partial pressure of C02(pC02)
Rice benefits from the increase in availability of iron but may suffer in acid
soils, from an excess. The reduction of iron has some important consequences: (i)
the concentration of water soluble iron increases, (ii) pH increases, (iii) cations are
displaced from exchange sites, (iv) the solubility of P and Si increases and (v) new
minerals are formed.
A schematic representation for the transformation of iron in submerged soils is

shown below:
Zinc
The transformation of zinc in submerged soils is not involved in the oxidation-
reduction process like that of iron and manganese. However, the reduction of
hydrous oxides of iron and manganese, changes in soil pH, partial pressure of C02,
formation insoluble sulphide compound etc. In soil on submergence is likely to
85
influence the solubility of Zn in soil either favourably or adversely and consequently

the Zn nutrition of low and rice. The reduction of hydrous oxides of iron and
manganese, formation of organic complexing agents, and the decrease in pH of
alkaline and calcareous soils on submergence are found to favour the solubility of
Zn, whereas the formation of hydroxides, carbonates, sulphides may lower the
solubility ofZn in submerged soils. Zinc deficiency in submerged rice soils is very
common owing to the combined effect of increased pH, HC03- and S2- formation.
The solubility of native forms of Zn in soils is highly pH dependent and
decreases by a factor of 102 for each unit increase in soil pH. The activity of Zn-pH
relationship has been defined as follow:
The pK value for the above reaction with the solid phase of soils is 6.0. This
equation holds good for submerged soils. Some equations relating to solubility of Zn
in submerged soils governed by various metastable compounds are given below :
Many of these compounds are metastable intermediate reaction products and

varying mean residence time in submerged soils. Applied Zn tends to approach the
solubility of the native forms instead of having residual effect in the former Zn forms.
When an aerobic soil is submerged, the availability of native as well as
applied Zn decreases and the magnitude of such decrease vary with the soil
properties. The transformation of Zn in soils was found to be greatly influenced by
the depth of submerged and application of organic matter. If an acid soil is
submerged, the pH of the soil will increase and thereby the availability of Zn will
decrease. On the other hand, if an alkali soil is submerged, the pH of the soil will
decrease and as a result the solubility of Zn will generally increase.
The availability of Zn decreases due to submergence may be attributed to the
following reasons:
(i) formation of insoluble franklinite (ZnFe204) compound in submerged soils.

86
(ii) Formation of very insoluble compounds of Zn as ZnS under intense reducing

conditions.
(iii) Formation of insoluble compounds of Zn as ZnC03 at the later period of soil

submergence owing to high partial pressure of C02(PC02) arising from the
decomposition of organic matter.
(iv) Formation of Zn(OH)2 at a relatively higher pH which decreases the availability

of Zn.
(v) Adsorption of soluble Zn2+ by oxide minerals e.g. sesquioxides, carbonates, soil
organic matter and clay minerals etc. decreases the availability of Zn, the possible
mechanism of Zn adsorption by oxide minerals is shown below :
Mechanism I:
In mechanism I, Zn2+ adsorption occurs as bridging between two neutral sites,

but in addition to this mechanism, Zn2+ could also be adsorbed to two positive sites
or to a positive and neutral site.
Mechanism II:
This mechanism occurs at low pH and results non-specific adsorption of Zn2+.

In this way Zn2+ is retained and rendered unavailable to plants.
(vi) Formation of various other insoluble zinc compounds which decreases the
availability of Zn in submerged soils, e.g. high phosphatic fertilizer induces the
decreased availability of Zn2+.

87
A simplified diagram illustrating dynamic equilibria of Zn in submerged soils is

shown in figure.
It shows that rice receives Zn from the soil solution and the exchangeable and
adsorbed solid phase including the soil organic fractions.
Zinc sulphide (ZnS, Sphalerite) in the presence of traces of hydrogen sulphide
(H2S) in submerged soils may control the solubility of Zn. Zinc is stable in submerged
soils. So it can be concluded that higher the pH and poorer the aeration, the greater
is the likelihood of Zn deficiency if the soil solution Zn activity is controlled by
sphalerite (ZnS).
Q/I relationship
In addition to these, the availability of Zn in submerged soils is governed by
the mutual interaction of quantity (q) intensity (c), and kinetic parameters as
regulated by the adsorption, desorption, chelation and diffusion of Zn from soils to
the plant roots. The quantity-intensity relationship of Zn in submerged soils may be
described by the linear form of the Langmuir type equation. The supply parameter
assumes the form,
where q is the quantity c is the intensity, K1 and K2 are constants.

