The Effects of Using Anhydrous Ammonia to Supply Nitrogen to Vegetable Crops

Gordon Rogers Applied Horticultural Research

Project Number: VG15062

Author: Adam Harber

VG15062 Horticulture Innovation Australia Limited (HIA Ltd) and Applied Horticultural Research make no representations and expressly disclaim all warranties (to the extent permitted by law) about the accuracy, completeness, or currency of information in this Final Report. Users of this Final Report should take independent action to confirm any information in this Final Report before relying on that information in any way. Reliance on any information provided by HIA Ltd and Applied Horticultural Research is entirely at your own risk. HIA Ltd is not responsible for, and will not be liable for, any loss, damage, claim, expense, cost (including legal costs) or other liability arising in any way (including from HIA Ltd or any other person’s negligence or otherwise) from your use or non-use of the Final Report or from reliance on information contained in the Final Report or that HIA Ltd provides to you by any other means.

This project has been funded by Horticulture Innovation Australia Limited using the vegetable industry levy and funds from the Australian Government.

ISBN <HIA Ltd to add>

Published and distributed by: Horticulture Innovation Australia Ltd Level 8 1 Chifley Square Sydney NSW 2000 Telephone: (02) 8295 2300 Fax: (02) 8295 2399

© Copyright 2016

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Contents

Summary ............................................................................................................... 3Introduction ........................................................................................................... 4

Anhydrous ammonia use in vegetable crops ............................................................. 5Application of anhydrous ammonia .......................................................................... 7

The ammonia retention zone ............................................................................... 8Application equipment ......................................................................................... 9

Retention of ammonia ......................................................................................... 9Benefit of anhydrous ammonia .............................................................................. 11

The soil environment ......................................................................................... 11Soil microbes ................................................................................................. 11

Earthworms ...................................................................................................... 12

Stability of nitrogen in the soil ............................................................................ 13Crop yields ....................................................................................................... 14

Risk of anhydrous ammonia .................................................................................. 15Ammonia toxicity .............................................................................................. 15

Commercial availability ...................................................................................... 16Cost ................................................................................................................. 16

Health risks .......................................................................................................... 16Environmental impacts ......................................................................................... 17

Energy use ....................................................................................................... 17Nitrous oxide emissions ..................................................................................... 17

Recommendations ................................................................................................ 20Outputs ............................................................................................................... 21

Scientific Refereed Publications ............................................................................. 22Intellectual Property/Commercialisation ................................................................. 23Acknowledgements .............................................................................................. 24Appendices .......................................................................................................... 25

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Summary

Anhydrousammoniaisahighnitrogen(82%)fertiliser,whichiscurrentlywidelyusedinthecottonandgrainindustriesinAustralia.ItisaproductthatneedstobehandledcorrectlyastherecanbeOH&Sissues.Anhydrousammoniaisappliedusingspecialisedequipment,whichcouldbeabarriertousebyvegetablegrowers.Supplylocationsarefocusedaroundgrainandcottonproductionareas.Anhydrouswasfoundtohavebeneficialeffectsonsoilmicrobes,nitrifyingbacteriaandworms.Anhydrousammoniaisconvertedinthesoilinitiallytoammonium,whichcanbeheldinsoilsandresistleaching.

TherewasverylittleresearchfoundontheuseofanhydrousammoniainvegetablecropsinAustralia.AHRreportsonanobservationaltrialcomparingtheuseofanhydrousammoniatocalciumnitrateasasourceofnitrogenonbabyspinachonacommercialfarmCowra,NSW.

Inconclusion,thereviewfoundthereispotentialforanhydrousammoniatobeusedasasourceofnitrogenforvegetablecropsbutthatitwasmoresuitedtorowcropsthancropssuchasbabyleaf,whichrequiremoreevendistributionofnitrogenacrossthebeds.

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Introduction

Propernitrogenmanagement(N)onvegetablefarmsisessentialforthehealthofthecrop,soilandecosystem.Ithaslongbeenrecognisedthatgroundwaterwithnitratefromfertiliseroriginisaseriousenvironmentalissueinareasofintensiveagriculturearoundtheworld.Areasofintensivevegetableproductiontypicallyproducetwotothreecropsannually,withfrequentirrigationandNapplications,sometimesatratesthatfarexceedtherateofNremovaloftheharvestedproduct1.Nitrogenfertilisersinteractwithsoilsandplantsindifferentways,andunderstandingthisiskeytoachievingthemostprofitableuseofnitrogen.AnhydrousammoniaisaNfertiliserthatinteractswiththesoilclayparticlesandmoistureinawaythatincreasestheretentioninthesoilandreducesleachingintogroundwater.

Atnormalroomtemperatureandpressureammoniaisagas,underhighpressureitconvertstoaliquefiedgas,andthisishowitistransportedandappliedtothesoil.Anhydrousammoniahasahighaffinitytowaterandonapplicationtothesoilitcombineswithsoilmoisturetoproduceammoniumions.Thefollowingreactionoccurs:

Ammoniagas(NH3)combineswithwaterinthesoiltoproduceammoniumnitrogen(NH4

+),plushydroxideions(OH-).

