EVALUATINGTHEEFFECTSOFCOVERCROPSONNITROGENCYCLINGINTHE

CENTRALSANDS

by

KathrynAnneIvancic

Athesissubmittedinpartialfulfillmentof

therequirementsforthedegreeof

MasterofScience

SoilScienceandAgroecology

atthe

UNIVERSITYOFWISCONSIN-MADISON

2016

Approvedby:

_________________________________

Dr.MatthewD.RuarkAssociateProfessor,DepartmentofSoilScience

Date:____________________________________

i

AcknowledgementsIwouldliketothankmyadvisor,Dr.MatthewRuark,forhisdirectionand

commitmenttothisprojectandmygraduateschoollearningexperience.He

spenttirelesshoursteachingmehowtocriticallythinkaboutdata,write

scientifically,andpresentthisimportantresearchstorytotheworld.Iamso

appreciativeforhisguidance,pushingmeeverydaytobeabetterscientist.

Iwouldalsoliketothankmycommitteemembers,Drs.ErinSilvaand

FranciscoArriaga.Theirattentiontodetailanduniqueareasofexpertise

challengedmetolookbeyondthetraditionalscopeofmyresearch.Thankyouto

myprofessorsinSoilScience,Statistics,Agronomy,andAgroecologyforteaching

metheprinciplesofinterdisciplinaryscientificlearningandtoPeterCrumpfor

hisstatisticalexpertiseandguidance.Thankyoutomyamazinglabmatesand

especiallytoourlabscientist,JaimieWest,forherguidanceandbrainpower.

Also,withouttheamazingfieldcrew’sattentiontodetailandbrutestrengthin

bothyearsofthisstudy,Iwouldstillbecollectingandsortingdata.Thankyouto

MackNaber,CaraArgus,TeganMcgillivray,RyanCurtin,CodyCalkins,Calvin

Doiron,RitaArgus,LauraSchulz,MeganChawner,andJohnFrame.

Thankyou,mostofall,tomyfriendsandfamily.Theycontinuetobemy

biggestfansnomatterwhatnewchallengeIface.Theykeepmegroundedwith

comedicreliefandperspectivethroughoutthisentirelifejourney;Iamso

grateful.

ii

iii

TableofContentsAcknowledgements....................................................................................................................................................i

Chapter1:Introduction...........................................................................................................................................1

Chapter2:EvaluatingtheEffectofCoverCropsonSweetCornYield................................................6

Abstract.....................................................................................................................................................................6

Introduction.............................................................................................................................................................7

MaterialsandMethods.......................................................................................................................................9

ResultsandDiscussion....................................................................................................................................14

Conclusion.............................................................................................................................................................21

TablesandFigures.............................................................................................................................................24

SASCode.................................................................................................................................................................30

Bibliography.........................................................................................................................................................32

Chapter3:OatCoverCropGrowthandInfluenceonNetNitrogenMineralizationinSandySoil....................................................................................................................................................................35

Abstract..................................................................................................................................................................35

Introduction..........................................................................................................................................................36

MaterialsandMethods....................................................................................................................................38

Results.....................................................................................................................................................................46

Discussion..............................................................................................................................................................50

Conclusion.............................................................................................................................................................57

TablesandFigures.............................................................................................................................................60

SASCode.................................................................................................................................................................69

Bibliography.........................................................................................................................................................73

Chapter4:OverallConclusionsandFutureWork....................................................................................79

iv

1Chapter1:Introduction

TheCentralSandsofWisconsinisoneoftheleadingvegetableproduction

centersintheU.S.Thestateisthehighestproducerofsnapbeansandthird

highestproducerofpotatoes,andalsorankedthirdforprocessingsweetcornin

theU.S.(WI2016AgriculturalStatistics).Theregion’ssandysoils,loworganic

matter,andclaycontentrequirepivotirrigationandnutrientinputsfor

productiveyields.Thiscombinationofporoussandysoilandhighinputscan

resultinnutrientleachingintolocalandnationalwaters.RecommendedNrates

foroptimalyieldproductioninsandysoilsinWisconsinis67kgNha-1forsnap

beans,280kgNha-1forpotatoes,and168kgNha-1forsweetcorn.

Recommendationsarenotuniformacrossstates,however,forexamplefor

optimalsweetcornproductioninMichiganthestaterecommendationis134kgN

ha-1andinMinnesotatherecommendationis146kgNha-1,botharelowerthan

Wisconsin’srecommendation(Warnckeetal.,2005;RosenandEliason,2005).