The optimum Zn supply to rice is ensured when the value of the supply parameter is
unity (1.0).
**************

88
CHAPTER- VIII: SOIL FERTILITY EVALUATION AND SOIL TESTING
The proper rate of plant nutrient is determined by knowing the nutrient

requirement of the crop and the nutrient supplying power of soil. Hence, the
evaluation of soil fertility becomes important. Soil fertility evaluation is essential for
balanced nutrition of the crops. Balance nutrients use refers to the application of
essential plant nutrients in right amounts and proportions using correct methods and
time of application suited for specific soil-crop-climatic situations. It helps in
maintenance and improving soil productivity. Thus soil fertility evaluation is the key
for adequate and balanced fertilization in crop production. Several techniques are
commonly employed to asses the fertility status of the soils. The diagnostic
techniques are
1. Soil testing
2. Analysis of tissues from plant growing on the soil
3. Biological tests in which the growth of higher plants or certain micro-organisms is
used as a measure of soil fertility
4. Nutrient deficiency symptoms of plant
8.1 Soil testing:
Soil testing is the chemical analysis that provides a guideline for amendments
and fertilizer needs of soils. The primary advantage of soil testing when it is
compared to the plant analysis is its ability to determine the nutrients status of the
soil before the crop is planted
The soil testing is done with following objectives:
1. Soil fertility evaluation for making fertilizer recommendation
2. Prediction of likely crop response to applied nutrient
3. Classification of soil into different fertility groups for preparing soil fertility maps of
a given area
4. Assessment of the type and degree of soil related problems like salinity, sodicity,
acidity etc., and suggesting appropriate reclamation / amelioration measure. The
following steps are involved in soil analysis
1. Sampling
2. preparation of samples
3. Analytical procedure
4. Calibration and interpretation of the results

89
5. Fertilizer recommendation
1. Sampling: Soil sampling is perhaps the most vital step for any analysis. Since, a
very small fraction of the huge soil mass of a field is used for analysis; it becomes
extremely important to get a truly representative soil sample from it.
2. Preparation of sample: Drying, grinding and sieving according to the need of
analytical procedure
3. Analytical procedure: A suitable method is one which satisfies the following
three criteria.
i. It should be fairly rapid so that the test results can be obtained in a reasonably
short period.
ii. It should give accurate and reproducible results of a given samples with least
interferences during estimation.
iii. It should have high predictability i.e., a significant relationship of test values
with the crop performance.
Following chemical methods are widely used for determination of different
nutrients
Nutrients Methods Merits and demerits
Total N Kjeldahl method  This method is time consuming, lengthy and

costly
 Rate of mineralization of N varies with the
soil
Organic C Walkley and  This method is simple and rapid

Black method  Based on C:N ratio which is varied (7.7 to
11.7)
Available N Alkaline-KMnO4  Extract part of organic and mineral N
Available Olsen's method  High efficiency of HCO3 ion to remove P from

P2O5 for alkaline soils Ca, Al and Fe
 Reduce the activity of Ca
 Used in slightly acidic, neutral and alkaline
soil
Bray's method  High efficiency of F ion in dissolving P

for acid soils  Useful in acidic or slightly calcareous soils
Available K2O NH4OAc  Higher efficiency of extraction as compared

90
extratable to salt solution

 Inefficiency to remove part of non
exchangeable K, which isconsidered to be
available to some extent
Available S 0.15% CaCl2  Extract water soluble S and adsorbed S

extractable
Heat soluble S  Heat soluble- extract WS + organic S

 Time consuming and lengthy procedure
Available DTPA extractable  Extract complexed, chelated and adsorbed

Micronutrients form of Fe, Mn, Zn, Cu
4. Calibration and interpretation of the results: For the calibration of the soil test
data, a group of soils ranging in soil fertility from low to high in respect of the
particular nutrient are selected and the test crop is grown on these soils with
varying doses of particular nutrient with basal dose of other nutrients.
The most common method is to plot soil test values against the percentage yield and
to calculate the relationship between soil test values and per cent yield response
Crop yield with Yield of control without addition

Percent adequate nutrient - of particular nutrient under x 100
=
yield study
Crop yield with adequate nutrient
► Critical level of nutrients in soil:

