Precision Agr for Nutrient management on farms

Mini-review

Received:16October2013

Revised:1April2014

Acceptedarticlepublished:9May2014

PublishedonlineinWileyOnlineLibrary:2June2014

(http://wendang.chazidian.com)DOI10.1002/jsfa.6734

Theroleofprecisionagricultureforimprovednutrientmanagementonfarms

CarolynHedley*

Abstract

Precisionagricultureusesproximalandremotesensorsurveystodelineateandmonitorwithin-?eldvariationsinsoilandcropattributes,guidingvariableratecontrolofinputs,sothatin-seasonmanagementcanberesponsive,e.g.matchingstrategicnitrogenfertiliserapplicationtosite-speci?c?eldconditions.Ithasthepotentialtoimproveproductionandnutrientusee?ciency,ensuringthatnutrientsdonotleachfromoraccumulateinexcessiveconcentrationsinpartsofthe?eld,whichcreatesenvironmentalproblems.Thedisciplineemergedinthe1980swiththeadventofa?ordablegeographicpositioningsystems(GPS),andhasfurtherdevelopedwithaccesstoanarrayofa?ordablesoilandcropsensors,improvedcomputerpowerandsoftware,andequipmentwithprecisionapplicationcontrol,e.g.variableratefertiliserandirrigationsystems.Precisionagriculturefocussesonimprovingnutrientusee?ciencyattheappropriatescalerequiring(1)appropriatedecisionsupportsystems(e.g.digitalprescriptionmaps),and(2)equipmentcapableofvaryingapplicationatthesedi?erentscales,e.g.thefootprintofaone-irrigationsprinklerorafertilisertop-dressingaircraft.Thisarticlereviewstherapiddevelopmentofthisdiscipline,andusesNewZealandasacasestudyexample,asitisacountrywhereagriculturedriveseconomicgrowth.Here,thehighyieldpotentialsonoftenyoung,variablesoilsprovideopportunitiesfore?ective?nancialreturnfrominvestmentinthesenewtechnologies.

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Keywords:precisionagriculture;variableratetechnology;nutrientmanagement;sensors;GPS

INTRODUCTION

Precisionagricultureismadepossiblebynewtechnologies[geo-graphicpositioningsystems(GPS),sensors,geographicinforma-tionsystems(GIS),andadvancedsoftwareandprecisionappli-cationequipment].Itaimstomodifyinputs(e.g.fertiliser,irri-gation,dairye?uent,seedrate)spatiallyandtemporallyatthesub-paddockscaleforcoste?cienciesandproductivityandenvi-ronmentalgains.Globally,thea?ordabilityandaccessibilityofthesetechnologieshelpedprecisionagricultureemergeasaresearchdisciplineinthe1980s1andastrongfocushasalwaysbeentoimprovenutrientusee?ciencybymatchinginputstosite-speci?c?eldconditions.2,3

Matchingfertiliserinputstosite-speci?c?eldconditionsrequiresmeasurementandunderstandingofsoilspatialvariabilityandcropnutrientstatus,anditsrelationtocropresponse.Precisionagricultureuseshighresolution(<10m)geo-referencedremoteandproximallysenseddatatoquantifyanddelineatevariabilitybetween‘managementzones’.4Thesensorsgeneratelargevol-umesofdata,andthesimultaneousadventofhigh-performingcomputersandtheinternethasmadeitpossibletoprocesslargesurveydatasetsanddatastreamsinnearreal-timetoinformprecisionmanagementdecisions.Fieldstudieshaveshownthatsite-speci?cin-seasonadjustmentsoffertiliserinputstoaccountforclimaticconditionsandvaryingyieldpotentialdi?erencesincreasefertilisernitrogen(N)usee?ciencyupto368%comparedwithcommonfarmerpractices.5,6

Beforetheintroductionofprecisionagriculturemethods,researchershadnotedsoilvariability7,8anddiscussedtheneedfordi?erentialinputs,e.g.fertiliserapplicationtohillcountry.9,10However,itwasthea?ordabilityoftheGPSandsensor

