Prospects of

Prospects of improving ef ?ciency of fertiliser nitrogen in Australian agriculture:a review of enhanced ef ?ciency fertilisers

D.Chen A ,D ,H.Suter A ,A.Islam A ,R.Edis A ,J.R.Freney A ,B ,and C.N.Walker C

A

School of Resource Management,Faculty of Land and Food Resources,The University of Melbourne,Vic.3010,Australia.B

CSIRO Plant Industry,GPO Box 1600,Canberra,ACT 2601,Australia.C

Incitec Pivot Ltd,PO Box 54,North Geelong,Vic.3215,Australia.D

Corresponding author.Email:delichen@https://www.wendangku.net/doc/c711938498.html,.au

Abstract.Fertiliser nitrogen use in Australia has increased from 35Gg N in 1961to 972Gg N in 2002,and most of the nitrogen is used for growing cereals.However,the nitrogen is not used ef ?ciently,and wheat plants,for example,assimilated only 41%of the nitrogen applied.This review con ?rms that the ef ?ciency of fertiliser nitrogen can be improved through management practices which increase the crop ’s ability to compete with loss processes.However,the results of the review suggest that management practices alone will not prevent all losses (e.g.by denitri ?cation),and it may be necessary to use enhanced ef ?ciency fertilisers,such as controlled release products,and urease and nitri ?cation inhibitors,to obtain a marked improvement in ef ?ciency.Some of these products (e.g.nitri ?cation inhibitors)when used in Australian agriculture have increased yield or reduced nitrogen loss in irrigated wheat,maize and cotton,and ?ooded rice,but most of the information concerning the use of enhanced ef ?ciency fertilisers to reduce nitrogen loss to the environment has come from other countries.The potential role of enhanced ef ?ciency fertilisers to increase yield in the various agricultural industries and prevent contamination of the environment in Australia is discussed.

Additional keywords:controlled release,urease inhibitors,nitri ?cation inhibitors,mitigation,greenhouse gases.

Introduction

As the intensity of agricultural production in Australia increases to keep pace with population growth,the need for food and ?bre,and maintaining pro ?t margin,fertiliser nitrogen use has increased from 35Gg N in 1961to 972Gg N in 2002(FAO 2007;Fig.1).This fertiliser nitrogen is used mostly on cereals (702Gg N),sugarcane,pasture,horticulture,cotton,and oilseeds.Rates of application varied from 2.5to 229kg N/ha (Table 1).

However,when fertiliser nitrogen is applied to soil it is not used ef ?ciently,and the plant seldom assimilates >50%of the nitrogen added.Plant uptake for a range of crops and pastures in Australia varies from 6to 59%of the nitrogen applied (Table 2).In general,bananas and ?ooded rice were the least ef ?cient of the crops studied (6–17%).The mean recovery of applied nitrogen in Australian dryland wheat was 41%(22–59%),which is marginally better than the estimated worldwide ef ?ciency of nitrogen for cereals of 33%(Raun and Johnson 1999).

One of the main reasons for the poor ef ?ciency of fertiliser nitrogen use is that much of the nitrogen applied (up to 92%)can be lost from the plant –soil system (Table 3).Fertiliser nitrogen can be lost by ammonia volatilisation,during nitri ?cation,and by leaching,erosion,runoff,and denitri ?cation,and the relative importance of these processes can vary widely depending on the agroecosystem,fertiliser form,and method of application.

For example,ammonia volatilisation was important when urea was applied to sugarcane ?elds covered with plant residues,while denitri ?cation was the major loss process when anhydrous ammonia was drilled into irrigated cotton (Table 3).In most of the systems studied in Australia,erosion and runoff were controlled and leaching was small.

Lost nitrogen represents a serious economic loss to farmers,but the impact of the lost nitrogen on the environment and human health is equally,if not more,important.As pointed out above gaseous emissions of nitrogen via ammonia volatilisation,nitri ?cation,and denitri ?cation are the dominant mechanisms for the loss of fertiliser nitrogen from Australian agroecosystems.These processes result in the release of ammonia,nitric oxide,and the greenhouse gas nitrous oxide into the atmosphere.Agriculture is the main source of nitrous oxide in Australia,contributing 67Gg in 2005(AGO 2007);using IPCC (1997)guidelines it is calculated that 21Gg of this comes from fertiliser nitrogen.In addition to the effect on global warming,the nitrogen gases produced from fertiliser can acidify soils,eutrophy lakes,rivers,and estuaries,decrease biodiversity in terrestrial ecosystems,affect atmospheric visibility,reduce the stratospheric ozone layer that protects the Earth from harmful ultraviolet radiation,and increase ozone concentrations in the troposphere with consequent health effects (Peoples et al .2004).Mitigation strategies aimed at reducing nitrogen loss are variable and can range from management practices through to

óCSIRO 2008

10.1071/SR07197

0004-9573/08/040289

CSIRO

PUBLISHING

www.publish.csiro.au/journals/ajsr

Australian Journal of Soil Research,2008,46,289–301

the development of new technologies.New technologies include the use of products such as controlled release fertilisers and urease and nitri ?cation inhibitors.Many of these products have been in some use for decades,with controlled release fertilisers commonly used in the nursery industry and inhibitors used for research purposes,yet their use in agricultural situations is relatively new and of particular interest in light of current concerns regarding greenhouse gas emissions.