Ammoniagas(NH3)ishighlyreactiveandionisestoammonium(NH4+)ionsinthepresenceof

water.Ammoniumionshaveahighpositivechargeandassuchareattractedtonegativelychargedsurfacessuchasclayparticlesandorganicmatter.Thisstrongattractionreducesthelossofammoniatotheatmosphereorbyleachingintothesoil.Ammoniumisthenconvertedintonitrate(NO3

-)bysoilmicrobes,allowingittomovewithsoilmoisture.2

Anhydrousammoniaisnormallyusedasapre-plantfertilisertosupplynitrogeninbroadacrecerealsandcotton.Itisapplieddirectlyundertheseedorassidedressing.Anhydrousammoniacanhavebeneficialeffectsonsoilmicrobes,nitrifyingbacteriaandworms.ItcanalsoincreaseNretentioninthesoil,reducingnitrateleaching,resultinginnitrogen-use-efficiencybenefits.Cautionneedstobeusedwhenapplyinganhydrousammonia,asitcanbetoxictoseedsandplantroots.

Anhydrousammoniahasresultedinyieldadvantagesinbroadacrecerealsandcottonin

1Hartz,T.,W.Bendixen,andL.Wierdsma,Thevalueofpre-sidedresssoilnitratetestingasanitrogenmanagementtoolinirrigatedvegetableproduction.HortScience,2000.35(4):p.651-656.2IncitecPivot.BigNAgronomyGuide.Availablefrom:http://bign.com.au/BigNFertiliser/BigNAgronomyGuide.

NH3+H2OàNH4++OH-

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Australia;ithasalsobeenusedtoincreaseyieldsinvegetablecropssuchaspotato,sugarbeet,cabbage,lettuce,tomato,radish,beansandspinach.

Anhydrous ammonia use in vegetable crops

Incorporatinganhydrousammoniaintovegetablecroppingsystemscouldprovidearangeofbenefitstoproducerssuchasincreasedsoilhealth,reducedcost,increasedyieldandreducedenvironmentalimpactfromareductioninnitrateleaching.

InNewZealand,yieldandtissuecompositioncomparisonweremadeonlettuce,radishandbabyspinachafterapplicationofurea,sulphateofammoniaandanhydrousammonia.AnhydrousammoniacomparedfavourablywithotherformsofNforradish,Coslettuceandspinach.Anhydrousammoniaproducedsignificantlyhigherradishdryweightinthefieldcomparedtoureaandthecontrol.Whenanhydrousammoniawasappliedinlow-temperaturemonthsofJuneandJuly,yieldsweresignificantlyhigherthanallothertreatmentsasanhydrousammoniastimulatedplantgrowthandincreasedrecoveryofnitrogenfromsoil3.

Anhydrousammoniahasbeenfoundtobeeffectiveinrowcropssuchaspotatoes,sugarbeets,andcabbage.Incabbage,200kg/haofanhydrousammoniaproducedthemaximumyieldoffirstgradecabbageheadscomparedto200kg/haofcalciumnitrate4.

Inpotatoes,areviewof22experimentsusinganhydrousammoniafoundthatinnearlyalltrials,yieldincreaseswerefound.Anhydrousammoniaincreasedyieldcomparedtosolidfertilisersby0.5t/hain6trials,1.9t/hain8trialsandby5.9t/hain6trials5.AnhydrousammoniahasalsobeenmoreeffectivethancalciumammoniumnitrateinpotatoproductionduetotheslowreleaseofavailableNinwetwinters6.Highestyieldhavebeenfoundwheninjected1-3weeksbeforeplantingorsowing7.

Insugarbeet,yieldswereonaverage7.4t/hahigherwithanhydrousammoniathanureaandurea-ammoniumnitrate(Table2).Duringhighprecipitation(260mm)afterapplication,urea

3Thomas,M.B.,Anhydrousammoniainvegetablecropping:I.Vegetativeresponsetovariousapplicationrates.NewZealandJournalofExperimentalAgriculture,1973.1(3):p.261-266.4Steen,T.N.,Anhydrousammoniaforwintercabbage.TidsskriftforPlanteavl,1979.83(3):p.278-286.5VanBurg,P.F.J.v.andJ.H.Schepers,Ammoniainjectionasamethodofnitrogenfertilization.10.Resultsfromexperimentalplotsofindustrialpotatoes1964-1970.Stikstof,1972.6(70):p.416-418.6VanBurg,P.F.,G.D.V.Brakel,andJ.H.Schepers,Theagriculturalvalueofanhydrousammoniaonarableland:experiments1963-1966.NetherlandsNitrogenTechnicalBulletin,1967.3:p.1-39.7VanBurg,P.F.J.,J.H.Schepers,andG.D.VanBrakel,Ammoniainjectionasamethodofnitrogenfertilization.7.Dateofinjectioninspring.Stikstof,1967.5(55):p.351-4.