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technologiesthatadvancedourabilitytomeasureandmonitorsoilandplantvariabilitytotailorinputstosite-speci?cconditionsinthelandscape.ResearchhasshownthattheintroductionofGPSalone(‘autosteer’)ontofarmmachinerycanincreasee?cien-ciesby5–10%(e.g.reduceoverlapsandgaps,whenspreadingfertiliser).11AGPSsystem,theInertialNavigationSystemTechnol-ogy,hasrecentlybeenintroducedfortheautomatedguidanceofagriculturalvehicles,makingpossibletheaccuracy,reliability,andabilitytodisplay,combine,andmanipulatespatialmapsof?eldcharacteristicsinstantlytothevehicleoperator.5WhensensorsareusedwithGPS,andGISisusedtoproduceprescriptionmaps(e.g.forguidingvariablefertiliserorirrigationapplications),savingscaneasilybeanother10–20%,dependingontheinherentvariabilityandneedforvariableinputsexistinginthatpaddock.ThisarticlereviewstheintroductionofprecisionagriculturetoNewZealand.NewZealandprovidesausefulcasestudybeingasmallcountrywhereagriculturedriveseconomicgrowth,afarm-ingcommunityexiststhatiscapableandwellplacedtorespondtochangingmarketforces,andpastureandcropyieldpotentialsarecomparativelyhighonaglobalscaleduetofavourablesoilandclimaticconditions.Thisprovidestheopportunitytoconvertcap-italexpenditureinnewtechnologiesandmanagementmethodstoproductivitygainsand?nancialreturn.

?

Correspondenceto:CarolynHedley,LandcareResearch,RiddetRoad,MasseyUniversityCampus,PalmerstonNorth4442,NewZealand,E-mail:Hedl-eyC@LandcareResearch.co.nz

LandcareResearch,RiddetRoad,MasseyUniversityCampus,PalmerstonNorth,4442,NewZealand

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http://wendang.chazidian.comEARLYSTUDIESSCOPINGTHEPOTENTIALGPSmappingandguidance‘Autosteer’,yieldmapping,roboticAPPLICATIONOFPRECISIONFARMINGINNEWmilking,RFIDtagging,electromagneticsensormapping).TheZEALAND?ndingsofthisreviewledtofurtherPAresearchinvariablerateAninitialNewZealandstudytoinvestigatethepotentialben-fertiliserapplicationtohillcountrybytop-dressing12–14andto?ate?tsofprecisionagriculturetoarablefarmerswasinitiatedinlandbygroundspreading.151998(Fig.1).11TheprojectwasdesignedtodemonstratetheOtherworkatthistime16reviewedthepotentialuseofsiteeconomicbene?tsofidentifyingdi?erentgrowthzones(termedspeci?cdatatechniquesandinformationmanagementsystemsin‘managementzones’)withinapaddockandalteringmanage-horticulturalenterprisesandstatedthattherewereopportunitiesmentofeachzonetomaximiseitspotential.Themainunderly-tousethismethodtooptimisephysicaland?nancialaspectsofingvariablesfoundatthesitesweresoildepth,moisturereten-horticulturalproductionsystems,alongwithprovisionofreliabletion,anddrainage,whichplayedsigni?cantcontrollingrolesonauditforproductsecurity.yieldandgrowerreturns.Aconclusionofthestudywasthat

inputssuchasNfertilisershouldbealteredtobestsuittheland

andsoilconditions,aswellasagronomicrequirementsofthePRECISIONAGRICULTUREATTHELANDSCAPE

particularcrop.VariablerateNfertilisertrialsindicatedthattheSCALE:ASSESSINGVRATFORAERIALabove-averageyieldingpartsofpaddockshadscopetorespondtoFERTILISERAPPLICATIONTOHILLCOUNTRYadditionalN.FARMS