The objective of this paper is to provide a review of the current literature on improving the ef ?cacy of nitrogen fertilisers through the use of controlled release coatings and urease and nitri ?cation inhibitors,concentrating speci ?cally on work carried out in Australia.

Approaches to improve ef ?ciency

The processes that generate nitrogen loss from soil are controlled directly by factors such as nitrogen availability and moisture,and indirectly by environmental or management factors (Granli and B?ckman 1994).Some of the factors that control loss such as soil type,rainfall,radiation,and temperature are outside the farmer ’s control,but there are others that the farmer can in ?uence.These manageable factors include fertiliser type,amount,method and time of application,water status (controlled by irrigation and drainage),soil pH (adjusted by

application of lime),and soil compaction (tillage and traf ?cking).

In general,nitrogen loss can be decreased by management practices which increase the crop ’s ability to compete with the loss processes (Minami 1997).The approaches that have been suggested for improving the ef ?ciency of fertiliser nitrogen include the following:

(i)using soil and plant testing to make best use of

indigenous nitrogen (Johnkutty and Palaniappan 1996;Dobermann and Cassman 2004);

(ii)using the optimal form,rate,method and time of

application of the fertiliser (Strong et al .1992;Smith et al .1997);

(iii)incorporation or deep placement of fertiliser (De Datta

et al .1989;Cai et al .2002;Roy and Hammond 2004);(iv)using split applications —several applications of small

amounts of fertiliser during the growing season are more effective than one large dose at the beginning of the season (Hooper 2004);

(v)minimising application in the wet season to reduce

leaching and denitri ?cation (McTaggart et al .1994);(vi)delaying the supply of fertiliser until a substantial canopy

has developed (Humphreys et al .1988),

(vii)using foliar application (Smith et al .1991);and

(viii)using inter seasonal cover crops to minimise the

accumulation of nitrate during fallow periods (McLenaghen et al .1996;Wagner-Riddle and Thurtell 1998;Cameron et al .2002).Where denitri ?cation is likely to be the main process responsible for nitrogen loss,nitrate forms of fertiliser should not be used.Thus,matching the type of fertiliser with rainfall and moisture conditions in the soil could result in appreciable reductions in nitrogen loss (McTaggart et al .1994).This is likely to be more bene ?cial and easier to manage than attempting to maintain a balance between appropriate water management and limiting denitri ?cation or nitrate leaching.For example,trickle or drip irrigation systems which allow delivery of nitrogen to the area of maximum crop uptake enable the application rate to be matched to the plants ’requirements.With careful operation,trickle systems can reduce deep percolation,runoff,and denitri ?cation (Doerge et al .1991).The aim of better water management should be to reduce denitri ?cation by ensuring that the water-?lled pore space of the soil does not exceed 60%(Smith et al .1997;Mosier et al .2002).

Returning crop residues to the soil instead of burning them allows reuse of the nitrogen contained in the residues.Incorporated residues can also improve soil structure,and reduce ammonia volatilisation by in ?uencing the conditions of the underlying soil,and by acting as a medium through which ammonia must pass before being lost to the atmosphere (Aulakh et al .1991;Freney et al .1992b ).Incorporating residues with high C/N ratio into soils will immobilise mineral nitrogen which can become available later when mineralised (Aulakh et al .1991).

Optimising plant growth and uptake of nitrogen through management of the plant ’s total nutrient requirements is another means of increasing nitrogen use ef ?ciency.The supply of one nutrient affects the absorption,distribution,

or

1960

1970198019902000

Year

F e r t i l i s e r n i t r o g e n (

G g )

Fig.1.Fertiliser used in Australia during the period 1960–2002.

Table 1.Fertiliser nitrogen used for crops and pasture in Australia

in 2000(FAO,IFA,IFDC,IPI,PPI 2002)Commodity Fertiliser consumption

Application rate (Gg N)

(kg N/ha)

Cereals 70242.9Sugarcane 96229.1Pasture 75 2.5Horticulture 71187.8Cotton 56121.2Oilseeds 5512.8

Total

1055

290Australian Journal of Soil Research D.Chen et al .

function of another nutrient,so that insuf ?cient amounts of plant-available phosphorus,sulfur,potassium,or other nutrient will reduce nitrogen use ef ?ciency.For example,nitrogen recovery in phosphorus-de ?cient corn was <40%,whereas it was 75%when adequate phosphorus was supplied (Oberle and Keeney 1990).

Site-speci ?c nitrogen management is used to synchronise the supply and demand of nitrogen,and it can be used to manage nitrogen in labour-intensive,small-scale farming or highly mechanised,large-scale production ?elds (Dobermann and Cassman 2004).Optimum nitrogen rates vary spatially and seasonally;thus,diagnostic tools are required to assess soil or crop nitrogen status during the growing season to make decisions on the amount of nitrogen to be applied (Schr?eder et al .2000).One diagnostic measure is leaf greenness,and several techniques exist to measure this,including near-infrared leaf nitrogen analysis,chlorophyll meters,leaf colour charts,crop canopy re ?ectance sensors,and remote sensing (Giller et al .2004).Signi ?cant increases in nitrogen use ef ?ciency have been achieved through reductions in nitrogen use.