SN Category
Nutrients
Low Medium High
1. Alkaline KMnO4-N (kg/ha) <250 250-500 >500
2. Olsens-P2O5 (kg/ha), <28 28-56 >56
3. Neutral N NH4OAc-K2O <140 140-280 >280
4. 0.15% CaCl2 –S (mg/kg) <10 10-20 >20
5. DTPA extractable Fe (mg/kg) <5 5-10 >10
6. DTPA extractable Mn (mg/kg) <5 5-10 >10
7. DTPA extractable Zn (mg/kg) <0.5 0.5-1.0 >1.0
8. DTPA extractable Cu (mg/kg) <0.2 0.2-0.4 >0.4
9. Hot water soluble B (mg/kg) <0.1 0.1-0.5 >0.5
10. Hot water soluble Mo (mg/kg)
91
This classification indicated that low class of soil would respond to added
fertilizer means add 25% more fertilizer than recommended dose. Medium class soil
may or may not respond to added fertilizer, add recommended dose of fertilizer. High
status soils do not respond to added fertilizer, add 25% less recommended dose.
8.2 Plant Testing:
1. Analysis of tissues from plant growing on the soil
Plant analysis in a narrow sense is the determination of the concentration of an
element or extractable fraction of an element in a sample taken from a particular part
or portion of a crop at a certain time or stage of morphological development
Plant analysis is complementary to soil testing. In many situations, the total or
even the available content of an element in soil fails to correlate with the plant tissue
concentration or the growth and yield of crop. This can be ascribed to many reasons
including the physico chemical properties of the soils and the root growth patterns.
On the other hand, the concentration of an element in the plant tissue is, generally,
positively correlated with the plant health. Therefore, the plant analysis has been
used as a diagnostic tool to determine the nutritional cause of plant
disorders/diseases. The plant analysis constitutes (1) the collection of the
representative plant parts at the specific growth stage, (2) washing, drying and
grinding of plant tissue, (3) oxidation of the powdered plant samples to solubilize the
elements, (4) estimation of different elements, and (5) interpretation of the status of
nutrients with respect to deficiency / sufficiency /toxicity on the basis of known critical
concentrations.
► Plant analysis has many applications such as:
1. Diagnosis of nutrient deficiencies, toxicities or imbalances
2. Measurement of the quantity of nutrients removed by a crops to replace them in
order to maintain soil fertility
3. Estimating overall nutritional status of the region or soil types
4. Monitoring the effectiveness of the fertilizer practices adopted
5. Estimation of nutrient levels in the diets available to the live stock
2. Collection and Preparation of plant samples
Plant scientists have been able to standardize the procedures for collection of
samples of plant tissue with respect to the plant part and growth stage, which reflect
the nutrient concentrations corresponding to the health of the growth because the
concentrations of different nutrients vary significantly over the life cycle of a plant.
92
Generally, the recently matured fully expanded leaves just before the onset of the
reproductive stage are collected and put in perforated paper bags. The plant
samples are often contaminated with dust, dirt and residues of the sprays, etc. and
need to be washed first under a running tap water followed by rinsing with dilute HCl
(0.001N), distilled water and finally in deionized water. The washed samples are
dried in a hot air oven at 60 ± 5°C for a period of 48 hours and ground in a stainless
steel mill to pass through a sieve of 40/60 mesh.
3. Oxidation of plant material
The main objective of oxidation is to destroy the organic components in the
plant material to release the elements from their combinations. The plant materials
can be oxidized by either dry ashing at a controlled high temperature in a muffle
furnace or wet digestion in an acid or a mixture of two or more acids.
(a) Dry-ashing : The powdered plant materials in tall form silica crucibles are
ashed at 500ºC in a muffles furnace for 3-4 hours. High temperatures are likely to
result in the loss of some volatile elements but with adjusting the time of muffling
between 2-72 hours, any significant effect on the analytical results can be avoided.
Nitrogen and sulphur, being highly volatile, are lost more or less completely during
dry ashing even at 500ºC but at higher temperatures, elements like K are also
reported to be lost. Thus, temperature is an important consideration in dry ashing.
The ash is dissolved in 2ml of 6N HCl, heated on a hot plate to near dryness and
taken in 10 ml dilute HCl (0.01N) or 20% aqua regia before making up the final
volume with distilled water. These extracts contain different amounts of insoluble
materials, mainly silica, depending upon the plant species. These insoluble materials
settle down on keeping for some time or can be separated by filtration before
estimation of different elements. All elements, except N and S, can be estimated in
these extracts by any technique. In general, the results obtained by this method, are
quite satisfactory and comparable to those obtained by this method, are quite
satisfactory and comparable to those obtained by wet digestion procedures.
Moreover, B can only be determined by dry ashing since it is volatilized during wet
digestion with di-or triacid mixtures.
(b) Wet Digestion :
The powdered plant samples can also be dissolved by digesting in acids,
usually HNO3, HClO4 and H2SO4. These acids are used either singly or in
combinations of two or three acids, e.g. a di-acid combination is HNO3 and HClO4 (in
4:1 ration) or a triple acid is a mixture of HNO3, HClO4 and H2SO4 (in 10:4:1 ration).
93
A triple acid combination destroys the organic matter in a shorter time without any
hazard. But the method is unsatisfactory for plant materials with high Ca and in
cases where S is one of the test elements. The insoluble sulphate renders the
method unsuitable because of adsorption of different element ions on the precipitate
and exclusion of Ca from the analysis. The use of perchloric acid in the di- or triple
acid digestion mixtures results in the formation of sparingly soluble potassium
perchlorate, resulting in lower estimates of K, especially when the plant material
contains K, more than 1%. As such for multi element analysis, the plant materials
should be digested in nitric acid alone.
Wet oxidation digestion reagents and their applicability
Sr. No. Reagents Applicability to Remarks
organic manure
1 H2SO4/HNO3 Vegetable origin Most commonly used
2 H2SO4/H2O2 Vegetable origin Not very common
3 HNO3 Biological origin Easily purified reagent, short
digestion time, temperature 350
0C
4 H2SO4/HClO4 Biological origin Suitable only for small samples,

danger of explosion
5 HNO3/HClO4 Protein, carbohydrate Less explosive
(no fat)
6 HNO3/ Universal (also fat No danger with exact
HClO4/H2SO4 and carbon black temperature control
4. Interpretation of results: The basis for plant analysis as a diagnostic technique

is the relationship between nutrient concentration in the plant and growth and
production response. This relation should be significant to have complete
interpretation in teem of deficient, adequate and excess nutrient concentration in the
plant. Curves representing the relationship between nutrient concentration and
growth response vary in shape and character depending on both the nutrient
concentration in the growth medium and the plant species.
1 2 3 4 5
100
elative growth or production
0
80
60
Critical deficiency
Critical toxicity
% maximum
40
20
value
value
94
1. Deficient 2. Marginal 3. Adequate 4. Excess 5. Toxic

