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 soiltest values, fertilizer recommendations are made. The aim is to getmaximum economic yield with minimum inputs. Of the various inputsfertilizer is the costly input. This costly input must be efficiently used andutilised. In order to get maximum benefit i.e. higher efficiency fromfertilizers 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 obtainedwith minimum possible amount of fertilizer application. It is indeed difficultto 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 extentof leaching is more in sandy soil than in clayey soils. The loss is more in baresoil than cropped soil. The losses can be reduced to and extent by suitablemethod and timing of application. Losses in leaching also occur when ammoniacal calcium cyanamideand urea fertilizers are applied to soils. In extreme acid soils or sandy acidicsoils, ammonium fertilizer are lost because ammonium ions cannot easilyreplace the aluminium ions in exchange sites. In alkali soils ammonium ionsare subjected to volatile loss. During summer losses from the ammoniacal,calcium cyanamide and urea are more because they are rapidly oxidized bynitrifying organisms. Recents works at TNAU show that when urea mixedwith 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 isminimized. There are also some chemical compounds when applied withnitrogen fertilizers inhabits the nitrifying organisms and reduces the leachingloss. 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 sandysoils and acid soils. However in clayey soils there is no appreciable loss. The
loss can be minimized by adjusting the time of application to synchronisewith maximum plant uptake period and also applying the fertilizer in 2 ormore split doses. There are some slow release potassic fertilizers which arenot subjected to leaching losses easily. E.g. potass frits, potassiummetaphosphate and fused potassium phosphate., Practically no leaching loss occurs from phosphatic fertilizersGaseous losses: The nitrogen compounds present in the fertilizer are lostas gases under certain soil condition. The following kinds of gaseous lossesare 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 becontrolled by proper placement of urea. As far as possible ammoniumfertilizer should be avoided. If there is no alternative to ammoniumfertilizers, the fertilizer should be placed at least 4-6 below the surface. Wherever loss of N by denitrification processes is observed, ureashould be used instead of ammonium and nitrate fertilizer. Preliminary studies at Tamil Nadu Agrl. University have indicated thatmixing the fertilizer with neem seed crush (4:5:1) can effectively reduce thethird type of loss.Immobilization of fertilizer nutrients: Nutrient elements may be immobilized or fixed or converted intounavailable 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 offertilizer which will have minimum interaction with soil and the time andmode of application should be such as to ensure minimum immobilization ofnutrients contained in the fertilizers. Ammonium and potassium ions in fertilizer may be immobilized bystrong adsorption by 2:1 type clay minerals. High soil pH enhances this typeof fixation. Practical means of reducing the fixation and increasing theefficiency 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 insolublephosphorus compounds. In such soils insoluble phosphatic fertilizer like rockphosphates should be utilised. Further a thorough mixing of the phosphoruswith soil increases the efficiency of the fertilizers. In calcareous soils applied phosphatic fertilizers invariably converted into tricalcium phosphate – a compound from which phosphorus is not easilyavailable. Under such conditions water soluble phosphorus are relativelymore efficient than water insoluble P like rock phosphate. Microbiological fixation of fertilizer N may be a serious problem whenun-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 byapplication of larger quantities of water soluble N fertilizers or by allowingenough time for complete decomposition of undecomposed organic matter.Interaction between different fertilizers: It is often a common practice to mix fertilizers containing differentnutrient carriers, just prior to application. The efficiency of the followingfertilizers will be lowered if mixed with the fertilizer or amendment notedagainst 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 bemixed just before use.Compaction and fertilizers efficiency: Soil compaction brings about the soil particles closer resulting in thedecreased 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, thecompacted soil holds higher amount of moisture at any suction greater then60 millibars. Thus in fine textured soil, available water capacity of soil isdecreased due to compaction. The combined effect of the changes indifferent physical properties of soils due to compaction, is the poor responsefor nitrogen and phosphorus fertilizers. Under mechanized farming, soilcompaction is not an uncommon observation.Soil temperature – Fertilizer response Soil temperature is one of the important environmental factorsaffecting plant growth and fertilizers response of crops. To and extent thesoil temperature is manoeurable by common management practices liketillage, mulching and irrigation. Soil temperature affects the fertilizersefficiency by changing solubility of fertilizers, concentration of solubilizedfertilizer cation exchange and also the ability of the plants to absorb and usenutrients.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 NO3fertilizers is almost nil. Maximum uptake of N by plants from NO 3 and NH4fertilizers is observed in the range of 19° - 24°c. The influence of