Decision support systems (DSS),based on comprehensive and process-based agro-ecosystem models,for optimum nitrogen fertiliser management have also been used recently.The advantage of such systems is the ability to integrate bio-physical variables/interacting processes and management practices and economical –environmental considerations.The best management practices can be identi ?ed by simulating the combination of different management practices,such as interaction of nitrogen application rates and time with irrigation rate and time,and trade-off between economical and environmental interests.The GIS-based DSS for fertiliser application and irrigation for North China Plain,derived from the Water and Nitrogen Management Model (WNMM),has signi ?cantly assisted the dissemination of the best management fertiliser nitrogen practices with substantial economical impact (Chen et al .2006).

Table 3.Nitrogen lost from agricultural systems in Australia (%of applied)

Crop and location

Loss

References

Volatilised

Denitri ?ed Total Bananas:East Palmerston,Qld 20525Prasertsak et al .(2001a )Cotton (irrigated):Narrabri,NSW 0

43–92

43–92

Freney et al .(1993),

Humphreys et al .(1990)Pasture:

Millaa Millaa,Qld 202040Prasertsak et al .(2001b )Ellinbank,Vic.

32–5713–1547–70Eckard et al .(2003)

Rice (?ooded):Grif ?th,NSW

0–1115–5640–56

Simpson et al .(1984,1985),Keerthisinghe et al .(1993)Sugarcane:Mackay,Qld

039–6239–62Chapman et al .(1991)South Johnstone,Qld 6–3722–4046–59Prasertsak et al .(2002)Sun ?owers:Tatura,Vic.

62935Smith et al .(1988)

Wheat (dryland):Hanwood,Murrami,Widgelli,Willurah,Wumbulgal,Yanco,NSW;Birchip,Chinkapook,Elmore,Wunghnu,Diggers Rest,Vic.1–242–2712–40

Bacon and Freney (1989),P.E.Bacon,J.R.Freney,unpublished data Wheat (irrigated):Tatura,Vic.

05050

Freney et al .(1992a )

Table 2.Recovery of fertiliser nitrogen by crops and pastures in Australia

Crop and location

Recovery (%of applied)References

Plant Soil Plant +soil Bananas:East Palmerston,Qld 156075Prasertsak et al .(2001a )Cotton (irrigated):Narrabri,NSW 27–298–288–57Freney et al .(1993),

Humphreys et al .(1990)Pasture:Millaa Millaa,Qld 421860Prasertsak et al .(2001b )Rice (?ooded):Grif ?th,NSW

6–17

37–48

44–60

Simpson et al .(1984,1985),Keerthisinghe et al .(1993)Sugarcane:Mackay,Qld

14–3823–4138–61Chapman et al .(1991)South Johnstone,Qld 19–2922–2541–54Prasertsak et al .(2002)Sun ?owers:Tatura,Vic.

353065Smith et al .(1988)

Wheat (dryland):Hanwood,Murrami,Widgelli,Willurah,Wumbulgal,Yanco,NSW;Birchip,Chinkapook,Elmore,Wunghnu,Diggers Rest,Vic.22–5920–5460–88

Bacon and Freney (1989),P.E.Bacon,J.R.Freney,unpublished data Wheat (irrigated):Tatura,Vic.

252550

Freney et al .(1992a )

Improving ef ?ciency of fertiliser nitrogen Australian Journal of Soil Research 291

Enhanced ef?ciency fertilisers

While the techniques described above have the potential to increase the effectiveness of applied nitrogen,considerable N losses still occur.For example,in?ooded rice the time of application had a big effect on the agronomic ef?ciency of fertiliser nitrogen and ammonia volatilisation,but even with the best system devised,around40%of the applied nitrogen was still lost by ammonia volatilisation,denitri?cation,or leaching (Bacon and Heenan1987;Humphreys et al.1988).In order to further reduce loss by these processes,alternative fertilisation techniques,such as the use of controlled release fertilisers, urease inhibitors,and nitri?cation inhibitors,need to be considered.These can be collectively referred to as enhanced ef?ciency fertilisers.

There have been numerous studies on enhanced ef?ciency fertilisers,either used alone or in combination in agroecosystems,with highly variable ef?ciencies demonstrated(Smith et al.1997;Trenkel1997;Zerulla et al. 2001;Drost et al.2002;Singh et al.2004;Watson2005). The high variability in effectiveness is often due to a lack of understanding of the interaction of these chemicals with soil and environmental variables(Mosier et al.2002).For example,the nitri?cation inhibitor dicyandiamide(DCD)was shown to be a very effective nitri?cation inhibitor under cold climatic conditions,but is less effective in warm/hot and wet climates due to its rapid decomposition(Zerulla et al.2001;Singh et al. 2004;Di and Cameron2004b;Hatch et al.2005).Most?eld studies have concentrated on the effect on production (grain yield or biomass)and few have considered gaseous nitrogen loss and nitrate leaching.While many studies have been carried out in other countries,few have been conducted in Australia.Thus,there is a need to evaluate the effectiveness of various formulations and strategies under conditions applicable to Australia’s major agroecological zones for fertiliser manufacturers and farmers.

Controlled release fertilisers

The supply of nitrogen by a single application of slow or controlled-release fertiliser should satisfy plant requirements and maintain low concentrations of mineral nitrogen in the soil throughout the growing season.As a result,labour and application costs should be low,nitrogen loss should be minimised,nitrogen use ef?ciency should increase,and yields should be improved.