ThestudyalsoexaminedhowtousecropyielddataforprecisionAstudywasconductedtoinvestigatethepotentialuseofprecisionmanagement,andfoundthatyieldpotentialvariesfordi?erenttechnologiesbyhillcountryfarmingcommunities.12–14Itassessedcropsindi?erentmanagementzones,aswellaswithseasonalthepotentialbene?tsfromautomatingfertiliser?owcontrolfromconditionsandthelevelofappliedcropmanagement.top-dressingplanestovaryapplicationratesbasedonthepoten-Thisinitialworkindicatedthatasigni?cantknowledgebaseistialoutputsofthefarmland.Topredictthedistributionpro?leofrequired,e.g.yieldmaps,soilandclimaticinformation,cropagron-anyparticle-sizedistributionfromspreaderducts,andthedeposi-omy,andequipmenttypetoassessneedsandabilityforprecisiontionfootprint,atransversedistributionmodelwasdevelopedthatmanagement.Thisisanunderlyingprincipleofprecisionagricul-modelledtheballisticsofsuperphosphategranulesfromaircraft.ture,i.e.‘measure,monitorandthenmanage’.Atthistime,someGoodagreementswerefoundbetweenthemodelpredictionsandmodernsprayequipmentwascapableofdi?erentiallyspraying?eldtrials.

di?erentzoneswithdi?erentratesofNalthoughthebene?tshadAsubsequentcomparisonoftheeconomicbene?tsofasingleyettobeeconomicallyproven.automatedapplicationofsuperphosphate,whereautomationAcomprehensivestudy11wassubsequentlyconductedtoassessreducedapplicationoutsideofthezone,wascomparedwiththepotentialimpactsofprecisionagricultureonNewZealand’samanuallyoperatedsystem.17Theautomationprovidedanetagriculturalandhorticulturalindustries.Thestudyreviewedthebene?tofNZD$2800fora1500hahillcountryfarmingsystem.currentuseofprecisionagriculture(PA)technologiesinNewThevalueofimprovingtheperformanceofatop-dressingair-Zealand,andexaminedtheenvironmentalandeconomicbene-craft,onanindustrylevel,wasalsoexamined.Thecostbene?t?ts,identifyingdi?cultiesinimplementationandfuturepotential,analysisbetweenamanualandautomatedsystemrevealedandareaswherefutureR&Dshouldbefocussed.Thebene?ttoabene?tofNZD$111th;700year?1forasingletop-dressingNewZealandfromtheapplicationofPAwasestimatedasNZDaircraftusingtheautomatedsystem.Thisamountequates$1.27billion,forthefourmainsectors:(1)viticulture,(2)sheepto10–25%oftypicalannualcostsofspreadingsuperphos-andbeef,(3)grainand(4)dairying.Theanalysisindicatedthatphate,basedon600h?yingtimeperyear,spreading12Th?1thegreatestbene?tofPAwouldbetosheepandbeeffarmingatNZD$60T?1.onrollingandhillyland,becausethelevelofvariabilityinyieldAspatiallyexplicitdecisiontreemodellingtechniquewaspotentialistypicallyfarhigherinthistypeoftopographythan?atdeveloped18topredictthevariationsofannualpastureproduc-land;perhaps?ve-foldhigherthanthatexpectedoncroppingortionwithtopographyoverthestudyarea,andanexampleofdairyfarms.Second,thecostsofimplementingprecisionagricul-theoutputofthismodelisshowninFig.2.Themodeltendedturetothissectorwasexpectedtobelowerthaninothersectors,tofollowthefarm’sdigitalelevationmodel,andshowedthatwithmostbene?tderivedfrompreciseplacementoffertiliser,suchvariable-rateapplicationtechnology(VRAT)wasthemoste?cientasdressingsofsuperphosphate,thusreducingapplicationrateonandhighestreturningapplicationmethodperhectare,http://wendang.chazidian.comparedwithconventionalaerialapplicationtechniques.Addi-Aspracticallyallthefertiliserisappliedbyaircraftintheseland-tionalcontractorcostsandtheresultantincreasedcharge-outscapes,mostofthecostwouldbebornebytheaerialcontractors.rateswerelikelytooccurunderVRAT;nevertheless,theanaly-Forthisexerciseitwasassumedanextrachargeof5%wouldcoversisindicatedthatsigni?cant?nancialincentiveswereavailablethecostofusingthistechnology.Atthattime,thebeefandsheeptothefarmer.Asensitivityanalysisrevealedthatevenwithasectorused49%ofthetotalfertiliserusedperannuminNew20%increaseincharge-outrateassociatedwithVRAT,thefarm’sZealand,withfertilisercostsmakingup22%ofannualcashexpen-annualcashpositionvariedbyonlyNZD$4500(0.4%),suggest-ditureonsheepandbeeffarms.Amodellingexerciseshowedingthecostofimplementingsuchasystemisnotprohibitiveapotential27%yieldincreasebyvaryingfertiliserapplications,andwouldallowaircraftoperatorstoaddvaluetotheirser-withdi?erentratesbeingappliedondi?erentslopeandaspectvices.Therehasbeenlittleuptakeofthistechnologytodate,categories.withthe?nancialviabilityofthetop-dressingindustryasaMurrayetal.concludedthatforproducerstoimproveproduc-wholebeingtestedbyrisingfertiliserprices,andfallingendusertione?ciencytheymust?rstbeabletomeasureit,forwhichpre-demandresultinginlowerreturnstotheindustrypertonnecisionagricultureprovidesanumberofenablingtechnologies(e.g.applied.17