When nutrients are in deficiency range, plant growth and yield are significantly
reduced and foliar deficiency symptoms appear. In this range, application of nutrient
results in sharp increase in growth. In marginal range, growth or yield is reduced, but
plant does not show deficiency symptoms. Sometimes the marginal range is also
called transition zone. Within the marginal or transition zone lies the critical level or
concentration. The critical level can be defined as that concentration at which the
growth or yield begins to decline significantly.
Rapid tissue tests:

These tests are rapid and are essentially qualitative. The nutrients are
absorbed by roots and transported to those parts of plants where they are needed.
The concentration of cell sap is usually good indication of how well the plant is
supplied at the time of testing.The plant parts, usually leaves are removed and plant
sap is extracted. The plant sap is usually tested for nitrate, phosphorus and
potassium. The use of specific reagent for each nutrient to be tested develops the
colour. The intensity of colour is a qualitative measure of the content of the nutrient.
DRIS approach
Recently Diagnosis Recommendation Integration System (DRIS) is suggested
for fertilizer recommendation. In this approach, plant samples are analyzed for
nutrient content and they are expressed as rations of nutrients with others. Suitable
ratios of nutrients are established for higher yields from experiments and plant
samples collected from farmer's fields. The nutrients whose ratios are not optimum
for high yields are supplemented by top dressing. This approach is generally suitable
for long duration crops, but it is being tested for short duration crops like soybean,
wheat etc.
8.3 Biological tests

95
The biological methods consist of raising a crop or a microbial culture in a

field or in a sample of the soil and estimating its fertility from the volume of crop or
microbial count. Although these methods are direct estimates of soil fertility, they are
time consuming and therefore, not well adapted to the practice of soil testing.
(i) Field tests: The field plot technique essentially measures the crop response
to nutrients. In this, specific treatments are selected, randomly assigned to an area
of land, which is representative of the conditions. Several replications are used to
obtain more reliable results and to account for variation in soil. Field experiments are
essential in establishing the equation used to provide fertilizer recommendation that
will optimize crop yield. Maximum profitability, and minimize environment impact of
nutrient use
(ii) Pot culture tests: The pot culture test utilize small quantities of soil to quantify
the nutrient supplying power of a soil. Selected treatments are applied to the soils
and a crop is planted and evaluated. Crop response to the treatments can be than
determined by measuring total plant yield and nutrient content
(iii) Laboratory tests
(a) Neubauer seedling Method: the neubaur technique is based on the uptake of
nutrient by growing a large number of plants on a small amount of soil. The
seedlings (plants) exhaust the available nutrient supply within short time. The total
nutrients removed are quantified and tables are established to give the minimum
values of nutrients available for satisfactory yield of various crops.
(b) Microbial methods: In the absence of nutrients, certain microorganisms
exhibits behaviour similar to that of higher plants. For example, growth of
Azotobacter or Aspergillus niger reflacts nutrient deficiency in the soil. The soil is
rated from very deficient to not deficient in the respective elements, depending on
the amount of colony growth. In comparison with methods that utilize higher
plants, microbiological methods are rapid, simple and require little space. These
laboratory tests are not in common use in India.
8.4 Nutrient deficiency symptoms of plant
As already mentioned, the plant requires sixteen essential nutrients for their
optimum growth and development. When a plant badly needs a certain nutrient
element, it shows deficiency symptoms. These symptoms are nutrient specific and
show different patterns in crops for different essential nutrients. It is good tool to

96
detect deficiencies of nutrient in the field but these techniques have several
limitations and are:
1. The visual symptoms may be caused by more than one nutrient.
2. Deficiency of one nutrient may be related to an excess quantity of another.
3. It is difficult to distinguish among the deficiency symptoms in the field, as disease
or insect damage can be resemble certain micronutrient deficiencies.
4. Nutrient deficiency symptoms are observed only after the crop has already
suffered an irreversible loss.There are some indicator plants which shoes the
nutrient deficiencies or excesses. Some of them are given as follows:
Plant Nutrient deficiency/toxicity

Oat : Mg, Mn and Cu deficiencies
Wheat and barley : Mg, Cu and some times Mn deficiencies
Sugar beets : B and Mn deficiencies
Maize : N, P, K, Mg, Fe, Mn and Zn deficiencies
Potatoes : K, Mg and Mn deficiencies
Brassica species : K and Mg deficiencies
Celery and sunflower : B deficiency
Cauliflower : B and Mo deficiencies
Barley : B, Mn and Al toxicities
Cucumber : N and P excess
**************

97
CHAPTER- IX: FERTILIZER RECOMMENDATIONS AND

APPLICATION
9.1 Blanket Recommendation

Based on the fertilizer experiments conducted in different regions with
improved varieties, fertilizer dose is recommended for each environment.
This approach does not consider soil contribution. However, it is suitable for
recommendation of nitrogen since residual effect of fertilizer N applied to previous
crop is negligible and soils are generally low in nitrogen content.
Problem: Let the recommended fertilizer dose for low land rice be, 120, 60, 40kg N-
P2O5 and K2O per hectare, respectively. The amount of fertilizer required in the form
of urea, single super phosphate (SSP) and muriate of potash (MOP) is calculated as
shown below:
Urea contain 46%N
To supply 46kg N, 100kg urea is necessary
100
To supply 120kg N/ha, x 120 =260.9 kg or 261 kg urea is required
46
Similarly,
SSP contain 16% P2O5
100
To supply 60kg P2O5/ha, x 60 =375kg SSP is required
16
MOP contain 58% K2O
100
To supply 40kg K2O/ha, x 40 =68.9 or 69kg MOP is required
58
Problem: In above example, fertilizer dose of paddy is 120, 60, 40kg N-P2O5 and
K2O per hectare, respectively. The recommendation of fertilizer is given below
► Nutrient application
Category N P2O5 K2O
Low 150 75 50
Medium 120 60 40
High 90 45 30
Fertilizer application
Category Urea SSP MOP
Low 326 469 86
Medium 261 375 69
High 196 281 52
9.2 Soil Test Crop Response (STCR) Approach