Many different controlled release forms of nitrogen have been suggested(Peoples et al.1995),and considerable advances have been made in the formulation of these materials. Shaviv(2005a,2005b)has classi?ed these fertilisers into3 main types:

(i)inorganic low solubility compounds(e.g.magnesium

ammonium phosphate);

(ii)organic low solubility compounds(e.g.urea formaldehyde and isobutylidenediurea);

(iii)coated materials in which a physical barrier controls the release(e.g.granules coated with hydrophobic polymers, or matrices in which the soluble fertiliser is dispersed so the dissolution of the fertiliser is restricted).The coated fertilisers can be further divided into those coated with inorganic material(e.g.sulfur-coated urea),sulfur-coated fertiliser,which is further coated with an organic polymer (e.g.polymer-coated sulfur-coated urea),and those coated with organic polymers,viz.thermosetting resin-coated fertilisers and thermoplastic polymer-coated fertilisers.

Sulfur-coated urea was developed in the1960s by the National Fertilizer Development Center and used with mixed success in a variety of applications,e.g.?ooded rice(Prasad and De Datta1979)and wheat(Mason1985).Sulfur coatings provide highly variable nitrogen release patterns depending upon coating damage that might occur,and as much as one-third can be released instantaneously Addition of a polymer coating to sulfur-coated urea signi?cantly improved its performance.Polymer sulfur-coated urea has improved ryegrass and bluegrass quality in2Paci?c north-west climates(Miltner et al.2004)and reduced leaching loss to only1.7%of the applied nitrogen after application to turf lawn in southern New England(Guillard and Kopp2004).

The main thermosetting resin-coated fertilisers are the alkyd-type resins(e.g.Osmocote)and those with polyurethane-like coatings such as Polyon,and Multicote(Trenkel1997;Shaviv 2005a).Nutrient release from these materials is controlled by the coating thickness(Trenkel1997;Shaviv2005a).According to Shoji and Gandeza(1992),the most accurate controlled release of nutrients is provided by the polyole?n thermoplastic-coated fertilisers(e.g.Meister)developed by Chisso-Asahi Fertilizer Co.,Japan.Fertiliser release is controlled by coating fertiliser particles with polyole?ns,such as polyethylene and polypropylene,which have low water permeability,and ethylene vinyl acetate,which has high water permeability.

The pattern of nutrient release from coated fertilisers can be parabolic,linear,or sigmoidal and long-or short-term(Shaviv 2005a).Nitrogen uptake of seasonal crops and perennial species is generally sigmoidal(Shoji and Kanno1994;Shoji et al.2001; Shaviv2005a).Because of the variety of polyole?n-coated fertilisers available it is now possible to use computers to program fertiliser release patterns to match the speci?c requirements of a crop,and Shoji(2005)illustrates how this can be used to supply nitrogen at the times of peak demand for ?ooded rice.

Use of polyole?n-coated urea instead of uncoated fertiliser has resulted in increased yields and nitrogen use ef?ciency in a range of crops including potatoes,rice,and direct-seeded onions (Mikkelsen et al.1994;Shoji and Kanno1994;Shoji et al.2001; Drost et al.2002;Fashola et al.2002;Shoji2005;Wu et al. 2005).Large reductions in the emission of nitrous oxide have also been achieved using polyole?n-coated ammonium nitrate (Minami1994),polyole?n-coated ammonium sulfate (Nutricote;Smith et al.1997),and polyole?n-coated urea (Shoji et al.2001)instead of uncoated nitrogen fertiliser. However,no yield effect was found in irrigated cotton in Australia by using polyole?n-coated urea,although there were signi?cant impacts on N uptake and mineral N(urea, ammonium,and nitrate)dynamics(Chen et al.2008). Ammonium-based fertilisers have been coated with polyole?ns for use in vegetable growing to prevent the build-up of nitrate,which affects quality and may constitute a health risk(Matsumoto1991;Takebe et al.1996;Shoji2005;

292Australian Journal of Soil Research D.Chen et al.

Wang et al.2005).A further decrease in nitrate uptake by

vegetables was achieved by adding the nitri?cation inhibitor

DCD to the fertiliser before coating the mixture with polyole?n

(Mimaki2003).

However,it has been pointed out that use of controlled

release fertilisers may result in nitrogen,in excess of the

crop’s requirements,remaining in the soil after harvest.This

nitrogen may then be lost to the environment in the same manner

as uncoated fertiliser(Delgado and Mosier1996).

The use of controlled-release fertilisers in agriculture is still

limited in spite of the technological developments and

availability.Only about10%of the total production is

consumed in agriculture,and the remainder is used for lawns,

golf courses,fruit trees,and vegetables(Shaviv2005a).The

main reason for the limited use seems to be the high cost,

which may be3–10times the cost of conventional fertiliser

(Shaviv2000).

Urease inhibitors

Urea has become the most widely used form of fertiliser

nitrogen,because it is the least expensive form of fertiliser

available,and its high nitrogen content(46%)means lower

transportation costs.Globally in developed countries urea

consumption has stabilised at around30Mt,while in

developing countries consumption is still increasing

dramatically and was around55Mt in2002(IFA2006).

However,it has the disadvantage that considerable losses of

nitrogen can occur if the urea is not incorporated into soil soon

after application.Losses have ranged from negligible amounts to >50%of the nitrogen applied,depending upon fertiliser practice and environmental conditions(Peoples et al.1995;Cai et al.

2002).The loss occurs by ammonia volatilisation after the urea is

converted to ammonia at the soil surface by reaction with

the enzyme urease.One approach to decreasing ammonia

volatilisation is to?nd compounds that inhibit urease activity,

thus allowing the urea to move into the soil before hydrolysis.