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yielded11.2t/halessthananhydrousammoniaduetoleachingofnitratefromthesoil8.

Incabbage,tomatoesandbeansanhydrousammoniaprovedaseffectiveasammoniumnitrateandsodiumnitrate,provingsuperiorforbeans.Intomatoesasplitapplicationat15cmgavesignificantlygreateryieldsthanasingleapplicationatthesamedepth9.

AnotheradvantageoftheuseofanhydrousammoniaistheresidualNinthesoilthatisavailableforthesubsequentcrop.Inasix-yeartrialfertilisingpotatoes,sugarbeetsandmaizewithanhydrousammoniaandcalciumnitrate,itwasfoundthathighresidualNafteranhydrousresultedinincreasesinyieldtothefollowingwinterwheat10.Anhydrousammoniahasalsobeenusedtosuppressroot-knotnematode.TheadditionofanhydrousammoniatoolivepomacereducedtheC:Nratioofsoil(increasedNcontent),reducedphytotoxicitytotomatoplants,supressednematodesandincreasedmicrobialactivityofthesoil.Thiswasadvantageousoverthetraditionaluseofureaasurea’shighsolubilitymeantitleachedoutofthesoil11.

Table1.ComparisonofformofnitrogenandmethodofapplicationonyieldofsugarbeetinNorthDakota,USA8.Nitrogensource Methodofapplication Rootyield(t/ha)

Averageof4years Urea Surface 43.9

Urea-ammoniumnitrate Surface +2.2

Ammoniumnitrate Surface +4.0

Ammonia Injected +7.4

Averageof2years

Urea Surface 48.6

Urea Injected +7.2

Urea-ammoniumnitrate Surface +0.7

Urea-ammoniumnitrate Injected +5.4

Ammonia Injected +7.4

8Draycott,A.P.andD.R.Christenson,Nutrientsforsugarbeetproduction:Soil-plantrelationships.2003:CABI.9Campbell,J.A.,Anhydrousammoniaasasourceofnitrogenforcabbage,tomatoes,andbeans.Proceedings.AmericanSocietyforHorticulturalScience,1950.56:p.253-6.10Nemec,A.,Theinclusionofautumnapplicationofanhydrousammoniainthereservefertilizationsystem.RostlinnaVyroba,1973.19(7):p.703-712.11Rodriguez-Kabana,R.,etal.,MixturesofolivepomacewithdifferentnitrogensourcesforthecontrolofMeloidogynespp.ontomato.JournalofNematology,1995.27(4SUPP):p.575-584.

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Application of anhydrous ammonia

Conventionally,anhydrousammoniaisappliedasapressurisedliquid,whichconvertstoagaseousformimmediatelyuponapplication.Thisisduetoapressuredrop,whichresultsin50%liquidand50%vapour.

Thisconversiontogaseousformmeansthatammoniacanbelosttotheatmosphereifthesoildoesnotflowfreelyaroundtheapplicationtime,limitingusefulnessinminimumtillageoperationsorincloddybeds.

WithCOLDFLO®technology,BigNcanbeappliedunderawiderangeofsoilconditions.InCOLDFLO®converters,ammoniaisconvertedtogaseousphaseandthenchilled,resultinginabout85%convertingbacktoliquid(Figure1).

WhenCOLDFLO®isused,thehigherliquidpercentageallowsfor“greaterresidencetime”asliquidammonia,resultingingreatercoveragebythesoil,increasedabsorptionbythesoilanddecreasedlossestotheatmosphere.12

Figure1:ComparisonofCOLDFLOandconventionalapplication3.

12BigNTechicalpoints.Availablefrom:http://bign.com.au/BigNFertiliser/BigNTechnicalGuide.

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Figure2.Applicationequipmentusingdiscs.PhotocourtesyofIncitecPivotFertilisers.

Theammoniaretentionzone

Theretentionzone–theareaofsoilimmediatelyaffectedbyapplication–hasbeenfoundtobe5–7.5cmacrossawiderangeofsoiltypes.Theretentionzoneundergoesdrasticchangesinchemical,biological,andphysicalsoilproperties.TheseincludeanincreaseofNH3andNH4

+concentrations,pHincreaseto9orabove,NO2

-increases,lowerpopulationofsoilmicrobesandsolubilisationofsoilorganicmatter.13

Researchintotheuseofanhydrousammoniainvegetablecroppingfoundthatitcouldbephytotoxic–inhibitingseedgermination,aswellasbeingtoxictogrowingplants.Itisimportant,therefore,toknowthedistributionofcroprootstoensurethatthefertiliserisplacedatthepointofgreatestabsorbance.IncreasingratesofNdecreasesratesofgerminations.However,placinganhydrousammonia7.5cmtothesideoftheseedoptimisedabsorptionforbabyleafspinach,lettuceandradish.Placementfurtherawayfromthissignificantlyreducesabsorptionby3–4weeks14.Forcropssuchaspotatoes,tomatoesandsugarbeetplacementof15cmawayfromtheseedisrecommended.CarefulplacementoffertiliserisneededasplacingBigNdirectlyunderneaththeseedcanreducegermination.

