Fertilizer Use Efficiency; Soil, Plant and Fertilizer Characters

1. FERTILIZER USE EFFICIENCY
M. Dhakshinamoorthy, Professor of Soil Science, Tamil Nadu
Agricultural University, Coimbatore
…
Based on the nutrient supplying power of soils as determined by soil
test values, fertilizer recommendations are made. The aim is to get
maximum economic yield with minimum inputs. Of the various inputs
fertilizer is the costly input. This costly input must be efficiently used and
utilised. In order to get maximum benefit i.e. higher efficiency from
fertilizers the following aspects must be considered.
1. Correct choice of fertilizers from a wide selection of fertilizers
having different chemical and physical characteristics and
2. The fertilizer recommendation based on nutrient supplying
power of soils and by specific soil, plant and climatic factors.
Fertilizers are considered as efficient when maximum yield is obtained
with minimum possible amount of fertilizer application. It is indeed difficult
to quantify the efficiency of a particular fertilizer since it depends on
1. Losses due to leaching
2. Losses in gaseous forms
3. immobilization by chemical precipitation, adsorption on
exchange complex and microbial cells.
4. chemical reactions between various components in fertilizers
during mixing, before application to soil.
5. physical properties of soil
6. chemical properties of soil
7. Fertilizer characteristics.
The above factors emphasise the following practical points (i.e. to get
maximum benefit from fertilizer)
1. Right type of fertilizers with favourable chemical and physical
properties.

2. 2. Timely application of fertilizers (time of application should
synchronise with the rapid crop uptake period and there should
be only a minimum time for soil fertilizer interaction)
3. Correct quantities of fertilizers based on the nutrient supplying
power of soils and crop need.
4. Right method of application.
Leaching losses: Nitrate fertilizers are easily lost in leaching. The extent
of leaching is more in sandy soil than in clayey soils. The loss is more in bare
soil than cropped soil. The losses can be reduced to and extent by suitable
method and timing of application.
Losses in leaching also occur when ammoniacal calcium cyanamide
and urea fertilizers are applied to soils. In extreme acid soils or sandy acidic
soils, ammonium fertilizer are lost because ammonium ions cannot easily
replace the aluminium ions in exchange sites. In alkali soils ammonium ions
are subjected to volatile loss. During summer losses from the ammoniacal,
calcium cyanamide and urea are more because they are rapidly oxidized by
nitrifying organisms. Recents works at TNAU show that when urea mixed
with nee seed crush is applied to paddy soil, the efficiency of urea is more.
The activity of nitrifying organism is reduced and thereby the leaching loss is
minimized. There are also some chemical compounds when applied with
nitrogen fertilizers inhabits the nitrifying organisms and reduces the leaching
loss.
Name Qty. to be added
N- Serve
(2 – chloro – 6 – 0.15 – 0.5 Kg/ha
trichloromethyl pyridine)
AM
(2 – Amino-4-chlore-6- 0.3 – 0.4% (of applied fertilizer)
methyl pyridine)
Thiourea 1.5 – 2.5% (of applied fertilizer)
Applied potassic fertilizers are easily lost in drainage water in sandy
soils and acid soils. However in clayey soils there is no appreciable loss. The

3. loss can be minimized by adjusting the time of application to synchronise
with maximum plant uptake period and also applying the fertilizer in 2 or
more split doses. There are some slow release potassic fertilizers which are
not subjected to leaching losses easily. E.g. potass frits, potassium
metaphosphate and fused potassium phosphate.,
Practically no leaching loss occurs from phosphatic fertilizers
Gaseous losses: The nitrogen compounds present in the fertilizer are lost
as gases under certain soil condition. The following kinds of gaseous losses
are noted.
1. Loss as ammonia under high pH conditions i.e. under alkaline
conditions.
2. Loss as N2, N2O, NO due to denitrification.
3. Loss as N2, N2O, or NO under nitrification of ammonium
fertilizers. The above losses are determined by soil pH, fresh
organic matter, moisture, temperature and type of micro-
organisms present in soil.
Losses in the form of ammonia under high pH conditions can be
controlled by proper placement of urea. As far as possible ammonium
fertilizer should be avoided. If there is no alternative to ammonium
fertilizers, the fertilizer should be placed at least 4-6 below the surface.
Wherever loss of N by denitrification processes is observed, urea
should be used instead of ammonium and nitrate fertilizer.
Preliminary studies at Tamil Nadu Agrl. University have indicated that
mixing the fertilizer with neem seed crush (4:5:1) can effectively reduce the
third type of loss.
Immobilization of fertilizer nutrients:
Nutrient elements may be immobilized or fixed or converted into
unavailable forms by one or more of the following three means
1. chemical immobilization
2. physicochemical immobilization
3. microbiological immobilization