The ammonia then released would be retained by the soil.

A large number of compounds with differing characteristics

have been tested for their ability to inhibit urease activity

(Medina and Radel1988;Watson2000,2005;Kiss and

Simihaian2002).Some inhibit the enzyme by reacting with

active sites on the enzyme or a key functional group elsewhere in

the molecule,or by changing the conformation of the active site.

Many organic and inorganic compounds and metal ions

inhibit urease by reacting with the sulfhydryl groups in the

enzyme(e.g.mercapto compounds),others by complexing with

nickel in the active site(e.g.hydroxamates),some by reacting

with the carboxylic acid group(e.g.arylorganoboron

compounds),and others because they are structural analogues

of urea(e.g.thiourea,methyl urea,and phosphoryl di-and

triamides)(Medina and Radel1988).

The most effective compounds for the inhibition of urease

activity appear to be the phosphoryl amides(e.g.N-(n-butyl)

phosphoric triamide and cyclohexylphosphoric triamide(Chai

and Bremner1987;Keerthisinghe and Blakely1995;Byrnes

and Freney1995),although hydroquinone and2,5-dimethyl

p-benzoquinone can provide inhibition at high concentrations

(Tomlinson1970;Xu et al.2005).

A host of natural products have been tested for their ability to inhibit urease activity,including coal and peat;humic substances;lignins and tannins;plant residues and extracts containing polyphenols and saponins;neem cake,oil,and extracts;karanja cake and mahua cake;and microbial products(Kiss and Simihaian2002).In India the press cake from the production of neem(Azadirachta indica)oil has been shown to inhibit urease activity(Trenkel1997),and when it was used to coat urea it reduced loss of nitrogen and improved nitrogen use ef?ciency(John et al.1989).Patra et al.(2006) showed that the natural essential oil,dementholised oil,and terpenes of peppermint(Mentha spicata)signi?cantly retarded soil urease activity.Natural inhibitors of urease activity have also been found in Artemisia annua(Patra et al.2002), Ranunculus repens(Khan et al.2006),and Aspergillus ochraccus(Lin et al.1997).

The compound which has been most widely tested for its capacity to reduce ammonia loss from urea is N-(n-butyl) thiophosphoric triamide(Trenkel1997;Singh et al.2004; Watson2005).However,like the other thiophosphoryl triamides it is not a urease inhibitor.The thio compounds are the precursors of oxygen analogues which are the actual inhibitors.Numerous tests of the pure thio compounds in vitro have shown their total ineffectiveness.The thio compounds have to be converted to the oxygen analogues on contact with soil or other material before inhibition can occur(McCarty et al.1989;Creason et al.1990).It might seem to be more logical to market the oxygen analogue of N-(n-butyl)thiophosphoric triamide(viz.N-(n-butyl) phosphoric triamide),but the oxygen analogue is not suf?ciently stable for it to be packaged and distributed for commercial application(Incitec Pivot,https://www.wendangku.net/doc/c711938498.html,m.). N-(n-butyl)thiophosphoric triamide,on the other hand,seems to be quite stable(Hendrickson and Douglass1993)although its effectiveness is controlled by temperature(Chai and Bremner1987;Carmona et al.1990).The results of Carmona et al.(1990)indicate that higher concentrations of N-(n-butyl) thiophosphoric triamide will be required to prevent ammonia loss from warm soils than for temperate soils.

Watson et al.(1994a,1994b)found N-(n-butyl) thiophosphoric triamide very effective at low concentrations (0.01%of applied urea nitrogen)for reducing ammonia volatilisation(by~50%)in?eld trials on temperate grassland.Its use also signi?cantly delayed and reduced ammonia and nitrous oxide emissions from soil after application of urea,urine,and urea ammonium nitrate (Bronson et al.1989b;Schlegel1991;Grant et al.1996; Wang and Douglas1996;Singh et al.2004)and produced signi?cant improvements in nitrogen use ef?ciency of corn following application of urea ammonium nitrate (Fox and Piekielek1993).In21upland?eld experiments, treating urea with N-(n-butyl)thiophosphoric triamide increased grain yields of maize by an average of750kg/ha (Bronson et al.1989b).An additional80kg N/ha would need to be applied to obtain that increase in yield (Byrnes and Freney1995).Similar positive results were reported by Hendrickson(1992)for maize fertilised with urea or urea ammonium nitrate in78trials conducted in the USA between1984and1989.

Improving ef?ciency of fertiliser nitrogen Australian Journal of Soil Research293

Both N-(n-butyl)thiophosphoric triamide and cyclohexyl phosphoric triamide have been used successfully to control ammonia emission from animal wastes,to prevent environmental damage,and to produce a more balanced nitrogen/phosphorus fertiliser from manure(Varel1997; Varel et al.1999).

Nitri?cation inhibitors

Maintaining nitrogen in the ammonium form in soil would prevent its loss by both nitri?cation and denitri?cation.One method of doing this is to add a nitri?cation inhibitor with the fertiliser.This prevents or slows the microbial conversion of ammonium to nitrate and hence the leaching of nitrate and production of nitric oxide,and nitrous oxide by both nitri?cation and denitri?cation.While this technique does not always produce increased crop yields it does provide a tool for managing nitrate leaching and nitrous oxide production (Edmeades2004).