temperature on the efficiency of fertilizer is dependent on soil moisture. Thisaspect is dealt with separately.Phosphorus: The efficiency of phosphatic fertilizers increases significantly with theincrease in soil temperature from 10-35°c as evidenced by increased Puptake by many plants with increase in temperature.Potassium: The effect of soil temperature on the uptake of K ions both from soilpotassium and fertilizer potassium is controversial. However, at low doses ofK fertilizers, there is possibility of increased uptake of K by plants withincrease in soil temperature up to 24 – 28°c.Soil moisture: One of the most singled out problem in agriculture is the lack andexcess of moisture. Efficient water management is complementary toefficient fertilizer management. Maximum efficiency of fertilizers can beobtained only in the presence of adequate soil moisture and vice versa.Excessive moisture leads to leaching loss of added fertilizers whereas lack ofmoisture results in poor availability of the added fertilizer and high osmoticpressure of soil solution due to concentration of fertilizers soils.Soil Chemical properties: Some important aspects of soil chemical properties have already beendealt with different kinds of immobilization. Some other properties which arerelevant to fertilizer use efficiency are mentioned below. Plant nutrient availability depends on the prevailing pH of soil. Instrongly acidic and alkali soils the efficiency of phosphatic fertilizer is low. Insuch situations, efficiency of fertilizers can be increased by correcting thesoil condition, using suitable amendments. Physiologically alkaline fertilizerslike calcium cyanamide basic slag etc. should receive priority on acid soilsand physiologically acid fertilizers like ammonium sulphate etc. on alkalinesoils. Nutrient contents in the soil should be tested. There may me noresponse at all to applied fertilizer if the initial nutrient content and its
availability are high. For example there are isolated patches in Tamil Nadu inwhich there is no response for phosphatic and potassic fertilizers. However,in such soils a nominal application of nutrients should be made in order tomaintain 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 thebuffering capacity and helps in many other ways. These above benefits inturn 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, betweendicots 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 upnutrients, the rooting pattern and habit have an important bearing on thenutrient removal. Plants which develop a vigorous deep-root system duringtheir early stages of growth require a large quantity of fertilizer as basaldressing. The fertilizer needs of deep rooted crops are generally lower thanshallow rooted crops.Fertilizer characteristics: The mobility of the fertilizer nutrients in the fertilizer, the type offertilizer and the time and mode of application decide the efficiency of afertilizer. The nitrogenous fertilizer are highly mobile and subjected bothdownward and sideward mobility. Phosphorus is highly immobile.Potassium is also mobile but compared to nitrogen its mobility is lower. Toget maximum efficiency N and K fertilizer should be applied in frequent splitdoses and phosphorus as basal dressing or near the root zone.
Type of fertilizer also decide the efficiency. Ammonium and ureafertilizer are more efficient for paddy under different Indian conditions thannitrate fertilizers. Water soluble phosphorus materials are more efficient forshort duration crops and in soils which are neutral to alkaline is reaction.There is also a certain amount of interaction noticed among crops andfertilizers. For example paddy performs better when ammonium sulphate isapplied as N carrier and tobacco when potassium sulphate is applied aspotassium carrier.Certain practical approaches to increase efficiency of fertilizers. 1. High yielding varieties of crops give higher yields than local varietieswithout fertilization as well as a higher unit response to fertilizer even at thelower rate of application. Therefore wherever possible, high yielding varietiesshould be grown. 2. Deviation from normal planting or sowing time suited for a particularcrop variety in a particular locality will effect the efficiency of fertilizers. 3. Optimum plant spacing and maintenance of optimum plant populationare essential to get maximum benefit from the applied fertilizers. 4. Ensure effective organic matter recycling, in order to maintain fertilityand productivity. Response for a nutrient is generally higher in soils suppliedwith adequate amount of organic matter. 5. While applying organic manures having high C:N ratio ensure thatadequate amount of nitrogenous fertilizers are applied to soils to compensatebiological 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 nativephosphorus and precipitated or fixed fertilizer P into available forms. 7. Excessive irrigation should be avoided as it results in the loss of N andK fertilizers. Further, there is also gaseous loss of N under waterloggedcondition. There should not be excess water in the soil particularly at thetime of fertilizer application. Fertilizer application should be made afterdraining the excess water.
8. Crop response to phosphatic fertilizers is generally more in dryseasons. 9. Balanced fertilization should be practiced based on the soil test values.Efficiency of a straight fertilizer containing nutrient) depends on thesufficiency of other nutrient in the soil. 10. The phosphates in general are more efficient when the entiredose applied as basal dressing, potash entire quantity as basal dressing orpart as basal and rest in split doses depending on the soil texture and thenitrogen in 2-3 (or 4) split doses. 11. Water soluble phosphatic fertilizers should be placed 4-6 cmbelow the soil and 4-6 cm away from the seeds to ensure maximumavailability to plants. Insoluble fertilizers should be thoroughly mixed in soil. 12. Sometimes it is better to cure the urea by mixing the urea with5-10 parts of soil thoroughly and keeping the mixture for overnight. Thisenhances the conversion rate of urea into ammonia carbonate. 13. Whenever N loss in drainage water is suspected due toefficiency of the N fertilizer can be increased by mixing the fertilizer withcrushed neem seed (5:1 parts) 14. Foliar application of fertilizers should be resorted to undercertain soil conditions and climatic conditions. 15. Zinc deficiency is becoming more and more widespread day byday. In such cases application of zinc sulphate at the rate of 10-25 kg of zincsulphate as basal dressing, not only corrects the zinc deficiency but alsoenhances generally the efficiency of the other applied fertilizers. 16. Adverse soil condition should be corrected by using appropriateamendments, to get maximum benefit from fertilizer. 17. Absence of weeds, pest and diseases ensures the efficiency offertilizer.