Followingapplication,theadsorptionofammoniabythesoilproducesanammoniaconcentrationandpHgradient.NitrificationbeginsattheoutsideedgeoftheammoniabandwheretheammoniaconcentrationandpHarefavourablefornitrifyingorganisms.AstheconcentrationofammoniaandpHdecreases,therateofnitrificationincreasestowardstothe

13Havlin,J.L.,etal.,Soilfertilityandfertilizers:Anintroductiontonutrientmanagement.Vol.515.2005:PearsonPrenticeHallUpperSaddleRiver,NJ.14Thomas,M.,II.Effectsofanhydrousammoniaplacementonrootgrowth,phytotoxicity,andnutrientuptake.NewZealandJournalofExperimentalAgriculture,1973.1(3):p.267-274.

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centreoftheapplicationbanduntiltheammoniumiscompletelynitrifiedorapHislowenoughtobealimitingfactor(Figure2)3.

Figure3.Theammoniaretentionzone.3

Applicationequipment

Theneedforspecialisedequipmentcouldbealimitingfactorforthewidespreadadoptionofanhydrousammoniainvegetablecroppingsystems.Pressurevesselsareneededforthestorageandsafehandlingofthegas.Thesevesselsrequiresignificantinvestmentandneedtoberegularlyinspected.

Insomeregions,ammoniainjectorsarerentedouttofarmerstospreadthecost.ThisisusefulifthereisnotalongdelaybetweenNapplicationandsowing.15

Retentionofammonia

Moistureisnotcriticalfortheretentionofammoniainthesoilasclayandorganicmatterprovidelong-termammoniaretentionsites.Highmoisturecontentofthesoilprovidespropersoilphysicalconditionstoensurerapidandcompletesealingoftheinjectionchannelandashort-termreservoirofammonia(initialcapacity)2.

Soiltextureisamajorfactorintheretentionofammonia.Thehighestretentionbeinginfinetexturedclaysoils,lowestincoursesandysoils.Thegreatestlossofammoniaisindrysandysoils.However,ifplacementofammoniaiscorrectandtheinjectionpointissufficiently

15Angus,J.F.,etal.,Effectsofbandedammoniaandureafertiliseronsoilpropertiesandthegrowthandyieldof

wheat.Crop&PastureScience,2014.65(4):p.337-352.

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coveredwithsoil,anhydrousammoniacanbejustaseffectiveindry,sandysoils.Theoretically,soilwithhighclaycontentandmoisturearemostsuitedforretention;inthefieldthesesoilscanloseahighproportionofammoniaifthesoiliscloddyanddoesnotprovidecoverageoftheinjectionfurrow2.

SoilpHaffectstheabilityofthesoiltoreactchemicallywithammonia.Underacidicconditionsclaymineralsarethemostattractivesites,whileunderalkalineconditionsorganicmatterismoreeffective2.SoilpHalsoinfluencesthepartitioningbetweenNH3andNH4

+.Followinginjection,NH3reactswithwaterandreleaseshydroxylsthatraisethepHofthesoilintheretentionzone.ThenitrificationofNH4

+ontheotherhandreleaseshydrogenions,whichreducesthepHlevelstooriginallevelsorlower16.ThepHofthesoilatinjectionhasbeenshowntoinfluenceretentionpercentage.AtpHbelow6,92%ofNinjectedintothesoilwasretained,whilethepHabove7.5,only64%wasretained.ThisisbecauselowpHfavoursammoniaconversiontoammonium.However,rateofnitrificationwashigherinsoilswithpHabove7.5-atlowpH,Nismorereadilycontainedinthesoilandammonium,butathighpH,Nisconvertedtonitratemorereadily.16

Figure4.AnhydrousammoniaBigNapplicationequipmentusingtines.PhotocourtesyofIncitecPivotFertilisers.

16Benke,M.B.,etal.,RetentionandnitrificationofinjectedanhydrousNH3asaffectedbysoilpH.CanadianJournalofSoilScience,2012.92(4):p.589-598.

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Benefit of anhydrous ammonia

Thesoilenvironment

Soilmicrobes

Theshort-termeffectsonsoilmicrobesi.e.thetimetakenforanhydrousammoniatobecompletelyconvertedtonitratehavebeenwellstudied.Duetothedrasticchangesthatthesoilundergoesintheretentionzone,populationsofmicroorganismsareeffected.Initially,thehighconcentrationofammoniaandincreaseinsoilpHintheretentionzonereducesmicrobialbiomasscarbonandprotozoabyabouthalf,whilenitrifyingbacterialpopulationsincrease.Fiveweekslater,microbialbiomassslightlyrecovers,withasmallimpactinthelong-term.However,protozoanumbersarereducedbyupto45%duetosensitivitytoammonia15.