Reliable data on the use of nitri?cation inhibitors in different crops and regions are not available.Surveys of USA farmers indicate that at present about9%of the national maize area is treated with nitri?cation inhibitors,and this proportion has remained unchanged in recent years(Christensen2002).

Many chemicals have been tested as nitri?cation inhibitors, but few are commercially available(Table4)or have proven to be agronomically and economically effective(Slangen and Kerkhoff1984;Prasad and Power1995;McCarty1999;Frye 2005).The persistence and behaviour of nitri?cation inhibitors in soil is determined by diffusion into the atmosphere, decomposition or degradation,differential movement in soils, sorption on clay or organic matter(Slangen and Kerkhoff1984), and by environmental and edaphic factors,such as temperature, moisture,and soil texture(Prasad and Power1995).While progress is being made towards understanding the mode of action of many inhibitors of ammonia oxidation,little is known about the action of others such as the heterocyclic nitrogen compounds(McCarty1999).

Of the inhibitors listed in Table4,the most extensively studied products are nitrapyrin,DCD,and more recently 3,4-dimethylpyrazole phosphate(Goos and Johnson1999; Dittert et al.2001;Pasda et al.2001;Weiske et al.2001a, 2001b;Zerulla et al.2001;Calderon et al.2005;Chao et al. 2005;Islam et al.2007a,2007b).

Nitrapyrin is often ineffective because of sorption on soil colloids,hydrolysis,and loss by volatilisation(Hoeft1984;Liu et al.1984),but it has reduced nitrogen losses and resulted in increased plant nitrogen uptake(Fillery and De Datta1986; Chen et al.1998a,1998b).When Wolt(2004)evaluated the performance of nitrapyrin across research trials conducted in diverse environments over many years in Midwestern USA,he found that,on average,nitrapyrin increased corn yield by7% and soil retention of nitrogen by28%.It also decreased nitrogen leaching by16%and nitrous oxide emission by51%.

Dicyandiamide inhibited nitri?cation when ammoniacal fertilisers were applied to?eld crops and vegetables(Frye et al.1989;Frye2005)with the result that nitrogen remained longer in the soil in the ammonium form(Irigoyen et al.2003). Yield increases have been obtained when DCD was applied to pastures(Di and Cameron2002;Smith et al.2005)and various cropping systems,e.g.maize(Ball-Coelho and Roy1999), wheat(Rao1996;Sharma and Kumar1998;Rao and Popham1999),and maize–wheat(Sharma and Prasad1996). However,application of DCD does not always lead to yield increases(Mason1987;Dachler1993;Frye2005)and in some cases can have deleterious effects on plant growth(Macadam et al.2003).Yield increases usually occurred at low fertiliser application rates(Frye2005).

Leaching of nitrate can be signi?cantly reduced by addition of DCD(Ball-Coelho and Roy1999;Serna et al.2000;Di and Cameron2002,2004a).Treatment of urine patches on a?ne sandy loam in New Zealand with DCD reduced nitrate leaching losses from85to20–22kg N/ha.year(Di and Cameron2002, 2004a).The bene?cial effect of the DCD was increased beyond the saving of nitrogen because it also reduced leaching of the cations associated with nitrate,calcium by38–56%and magnesium by21–42%(Di and Cameron2004a,2004c) Because DCD effectively retards nitri?cation,when it is added to soil along with ammonium based fertilisers, emissions of nitric oxide and nitrous oxide are substantially reduced compared with fertiliser alone(Majumdar et al.2000; Shoji et al.2001;Vallejo et al.2001;Singh et al.2004;Hatch et al.2005;Merino et al.2005;).For example,Skiba et al. (1993)showed that addition of DCD reduced nitric oxide emission by about92%and nitrous oxide emission by40%. Signi?cant reductions have also been reported for DCD-treated pig slurry(Vallejo et al.2005)and DCD-treated animal urine patches in grazed perennial ryegrass–white clover pastures(Di and Cameron2003).Di and Cameron(2003)showed that repeated applications of DCD offered no advantage over a single application of DCD immediately after urine deposition.

However,the effect of DCD on reducing the rate of nitri?cation in soil is variable and in some cases no effect on nitrate leaching was obtained(Davies and Williams1995;

https://www.wendangku.net/doc/c711938498.html,pounds produced commercially as nitri?cation inhibitors(modi?ed from Nelson and Huber2001) Chemical name Common or trade name Manufacturer

2-Chloro-6-(trichloromethyl)-pyridine Nitrapyrin,N-Serve Dow Chemical Co.

5-Ethoxy-3-trichloromethyl-1,2,4-thiadiazol Dwell,Terrazole,Etradiazo)Uniroyal Chemical

Dicyandiamide DCD SKW Trostberg AG

3,4-Dimethylpyrazole phosphate DMPP(ENTEC)BASF AG

2-Amino-4-chloro-6-methyl-pyrimidine AM Mitsui Toatsu Co.

2-Mercapto-benzothiazole MBT Onodo Chemical Industries

2-Sulfanilamidothiazole ST Mitsui Toatsu Co.

Thiourea TU Nitto Ryuso

294Australian Journal of Soil Research D.Chen et al.

Beckwith et al.1998).The effectiveness of DCD in soil is controlled by temperature,texture,and moisture content (Prasad and Power1995;Irigoyen et al.2003).With increasing temperature the inhibiting effect of DCD is greatly decreased(Bronson et al.1989a;Irigoyen et al.2003; Di and Cameron2004b).Bronson et al.(1989a)found that the half-life of DCD in a sandy loam was reduced from52to 14days when the temperature was increased from88C to228C, and Di and Cameron(2004b)observed a greater reduction in a silt loam.

