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. 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 –

trichloromethyl pyridine)

0.15 – 0.5 Kg/ha

AM

(2 – Amino-4-chlore-6-

methyl pyridine)

0.3 – 0.4% (of applied fertilizer)

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

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

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.

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 13c the uptake of N from NH4 or NO3

fertilizers is almost nil. Maximum uptake of N by plants from NO3 and NH4

fertilizers is observed in the range of 19 - 24c. The influence of

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 10-35c 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 – 28c.

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

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.

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.

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.