Whencomparedtoureaapplication,anhydrousammoniaincreasedthemicrobialdiversityforbothbacteriaandfungiinthesoil.17Themicrobialdiversityinthesoilisseentobecriticaltothemaintenanceofthesoilshealthandquality,asawiderangeoforganismsareinimportantsoilfunctions18.Themicroorganismsinthesoilareinvolvedinimportantprocessessuchassoilstructureformation,decompositionoforganicmatter,toxinremovalandcyclingofcarbon,nitrogen,phosphorusandsulphur,aswellasplayingaroleissuppressingsoil-borneplantdiseasesandpromotingplantgrowth18.

Protozoainthesoilarealsoimportant,astheyarekeycomponentsofthesoilcommunityandregulatepopulationofsoilmicrofloraandcontributetodecomposition,mineralisationandnutrientcycling5.TheinitialdecreaseinsoilmicrobialbiomassandincreaseinpHalsoresultsinincreasedsoil-dissolvedorganiccarbon,asorganicmatterismadesoluble5.

Anhydrousammoniahasbeenshowntoreducepopulationsoffungi,bacteriaandnematodes19.Researchindicatesanhydrousammoniacansupresssoil-bornepathogens.AnhydrousammoniahasbeenshowntorapidlykillPhymatotrichopsisomnivorumthatcausesPhymatotrichumrootrot,alsoknownascottonroot,oneofthemostdestructiveanddifficulttocontrolsoil-bornediseases.FusariumroseumandFusariumsolanipopulationsalsodeclinedtozerowithintheammoniumretentionzone,withnorecoveryuntil225daysafterinjection20.

17Biederbeck,V.,etal.,Soilmicrobialandbiochemicalpropertiesaftertenyearsoffertilizationwithureaandanhydrousammonia.CanadianJournalofSoilScience,1996.76(1):p.7-14.18Garbeva,P.J.A.,etal.,Microbialdiversityinsoil:selectionofmicrobialpopulationsbyplantandsoiltypeandimplicationsfordiseasesuppressiveness.Annu.Rev.Phytopathol,2004.42:p.243-270.19Eno,C.F.,W.G.Blue,andJ.M.Good,Theeffectofanhydrousammoniaonnematodes,fungi,bacteria,andnitrificationinsomeFloridasoils.SoilScienceSocietyofAmericaJournal,1955.19(1):p.55-58.20Smiley,R.,R.Cook,andR.Papendick,AnhydrousammoniaasasoilfungicideagainstFusariumandfungicidalactivityintheammoniaretentionzone.Phytopathology,1970.60(8):p.1227-1232.

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Itisevidentthatanhydrousammoniainfluencesthemicrobialcommunitiesinthesoil.Themaineffectisintheretentionzone,averysmallportionofthesoil.Inthelong-term,thepopulationswithintheretentionzonearenotaffected,ifnotincreased.RepeatapplicationalongthesameinjectionpointcouldhaveanimpactonmicrobialcommunitiesbyreducingthepHofthesoil.ChangesinsoilpHcanhavealargeeffectonmicrobialcommunities21.BacterialcommunitiestendtosignificantlydecreaseassoilpHdeclines,whilefungalcommunitiestendtoincreaseinpopulation22.

Earthworms

Aswithmicroorganisms,thedrasticchangethatoccursintheretentionzoneofammoniainfluencesearthwormnumbers.Initially,earthwormnumbersarereducedduetothesechangesinthesoilenvironment.However,oncenumbersrecover,applicationofanhydrousammoniahasbeenshowntodramaticallyincreasethenumberofearthworms.

Whenanhydrousisapplied,approximately15%oftheearthwormpopulationiskilled.Afterthis,anhydrousincreasestheamountofavailablenutrients,resultingingradualincreaseinearthwormsintheapplicationzone.Afterthis,numbersmultiplyquicklyduetofertileconditions,6–8weeksafterinjectionandthetotalnumbersnormallygrowhigherthantheywerethereoriginally23.

IncreasesinearthwormnumbersareduetoaddedNincreasingbiologicalactivityresultinginenhancedearthwormgrowthandsexualactivity.Increaseinearthwormnumbershasbeenshowntoincreasesoilaggregation,improvedsoilstructure,increasedwaterinfiltration,increasedsoilaeration,assistinplantresiduedecompositionandincreasemicrobialmineralisationcycles24.

21Lauber,C.L.,etal.,Pyrosequencing-basedassessmentofsoilpHasapredictorofsoilbacterialcommunitystructureatthecontinentalscale.Appliedandenvironmentalmicrobiology,2009.75(15):p.5111-5120.22Rousk,J.,P.C.Brookes,andE.Bååth,ContrastingsoilpHeffectsonfungalandbacterialgrowthsuggestfunctionalredundancyincarbonmineralization.AppliedandEnvironmentalMicrobiology,2009.75(6):p.1589-1596.23Johnson,J.W.andC.Hudak,Mostaskedagronomicquestions.OhioStateUniversityExtension,1999.24Deibert,E.andR.Utter,Earthwormpopulationsrelatedtosoilandfertilizermanagementpractices.BetterCrops,1994.78(3):p.9-11.