A relatively new nitri?cation inhibitor,3,4-dimethylpyrazole phosphate(DMPP),was developed by the German company BASF AG(BASF1999;Zerulla et al.2001).It is generally more effective and longer lasting than DCD in inhibiting nitri?cation, and inhibition was achieved with lower rates of application (0.5–1.5kg DMPP/ha).DMPP has been found to reduce nitrate and nitrite levels in soil after application of ammonium-based fertilisers and cattle slurry,leading to signi?cantly lower nitric oxide and nitrous oxide emissions,and nitrate leaching,and to improve crop yields(Dittert et al.2001;Pasda et al.2001; Zerulla et al.2001;Chao et al.2005;Menéndez et al.2006). Weiske et al.(2001b)showed that DMPP reduced emission of nitrous oxide by49%(averaged over3years),which was considerably more than DCD(average reduction26%). European?eld trials demonstrated that addition of DMPP increased yields of winter wheat,wetland rice,maize, potatoes,sugar beets,carrots,lettuce,radish,cauli?ower,and onions,allowed lower rates of nitrogen fertiliser,or permitted fewer applications to be used to attain the same yields as treatments without DMPP(Pasda et al.2001).

The effectiveness of DMPP,like DCD,is in?uenced by temperature,soil texture,and moisture(Barth et al.2001; Pasda et al.2001;Merino et al.2005).Merino et al.(2005) found that DMPP applied with cattle slurry was able to maintain soil mineral nitrogen in the ammonium form for22days and reduce nitrous oxide emission by69%in autumn,but in spring its effect on soil mineral N lasted for only7–14days,and reduced nitrous oxide loss by48%.

Other nitri?cation inhibitors that have been used successfully in?eld trials include acetylene,substituted acetylenes, etridiazole,and a natural product from the Neem tree (Azadirachta melia).Acetylene is a potent inhibitor of nitri?cation,but because it is a gas,it is dif?cult to add and keep in soil at the correct concentration to inhibit the oxidation of ammonium.Calcium carbide coated with layers of wax and shellac has been used to provide a slow-release source of acetylene to inhibit nitri?cation(Mosier1994).This technique has increased the yield or recovery of nitrogen in irrigated wheat,maize,cotton,and?ooded rice(Bronson and Mosier1991;Bronson et al.1992;Freney et al.1992a,1993; Zhang et al.1992).Another product,a polyethylene matrix containing small particles of calcium carbide and various additives to provide controlled water penetration and acetylene release,has been developed as an alternative slow-release source of acetylene.In laboratory studies,this matrix inhibited nitri?cation for90days and considerably slowed the oxidation for180days(Freney et al.2000).It also retarded nitri?cation in an irrigated corn?eld for at least 48days(Randall et al.2002).The substituted acetylenes 2-ethynylpyridine and phenylacetylene are very effective

inhibitors of nitri?cation in the?eld(Freney et al.1993;

Chen et al.1994,1998a,1998b),but their current price

restricts their use by farmers.

Etridiazole(Terrazole,Dwell)was found to be a very

effective nitri?cation inhibitor in laboratory investigations

(Liu et al.1984;Ra?i et al.1984;McCarty and Bremner

1990),and it has been shown to inhibit nitri?cation for

prolonged periods in the?eld(Somda et al.1989;Rochester

et al.1994)and to substantially improve yields for a variety of ?eld and horticultural crops(Somda et al.1990)and irrigated cotton(Rochester et al.1994,1996).

Various products(cake and oil)from the seeds of the Neem

tree have been tested to determine whether they could be used as

cheap nitri?cation inhibitors for resource-poor Indian farmers

(Majumdar et al.2000;Malla et al.2005).Field experiments on

the Indo-Gangetic plain showed that application of neem cake

and neem oil with the fertiliser signi?cantly reduced the

emission of nitrous oxide.Addition of neem cake also

signi?cantly increased the yield of rice(Malla et al.2005).

Unless care is taken to place ammonium-based fertilisers

below the soil surface,use of nitri?cation inhibitors may result in

increased ammonia volatilisation(Rodgers1983;Chaiwanakupt

et al.1996).

Potential for use of enhanced ef?ciency fertilisers

in Australia

Research suggests that the effectiveness of different controlled

release fertilisers,and urease and nitri?cation inhibitors will

depend upon crop,soil climate,and management factors.The

broadacre agricultural industries in Australia which have been

identi?ed as high nitrogen users are those producing cereals,

sugarcane,cotton,and pasture(Table1).Some dairy pastures

receive up to300kg N/ha.year(Eckard2004).Horticultural

cropping and turf production are also big users of nitrogen,but

these industries are beyond the scope of this review.Each of

these industries is likely to bene?t from the use of the enhanced

fertilisation techniques,but the best technique for each crop is

likely to vary.

The major wheat-producing regions are in southern Western

Australia,New South Wales,South Australia,and western

Victoria where the climate is temperate and the soils are

mainly Chromosols,Sodosols,Vertosols,and Calcarasols

(Isbell1996).The pasture-producing areas that have high

nitrogen inputs are the rainfed or irrigated dairying regions

(Eckard2004).Most of the dairy pastures are in Victoria,

which is responsible for64%of Australia’s milk production

(Dairy Australia2006),and most of the dairy cattle are in the

Western District(rainfed),Goulburn(irrigated),and Gippsland

(ABS2005).The main soils in these regions are,respectively,

Chromosols,Sodosols,and Vertosols;Sodosols;and Dermosols

and Ferrosols.The climate in these regions is temperate.