Agriculturalproductioncontributesatleast90%ofnitratecontamination

toWisconsin’sgroundwater(Shaw,1994)andnitratecontaminationhasbecome

thetopgroundwatercontaminantinthestate(WIgroundwaterCoordinating

Council,2015).Nitrate-Nisawater-solubleformofnitrogenthatisregulatedin

drinkingwaterat10mgL-1nitrate-NbytheU.S.EnvironmentalProtection

Agencyat(USEPA,1992).Nitratecontaminationismostdangerousforinfants,

2whereinexposureover10mgL-1cancauseMethemoglobinemiaor“bluebaby

syndrome”,leadingtoareductioninthechild’sbloodoxygenlevels.Travelling

beyondregionalboundaries,nitratecontaminationisariskfornational

waterwaysaswell.

CentralSands’drainagefeedsintothesurfacewatersoftheMississippi

RiverBasin,impactingecosystemshundredsofmilesaway.Nitrogenloading

fromagriculturalproductionisestimatedtoprovideatleast65%ofthetotalN

contributingtooxygendepletionandhypoxicconditionsintheGulfofMexico

(Justicetal.1995;BurkartandJames1999;Goolsbyetal.1999).In2105the

hypoxiczoneintheGulfofMexicowasthesizeofConnecticutandRhodeIsland

combined(16,760squarekilometers),threetimeslargerthanthe2001approved

EPAtaskforcegoal(5,000squarekilometers)(LouisianaMarineConsortium,

2015).AsnitratecontaminationgrowsintheGulf,researchersworktoreduce

impactandoptimizenutrientmanagementpracticesinagriculturalsystems.

Biologicalcontrolofnutrientcyclingwithcovercropshasthepotentialto

reduceNrateandleachingwhilemaintainingoptimalyieldsinagricultural

systems.LeguminouscovercropscontainhighamountsofN,havelowC:N,and

releasefixedNquickly.Typicalreleaseof50%oflegumeNoccurswithinfour

weeksofterminationandreleasesoftherestbyapproximately10weeks(Stute

andPosner1995;LupwayiandSoon2015).ThisrelativelyquickreleaseofNcan

betakenupbythecropandreduceNrate.Additionally,legumecovercropscan

3impactsoilmicroclimates,reducingsoilheatandmoisturestress(Thiessen

Martensetal.2001).Infine-texturedsoils,clayparticlesandorganicmatterbind

tosoilnitratemineralizedfromlegumecovercrops,reducingleachingpotential

(KraftandStites2003).Oncourse-texturedsandysoils,legumecovercropsare

notboundinthesoilprofileandhavegreaterpotentialforNlossbeyondtheroot

zonebeforecashcropuptake(Cherretal.,2006;Parretal.,2011).IntheCentral

Sands,Westetal.(2016)measurednoNcreditfromspringplantedfieldpea.

Alsoonasandysoil,Cherretal.(2006)documentednoreductioninoptimalN

rateafterthreedifferentlegumecovercrops.Speedydecompositionof

leguminouscovercropsdependsgreatlyonclimaticconditionsandcovercrop

nutrientcomposition;speciesselectionisspecifictoeachenvironment.

GrasscovercropshavehigherC:NandlowerNcontentthanlegumes,

requiringsoilNfordecomposition,potentiallycompetingwithcashcropN

uptakeandmineralizingmoreslowlythanlegumes(Snappetal.,2005;Kasparet

al.,2012).However,intheCentralSandsBundyandAndraski(2005)measured

sweetcornyieldbenefitandreductionineconomicoptimumNratefromfall

plantedryecovercrop.Similarly,Gentileetal.(2009)measuredachangeinN

transformationwiththecombineduseofNfertilizerandhighC:Norganic

residues.GrasscovercropsarealsousedforreductionofresidualsoilNleaching

followingcashcropharvest.Ameta-analysisofnon-leguminouscovercrop

studiesreporteda70%reductioninleachingpotentialwithgrasscovercrops

4comparedtofallow(Tonittoetal.,2006).However,leachingreductionpotential

iscloselyrelatedtosoiltypeandbiomassproduction(Kasparetal.,2012).Inthe

CentralSandsgrasscovercropsaremostcommonlyusedtocombatwind

erosion,however,covercropvarietyandclimaticconditionshavepotentialto

altersoilNtransformations.

UnderstandingtherateatwhichcovercroporganicNmineralizesinto

plantavailablenitrogeniscriticalforoptimizingNefficiencyandminimizing

losses.Ntransformationsvaryaccordingtoenvironmentalconditions,microbial

community,moisturecontentandflow,soilmicroclimate,andmanagement

practicesthatarenotrepresentedinthelaboratorysetting(BinkleyandHart,

1989).Therefore,in-situNmineralizationmeasurementtechniquesarearguably

morereliablethanlaboratory.Variousin-situmethodshavebeenusedto

quantifyNtransformations,advancingwithtime.Eno(1960)usedburiedresin

bags,foramoreprecisetechniquethatcombinedburiedresinbagsandPVC

columns,DiStefanoandGholz(1986)andBryeetal.(2002)quantifiedsoil

volumeandwithmineralizationmeasurements.Gentileetal.(2009)usedthe15N

tracermethodtodocumentNimmobilizationincombined,highcarbonto

nitrogenratioorganicresiduesandmineralNfertilizertreatments.Inthisstudy

weusedamodifiedversionoftheburiedresinbaginPVCcolumnprocedureof

Bryeetal.(2002).Thismethodismorecosteffectivethanthe15Ntracermethod

andsoilcolumnvolumeallowsforfield-scalequantificationofmineralization.

5ThroughquantificationofNmineralizationafteroatcovercropinsandysoilsand

sweetcornyieldimpactfollowingoatandlegumecovercrops,welearnofthe

potentialforbiologicalNcontrolthroughcovercroppingintheCentralSands

region.

Tofurtherunderstandcovercropimpactonsweetcornproductionthis

studyquantifiedmineralizationofspringplantedoatinsandysoilandevaluated

springplantedoatandlegumecovercroppotentialforsweetcornnitrogen

credit.Specificstudyobjectiveswereto:(i)quantifyspring-plantedcovercrop

growthandNuptake,(ii)determinetheeffectofoatcovercropandNfertilizer

onin-situN-mineralizationandseasonalPAN,(iii)determinetheeffectofspring

plantedcovercropsonsweetcornyield.

6Chapter2:EvaluatingtheEffectofCoverCropsonSweetCornYield

Abstract

Spring-plantedcovercropsintheupperMidwesternUnitedStates(U.S.)

mayprovideanitrogenbenefittosubsequentsweetcorncropsinfieldswhere

latefall-harvestedcropslimittheuseoffall-plantedcovercrops.Theobjectives

ofthisstudyweretomeasurespring-plantedcovercropgrowthandnitrogen(N)

uptakeandsubsequenteffectonsweetcorn(ZeamaysL.)yield.Conductedacross

twogrowingseasonsattheUniversityofWisconsinHancockAgricultural

ResearchStationintheCentralSandsregionofWisconsin,theexperimental

designwasarandomizedcompleteblock,split-plotdesignwithfivecovercrop

whole-plottreatments(chicklingvetch(Viciavillosa),berseemclover(Trifolium

alexandrinum),oat(Avenasativa)+berseemclover,oat,andnocover)andsix

split–plotN-ratetreatments(0,56,112,168,224and280kg-Nha-1).Covercrop

biomassandNuptakevariedgreatlybetweenseasons,mostlikelydueto

differencesinaccumulationofgrowingdegreedaysinthespring.Inbothstudy

years,covercropsdidnotaffecttheagronomicoptimalNrate(AONR)forsweet

corn.Thesefindingssuggestthatregardlessofcovercropbiomassproduction,N

fromspring-plantedcovercropsisnotavailableforsweetcorncropuptakein

thisregiononitsirrigatedsandysoils.

7Introduction

WisconsinisthethirdlargestsweetcornproducingstateintheU.S.

(Wisconsin2014AgriculturalStatistics),withthemajorityofthestate’ssweet

cornproductionproducedunderpivotirrigationinthesandysoilsoftheCentral

Sandregion.Inthisregion,therecommendednitrogenapplicationrateforsweet

cornproductionis168kgNha-1forirrigatedsandswithlessthan2%soil

organicmatter(LaboskiandPeters,2012).Thismanagementsystem,with

significantquantitiesofreadily-mineralizableNonhighlyleachingsoils,

contributes,atleastpartially,toelevatednitrateconcentrationsintheregion’s

groundwater(Kraftetal.,2003).Onsandysoils,covercropscanbeusedtoboth

reduceNleaching(Snappetal.,2005)andsupplyNtothecashcrop,allowingfor

thepotentialmitigationofNleachingfromthesesystemswhileretainingNfor

thecashcrop,loweringeconomicallyoptimalNratesinthesesystems(Bundy

andAndraski,2005).

Withcashcropsoccupyingfieldsforthemajorityofthegrowingseason,

covercropstendtobelimitedtograsses(typicallycerealrye(Secalecereale)or

oat)plantedinlatefalltominimizewinderosion.Infieldswherecashcropsare

notharvesteduntillateOctober,suchasfieldcorn(Zeamays)orsoybeans

(Glycinemax),farmersarelimitedtoplantingspring-seededcovercrops.Sweet

cornisa90-daycropandcanbeplantedfromearlyMaythroughearlyJuly.For

thesweetcornplantedlaterinthegrowingseason(JuneandJuly),thereisan

8opportunityforaspring(MarchorApril)plantingofacovercrop,whichallows

adequatetimeforcovercropstoestablishandserveasasupplementalNsource

duetoeithersequestrationofexistingNsoilresourcesorfixationofatmospheric

Nbylegumes.

Pastresearchonnitrogenuptakeofcashcropsfollowingspring-planted

legumeandgrasscovercropsintheCentralSandshasreportedvaryingN

benefitsforsweetcornproducedfollowingcovercropintegration(Westetal.,

2016;AndraskiandBundy,2005).Investigatingthepotentialbenefitsoffieldpea

(Pisumsativum)asaspring-seededcovercropprecedingsweetcorninthe

CentralSands,Westetal.(2016)andJohnsonetal.(2012)determinednoto

minimalNbenefitfromfieldpeainthissystem.Incontrast,AndraskiandBundy

(2005)determinedanNcreditintwooutofthreefieldseasonsfromfall-planted

oatforfieldcornintheCentralSands.Therefore,basedonthesethreeregionally-

basedstudies,fall-plantedgrasscovercropsaremorelikelytoprovideanN

creditcomparedtospring-plantedlegumes.

Althoughtheaforementionedstudiesprovideabasistobegintoderive

covercroprecommendationsforthisregion,severalmanagementvariables

requirefurtherinvestigation.Beyondfieldpea,otherlegumecovercropshave

notbeentestedforpotentialbiomassproductionorNcontributiontothecash

cropproductionseason.Additionally,covercropterminationmethodsand

subsequenteffectsonNuptakebythecashcrophavenotbeenstudied.Westet

9al.(2016)andJohnsonetal.(2012)bothterminatedthefieldpeacovercrop

throughmechanicaltillageand/orcultivation.Theseaggressivetermination

techniques,incorporatingresidueintothesoil,mayhavehastenedthe

mineralizationofNpresentinthecovercropbiomass.Thus,optimalcovercrop

managementpracticesforcroppingsystemsoftheCentralSandsremaintobe

determined,particularlyasrelatedtoselectionofspring-plantedspecies(grasses

andlegumes)andterminationmethod(chemicalversusmechanical).Thegoalof

thestudywastodeterminethenitrogencreditofspring-plantedgrassand

legumecovercropsforsweetcornonirrigatedsand.Specificstudyobjectives

wereto:(i)measurespring-plantedcovercropgrowthandNuptakeand(ii)

determinetheimpactofspringplantedcovercropsonsweetcornyield.

MaterialsandMethods

SiteDescriptionandExperimentalDesign

Atwo-yearstudywasconductedin2014and2015attheUniversityof

Wisconsin,HancockAgriculturalResearchStation(HARS)(latitude:44°8’23”N;

longitude:89°31’23”W;elevation:328m)onandoverhead-irrigatedPlainfield

loamysandsoil(mixed,mesicTypicUdipsamments).The2012fallsoiltestfor

the2014fieldindicated6.5pH,0.9%organicmatter(OM),89mgphosphorus(P)

kg-1,and66mgpotassium(K)kg-1.The2013fallsoiltestforthe2015field

indicated6.5pH,0.9%OM,121mgPkg-1,and85mgKkg-1.Theexperimental

designwasarandomizedcompleteblocksplit-plot,replicatedfourtimes.Whole

10plottreatments(7.3mx27.4m)werespring-plantedoat(OAT),chicklingvetch

(CV),berseemclover(BC),oat+berseem(O+B)cloverandnocovercrop

(NONE).Splitplottreatments(4.6mx7.3m,sixcornrowswide)consistedof

urea-Nfertilizerapplications:0,56,112,168,224,and280kg-Nha-1.