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Table2.Earthwormnumberspost-anhydrousapplicationpersquaremetre24.

Stabilityofnitrogeninthesoil

Afterthereactionofammoniawithwatertoproduceammonium,thenitrogenislockedintothesoilexchangecomplexandwillnotleachoutofthesoilwithwater.Nitrogenwillonlyleachoutoftherootzoneafternitrification,andisduetotheprocessofsoilmicrobesconvertingammoniumtonitrate.Onceconvertedtonitrate,thenitrogenisreadilyavailableforuptakefromplantsandleachingwithwaterrunoff.

Delayingthenitrificationofammoniawithnitrificationinhibitorscanbebeneficialforcroppingsystems.Theuseofnitrapyrin,anitrificationinhibitor,reducednitrification(increaseNH4

+)andimprovedNretentionintheretentionzone.Nitrateleachingoutsideoftheretentionzonewasalsodecreasedwiththeuseofanitrificationinhibitor25.However,thesearenotcurrentlycommerciallyavailableinAustralia.

VegetablegrowerEdFagan(MulyanFarms)hasbeenusinganhydrousammoniaonpopcornandmorerecentlyinbabyleafspinach.Themainbenefitshehasnoticedinvegetablecropsare:(1)thenitrogenremainsavailabletothecropuntilharvest;(2)residualnitrogenmovesdownthesoilprofileslightly,butremainsintherootzone(0-30cm).ThisresidualNisthenavailableforasubsequentcropbecauseitisnotlosttodeepleachingorvolatilisation26.

StudiesoncornintheUSAinasandyloam,foundthatusinganhydrousammoniatosupplynitrogenreducednitrateleachingby56%,from43kgN/hato19kgN/ha,comparedtourea-ammonium.Theuseofthenitrificationinhibitornitrapyrinwasfoundtoreducenitrateleachingbyafurther18%.27

25Kidwaro,F.M.andK.D.Kephart,RetentionofnitrogenfromstabilizedanhydrousammoniainthesoilprofileduringwinterwheatproductioninMissouri.CommunicationsinSoilSc.andPlantAnal,1998.29(3-4):p.481-499.26Rogers,G.(2016)Theuseofanhydrousammoniaonbabyleafspinach,CowraNSW.AppliedHorticulturalResearchwww.ahr.co.au27Motavalli,P.P.,K.W.Goyne,andR.P.Udawatta,EnvironmentalImpactsofEnhanced-EfficiencyNitrogenFertilizers.CropManagement,2008.7(1).

AmmoniaApplicationrate(kg/Ha)055

Earthworms 98 292Cocoons 62 98Total 160 390

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Cropyields

InAustralia,cropyieldadvantageshavebeenfoundinbroadacrecerealsandcotton.Incomparisonwithurea,anhydrousammoniahasconsistentlyresultedinyieldincreases.IncerealcroppingsystemsinsouthernAustralia,shallowpre-sowingofanhydrousammoniahasresultedhigheryieldcomparedtotheequivalentureaapplicationinwetconditions,suggestinganhydrousammoniaresultsinhighercropyieldsthanureawhenconditionssuit15.

Inbroadacrecereals,yieldswere0.68tonnes/HahigherafterapplicationofanhydrousammoniainNorthernNSW,resultinginan$110/haincreaseingrossmarginsafterthecostofanhydrousammoniawasconsidered.28Incotton,yieldincreasesofseedcottonfrom3104kg/hato3203kg/hawereobservedusingureaandanhydrousammonia,respectively.Cottonbollnumber,weightandseedindexwerehighestwithanhydrousammoniaat100kgN/ha29.

Figure5.Sideviewoftheknifepointforanhydrousammoniaandgranularseed/fertiliserontheapplicationequipmentonthecommercialvegetablefarminCowra,NSW.

28GrainsresearchandDevelopmentCorporationGasandliquidfertiliserdrivesyieldgainsatTulloona.https://grdc.com.au/Media-Centre/Over-the-Fence/2015/08/Gas-and-liquid-fertiliser-drives-yield-gains-at-Tulloona29Suryavanshi,G.B.andA.V.Tendulkar,StudiesoneffectofanhydrousammoniaonirrigatedsummercottonKOP-498incomparisonwithureafertilizers.JournalofCottonResearchandDevelopment,1993.7(2):p.372-375.

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Figure6.Frontviewoftheknifepointforanhydrousammoniaandgranularseed/fertiliserontheapplicationequipmentonthecommercialvegetablefarminCowra,NSW.