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Hedley

Figure1.AtimelineofprecisionagricultureresearchanduptakeinNew

Zealand.

Figure2.AnexampleofthedecisionsupporttreeoutputpredictingannualpastureproductionatLimestoneDownspastoralhillcountryfarm,NorthIsland,NewZealand.12–14,17

PRECISIONAGRICULTUREATTHEPADDOCKSCALE:VRATFORGROUND-SPREADINGFERTILISERVEHICLES

Inaccurateapplicationofnutrientsfromground-basedfertiliserspreadingvehiclescanleadtomajoragronomicandeconomiclosses.15Astudywasconductedtodevelopmethodstotestgroundspreaderapplicationperformance,andthenevaluatedtheeconomicbene?tofusingprecisionagriculturetechnologiesinNewZealanddairyfarmingsystems.15

Atransversespreadertestgaveagoodindicationofmachineperformanceincontrolledconditions.Thistestmeasuresthedis-tributionpatternofappliedfertiliserinaseriesoftrayslaidoutinthe?eldtocollectthefertiliserduringonepassofthespreader.A?eldmethodwasthendevelopedtoaccountfortheinteraction

ofthespreaderinitsoperationalenvironment.This?eldmethodloggedandusedvehiclelocationwiththetransversespreadpat-ternofsuperphosphateorureatocreate?eldapplicationmaps.Astudyonfourdairyfarms,over102paddocks,showedanaver-agespreadingvariationwas37.9%,anditwassuggestedthattheaccuracyofthis?eldfertiliserdeliveryneededtobeimproved.AmethodwassuggestedusingGPSautosteerguidanceonthefer-tiliserspreader.

Theabilitytoexecuteanutrientplanusingbothactualandoptimisedspreadingdatacollectedduring?eldapplicationwasassessed.AlossofNZD$66ha?1wascalculatedwhencompar-ingthee?ciencyofusingcurrentspreadingmethodswiththoseassumedinnutrientbudgetingpractice,i.e.accurateapplica-tionrates.WhenGPSguidanceandcontrolsystemswereusedtoimprove?eldapplicationthelosswasshowntoreducetoNZD$46ha?1.

Thishighlightedthedi?cultiesinachievingaccurate?eldnutri-entapplicationwithexistingfertiliserspreadingequipment;how-ever,bydevelopingtheabilitytoquantify?eldperformance,eco-nomicopportunitiescouldbeevaluated.Overall,thisworkfoundthattherewasastrongagronomicandeconomiccasefortheimplementationofprecisionagriculturaltechnologiesintheNewZealandfertiliserindustry.