98
In this approach, soil contribution and yield level are considered for
recommending fertilizer dose. This approach is also called as rationalized fertilizer
prescription. From the soil test crop response experiments, following parameters are
available.
Nutrient requirement : Total uptake of nutrient (kg/ha)
(kg nutrient/q of Grain yield (q/ha)
grain)
Total uptake of nutrient in control
% contribution from soil plot(kg/ha)
: x 100
(CS) Soil test value of nutrient
In control plot (kg/ha)
Total uptake of Soil test value of CS

Contribution from
: nutrient inTreated - nutrient In treated plot x
fertilizer (CF) 100
plot (kg/ha)
% Contribution from CF (kg/ha)

: x 100
fertilizer Fertilizer dose
Nutrient requirement in % contribution
kg/q of grain x100 from soil STV
Fertilizer dose(kg/ha) : x T - x
% Contribution from % contribution (kg/ha)
fertilizer from fertilizer
Fertilizer dose (kg/ha): Constant(kg/ha)x T(q/ha)- Constant x STV(kg/ha)
Based on this, fertilizer recommendations are developed for different regions.

One such equation developed to recommend P and K, fertilizers for sugarcane in
south Gujarat is given below:
Dose of P2O5 (kg/ha) = 2.24T - 3.97 x STV for available P2O5
Dose of K2O (kg/ha) = 2.67T - 0.383 x STV for available K2O
Nutrient use efficiency (NUE):
"Nutrient use efficiency defined as yield (biomass) per unit input (Fertilizer,
nutrient content)". The nutrient most limiting plant growth are N, P,K and S. NUE
depends on the ability to efficiently take up the nutrient from the soil, but also on
transport, storage, mobilization, usage within the plant and even on the environment.
Two major approaches may be taken to understand NUE. Firstly, the response of
plants to nutrient deficiency stress can be explored to identify processes affected by
such stress and those that may serve to sustain growth at low nutrients input. A
second approach makes use of natural or induced genetic variation.

99
Increasing nutrient efficiency is the key to the management of soil fertility. The
proportion of the added fertilizer actually used by plants is a measure of fertilizer
efficiency. Soil characteristics, crop characteristics and fertilizer management
techniques are the major factors that determine fertilizer efficiency.
9.3 Factors influencing nutrient use efficiency (NUE)

9.3.1 Soil characteristics
(1) Nutrient Status of Soil: The response of any crop or a cropping system to
added nutrient depends largely upon the inherent capacity of soil to supply that
nutrient as per the requirement of crop. In a low nutrient soil, the crop responds
remarkably to its application. On the other hand, in a high nutrient soil, the crops may
show little or no response. In medium test soil, the response is intermediate. Soil
testing helps in adjusting the amount of fertilizer and thus improves the efficiency of
fertilizers use. By demarcating the areas responding differently to different plant
nutrients, right type and proper amount of fertilizers can be applied to them.
(2) Nutrient Losses and Transformations: The amounts of nutrients estimated by
soil tests may not be entirely available to plants because of their leaching,
volatilization, denitrification and transformations to unavailable forms. Leaching
losses are important for nitrate nitrogen because it is not held by exchange sites in
the soil, it is lost. Such losses are of particular significance in sandy soils and in
situations if heavy rain or irrigation follows its application. In acid soils, leaching
losses of calcium, sulphate, potassium and magnesium are more common.
Volatilization of ammonia in high pH surface soils is considerable when urea is
applied at the surface. Denitrification loss of nitrogen mainly occus under
waterlogged conditions prevailing during rice cultivation, particularly under higher
temperatures and in the presence of easily decomposable organic materials.
The conversion of a portion of available nutrients into insoluble mineral forms
is also important. Thus, the efficiency of added phosphorus is 20 to 30 per cent.
Microbial immobilization also converts temporarily the soluble forms of nutrients into
unavailable forms. Similarly, the efficiency of zinc applied to soil is less than 3%.
Soil characteristics play a dominant role in the transformation of nutrients. Soil
reaction (pH) is one of the important soil properties that affects plant growth. The
harmful effects of soil acidity are more due to secondary effects except in extreme
case. The important secondary effects of high acidity or low pH in a soil are the
inadequate supply of available calcium, phosphorus and molybdenum on one hand
100
and the excess of soluble aluminum, manganese and iron on the other. Likewise, in
saline-alkali soil, the deficiency of Ca, Mg, P, Zn, Fe and Mn is very common. The
fertilizers practices are, therefore, to be modified accordingly for soils with different
soil reactions. The main aim of liming of acid soils and addition of gypsum to alkali
soils is to change the soil pH suitable for the availability of most plant nutrients.
(3) Soil Organic Matter: Soil organic matter content is generally considered as the
index of soil fertility and sustainability of agricultural systems. It improves the
physical and biological properties of soil, protects soil surface from erosion and
provides a reservoir of plant nutrients. In tropics, the maintenance of soil organic
matter is very difficult because of its rapid decomposition under high temperatures.
The cultivation of soils generally decreases its organic carbon content because of
increased rate of decomposition by the current agricultural practices. In cultivated
soils, prevalent cropping system and associated cultural practices influence the level
at which organic matter would stabilize in a particular agro-eco-system. Long-term
fertilizer experiments have shown that the integrated use of organic manures and
chemical fertilizers can maintain high productivity and sustainable crop production.
Recent studies have indicated that a periodic addition of large quantity of crop
residue to the soil maintains the nitrogen and organic matter at adequate levels even
without using legumes in the rotation. The application of FYM, compost and cereal
residues effectively maintains the soil organic matter. There is a significant increase
in soil organic matter due to incorporation of rice or wheat straw into the soil instead
of removing or burning it. Yields are, however, low in residue incorporated
treatments due to wide C:N ratio of the residues. This ill effect, however, can be
avoided if the rice straw is incorporated at least 20 days before seeding wheat.
(4) Soil moisture: Fertilizer application facilitates root extension into deeper layers
and leads to grater root proliferation in the root zone. Irrigated wheat fertilized with
nitrogen used 20-38 mm more water than the unfertilized crop on loamy sand and
sandy loam soils and increased dry matter production Soil moisture also affects root
growth and plant nutrient absorption. The nutrient absorption is affected directly by
soil moisture and indirectly by the effect of water on metabolic activities of plant, soil
aeration and concentration of soil solution. If soil moisture becomes a limiting factor
during critical stage of crop growth, fertilizer application may adversely affect the
yield.