Sugarcane is grown along a2000-km strip of land on the east

coast of Australia from northern New South Wales to north

Queensland.About one-third of this crop is grown in north

Queensland from Ingham to Mossman.This area has a humid

tropical climate,and sugarcane is grown on soils formed from

alluvial deposits,the deep red and yellow friable loams and the

Improving ef?ciency of fertiliser nitrogen Australian Journal of Soil Research295

krasnozems(Wood1991).In the subtropical areas,the crop is

grown on red loams around Bundaberg,and on acid sulfate soils

in the coastal lowland regions.Cotton is grown throughout NSW

and Queensland on alkaline heavy clay soils where the climate

ranges from temperate to subtropical.

Urease inhibitors are expected to be most bene?cial on

soils where loss of ammonia from application of urea

fertiliser is high.This is likely to be when urea is applied to

the surface of pasture soils(e.g.in the dairy industry)or

other soils which have high urease activity due to lack

of cultivation or the accumulation of organic matter

(e.g.sugarcane trash).Ammonia loss will also occur when

incorporation of urea is dif?cult and there is little opportunity

for the urea to move into the soil with in?ltrating water

(e.g.rainfed wheat).Nitri?cation inhibitors are likely to have

the greatest bene?t on soils where nitrogen losses due to

leaching or denitri?cation are large.Leaching losses are more

likely to occur on coarse-textured,free-draining soils under

heavy rainfall(e.g.sugarcane soils in the tropics)than on ?ne-textured clay soils with low rainfall(cotton soils in western NSW).Losses due to denitri?cation are expected to

be large in warm,?ooded,or waterlogged soils(cotton and rice

soils),in soils to which plant residues have been added

(sugarcane and banana soils),and in dung and urine patches

(pasture soils).Bene?ts from the use of controlled release

fertilisers could potentially occur in all the agricultural

industries,as their use should limit losses by all processes.

The choice of controlled release fertiliser,urease inhibitor,or

nitri?cation inhibitor is likely to be determined more by factors

such as price and availability rather than by degree of

effectiveness,as many of the compounds shown to be very

effective in the laboratory and small-scale trials are not available

commercially.Available products which have the potential to

increase yield,nitrogen use ef?ciency,or loss of nitrogen are

described below.

Controlled release fertilisers

The controlled release fertilisers that appear to show the greatest

potential for dryland and irrigated cropping,and pasture are

(i)a polymer-coated urea(Environmentally Smart Nitrogen;

Agrium2006);(ii)a polyole?n-coated urea(Meister;Chisso

Corporation2006);and(iii)a humic-acid-coated urea(Black

Urea;Advanced Nutrients Australia2006).

Environmentally Smart Nitrogen has been extensively used

in the USA and Canada and recently in trials in subtropical

Queensland.It maximised nitrogen use ef?ciency and

minimised nitrogen losses to the environment(Blaylock et al.

2005;Agrium2006).Meister comes in several forms having

different release types and times.Meister-SS15shows a

sigmoidal-type release,with a lag period of70days and a

release period of80days(Shoji et al.2001).This makes it

ideal for dryland wheat,which requires nitrogen fertilisation

approximately80days after sowing to supply nitrogen for

grain-?ll.Urea coated with humic acid has signi?cantly

reduced nitrogen loss and enhanced nitrogen uptake by

dryland wheat in?eld trials at Quirindi,NSW,and increased

dryland pasture yields compared with urea(Advanced

Nutrients Australia2006).Addition of humic acid to urea has also reduced ammonia loss from acid soils(Garcia Serna et al. 1996;Siva et al.2000).

Urease inhibitors

The most readily available compound,N-(n-butyl) thiophosphoric triamide,is sold in Australia as Agrotain, which contains20–25%active ingredient(IMC-Agrico1997). Agrotain is marketed by Incitec Pivot Ltd in the following formulations:(i)Green Urea14,which contains45.8% nitrogen as urea and Agrotain@5.0L/t to reduce the loss of ammonia by volatilisation for up to14days;and(ii)Green Urea 7,which contains45.9%nitrogen and Agrotain@3.0L/t to reduce ammonia volatilisation for up to7days(Incitec Pivot Ltd 2006).

Nitri?cation inhibitors

The products which show the greatest potential for reducing nitrogen loss from agricultural industries in Australia are(i) DMPP(rainfed wheat and pasture),(ii)DCD(rainfed and irrigated pasture,wheat),and(iii)etridiazole(irrigated cotton).DMPP seems to be the best product because of its positive effects on yield and nitrogen loss at low concentrations, and because of its stability and lack of movement in soil.It may need to be applied at slightly higher concentrations in warm conditions.It is marketed as ENTEC by BASF and is distributed by Incitec-Pivot in Australia(Incitec Pivot Ltd2006).DCD (marketed as Didin by SKW Trotsberg,Germany)needs to be applied at higher rates than DMPP.It is unstable at high temperatures,and thus is likely to be more effective when used during winter and autumn.

Further testing of these materials under a range of conditions is required to select the best material for a particular industry in Australia,and to determine the economics of its use. References

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