Theseinitialstudies,completedin2007,providedsomebench-markmethodsforassessingthespatialvariabilityoffertiliserspreadingbothinhillcountryand?atland.Theyalsodiscussedwaysinwhichfertiliserapplicationratescouldbemoreaccuratelydeliveredtotheland,andvariedaccordingtotheyieldpotentialatanyspeci?cposition.TheeconomicanalysesshowedthatforuptakebytheNZfertiliserindustryandthefarmingcommunity,precision-farmingmethodsdeservedfurtherstudyanddevelop-ment.Theworknotedatthattime,thattherangeofequipmentusedbythespreadingindustrywasinadequateforvariablerateapplication,sothattheseestimatedbene?tscouldnotbeopera-tionallyrealised.

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Arangeofvariableratefertiliserapplicatorsarenowavailable?Potentialforhighlye?cientcontrolleduniformorvariableinNewZealand.Thelatesttechnologyforprecisionspreadersapplicationtomeetthesite-speci?cneedsofthecrop,overausesvariableapplicationplacementcontrol,whichincorporateslargearea(50haorlarger)

avariablespreadingdiscspeedandelectricaladjustmentofthe?Ahighdegreeofautomationrequiringlesslabourthanmostdeliverysystemsothatforthe?rsttimethespreadwidthofotherirrigationsystems

therightandleftsidescanbeindividuallycontrolled.Toprevent?Abilitytoapplywaterandwatersolublenutrientseconomicallyover-andunder-fertilisation,theapplicatoralsohasa‘headlandoverawiderangeofsoil,crop,andtopographicalconditionscontrol’toavoidoverlapsinheadlandsandwhendrivingaround

curves.19Precisionfertigationsystemsneedtobeguidedbyprescription

mapsof(1)cropwaterand(2)nutrientstatus,whicharelikelytobe

di?erent,e.g.soildrynessindicatestheneedforirrigation,butdoes

VARIABLERATEIRRIGATIONMINIMISINGnotnecessarilyindicateafertiliserrequirement;thelatterbeingNUTRIENTLEACHINGLOSSEScontrolledbypastfertiliserandlandusehistory,aswellassoilTherelevanceofapplyingvariableratetechnologytoirrigationconditions.Considerableresearchisrequiredtodevelope?ectivesystemshasbeenresearchedandfoundusefultoreducedrainagedecisionsupporttoolsforprecisionfertigationsystems.andaccompanyingnutrientleachinglosseswherevariablesoilsDripirrigationisthemoste?cientmethodtodeliverwaterandexistunderanirrigationsystem.20,21Avariableratemodi?cationnutrientstoaplant,butisnotalwayspracticable(e.g.incultivated

soils),isexpensivetoinstall,andrequiresregularmaintenance,forsprinklersystemswasdeveloped22within3yearsofthedevel-e.g.acidwashingtokeepdriplinesclean.Anumberofearlieropmentoftheirrigationprescriptionmapmethod.ThevariableNewZealandstudiesexaminedfertigationofcropsusingdripratemodi?cationprovidesindividualsprinklercontrol,andispro-irrigationsystems,andfoundthatfertigationwasofnobene?tgrammedtovaryirrigationtodi?erentsoilmanagementzonesforkiwifruitondeepfree-drainingsoils.32,33Otherresearchfoundunderoneirrigationsystem.23Themappingmethoduseselec-mixedbene?tstofertigatingonionsandsquashinafertilesandytromagneticsoilmappingtoquantifysoilvariabilityonabasisloamsoil.34