101
(5) Physical Conditions of Soil: Despite adequate nutrient supply, unfavorable

physical conditions resulting form a combination of the size, shape, arrangement and
mineral composition of the soil particles, may lead to poor crop growth and activity of
microorganisms. Soil nitrogen generally increases as the texture becomes finer. The
basic requirements for crop comes finer, The basic requirements for crop growth in
terms of physical conditions of soil are adequate soil moisture and aeration, optimum
soil temperature and freedom from mechanical stress. Tillage, mulching, irrigation,
incorporation of organic matter and other amendments like liming of acid soils and
addition of gypsum to sodic soils are the major field management techniques that
aim at creating soil physical environment suitable for crop growth. Tillage affects
water use by crops not only through its effect on root growth but also affects the
hydrological properties of soils. Mulching with residues, plastic film etc., influences
evaporation losses from soil by modifying the hydro-thermal regime of the soil and
affects root growth and rooting pattern. Use of organic mulch also decreases
maximum soil temperature in summer and increases minimum soil temperature in
winter and help in the conservation of soil moisture.
9.3.2 Crop Characteristics
(i) Nutrient Uptake: The total amount of nutrients removed by a crop may not serve
as an accurate guide for fertilizers recommendations; it does indicate the differences
in their requirement among crops and the rate at which the nutrients reserves in the
soil are being depleted. The nutrient uptake may vary depending upon the crops and
its cultivars, nutrient level in the soil, soil type soil and climatic conditions, plant
population and management practices. It is estimated that 8t of rice grain remove
160 kg N, 38 kg P, 224 kg K, 24 kg S and 320 g Zn as compared to a removal of 125
kg N, 20 kg P, 125 kg K, 23 kg S and 280 g Zn by 5t of wheat from one hectare field.
(ii) Root Characteristics: Roots are the principal organs of nutrient absorption. A
proper understanding of their characteristics helps in developing efficient fertilizer
practices. The absorption of nutrients depends upon the distribution of roots in soil.
The shallower the root system, the more dependent the plant is on fertilizers. Hence,
any soil manipulation, which encourages deep rooting, will encourage better
utilization of fertilizers. It is well known that some plants are better scavengers of
certain nutrients than others. This is mainly because of the preferential absorption of
these nutrients by the roots of those plants. For example, legumes have a marked