4. In selecting the fertilizer care should be taken to select such a type of
fertilizer which will have minimum interaction with soil and the time and
mode of application should be such as to ensure minimum immobilization of
nutrients contained in the fertilizers.
Ammonium and potassium ions in fertilizer may be immobilized by
strong adsorption by 2:1 type clay minerals. High soil pH enhances this type
of fixation. Practical means of reducing the fixation and increasing the
efficiency of fertilizer under these conditions are
1. timely application of fertilizers
2. proper placement of fertilizer
3. application of nitrate fertilizers
4. application of relatively insoluble potassium fertilizers and
5. increasing he dosages of fertilizers.
In acid soils, the efficiency of water soluble phosphotus is very low.
The water soluble phosphorus is immediately converted into insoluble
phosphorus compounds. In such soils insoluble phosphatic fertilizer like rock
phosphates should be utilised. Further a thorough mixing of the phosphorus
with soil increases the efficiency of the fertilizers.
In calcareous soils applied phosphatic fertilizers invariably converted in
to tricalcium phosphate – a compound from which phosphorus is not easily
available. Under such conditions water soluble phosphorus are relatively
more efficient than water insoluble P like rock phosphate.
Microbiological fixation of fertilizer N may be a serious problem when
un-decomposed organic materials of high C/N ratio is present in the soil.
This type of immobilization is of short duration only. It can be overcome by
application of larger quantities of water soluble N fertilizers or by allowing
enough time for complete decomposition of undecomposed organic matter.
Interaction between different fertilizers:
It is often a common practice to mix fertilizers containing different
nutrient carriers, just prior to application. The efficiency of the following
fertilizers will be lowered if mixed with the fertilizer or amendment noted
against them.

5. Ammonium sulphate - Basic slag
Ammonium sulphate - Calcium carbonate
Super phosphate - Basic slag
Ammonium phosphate - Basic slag
Ammonium phosphate - Calcium carbonate
Super phosphate - Calcium carbonate
Urea can be mixed with all fertilizers. Other fertilizers can be
mixed just before use.
Compaction and fertilizers efficiency:
Soil compaction brings about the soil particles closer resulting in the
decreased bulk density or apparent density. The porosity is changed
(decreased). Since the points of contact between soil particles are increased,
compaction also results in an increase of soil strength. Because of this, the
compacted soil holds higher amount of moisture at any suction greater then
60 millibars. Thus in fine textured soil, available water capacity of soil is
decreased due to compaction. The combined effect of the changes in
different physical properties of soils due to compaction, is the poor response
for nitrogen and phosphorus fertilizers. Under mechanized farming, soil
compaction is not an uncommon observation.
Soil temperature – Fertilizer response
Soil temperature is one of the important environmental factors
affecting plant growth and fertilizers response of crops. To and extent the
soil temperature is manoeurable by common management practices like
tillage, mulching and irrigation. Soil temperature affects the fertilizers
efficiency by changing solubility of fertilizers, concentration of solubilized
fertilizer cation exchange and also the ability of the plants to absorb and use
nutrients.
Nitrogen:
Variation in temperature causes differential response to crop uptake,
of NH4+ and NO3- - N fertilizers. Below 13°c the uptake of N from NH4 or NO3
fertilizers is almost nil. Maximum uptake of N by plants from NO 3 and NH4
fertilizers is observed in the range of 19° - 24°c. The influence of

6. temperature on the efficiency of fertilizer is dependent on soil moisture. This
aspect is dealt with separately.
Phosphorus:
The efficiency of phosphatic fertilizers increases significantly with the
increase in soil temperature from 10-35°c as evidenced by increased P
uptake by many plants with increase in temperature.
Potassium:
The effect of soil temperature on the uptake of K ions both from soil
potassium and fertilizer potassium is controversial. However, at low doses of
K fertilizers, there is possibility of increased uptake of K by plants with
increase in soil temperature up to 24 – 28°c.
Soil moisture:
One of the most singled out problem in agriculture is the lack and
excess of moisture. Efficient water management is complementary to
efficient fertilizer management. Maximum efficiency of fertilizers can be
obtained only in the presence of adequate soil moisture and vice versa.
Excessive moisture leads to leaching loss of added fertilizers whereas lack of
moisture results in poor availability of the added fertilizer and high osmotic
pressure of soil solution due to concentration of fertilizers soils.
Soil Chemical properties:
Some important aspects of soil chemical properties have already been
dealt with different kinds of immobilization. Some other properties which are
relevant to fertilizer use efficiency are mentioned below.
Plant nutrient availability depends on the prevailing pH of soil. In
strongly acidic and alkali soils the efficiency of phosphatic fertilizer is low. In
such situations, efficiency of fertilizers can be increased by correcting the
soil condition, using suitable amendments. Physiologically alkaline fertilizers
like calcium cyanamide basic slag etc. should receive priority on acid soils
and physiologically acid fertilizers like ammonium sulphate etc. on alkaline
soils.
Nutrient contents in the soil should be tested. There may me no
response at all to applied fertilizer if the initial nutrient content and its