ofsoiltextureandmoisture.24ThesemapsarethenconvertedtoSub-surfacedripirrigationofpastureshasbeentrialledinAus-irrigationprescriptionmaps,bycharacterisingsoilwaterholdingtralia,duringasevereshortageoffreshwater.35Itappearslikelypropertieswithineachmanagementzonede?nedontheelectro-thatthishighlye?cientmethodofintroducingnitrogenfertilisermagneticmap,andmonitoringdailysoilmoistureineachman-totherootzonewillmilitateagainstnitrateleachinglossesandagementzone.Newsmarttechnologiesexisttomonitorsoilmois-nitrousoxideemissionsinawell-managedsystem,butissuesoftureinreal-time,continuouslywithwebaccess,e.g.wirelesssoilacidi?cationwillneedtobefurtherinvestigated;andappropriatemoisturesensornetworks.25,26Irrigationisvariedtoeachman-decisionsupportsystemsneedtobedeveloped.agementzonebecausedi?erenttexturalsoilclasseswilldryout

atdi?erentrates,eachreachingthecriticalsoilmoisturede?cit

atwhichirrigationisrequiredondi?erentdays.Thecalculated

watersavingsofthisvariablerateirrigationsystem,wasmodelledDAIRYFARMEFFLUENTIRRIGATION

for?vecasestudysites,andshowntobe9–26%withequiva-In2003theNewZealanddairyindustryincreasedthenationallentenergysavingsandimprovede?ciencyinuseofirrigationdairycowherdby44%from2.6millionin1993to3.74mil-water.Modelleddrainageandrun-o?werereducedby0–55%dur-lion.In2011ithadincreasedfurtherto6.2millioncows.36,37ingtheperiodofirrigation,withanaccompanyingreducedriskofTheseincreasesincownumbershavegeneratedverylargevol-Nleaching.umesofdairy-farme?uent(DFE),requiringappropriateman-Internationaluseofthistechnologyhasbeenreviewed27andagement.TheintroductionoftheResourceManagementActfoundtobeunder-utiliseddespiteitspotentialtoimpactposi-in1991opposedthetraditionalprocedureofthedischargeoftivelyoncropwaterproductivity,waterandenergyconservation,two-pond-system-treatede?uenttowaterways,makingitaregu-andtheenvironment.Thetechnologicalmodi?cationofirriga-latedactivity,i.e.restrictionswereimposedontimingandamounttionsystemsisnowcommerciallyavailable,butfurtherresearchisofdischargetowaterways.Thepreferredoptionbecamelandrequiredtodevelopauser-friendlydecision-supportsystemcapa-applicationofDFEtakenfromthetwo-pondsystemordirectlybleofde?ningmanagementzones,sensingwithin-?eldvariabilityfromasumpholdingthedairywash-down.Researchwasnec-inreal-time,andadaptivelycontrollingsite-speci?cvariable-rateessaryto?ndthemostappropriatemethodforlandapplica-waterapplications.27–30tionofDFE.Deferredirrigationwastrialledasamethodforlandtreatment,whichisaformofprecisionmanagement(temporal)

becauseitdelaysirrigatingverywetsoilsuntilaspeci?edsoilmois-

PRECISIONFERTIGATIONOFNUTRIENTSturede?citisreached.38Muchgreaterspatialoptimisationofnutri-

entmanagementispossible,usingtargetedapplicationtoensure

Fertigation,theapplicationofnutrientsinirrigationwatertoDFEisplacedaccordingtoplantneedsandnutrientinputs,andplants,hasevolvedwithirrigationtechnology,andismoretimetoavoidcriticalsourceareasofnutrientloss.38Goodprogresshasandcoste?cientthantwoseparateoperationsapplyingwaternowbeenmadewiththeautomationofDFEschedulingandappli-andnutrients.Thereareahandfulofearlyadoptersofcentrecation,usingreal-timedailyweatherrecords,modelling,andsen-pivotfertigation31inNewZealand,andthetechnologyisshowingsorstotrackstoragepondvolumesandsoilmoisturede?citsandasteadyrateofuptakeinotherpartsoftheworld.Whensolididentifyopportunitiesforirrigation.39GPSontheirrigatoriden-ureaisdissolved,theendothermicreactioncanbeproblematicti?esitspositioninthelandscapeandcustomisesapplicationsinfarmfertigationsystems,andsotheuseofureaasasolutiontore?ectsoilmoisturede?cit.Aproductwasdevelopedin2010isadvisable.31Thepotentialbene?tsofusingcentrepivotsforwhichsendsatextmessagetothefarmereverymorning,toinformfertigationthereforeinclude:27onsoilmoisturede?cit,andtherehasbeensomeinitialuptakeJSciFoodAgric2015;95:12–19©http://wendang.chazidian.com/jsfa15

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byendusersofthisproduct.40TheautomationofDFEmanage-mentsystemso?ersadvantagesintermsofreducedfarmlabourrequirementsandfeweropportunitiesforoperatorerror.Whilethereissomeslowuptakeofthesecommercialsystems,theycouldbecomearegulatoryrequirementinthefuture,becausetheyassistpreciserecyclingofnutrientstopastures,withlessriskofrun-o?towaterways.38

CHedley

PASTUREYIELDMAPPINGANDPASTUREQUALITYASSESSMENT

Pasturequantity

Wherepastoralagriculturedominatesoverarableagriculture,asinNewZealand(only3%ofagriculturallandiscroppedandmorethan50%isgrazed),theabilitytoyield-mappasturesisrelevantandprovidesadecisionsupporttoolforimprovedpastureman-agement.Anon-the-gopasturemeterwasthereforedevelopedinNewZealandtoaddressthisneed.43Theequipmentusesopticalsensorstodeterminepastureheight,andneedstobecalibratedforpasturedensity.Itcanbeusedasastand-alonepasturemeterorwithGPSforpasture-yieldmappingtoprovideinformationfor(1)feedbudgetingand(2)strategicvariableNinputdecisions.Aneconomicanalysiswasconducted,usingapastureyieldmaptoindicatepotentialbene?tsfromapplyingvariableratesofNfertilisertopasture.Uniformapplicationsof150kgha?1y?1urea-Nappliedtoa?eldwherepastureproductionisvariableshowsthatproductionreturnvariesindi?erentpartsofthe?eld,perkgNaddedtothepasture.Astudyofadairypastureshowedthatthehighproducingareaproduces15kgDMkg?1Ncomparedwith7kgDMkg?1Nforalowproducingarea.Assumingpasturevalueis20cNZD$0.20kgDM,theextraproductionvalueinthelowproducingareaisworthNZD$225andinthehighproducingareaisworthNZD$455.Thenetbene?toffertiliserapplicationcanbecomparedbysubtractingthe?xedcostofapplication($10hakg?1comparedwithNZD$239hakg?1).Thisprovidesacaseforvaryingfertiliserinputstomeettheyieldpotentialofdi?erentmanagementzones,e.gwheretheyielddi?erencesareduetosoildi?erences.44

Furtherresearchwillneedtoconsiderthee?ectofurinepatchesonfertiliserapplicationrates.Thevariabledepositionofurinepatchesacrossapaddock,duetopreferentialmovementandcampingofgrazingstockwillpartiallyexplainthevariableyieldmapandthereforeneedstobeconsideredwhendesigningavariableNfertilisationstrategy.

ASSESSINGVARIABLECROPRESPONSEUSINGOPTICALSENSORSFORIMPROVEDSTRATEGICINPUTMANAGEMENT

Currently,mostgrowerscalculatetheirNfertiliserrequirementswithanutrientbudgetbasedonsoilmineralNtestresultsandpotentialyieldofthesite.ThepracticeofasinglerateofNfer-tiliserappliedacrossawholecropmayresultininsu?cientorexcessiveNfertiliserratesincertainpositionsbecauseofthespa-tialvariabilityofsoilmineralNandpotentialyieldwithinanyonepaddock.AmoreaccurateestimateofplantNrequirementsisthereforerequiredforeconomicandenvironmentalsustainabil-ity.Measurementofcanopyre?ectancewithcropsensorscouldpotentiallyusetheplantasanindicatorofNrequirements.InwheatcropsNistypicallyappliedintwoorthreeapplications.Itisenvisagedthatthenormaliseddi?erencevegetationindexmaybetterassessNrequirementsatthesecondandthirdappli-cationstodeterminewhichzoneswillorwillnotrespondtofur-therapplicationsofN.Cropsensors,measuringthere?ectancefromthecerealcropcanopy,mayo?erabetteropportunityformatchingcropneedstoNinput,whencombinedwithGPStechnology.41,42

Anumberofopticalsensorsarenowavailabletofarmerstoactivelymonitorthedevelopmentofgrowingcropssuchascere-als,brassica,maizeandryegrass.Thesevehicle-mountedsensorsarelinkedtoGPSsothatthepositionofthereadingsisrecordedandcanbeaccuratelymappedtoinformvariableratefertiliserorgrowthregulatorapplication.Estimatesofcropbiomassaremadeatdiscretewavelengthsinthevisibleandnearinfraredregionoftheelectromagneticspectrum.A3-yearprojectcom-paredthedatafromthreecropsensors,aswellastheiruseful-nessasreal-timedecisionsupporttoolsforstrategicNfertiliserapplications.41Themostcommonlyusedcropsensorindexisthenormaliseddi?erencevegetationindex,whichcanberelatedtobiomass.

ThesensorswereGreenseeker®,fromTrimble(Sunnyvale,California,USA),CropCircle®fromHollandScienti?c(Lincoln,Nebraska,USA),andCropSpec®fromTopcon(Livermore,Califor-nia,USA).Eachsensorusesatleasttwowavebands,oneinthevisiblerange,theotherinnearinfrared.Thesystemsweretestedinarangeofcrops,overarangeofcropgrowthstages,onfarmsinbothNorthIslandandSouthIsland.Thesensors,operatingatslightlydi?erentwavebands,haveslightlydi?erentsamplingfoot-prints.ThecollecteddataweremappedinaGISpackageandthegeo-referenceddatawereanalysedtodeterminetherelationshipsbetweensensorsinthedi?erentcropsduringtracking.

Keypointsfromthestudywerethatsensorresponseswouldvarywithseasonandsiteandbetweensensortypes.Thesensordataalsoneedtobe?eldvalidated,forexample,additionalbiomassmaybeweedsratherthancrop.However,thesensorscandetectbiomassdi?erencesandmapscanbeproducedtohelpstrategicnutrientmanagementofcrops.41TheresearchisongoingandhasapplicationsforprecisionNfertiliserrequirements.

Pasturequality

Ahyperspectralsensorwastestedinthe?eld,providinganimprovedmethodforassessingpasturequalityparametersasadecisiontoolfor(1)feedbudgetingand(2)strategicNapplication.45–47Theinstrumentmeasuresre?ectanceeverynanometrebetween350nmand2500nm,andthesigni?cantlylargeramountofinformationprovidesmorerobustdatasetstodeveloppredictionmodels.Thesemodelsrelatethespectraldatatoanumberofpasturequalityparameters:includingcrudeprotein,aciddetergent?bre,lignin,lipid,metabolisableenergyandorganicmatterdigestibility.Whensuchsensorsaremountedonagriculturalmachinerytocollectdataduringroutinefarmingoperations(e.g.pastureyieldmapping,cropspraying)thiscanbeusedasareal-timedecision-supporttooltoovercomeissuesofspatialandtemporalvariabilityinpasturequality.Thepasturequalityindicatorsprovidevaluableinformationforfeedbudget-ing,facilitatingthecorrectenergyandproteinbalanceinfeed,whichiscriticaltomaintainahigh-performingdairyherd,forexample.

Furtherresearchisnecessarytofullyunderstandtherelationbetweenpasturequalityandfertiliserrequirements.Thesetech-nologiesareintheirinfancy,andfurtherresearchneedstobeundertakenbeforetheycanbee?ectivelyimplementedon-farm.Theyhavepotentialtobeusedasareal-timemanagementtool

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