102
preference for divalent cations like Ca2+ whereas grasses feed better on monovalent
cations like K+.
The efficiency of the applied fertilizer can be improved considerably if the
rooting habits of various plants during early growth stages are known. This is
particularly true for relatively immobile nutrients and for situations where the fixation
of applied nutrients is very high. If a plant produces tap root system early, fertilizer
can best be placed directly below the seed. On the other hand, if lateral roots are
formed early, side placement of fertilizer would be helpful.
Mycorrhizal fungi often associated with plant roots, increase the ability of
plants to absorb nutrients particularly under low soil fertility. However, fertilizer
additions generally reduce their presence and activity.
9.3.3 Crop Rotation: The nature of cropping sequence has a profound effect on the
fertilizer requirement and its efficiency. Crops are known to differ in their feeding
capacities on applied as well as native nutrients. The crops requiring high levels of
fertilizers such as maize, potato may not use the applied fertilizers fully and some
amount of the nutrient may be left in the soil which can be utilized by the succeeding
crop. Phosphorus, among the major nutrients, is worthy of consideration because
only less than 20 per cent of the applied phosphatic fertilizer is utilized by the first
crop. Similarly, less than 3% of the applied zinc is used by the first crop. The
magnitude of the residual effect is, however, dependent on the rate and kind of
fertilizer used, the cropping and management system followed and to a great extent
on the type of soil. Crops have a tendency of luxury consumption of N and K and
may not leave any residual effect unless doses in excess of the crop requirement are
applied. On the other hand, if sub-optimal doses of fertilizers are applied to a crop,
they may leave the soil in a much exhausted condition and the fertilizer requirement
of the succeeding crop may increase. The legumes leave nitrogen rich root residues
in the soil for the succeeding crop and thus reduce its nitrogen requirement.
9.4 Methods of fertilizer application
An important item in efficient use of fertilizer is that of placement in relation to
plant.
(1) Solid fertilizers
Broadcasting is the method of application of fertilizer uniformly over the entire
field. It may be at planting or in standing crop as top dressing.
(i) Broadcasting at planting is adopted under certain conditions.

103
1. Soils highly deficient, especially in nitrogen,

2. Where fertilizers like basic slag, dicalcium phosphate, bone meal and rock
phosphate are to be applied to acid soils, and
3. When potassic fertilizers are to be applied to potash deficient soils.
(ii) Top dressing is application of fertilizer to the standing crop. Usually, nitrate
nitrogen fertilizers are top dressed. Depending on the duration of the crop and soil
type, top dressing may be more than one to meet the crop needs at times of greatest
need of the crop.
(iii) Placement: Fertilizers are placed in the soil either before sowing or after sowing
the crop.
(a) Plough-sole placement consists of placing the fertilizer in a continuous band at
the bottom of the furrow during the process of ploughing, which is usually covered by
the next furrow adjacent to it.
(b) Deep placement is application of fertilizers, especially nitrogen, in the reduced
zone to avoid nitrogen losses in low land rice.
(c) Localized placement: In this method fertilizer are applied close to the seed or
plant. It is usually adopted when relatively small quantizes of fertilizers are be
applied.
(d) Contact placement or drill placement refers to drilling seeds and fertilizer
simultaneously at sowing. Care must be taken to place the seed and fertilizer at
different depths to avoid salt injury to the germinating seed.
(e) Band placement consists of applying the fertilizer in continuous bands, close to
the seed or plant. This method is ideal for crops grown in wide space i.e., cotton,
castor, sugarcane, tobacco, maize etc.
(f) Pellet placement is application of fertilizer, especially nitrogen in pellet from in
the low land rice avoid nitrogen loss from applied fertilizer.
(2) Liquid Fertilizers
(i) Starter solution: These are solutions of fertilizers prepared in low concentrations
used for soaking seed, dipping roots or spraying on seedlings for early establishment
and growth.
(ii) Foliar application: This method, nutrients are applied are to the standing crops
in the from of spray for quick recovery from the deficiency. It avoids fixation of
nutrients in the soil.

104
In the case of calcium, transport from roots to fruit is limited, so foliar

applications are the best method we know of go get more calcium into fruit tissue to
reduce post harvest disorders. The expense of the calcium sprays is more than
justified by the potential post-harvest losses.
If soil pH limits nutrient availability, and ground applied fertilizes are not taken
up, foliar fertilizers may be a valid option. In this case, a soil sample should be taken
to determine pH, and a leaf tissue sample taken to determine the need for addition
foliar fertilization. In some cases poor root health from compaction, replant disease,
crown rot, mouse damage, water logging or other problem may warrant foliar feeding
of trees. However, the fertilizer in the required amount cannot be phototoxic as a
foliar spray, and uptake must have been demonstrated with the product under
consideration.
Zinc uptake deserves special attention. In our soils zine is largely immobile
and it is difficult to supply roots with adequate amounts of available Zn. As a result of
limited soil availability, zine is applied as a foliar spray. Research has shown that
only a small amount of Zn can be taken up by leaves, however foliar application are
still more successful than soil applied Zn.
(iii) Soil application: Liquid fertilizer such as anhydrous ammonia are applied
directly to the soil with special injecting equipment. Liquid manures such as urine,
sewage water and shed washing are directly let into the field.
(iv) Fertigation: This is the application of fertilizer in irrigation water in either open or
closed system. The open system includes lined and unlined open ditches and gated
pipes that are used for furrow and flood irrigation. Sprinkler and trickle systems are
main closed systems. Nitrogen and sulphur are the principal nutrients applied by
fertigation.
The fertigation allows to apply the nutrients exactly and uniformly only to the
wetted root volume, where the active roots are concentrated. This remarkably
increases the efficiency in the application of the fertilizer, which allows reducing the
amount of applied fertilizer. This not only reduces the production costs but also
lessens the potential of groundwater pollution caused by the fertilizer leaching.
Other advantage of the fertigation are: (1) the saving of energy and labor, (2)
the flexibility of the moment of the application (nutrients can be applied to the soil
when crop of soil conditions would otherwise prohibit entry into the field with
conventional equipment), (3) convenient use of compound and ready-mix nutrient