7. availability are high. For example there are isolated patches in Tamil Nadu in
which there is no response for phosphatic and potassic fertilizers. However,
in such soils a nominal application of nutrients should be made in order to
maintain their fertility on long term basis.
The organic matter in soil not only supplies different nutrient elements,
but also improves physical conditions of soils, stimulates microbial activity,
protects the soil from erosion, retard the fixation of nutrients increases the
buffering capacity and helps in many other ways. These above benefits in
turn increases the efficiency of applied fertilizers.
Plant characteristics:
Different crops remove varied amount of plant nutrients from soils.
There is also appreciable variation within varieties of same plants, between
dicots and monocots etc. To get higher recovery from applied fertilizer,
recommendation of fertilizer doses should be made based on
1. Soil test values
2. Efficiency of available nutrients in soil
3. Crop requirement and crop characteristic
4. Efficiency of fertilizer to be applied
Since the roots are the principal organs through which plants take up
nutrients, the rooting pattern and habit have an important bearing on the
nutrient removal. Plants which develop a vigorous deep-root system during
their early stages of growth require a large quantity of fertilizer as basal
dressing. The fertilizer needs of deep rooted crops are generally lower than
shallow rooted crops.
Fertilizer characteristics:
The mobility of the fertilizer nutrients in the fertilizer, the type of
fertilizer and the time and mode of application decide the efficiency of a
fertilizer. The nitrogenous fertilizer are highly mobile and subjected both
downward and sideward mobility. Phosphorus is highly immobile.
Potassium is also mobile but compared to nitrogen its mobility is lower. To
get maximum efficiency N and K fertilizer should be applied in frequent split
doses and phosphorus as basal dressing or near the root zone.

8. Type of fertilizer also decide the efficiency. Ammonium and urea
fertilizer are more efficient for paddy under different Indian conditions than
nitrate fertilizers. Water soluble phosphorus materials are more efficient for
short duration crops and in soils which are neutral to alkaline is reaction.
There is also a certain amount of interaction noticed among crops and
fertilizers. For example paddy performs better when ammonium sulphate is
applied as N carrier and tobacco when potassium sulphate is applied as
potassium carrier.
Certain practical approaches to increase efficiency of fertilizers.
1. High yielding varieties of crops give higher yields than local varieties
without fertilization as well as a higher unit response to fertilizer even at the
lower rate of application. Therefore wherever possible, high yielding varieties
should be grown.
2. Deviation from normal planting or sowing time suited for a particular
crop variety in a particular locality will effect the efficiency of fertilizers.
3. Optimum plant spacing and maintenance of optimum plant population
are essential to get maximum benefit from the applied fertilizers.
4. Ensure effective organic matter recycling, in order to maintain fertility
and productivity. Response for a nutrient is generally higher in soils supplied
with adequate amount of organic matter.
5. While applying organic manures having high C:N ratio ensure that
adequate amount of nitrogenous fertilizers are applied to soils to compensate
biological locking up of N in microorganisms.
6. Include a legume either in rotational sequence or as a intercrop.
Legumes besides fixing atmospheric N, transform non-available native
phosphorus and precipitated or fixed fertilizer P into available forms.
7. Excessive irrigation should be avoided as it results in the loss of N and
K fertilizers. Further, there is also gaseous loss of N under waterlogged
condition. There should not be excess water in the soil particularly at the
time of fertilizer application. Fertilizer application should be made after
draining the excess water.

9. 8. Crop response to phosphatic fertilizers is generally more in dry
seasons.
9. Balanced fertilization should be practiced based on the soil test values.
Efficiency of a straight fertilizer containing nutrient) depends on the
sufficiency of other nutrient in the soil.
10. The phosphates in general are more efficient when the entire
dose applied as basal dressing, potash entire quantity as basal dressing or
part as basal and rest in split doses depending on the soil texture and the
nitrogen in 2-3 (or 4) split doses.
11. Water soluble phosphatic fertilizers should be placed 4-6 cm
below the soil and 4-6 cm away from the seeds to ensure maximum
availability to plants. Insoluble fertilizers should be thoroughly mixed in soil.
12. Sometimes it is better to cure the urea by mixing the urea with
5-10 parts of soil thoroughly and keeping the mixture for overnight. This
enhances the conversion rate of urea into ammonia carbonate.
13. Whenever N loss in drainage water is suspected due to
efficiency of the N fertilizer can be increased by mixing the fertilizer with
crushed neem seed (5:1 parts)
14. Foliar application of fertilizers should be resorted to under
certain soil conditions and climatic conditions.
15. Zinc deficiency is becoming more and more widespread day by
day. In such cases application of zinc sulphate at the rate of 10-25 kg of zinc
sulphate as basal dressing, not only corrects the zinc deficiency but also
enhances generally the efficiency of the other applied fertilizers.
16. Adverse soil condition should be corrected by using appropriate
amendments, to get maximum benefit from fertilizer.
17. Absence of weeds, pest and diseases ensures the efficiency of
fertilizer.