Risk of anhydrous ammonia

Ammoniatoxicity

Placementofanhydrousammoniaisimportanttoavoidtoxicitytoseedsandyoungplants.Whenfertilisersareplacedclosetoseedsorplants,theosmoticpressureofthesoilincreases,whichcancauseinjurytoplants.The“saltindex”referstotheeffectofafertilisercomparedtosodiumnitrate,whichhasaratingof10030.

Anymaterialwithahighsaltindexmustbeusedwithcare.Anhydrousammoniahasasaltindexof47.1;thisisrelativelylowcomparedtoothercommonfertiliserssuchascalciumnitrate(52.5)andurea(75.4)30.However,carefulplacementofanhydrousammoniaisessentialtoensureitisnotphytotoxictoseedandyoungplants.

Notonlycananhydrousammoniareducegerminationofseeds,itcanalsoeffectcropestablishmentbyaffectingrootandshootelongation.Highconcentrationofammoniainthesoilcanresultinasignificantreductioninbothrootandshootelongationinmanycrops.Iftherateofrootextensionisbelowtherateofdryingsoil,poorgrowthoccurs2.Rootsalsobecome

30Lorenz,O.A.andD.N.Maynard,Knott'shandbookforvegetablegrowers.1988:JohnWiley&Sons.

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stunted,branchedaroundtheseed,thickerandhaveascorchedappearanceatthetip.Thismayleadtoproblemswithuptakeofothernutrientssuchasphosphorous,zincandcopper2.

Commercialavailability

AnhydrousammoniaisavailableinAustraliaas“BigN”suppliedsolelybyIncitecPivotFertilisers.ThemainusersofBigNaregrainandcottongrowersandthereforeanhydrousammoniaisnotavailableinallcroppingdistricts.Thismeansthatonlyvegetablefarmslocatedclosetograinandcottongrowingregionsarelikelytohaveanhydrousammoniaavailable.

Cost

Anhydrousammoniahaslowhandlingandapplicationcostanddirectapplicationtothesoilwithoutfurthermanufacturingcosthasmadeitoneofthemosteconomicalformsofnitrogen.ThetransportcostofammoniaperunitofNisrelativelylow.Itisalsomoreconvenienttohandleon-farmthansolidfertilisersasitcanbepumpedfromdeliveryvehiclestofarmimplements.Applyinganhydrousammoniaatthetimeofsowingalsosavessowingcostandtimeofaseparatefertiliserapplication15.

However,largeinitialcostcanoccurforthepurchaseofequipmentstorageandapplicationequipment.Dependingonthesize,equipmentcancost$20,000–$30,000.Onaverage,itcosts$2000permetreofBigNequipment.CostofanhydrouspertonneofNisnear-paritytourea,howeveritcontainsamuchhigh%Nconcentration.Therefore,therecanbesavinginthelong-termoncostperunitofnitrogen.

Health risks

Ammoniaisacaustic,toxicgaswithpowerfulcorrosiveactionontissue.InaUSstudy,30%ofallchemicalburnsadmittedtohospitalwerearesultofanhydrousammonia.Ammoniaexposurecanleadtodangerousinhalationandthird-degreeburnstothebody.

Ammoniaisapungentgasandcanbedetectedat53mg/L.Aconcentrationof100mg/Listolerableforseveralhours;coughingandlaryngospasmoccursatabout1700mg/Landitcanbefatalat2500mg/L.Ifexposurelastsfor30minutesat5000ppm,rapidrespiratoryarrestoccurs.31

However,inmostcases,ammoniacanbedetectedbeforeanyinjuryoccurs.Exposureshouldbetreatedimmediatelybyremovingcontaminatedclothesandwashingtheaffectedareainwaterforatleast20minutes.Farmworkersneedtobeeducatedofthepotentialrisksof

31Amshel,C.E.,etal.,Anhydrousammoniaburnscasereportandreviewoftheliterature.Burns,2000.26(5):p.493-497.

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anhydrousammonia,treatmentsandhowtoproperlyuseequipment.FarmoperatorsshouldbefamiliarwithandfollowtheBIGN®Farmeroperationalmanual32.

Environmental impacts

Energyuse

TheproductionofanhydrousammoniarequireslessenergythanureabecauseofitshighNconcentration,requiringtheleastamountofprocessing.Therearealsoenvironmentalbenefitsfromuseofanhydrousammoniainlessleachingofnitrates,whichcancontaminatewatersuppliesandleadtosoilacidification.

Nitrousoxideemissions

Theemissionofnitrousoxideishighlydependentonsoiltype,croptype,soilorganicCcontent,soilpH,tillageregime,nitrogensource,placement,timingandrate33.Applicationofanhydrousammoniatosoilshashadvariedresultsinrelationtonitrousoxide(N2O)emissions.

Anhydrousammonia,ammoniasulphate,ureaandcalciumnitratewerecomparedonawheatcroponsiltyclayloam.Theareaswhereanhydrousammoniawasknife-injectedpre-planthadhigherN2Oemissions(2.08kgNHa)comparedwithammoniumsulphate(1.31kgNha).However,theseanhydrousammoniatreatmentsdemonstratedthehighestnitrogenuseefficiencyduetoavailableammoniumintherootzone.34

Anhydrousammoniaappliedaspre-plantfertilisertocorncropsonsiltyclayloamsoilsresultedin2.45kgN/hainnitrogenemissions.Thisisreducedbyupto65%byreducingtherateofapplicationfrom202kg/hato145Kg/ha.35

N2Oisagreenhousegas,beingattributedtodeleteriouseffectsonglobalwarminganddestructionoftheozone.Environmentalstewardshipneedstobemaintained:thisshouldincludeonlyapplyingwhenweatherandsoilconditionsarepermitting,ensuringtheinjectionchannelisfullyenclosedbysoil,hence,reducingemissions.

32BigNFarmerOperatingManual.Availablefrom:http://bign.com.au/~/media/BigN/071016_website_-_online_tools_-_farmer_op_manual_-_f.pdf.33Stehfest,E.andL.Bouwman,N2OandNOemissionfromagriculturalfieldsandsoilsundernaturalvegetation:summarizingavailablemeasurementdataandmodelingofglobalannualemissions.NutrientCyclinginAgroecosystems,2006.74(3):p.207-228.34Zhu-Barker,X.,W.R.Horwath,andM.Burger,Knife-injectedanhydrousammoniaincreasesyield-scaledN2Oemissionscomparedtobroadcastorband-appliedammoniumsulfateinwheat.Agriculture,Ecosystems&Environment,2015.212:p.148-157.35Omonode,R.A.,P.Kovács,andT.J.Vyn,TillageandNitrogenRateEffectsonArea-andYield-ScaledNitrousOxideEmissionsfromPre-PlantAnhydrousAmmonia.AgronomyJournal,2015.107(2):p.605-614.

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Figure5.AnhydrousammoniaBigNbeingappliedintorows.PhotocourtesyofIncitecPivotFertilisers.

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Conclusions Thisreviewsthecurrentinformationontheuseofanhydrousammoniaasasourceofnitrogeninagriculturalcrops.AnhydrousammoniaiswidelyusedinAustraliaforsupplyingnitrogentograinandcottoncrops.Itishighinnitrogen(82%).Theavailabilityofanhydrousandequipmentforitsapplicationismainlyfocusedaroundcottonandgrainproducingareas.

Anhydrousammoniaisatoxicmaterialthatmustbehandledwithcare.Ifitcontactstheskinitcancauseseriousburns.

Anhydrousammoniahasbeneficialeffectsonsoilmicroflora,nitrifyingbacteriaandearthworms.

Anhydrousammoniaisconvertedtotheammoniumform,which,beingapositivelychargedion,allowsittobeheldonthesoilexchangecomplex(claycolloidsandorganicmatter);thiscanbeimportantbecauseithelpstomaintainnitrogeninthesoilintherootzoneofcrops.Thepersistentnatureofanhydrousammoniacanbefurtherimprovedbytheadditionofnitrificationinhibitorstokeepthenitrogenintheammoniumformbyslowingitsconversionintothemorewater-solublenitrate.

Anhydrousammoniaperformedwellasasourceofnitrogenforthelimitednumberofvegetablecropswhichhavebeenassessed,andresistsleachingunderwetconditions.Therecanbeissueswiththelimitedlateralspreadofnitrogeninthesoil,leadingtovariabilityinbabyleafcrops.

Thereviewconcludesthatanhydrousammoniadoeshavepotentialasanitrogensourceforvegetablecropsbutismoresuitedtorowcropsratherthanbabyleafcrops,whereanevendistributionnitrogeninthesoilisrequired,althoughapplicationequipmentcouldpossiblybeadaptedtoapplyanhydrousammoniainawaythatismoresuitableforbabyleafcrops.

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Recommendations

1. Thatabestpracticeandhandlingguidebeproducedtoguidegrowersandagronomistsonhowtouseanhydrousammoniaforvegetablecrops(completed).

2. Thatfurthertrialsarerequiredtodeterminetheoptimumusagepatternforanhydrousammoniainarangeofvegetablecrops.

3. Thefocusofanyfurtherresearchontheuseofanhydrousammoniaonvegetablecropsbeconfinedtorowcropsratherthancropsuchasbabyspinachwhichrequireanevenspreadofnitrogenacrossthebed.

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Outputs

Desktop review- The potential of anhydrous ammonia as a nitrogen fertiliser for the vegetable industry.

Fact sheet- The benefits and risk of anhydrous ammonia as a nitrogen fertiliser in vegetable cropping.

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Scientific Refereed Publications

Nil.

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Intellectual Property/Commercialisation

No commercial IP generated.

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Acknowledgements

Incitec-Pivot Fetilisers Ed and James Fagan, Cowra.

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Appendices

Appendix 1- Anhydrous ammonia fact sheet for the vegetable industry- Anhydrous ammonia for vegetable crops: Could it be a viable proposition?