105
solutions containing also small concentrations of micronutrients which are otherwise

very difficult to apply accurately to the soil, and (4) the supply of nutrients can be
more carefully regulated and monitored. When fertigation is applied through the drip
irrigation system, crop foliage can be kept dry thus avoiding leaf burn and delaying
the development of plant pathogens.
Fertilizers management under rainfed conditions:
In dryland agriculture, limited water availability is usually the factor that
ultimately limits crop production. However, it is not unusual for limited availability of
one or more soil nutrients to further decrease production potential. Often, the effects
of water and nutrient deficiencies are additive. Because soil used under dryland
agriculture are developed under widely varying conditions, their ability to supply
nutrients is highly variable.
Fertilizer practices greatly affect nutrient cycling and availability in rainfed
conditions. Because of frequent dry periods, placement of soluble fertilizers with the
seed is extremely hazardous in dryland soils. The higher rates of fertilizer application
may result in high osmotic potentials near the germinating seed. For oil crops,
applying no fertilizer N with the seed is usually recommended. however, up to 20 to
30 kg P/ha can be applied with the seed because of the considerably lower solubility
of most P fertilizer. It is also reported that P availability is particularly critical for an
eroded soil. In dryland soils, the surface layers often remain dry for a major part of
the growing season. Such a condition might suggest that fertilizers should be placed
deeper in the region of the active root zone for more of the growing season.
Timing of fertilizer application could also affect nutrient cycling. Applying N
fertilizers near the time of maximum N uptake rate of the crop results in the most
efficient uptake of the fertilizer. Fertilizer sources also determine the growth the
crops under rainfed conditions. Most dryland experiments showed that ammonium
nitrate is usually one of the most efficient N sources for dryland crops. At the other
extreme, these experiments showed that urea is the least efficient form of N
fertilizers. One must exercise considerable caution when using urea on dryland to
avoid excessive losses by ammonia volatilization.
By concentrating the urea (liquid or solid) in a band or pellets, surface contact
is reduced, reducing volatilization. Injecting or incorporating urea beneath the soil
surface is by far the best way in which to apply this material to dryland soils.
**************

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1

COURSE NO.: AG.CHEM.3.2

1. Manures and Fertilizes (1992), Seventh Edition by K. S. Yawalkar, J. P.

Dr. S. M. Bambhaneeya (Ph.D.- Soil Science)

CHAPTER- I: ORGANIC MANURES

Difference between manures and fertilizers:

Dr. S. M. Bambhaneeya (Ph.D.- Soil Science)

Effect of bulky organic manures on soil:

i) Direct effect on plant growth

FYM is one of the most important agricultural by products. Unfortunately,

(I) Losses during handling:

Dr. S. M. Bambhaneeya (Ph.D.- Soil Science)

i) Loss of liquid portion or urine

NH2 CO NH2 + 2H2O (NH4)2CO3

(NH4)2 CO3 + 2H2O 2NH4OH + H2 CO3

(II) Loss during storage:

During storage considerable amount of NH3 is produced in the manure heap

compounds in urine and dung NH3

2. 2NH3 + H2CO3 (NH4)2 CO3

3. (NH4)2 CO3+2H2O 2NH4 OH+H2CO3

4. NH4OH NH3 + H2O

Loss of NH3 increases with

Among these methods are described here under:

i) Trench method of preparing FYM

Dr. S. M. Bambhaneeya (Ph.D.- Soil Science)

ii) Use of gobar gas-compost plant

Methane gas is generated due to anaerobic fermentation of the most common

1000 Kg fresh dung manure obtained by

Dr. S. M. Bambhaneeya (Ph.D.- Soil Science)

Chemical preservatives are added to the FYM to decrease N losses. To be

(NH4)2 CO3 + CaSO4 CaCO3 + (NH4)2 SO4

Superphosphate has been extensively used as a manure preservative:

1. It will reduce loss of N as ammonium from FYM.

Supply of plant nutrients through FYM:

On an average, FYM applied to various crops by the cultivators contains the

Dr. S. M. Bambhaneeya (Ph.D.- Soil Science)

% N : 0.5 % P2O5 : 0.2 % K2O : 0.5

Based on this analysis, an average dressing of 10 tones of FYM supplies

Mechanical Composting Plants:

Factors controlling process of decomposition:

1) Food supply to micro-organisms and C : N ratio:

The suitable ratio of carbonaceous to nitrogenous materials is 40, if it is wider

About 60-70 per cent moisture is considered to be the optimum requirement

The microorganisms liberate certain organic acids during the course of

A neutral or slightly alkaline reaction between pH 7.0 and 7.5 is considered

Heap V/S Pit decomposition:

2. Turning is required 2. No turning is required

3. Physical disintegration 3. Very little physical disintegration

4. Quick oxidation 4. Slow rate of decomposition

Dr. S. M. Bambhaneeya (Ph.D.- Soil Science)

organisms due to toxic products of

6. Loss of OM is about 50% 6. Loss is about 25%

7. If not properly protected, 7. Moisture loss is minimized. No

8. If rainfall is high, leaching takes 8. Protected from leaching but

Dr. S. M. Bambhaneeya (Ph.D.- Soil Science)

cycle of 40-45 days. The length of shed can be increased/decreased depending

 Vermicompost is an ecofriendly natural fertilizer prepared from

Improved methods of handling night soil: