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Grosssoilsurfacenutrientbalances:TheOECDapproachimplementedunderGermanconditions

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K. Panten, J. Rogasik, F. Godlinski, U. Funder, J.-M. Greef, E. Schnug / Landbauforschung - vTI Agriculture and Forestry Research 1 2009 (59):19-28

�9

Gross soil surface nutrient balances: The OECD approach implemented under German conditions

KerstinPanten�,JuttaRogasik�,FraukeGodlinski�,UteFunder�,Jörg-MichaelGreef�andEwaldSchnug�

� JuliusKühn-Institut(JKI),FederalResearchCentreforCultivatedPlants,In-stitute forCrop and Soil Science, Bundesallee 50, 38116Braunschweig,Germany

Abstract

Plant and therefore food and feed production requireanadequatesupplyofnutrients.Efficientnutrientuse isamajortasktoensureeconomicallyandenvironmentallysound food productionminimizing the impact of nutri-entsongroundwater, the riskofeutrophicationcausedbyrisingnutrientconcentrationsinsurfacewatersandtheemissionof tracegases suchasnitrousoxide (N2O) andammonia(NH�).Agri-environmentalindicators(AEI)devel-opedbytheOECDshallidentifyandquantifytheextentofimpactsbyagriculturalmanagementontheenvironmentandtracktheeffectsofpolicymeasures.Nutrientbalancesfornitrogen(N)andphosphorus(P)onthenationallevelaretwooftheseagri-environmentalindicatorsusedbytheOECD tocomparemember statesanddrawconclusionsabout nutrient loads from agriculture into the environ-ment.OECDmemberstatesarerequiredtocalculateandpro-

videgrosssoilsurfacenutrientbalancesforNandPonanannualbase.TheGermanNgrosssoilsurfacebalanceforthetimeperiodfrom1992to2006showsasurplusbe-tween89and�2�kgha-1a-1N.Becausenutrientbalancesaresimplificationsofcomplexandvariableprocessestheycompriseaseriesofuncertainties.Theseuncertaintiesaremainlyassociatedwitheither thestatisticaldatabaseorthecoefficient libraryusedtoconvertthestatisticaldatainto nutrient quantities. Therefore, it is essential to beawarethattheabsolutebalancevaluesdonotreflecttheactualsituationinacountry.Nevertheless, incasethataconsistent method of balance calculation is used for allyearsacomparisonbetweentheseyearstoderivetrendsinnutrientsurplusesordeficitsispossible.

Keywords: OECD guideline, nutrients, gross soil surface balance, data uncertainties, nitrogen coefficients

Zusammenfassung

DasWachstumvonPflanzenunddamitdieErzeugungvon Nahrungs- und Futtermitteln erfordern eine bilanz-orientierte Zufuhr von Nährstoffen. Die effiziente Aus-nutzungvonNährstoffen ist füreinewirtschaftlicheundumweltgerechteNahrungsmittelproduktionentscheidendundermöglichtdieEinflüssedieseraufdasGrundwasser,dasEutrophierungsrisikodurchansteigendeNährstoffkon-zentrationen inOberflächengewässern unddie EmissionvonSpurengasenwiez.B.Distickstoffmonoxid(N2O)undAmmoniak(NH�)zuminimieren.VonderOECDentwickel-teAgrar-UmweltindikatorensollendenEinflussderLand-wirtschaftaufdieUmweltidentifizierenundquantifizierensowiedazudienen,AuswirkungenpolitischerMaßnahmenzu verfolgen. Nationale Stickstoff- (N) und Phosphorbi-lanzen(P)zählenzudiesenAgrar-Umweltindikatoren,dievonderOECDzurBewertungvonNährstofffrachtenausderLandwirtschaftindieUmweltherangezogenwerden.Mitgliedsstaaten der OECD sind verpflichtet, jährliche

bruttoFlächenbilanzenfürNundPzuberechnenundbe-reitzustellen.DieBerechnungderNbruttoFlächenbilanzfürDeutschlandzeigtN-Überschüssezwischen89und121kgha-1a-1imUntersuchungszeitraumvon�992bis2006.Da es sich bei Nährstoffbilanzen umdie vereinfachendeZusammenfassungundBerechnungvonkomplexenundsowohlräumlichalsauchzeitlichvariablenProzessenhan-delt,sinddiesefehlerbehaftet.DiemeistenUnsicherheitenberuhen entweder auf der statistischenDatenbasis oderderverwendetenKoeffizientenzurUmrechnungvonsta-tistischenDateninNährstoffmengen.Daher istnichtda-vonauszugehen,dassdieabsolutenBilanzsaldendietat-sächliche Nährstoffsituation eines Staates wiedergeben.JedochsindjährlicheBilanzengeeignetumTrendsinderEntwicklung von Nährstoffüberschüssen oder -defizitenzuverfolgen.FürvergleichendeBetrachtungenmussaller-dingssichergestelltsein,dassdieBerechnungenmiteinerkonsistentenMethodeerfolgen.

Schlüsselwörter: OECD Richtlinie, Nährstoffe, brutto Flä-chenbilanz, Datenunsicherheiten, Stickstoffkoeffizienten

20

Introduction

Plant and therefore food and feed production requireanadequatesupplyofnutrients.Cassmanetal.(2003)re-vealthecomplexrelationshipbetweennutrientavailability,cropyieldandnutrientefficiencyconsideringthedifficultytomeetfooddemandswhileprotectingnaturalresources.Soilswill losetheir fertility ifnutrientminingtakesplaceoveralongerperiod.Thenagain,nutrientloadsfromagri-cultureintotheenvironmentincreasetheriskofeutrophi-cation insurfacewaterscausedbyrisingphosphorus (P)concentrations,canhaveasevereimpactongroundwaterqualitybyincreasingnitrate(NO�¯)

orPconcentrationandcanemittracegasessuchasnitrousoxide(N2O)andam-monia(NH�)intotheair.Forabetterprotectionofnaturalresources likeforexamplesoilandwater, it is importantto identifywhereandtowhatextentpersistentnutrientsurplusesordeficitsoccur.Impacts of agriculture and agricultural policies on the

environmentareamajorissueinOECD(OrganisationforEconomicCooperationandDevelopment)memberstates.A set of agri-environmental indicators (AEIs) was devel-opedbytheOECDtoidentifyandquantifytheextentoftheseimpactsandtobetterunderstandtheeffectsofpol-icymeasuresontheenvironment(OECD,1999).Nutrientbalancesfornitrogen(N)andPcalculatedonthenationallevelarecommonlyusedasAEIsbypolicymakers.OECDmemberstatesarerequiredtokeeprecordaboutnutrientsurplusesanddeficitsfromagricultureonanannualbase.Nutrientbalancescanbecalculatedusingdifferentap-

proaches.Inadditiontothegrosssoilsurfacebalancecal-culation recommended by the OECD (OECD/EUROSTAT,200�),thesearethenetsoilsurfacebalance,thelivestockbalance and the farm gate balance. Each of these ap-proachesbalancesnutrientsaddedtoanagriculturalsys-temandnutrientsremovedfromthesystemperhectareofagriculturalland.Dependingonthebalancetobecalcu-latednutrientinputandoutputvariablesvary(Table1).Besides of different approaches to calculate balances

theycanalsobecalculated inavarietyof spatial scales.WhereasforexampleBachandFrede(1998)calculatedNbalances forGermany,Bachetal. (200�)andOsterburgand Schmidt (2008) calculated balances on a regionalscale. An overview regarding some of the different ap-proaches was published by Bach and Frede (2005). Toevaluatefertiliserstrategiesonthefarmlevelitisnecessarytocalculatebalancesforsinglefarmsorevenbetterfields.ThiswasshownbyQuirinetal.(2004),whodemonstratedhowNsurplusescouldbetrackedbacktovaryingfertilisa-tionpractisesondifferentfieldsofonefarm.InGermanyfarmersarerequiredtokeepsocalledannualandmulti-yearnutrientmanagementplanstorecordthefarmnutri-entin-andoutputs.

Table1:

Inputandoutputvariablesofgross-andnetsoilssurfacebalances, livestockbalancesandfarmgatebalances

Gross soil

surface balance

Net soil surface balance

Live-stock

balance

Farm gate

balance

Input

Mineralfertiliser + + +

Organicfertiliser + + +

Livestockmanure + +

Atmosphericdeposition� + + +

BiologicalN-fixation� + + +

Seedandplantingmaterial + + +

Importedfodder + +

Fodderfromdomesticfoodindustry + +

Fodder(internalproduction) +

Output

Totalharvestedcropsandfodder - -

Cashcrops -

Livestockmarkedproducts - -

Livestockmanure -

Nemissions� -

Ndemandforturnoverprocesses� -

Surplus/deficit =Sum =Sum =Sum =Sum�forNbalancesonly

Nutrient balances will be calculated as difference be-tween input and output in the agricultural system. FortheNandPbalancessimilarstatisticalinputvariablesandcorrespondingNandPcoefficientsarerequired.Whereasin N balances emission from agriculture into soil, waterandairareincluded,thesepathsarenotconsideredforP.TheremainderofthispaperemphasisonNbalances.TheOECDhandbookongrossNbalanceswasfirstpublishedin2003(OECD/EUROSTAT,2003)andisusedasguidanceforthecalculation.Thegrossbalancemethodologyiscon-sideredtheappropriateindicatorforOECDmemberstatestoallowcomparisons.Itensuresasfaraspossibleaconsis-tencyoftheusedmethodbetweencountries.Theaimofthispaperistooutlinetheimplementationof

theOECDgrossNbalanceforGermany.AssumptionsandestimationsmadetoovercomedatashortagesintheGer-mandatabasesarehighlightedanduncertaintiescriticallydiscussed.TheNgrosssoilsurfacebalanceforGermanyiscalculatedfortheyears1992to2006andsomeinterpre-tationavenuesareshown.

K. Panten, J. Rogasik, F. Godlinski, U. Funder, J.-M. Greef, E. Schnug / Landbauforschung - vTI Agriculture and Forestry Research 1 2009 (59):19-28

2�

Materials and method of the OECD nitrogen balance

Thefollowingcalculationsarebasedondatafrom�992to2006coveringa15yeartimeperiodaftertheGermanreunification.CalculationsofNbalancesforyearsbeforeandshortaftertheGermanreunificationneedsomespe-cialconsiderationsbecauseofthedifferencesindataavail-ability.Thisissuewillnotbediscussedinthispaper.

Statistical and other input data

Data required for thecalculationof thenationalgrossN soil surface balance are mineral and organic fertiliser,livestockmanure,biologicalNfixation,seedsandplantingmaterialandthetotalharvestedcropsandfodder(Table1).Eachofthesevariablesisfurthersegmented(Table2).Ad-ditional,landusedataisrequiredforcalculationsreferring

Table2:

OECDcodes,in-andoutputvariables,NcoefficientsandunitsusedtocalculatethegrossNsoilsurfacebalancesforGermanyaccordingtotheOECDmethod

OECD code

Variables and N coefficients1 Unit of N coefficients

L� Totalarea

L�� Totallandarea

L��� Agriculturalland(arablecropland,permanentcroplandandpermanentpasture)

F� Totalfertilisers

F�� Totalinorganicfertilisers(Nfertilisers)

F�2 Totalorganicproducts(sewagesludge[39.5],urbancompost[14.3]) kgMg-1N

A� Livestockmanureproduction

A�� Totalcattle(calvesforslaughter,othermaleandfemalecalves(<1yr)[25],maleandfemalecattle(1-2yrs)[47],malecattle,breedingheifers,heifersforslaughter(>2yrs)[59],dairycows[115]andothercows[98])

kghead-1yr-1N

A�2 Totalpigs(piglets(<20kg[4]and20-50kg[13]),fatteningpigs[13],breedingboars[13]andsows(>50kg)[26]) kghead-1yr-1N

A�� Totalsheepandgoats(sheep[10],lambs[10]andgoats[13]) kghead-1yr-1N

A�4 Totalpoultry(broilers[0.29],layers[0.73]andotherchickens[0.28]),ducks[0.55],turkeys[1.6]andotherpoultry[0.8]) kghead-1yr-1N

A�9 Totalotherlivestock(horses[68]) kghead-1yr-1N

C2 Totalharvestedcropsandforage

C21 Totalharvestedcrops

C211 Totalcereals(springwheat[18],winterwheat[22],durumwheat[18],barley[17],maize[15],oats[15],rye[15],othercoarsegrains[14],triticale[18]andotherscereals[17])

kgMg-1N

C212 Totaloilcrops(sunflowerseed[28],rapeseed[33]andotheroilcrops[35]) kgMg-1N

C213 Totaldriedpulsesandbeans[39] kgMg-1N

C214 Totalrootcrops(potatoes[3.5]) kgMg-1N

C215 Totalfruitarea(fruit[44]andviticulture[25]) kgha-1N

C216 Totalvegetables[2.9] kgMg-1N

C217 Totalindustrialcrops(sugarbeet[1.8],tobacco[30]andhop[30]) kgMg-1N

C22 Totalforage

C221 Totalharvestedfoddercrops(fodderbeets[1.4],otherfodderroots[1.4],clover[25],alfalfa[25],silagemaize[3.8]andotherharvestedfoddercrops[3.5])

kgMg-1N

C222 Totalpastureconsumption(temporary[24],permanentpastureconsumption[22]andalpinepastureandroughgrazing[15.5]) kgMg-1N

C23 Totalcropresiduesremovedfromthefield(straws[5]andothercropsresidues[3]) kgMg-1N

C11 Totalseedsandplantingmaterials

C111 Totalcereals(wheat[18],barley[16.1],maize[15],oats[15],rye[15]andothercereals[18]) kgha-1N

C112 Totaloilcrops(sunflowerseed[28],rapeseed[33]andotheroilcrops[35]) kgha-1N

C113 Totalrootcrops(potatoes[3.5]) kgha-1N

C213 Totaldriedpulsesandbeans kgha-1N

B� BiologicalNfixation

B�� Totalareaoflegumecrops(pulses[176],clover[198]andalfalfa[285]) kgha-1N

B�2 Freelivingorganisms(permanentpasture[30]) kgha-1N

D� Atmosphericdeposition�Ncoefficientsareshownin[brackets]andarebasedon86%drymatter(DM)forcereals,91%DMforrapeseedand28%DMforsilagemaize

22

to theareaunit.Mostof these in-andoutputvariablesareprovidedbytheFederalStatisticalOffice(Destatis).Theannually published statistic fornutrition, agriculture andforestrybuildsmostofthedatabase(exemplarily:Statist-ischesJahrbuch,2005).Since2002/2003on-linestatisticaltables (GENISIS) are usedwhen available from the Des-tatishomepage(https://www-genesis.destatis.de/genesis/online/logon).Table2enlists thecodeof theOECD, thecorrespondingnecessaryvariablesandcoefficientsforthecalculationandtheunitsinwhichtheyareprovided.Ad-ditionaldatafortheatmosphericdeposition,wasderivedfromlongtermtrendsindepositionloadsofairpollutantsinGermanyandwassetto2�kgha-1a-1N(Gaugeretal.,2002).

Nitrogen coefficients

Allstatistical livestockandcropproductiondataneedstobeconvertedintoNequivalentswhichallowtosumupthetotalamountofNinputsandoutputsandtobalancethese.Toconvertthevariousvariablesfromtheiroriginalrecordedunitintocommonunits,Ncoefficientsareused.MostoftheNcoefficientsarederivedfromtheGermanFertiliser ApplicationOrdinance (MVV, 1996). In case ofsomeanimalcoefficients,adifferentdatasourcewasused(VwV,1996).Table2showstheusedcoefficientsinbrack-etsafterthevariables.Table�andEquation�revealexem-plarilythecalculationoftheNamountremovedby‘totalcereals’.Itcanbeseen,thatsomeoftheOECDspecifiedvariables likee.g. riceand sorghumarenot relevant forGermanbalances.InothercasestheGermanstatisticsandcoefficientdatabaseallowtoimprovethecalculationbyfurtherdiversification.Nitrogen coefficients for compost and sewage sludge

arenotprovidedbytheGermanFertiliserApplicationOr-dinance(MVV,1996),thesecoefficientsarederivedfromother available sources. The N coefficients for compostwere derived from the Federal Environmental Agency(Bannicketal.,200�)andforsewagesludgefromthetri-ennialcompiledGermanreportaboutsewagesludgefortheEuropeanCommission(BMU,2004;BMU,2007).Forthedatapresented in this paper an averageof 39.5 kgMg-1Ninsewagesludgewasusedforallyearsdrawnfromthe2004report(BMU,2004).Ifthisseriesiscontinueditmightbepossibletouseannualvaluesinsteadofaveragesinfuturecalculations.

Table3:

NitrogencoefficientstocalculatethetotalharvestedNfromcereals

C211 Total harvested cereals[Mg]

N coefficient5

[kg Mg-1 N]

C2111 Wheat

C21111 Commonwheat

C211111 Springwheat(SWy) �8

C211112 Winterwheat(WWy) 22

C21112 Durumwheat(DWy) �8

C2112 Rice

C2113 Coarsegrains

C21131 Barley�(By) �7

C21132 Maize(My) 15

C21133 Millet

C21134 Oats(Oy) 15

C21135 Rye2(Ry) 15

C21136 Sorghum

C21139 Othercoarsegrains�(CGy) �4

C2119 Othercereals

C21191 Triticale(Ty) �8

C21199 Othercerealstypes4(OCy) �7�winterbarley;2winterrye;�brewingbarley;4springbarley,5basedon86%DM

totalcereals[kgN]= (SWy�18+WWy�22+DWy��8) +(By��7+My�15+Oy�15+Ry

�15+CGy��4)+(Ty�18+OCy��7) [Equation1]

Data uncertainties

Statistical data

StatisticaldatapublishedbyDestatishaveaneffectonbalance calculations mainly through the following threeuncertainties:(i)inputdataarenotrecordedonanannualbase,(ii) inputdataareestimationsand(iii)byOECDre-questedinputvariablesarenotsupportedbythestatistic.DependingontheproportionoftheinputvariablesonthegrossNsoilsurfacebalance,theirinfluenceontheoveralluncertaintycanbesubstantial(Figure�).Ascanbeenseen,mineralfertiliserandlivestockmanurearethemajorcon-tributinginputvariablesinthebalance.Bothdatasourcesoftheseinputvariableshavetheiruncertainties.WhilsttheNinputfrommineralfertiliserisbasedonsalesfiguresandnotontheactualappliedamountofNfertiliser,theinputfromlivestockmanureiscalculatedfromanimalnumbers.Cattle andpigs are counted twicea year (MayandNo-vember)and itwasdecidedtousetheNovembercountin thebalance.Allotheranimalsarenotcountedannu-ally,whereasforyearswithoutcounts,thenumberofthepreviousyearisused.Becauseofthenecessitytoupdate

K. Panten, J. Rogasik, F. Godlinski, U. Funder, J.-M. Greef, E. Schnug / Landbauforschung - vTI Agriculture and Forestry Research 1 2009 (59):19-28

2�

thebalanceonanannualbasis,itisnotpossibletouseameanvaluefromapreviousandfollowingyear,becausethelatterdataisnotavailableyet.Furthermoresomedataareonlyestimates,likethenumberofgoats.Sewage sludge and urban compost which are cumu-

latedtothevariableorganicfertilisersareonlyerraticallyrecordedinGermanstatisticsandthereforemissingdatawerereplacedbydataofpreviousyears.TheNoutputvaluesaremainlydrivenbycereals,pas-

tureandharvestedfoddercrops(Figure1).Yieldsofcrops,sugar and fodder beet leaves, pasture, fruits, viticultureandvegetablesareestimatedbythestatestatisticalofficesinGermanyand reported toDestatis. Incaseofcereals,potatoesandwinter rapeactual yield valuesof selectedfields(maximumof10,000)arerecordedandextrapolatedontothenationallevel.Sugarbeetyieldsareprovidedbythesugarindustryandarebasedontheamountsofbeetsdeliveredtothesugarfactory.Grapeyieldsarealsobasedon notifications about vintage to the viticulture register(Weinbaukartei).Calculationsoffruityieldsarebasedei-theronthecroppingareaorontreeyields.Yieldsofveg-etablesareestimatedaccordingtothecroppedarea.Ageneralmajorconcernistheestimationofthepasture

yieldsbecauseofthelargeproportional influenceofthisvariable(Figure�).Notonlyisthisvariableestimated,itisfurtherrequiredtoaccountforNlossesduringagriculturalmanagement.InGermany,alossof15%inpastureyieldisassumed,whichislowerthantheproposed30%oftheOECD.Theamountofstrawremovedfromthefieldneedsto

be considered in the calculation.Becauseof the lackofstatisticaldataitisestimatedthatstrawinthedimensionof10%ofthegrainyieldisremovedannuallyfromag-riculturalfields.Thisvaluemightneedtobereconsideredforfuturecalculationsbecauseitcanbeexpectedthattherisingdemandonrenewableenergysourceswillincreasethestrawcollectionpracticeoffarms.Changesinagriculturalmanagementpracticealsoinflu-

encetheprovidedstatisticaldata,ascropswhicharenotcommonlyor not any longer cultivatedwill be removedfromthestatisticaldataset.Fodderbeetyieldsareforex-amplenot any longerpublished since2003. This incon-sistency indataseries results insome inaccuracieswhencalculatingbalances.A furtherdifficulty is theallocationofstatisticaldatafrommanagementyears(JulytoJune)tobalanceyears (January toDecember).Mostvariablesarereportedinbalanceyears,butmineralfertiliserandseedsand plantingmaterial are listed for management years.Hencethedatawereassignedtothebalanceyearsasfol-lows: It isassumedthat themajorityofmineral fertiliserandseedsandplantingmaterialbought in themanage-mentyearisusedtoachievetheyieldofthesecondnamed

managementyear(e.g.managementyear2004/2005willbeallocatedtothebalanceyear2005).Furthermore,thesubsequentprecisionofstatisticaldata

causesconfusionswhencomparinganactualbalanceofonetimeperiodtoanolderoneanddiscoveringthatthesurpluscalculatedforoneofthepreviousyearshasbeenaltered.Eventhoughchangesaregenerallyminorconsid-eringtheoverallimprecisionofthemethod,theytendtoirritateusersofnutrientbalances.

Input

Mineral fertiliser

Organic fertiliser

Livestock manure

Biological Nfixation

Atmospheric deposition

Seed and planting material

Output

Cereals

LegumesIndustrial crops

Harvested fodder crops

Pasture

Crop residues (removed)

Other crops

Oil crops

Input

Mineral fertiliser

Organic fertiliser

Livestock manure

Biological Nfixation

Atmospheric deposition

Seed and planting material

Output

Cereals

LegumesIndustrial crops

Harvested fodder crops

Pasture

Crop residues (removed)

Other crops

Oil crops

Figure1:

ProportionalshareofNinputandoutputvariablesontheNbalance(average�992to2006)

24

Nitrogen coefficients

CoefficientsusedfornationalbalancesareprovidedbytheGermanFertiliserApplicationOrdinance(MVV,1996;DüV,2007).Thesepublishedvaluesarederivedfromvari-ous sources like the German Agricultural Society (DLG)whopublishesforexamplecoefficientsforNcontentsofanimalmanure(DLG,2005).

Uncertainties in thebalancearecausedby thefollow-inginconsistencieswhenusingNcoefficients:(i)reportedNcoefficientsarenotcongruentwiththeclassificationofvariablesand(ii)Ncoefficientsaremodifiedbyrevisedleg-islations.ExamplesforthenonconsistencybetweenNcoefficients

andvariablesasclassifiedbytheOECDcodeare:• DifferentiationoftheOECDvariablesintomaleandfe-

malecattle(�to2yrs)isnotmatchedbytheGermanNcoefficients (MVV,1996)whicharesegmentedde-pendingonthefeedingmanagement,likeforexamplegrasslandorforagecropping.

• TheFertiliserApplicationOrdinance(MVV,1996)diffe-rentiatestheNcoefficientsforcerealsfurtherthanthevariablesoftheOECDcodeareclassified.Forexample,thebarleyproductionissummarizedintoonevariablebutGermanNcoefficients forwinterbarley,maltingbarleyandfeedingbarleyarereportedwith17,14and�7kgMg-1N,respectively.

• TheOECDcodedifferentiatesonlybetweentemporaryandpermanentgrassland,whilsttheGermanFertiliserApplicationOrdinance (MVV,1996)separates furtherintothenumberofannualgrasscuts.ChangesofcoefficientsintheGermanFertiliserApplica-

tionOrdinanceresultalsoininconsistencieswhenbalanc-esarecalculatedwiththeemphasistoevaluatelongtermtrends.ThisisactuallythecasewiththenewlypublishedFertiliserApplicationOrdinance,comingintoeffect2007(DüV,2007).ThepresentedresultsarecalculatedusingthecoefficientsoftheformerFertiliserApplicationOrdinance(MVV,1996).ComparisonsofNbalancescalculatedwiththe same statistical input data but old and new coeffi-cientsshowed,thatthegrossNsoilsurfacebalancesfrom�992to2006wouldhavebeeninaverage�.8kgha-1Nlowerwhencalculatedwith thenewer coefficients. Thisposesthequestionhowtoproceedafterchangesinthecoefficientlibraryespeciallywhenbalancesoverlongtimeperiodsarecomparedandinterpreted.Itcanbeexpectedthat,ongroundsofchangesincropvarieties,cultivationandmanagement practices, several adoptions of coeffi-cientswillhavebeen takenplaceover the lastdecades.It is thereforequestionable, if actual coefficients canbeusedforlongertimeperiods.Incaseswhendifferentcoef-ficientsforcertaintimeperiodsareused,itisnecessarytoquantifythechangesandtocommenttheseintheinter-

pretationofthebalances.Otherwisechangesinbalancescanbemisleadingandtheuseasevaluationtoolforpolicymeasuresisrestricted.Thesecondpossibilitywouldbetousetheactualcoefficientsinretrospective.Thiswouldalsoneedtobecommentedinthebalanceinterpretation.Bothmethods are obviously unsatisfactory, but unavoidablewhenlongertimeserieswillbestudied.AfurthercriticalpointisthecomparisonofOECDbal-

ancesinternationallycausedbythedifferencesinNcoeffi-cientsofthememberstates.TheOECDthereforeenforcesaharmonisationofthecoefficientlibraryasfaraspossible,butthistaskisstillinprocess.Anabsoluteagreementwillprobablynotbeachievedbecauseofregionallyspecificin-fluencesonthecoefficients.

y = 3.2801x-0.3998

R = 0.52512

1.0

1.5

2.0

2.5

3.0

2 3 4 5 6 7 8 9

Yield [Mg ha ]-1

BraunschweigMüncheberg

N coefficient according to MVV (1996)

Nconte

nt[%

]

y = 3.2801x-0.3998

R = 0.52512

1.0

1.5

2.0

2.5

3.0

2 3 4 5 6 7 8 9

Yield [Mg ha ]-1

BraunschweigMüncheberg

N coefficient according to MVV (1996)

Nconte

nt[%

]

Figure2:

RelationshipofyieldandNcontentofspringfeedingbarleyderivedfromlong-termfieldexperimentsinMünchebergandBraunschweig,Germany,1976to2005

y = -0.0662x + 2.561

R = 0.62792

y = -0.0377x + 2.126R = 0.5672

2

1.0

1.5

2.0

2.5

7 8 9 10 11 12

Yield [Mg ha ]-1

WW Variety EWW Variety A

N coefficients according to MVV (1996)

Nconte

nt[%

] y = -0.0662x + 2.561

R = 0.62792

y = -0.0377x + 2.126R = 0.5672

2

1.0

1.5

2.0

2.5

7 8 9 10 11 12

Yield [Mg ha ]-1

WW Variety EWW Variety A

N coefficients according to MVV (1996)

Nconte

nt[%

]

Figure3:

RelationshipofyieldandNcontentoftwowinterwheatvarieties inClauen,Germany1995to2007.ThedatawasprovidedbytheFederalOfficeofPlantVarietiesinGermanyandderivedfromthevarietytestingdatabase

Additionally,ithastobeclearthatcoefficientsaregen-erallymean values agreedon and can vary substantiallyforexamplebetween regions,years,fields, varietiesandfertilisationmanagement.Figure2demonstratesthede-pendencyofNcontentinspringfeedingbarleyandyieldlevel.ItcanbeseenthatwithincreasingyieldtheNcon-

K. Panten, J. Rogasik, F. Godlinski, U. Funder, J.-M. Greef, E. Schnug / Landbauforschung - vTI Agriculture and Forestry Research 1 2009 (59):19-28

25

tentofspringfeedingbarleygraindecreases.Obviously,asingleNcoefficientusedforthecalculationofNbalancescannot comprehend the variabilityofgrainN contents.Thiscanalsobeseeninasecondexamplewhencompar-ingtwowinterwheatvarieties(Figure3).AsexpectedaretheNcontentsofvarietyAlowerasofvarietyE.Figure�alsoconfirmsthatwinterwheatyieldandtheNcontentofgrainarecorrelatednegatively.Consideringthevarietyandnatureoftheabovemen-

tioned uncertainties it can be concluded, that some ofthesecouldbeimprovedlikeforexampletheannualdataavailability.Otherswillalwaysbeacompromiseandagree-mentofcommonknowledge,likeNcoefficients.Becauseoftheseuncertaintiesitismostimportantthatthecalcula-tionofnutrientbalancesiskeptastransparentandopenaspossibletoallowusersofthebalanceinsightsintothecalculationparameters.

Gross soil surface nitrogen balance for Germany 1992 to 2006

ThegrosssoilsurfaceNbalancewascalculatedfortheyears�992 to2006 (Figure4). Therefore the results ex-clude issues like the above mentioned influence of thealteredNcoefficientsofthenewlegislation(DüV,2007).Further, the incomparability of statistical data compiledbythetwoformerGermancountriesuntil�989andthetransitionyearsof�990and�99�areirrelevant.Datainnutrientbalancesalwaysreferstotheagriculturallandusearea(AL).

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Figure4:

GrosssoilsurfaceNbalanceforGermany�992to2006calculatedaccordingtotheOECDmethod

During this 15 year time period the agricultural landuse,includingarableland,permanentcroplandandper-manentpasture (Table2)was reduced from16,950,072to�6,9�9,�00ha,whichequalsareductionoflessthen0.1%.The annual N surpluses show a slight overall declin-TheannualNsurplusesshowaslightoveralldeclin-ingtrend,hencewithconstantoutliers.Theyear200�hadanexceedinghighNsurplus,whichwascausedbyunusu-

alweatherconditions.Whiletheyears1999to2003wereclassifiedastoowet,thesummerof2003wasexceptionalhotanddry.Averageweatherconditionsatthebeginningoftheyearsupportedfarmerstoaveragenutrientsupply,butthehotanddryweatherthroughoutGermanyduringthesummerresultedinhighyieldlosses(Figure5)whichreturnedthehighNsurplus.Whereas the yearly fertiliser and manure application

arecontrolledbythefarmersandbasedonaverageyieldexpectations, the subsequent yield depends onweatherconditionsandisthereforedifficulttopredict.Becauseofthis,longtermtrendsaremuchmorereliablethansingleorshorttermcalculationsandthereforetheonlysourcetoverifypolicymeasures.The resultsofNbalances are in regards to input vari-

ablesmostlyaffectedbytheamountofmineral fertiliserandmanureapplication.NitrogendepositionisaccountedforwithaconstantfactorandtheNinputfromsewagesludge, urban compost, biological N fixation and seedandplantingmaterialcontributesinaverageonlyasmallamountwithtogetherabout18%(Figure1).ThechangesinNinputbymineralfertiliserandlivestockmanureinkgha-1from1992to2006areshowninFigure5.

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erprice[€Mg] -170

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erprice[€Mg] -170

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Figure5:

ChangesoftheN inputvariablesmineral fertiliserand livestockmanure, theNoutputvariableharvestedcropsandforageandthemineral fertiliserpricefrom�992to2006

TheamountoflivestockmanureandthereforeNinputwithmanuredecreasedduringthistimeperiod,causedbyadecreaseintotalanimalproduction(Figure6).Whilethemanureproductionofpigs, sheepandpoultry remainedon a constant level, the number of cattle was reducedfrom �6,207,�40 head in �992 to �2,676,800 head in2006.Nevertheless,cattlemanurecontributes22%Nasinput to the balance. The sales numbers ofmineral fer-tiliservariedforthesametimeperiodbetween93and118kgha-1.Mineralfertiliserapplicationratesare influencedby a number of factors. Besides the implementation of

26

goodagriculturalpracticeitcanbeseenthatforexamplemineral fertiliser pricesbias the application rates. This isobviousfortheyear2000,forwhichhigherfertiliserap-plicationratesarecorrelatedtolowerpricesofmineralNfertiliser(Figure5).

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Figure6:

ChangesoftheNinputbytotallivestockmanureaswellassplitforcattle,pigsandothers(sumofsheepandgoats,poultryandhorses)from1992to2006

Implementation issues of soil surface nutrient balances

Langeveld et al. (2007) summarized that agri-environ-mentalindicators(AEIs)should(i)refertorelevantissues,(ii)bebasedonsoundscience,(iii)bequantifiable,(iv)berelevantfortargetgroupsinvolved,(v)beeasytointerpret,(vi) be cost-effective, and (vii) facilitate communication.Thesedemandswillbeusedinthefollowingasaguide-linetoevaluatethegrosssoilsurfacebalanceapproachasAEIforGermanyonthenationallevelandinthecontextofinternationalcomparisonslikebetweenOECDmembercountries.Basedontheknowledgeaboutthepotentialrisknutri-

entsurplusesimposeontheenvironmentandnaturalre-sourceslikeforexamplesoilandwater,thequantificationofthisriskisarelevanttask.Obviously,toensurethatriskassessments basedonnutrient balances canbe reliable,thescienceshouldbesound.Unfortunately,nationalnu-trient balanceswill always be a compromise. Besides ofthe lack of statistical data for certain variables or years,the N coefficients used are not able to reflect regionaldistinctionsbetweenlanduseandmanagementpractice,varietiesusedorannualvariationscausedbyweatherde-pendentyieldfluctuations.Twomainissuesarisefromtheused coefficients. First, because nutrient balances needto be calculated over longer periods to bemeaningful,changesinthecoefficientlibrarycausedbychangesofco-efficientsinofficialdatabasescanresultininconsistenciesofthecalculations.Second,ifnationalbalancesareused

to compare countries, like it is the casewith theOECDbalances,differentcoefficientsareusedinthecalculationof different countries. This poses some risk in the inter-pretationofnationalbalanceinaninternationalcontext.ThereforetheOECDaimstodefineacommoncoefficientlibrary,butthisisnotyetavailable.

Nutrient balances are a tool to quantify nutrient sur-plusesandtheycanbeusedtodemonstratetrendsinthedevelopmentover longertimeperiods.Nevertheless,be-causeofthelackindataandcoefficientavailabilityandac-curacytheabsoluteNsurpluscalculatedcomprisesahighuncertaintywhichisdifficulttoovercome.Onthecontrarythecomparisonbetweenyearscalculatedwiththesamemethodcanbeevaluatedconsideringweatherconditions,prizesforfertilisersandcropsaswellaspolicymeasuresintroduced.Cautiousinterpretationsandconclusionscanbedrawnifallinfluencingfactorsareconsidered.NationalnutrientbalancesareoneoftheAEIsrelevant

forpolicymakersand researchersandbuild thebase tocommunicate developments in environmental perfor-manceandtoperformriskassessments.Farmersneedtocompiletheirownnutrientmanagementplanstoensurethat they complywith theGerman FertiliserApplicationOrdinance(MVV,1996;DüV,2007)andtoassesstheap-pliedfertilisationstrategy.Quirinetal.(2004)discussedtheuseofthesefarmandfieldrelatedbalances.Thecoststocalculatenationalnutrientbalancesaremoderateafterthesources for statisticaldataandcoefficientsareexplored,thecalculationmethodisadoptedandadjustmentsofthemethodtotheavailabledataaremade.Aslongthesta-tisticaldatabaseandcoefficientlibraryarenotalteredtheannualupdateofthebalanceinvolvesonlyanextensionofthedatainputandcanbeconsideredasminor.

Becauseoftheuncertainties inhered inthecalculationofnutrientbalancesitisinevitabletokeepthecalculationproceduresaswellasinputandoutputdataastransparentaspossible.Onbaseofthisinsightintothecalculationasoundcommunicationbetweenusersofnutrientbalancesispossible.Eventhough,thisbearstheriskthatinsteadoffocusingonmuch-neededsolutionstoovercomenutrientsurplusesordeficits,discussionsaroundinsufficientdata-basesandcoefficientsdevelop.

Conclusions

Gross soil surface nutrient balances are influenced bynumerousuncertainties in thedatabaseand thecoeffi-cientlibrary.TobeabletousenutrientbalancesasAEIsitisessentialtobeawarethattheabsolutebalancevaluesdonotmirrortheactualsituationinacountry.Nevertheless,incasethataconsistentmethodofbalancecalculationisused for all years a comparisonbetween these years toderivetrendsinnutrientsurplusesordeficitsispossible.

K. Panten, J. Rogasik, F. Godlinski, U. Funder, J.-M. Greef, E. Schnug / Landbauforschung - vTI Agriculture and Forestry Research 1 2009 (59):19-28

27

FinallyitcanbefollowedtheconclusionofLangeveldetal.(2005),thatgrosssoilsurfacebalancesshouldbeusedwithcareandthatalwaysbekeptinmindthatindicatorsaresimplificationsofcomplexandvariableprocesses.

Acknowledgement

Wearemostgratefulforthedatafromthevarietytest-ingdatabaseprovidedbytheFederalOfficeofPlantVari-etiesinGermany.

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