Theexperimentin2014followedtwoyearsoffieldcornandinfall2013,

thefieldreceivedasingletillagepasswithaTurbo-Till®,(GreatPlains

Manufacturing,Inc.;Salina,Kansas)fieldcultivatorat20cmdepth.Inspring

2014,thefieldreceivedseedbedpreparationwiththreepassesoftheTurbo-

Till®,followedbyonepasswitha20cmBrillion™(LandollCorporation;

Marysville,Kansas)soilfinisher.Instudyyear2015,theexperimentfolloweda

soybean-potatorotation,withnotillageinfall2014.Covercropseedbed

preparationin2015consistedofonepasswiththeTurbo-Till®fieldcultivatorat

20cmdepthand112kgha-1potash(0-0-60).

CovercropwasdrillseededwiththeOliver-Superior No. 64® Grain Drill on21

April2014andon16April2015.Seedingrateswere134kgha-1foroat(variety

notstatedin2014,‘Saber’in2015),67kgha-1forchicklingvetch(‘ACGreenfix’),

13kgha-1forberseemclover(varietynotstatedin2014;‘Balady1’in2015),and

thecombinedtreatmentwas67kgha-1foroatand11kgha-1berseemclover.

Chicklingvetchwasinoculatedwith‘N-DureTM’(Verdesian;Cary,NorthCarolina)

andberseemwithNitragin®Gold(Novozymes;RiverFalls,Wisconsin).Cover

11cropseedswereobtainedfromAlbertLeaSeed(AlbertLea,Minnesota)both

yearsofthestudy.

Covercropwasterminatedon10June2014withCreditExtra®(Nufarm

AmericasInc.;Alsip,Illinois;activeingredient(a.i.)2.3%glyphosate,mixedwith

nonionic80/20surfactant,andammoniumsulfate(AMS,21-0-0-24S,1.2Lha-1)).

Chicklingvetchplotswerealsotreatedwith2,4DAmine4,(LovelandProducts

Inc.;Greenley,Colorado,a.i.46.5%dimethylaminesaltof2,4-Dichloro-

phenoxyaceticacid)andParallel®PlusHerbicide(MakhteshimAganofNorth

America,Inc.;Raleigh,NorthCarolina,a.i.atrazine2-chloro-4-ethylamino-6-

isopropylamino-s-triazineandmetolachlor2-chloro-N-acetamide)on16June

2014.Chicklingvetchplotsreceivedtheirlastherbicidetreatmenton31July

2014ofLaudis®(BayerCropScienceLP;ResearchTrianglePark,NorthCarolina,

a.i.34.5%tembotrione2-cyclohexanedionemixedwithAMSandmethylated

seedoil)on31July2014.Inthe2015season,allcovercropswereterminated12

June2015withanapplicationofMadDogPlus®(LovelandProductsInc.;

Greenley,Colorado,a.i.41%glyphosatemixedwith,nonionic80/20surfactant,

andAMS).TheoatcovercropstandrequiredsurfacecultivationwithanM&W®

10'Dyna-Drive®(AlamoGroupInc.;Seguin,TX)on16June2015andasecond

herbicideapplication[Parallel®(Atrazine)(1.6Lha-1)]on19June2015for

completecovercroptermination.

12

Sweetcorn(‘DMC21-84’,DelMonteFoodsHybridYellowSweetCorn

Seed)wasplantedon13June2014and19June2015withaJohnDeereMax

EmergeTM(Deere&Company;Olathe,Kansas)2four-rowplanterataseeding

densityof24,500plantsha-1.Sixrowswereplantedperplotat28.5cmrow

spacingandstarterfertilizer(10-20-20-4S-2Ca+micronutrients)wasappliedat

planting(224kgha-1).Urea-Nfertilizerwashandappliedat56kg-Nha-1during

theV4sweetcorngrowthstageand56kg-Nha-1,112kgha-1,168kg-Nha-1,and

224kg-Nha-1attheV8growthstage.Fertilizerwasirrigatedwithin24hoursof

applicationin2014andonthesamedayofapplicationin2015.Irrigation,

insecticide,andherbicidewereappliedtothesweetcornasneeded.

SampleCollectionandAnalysis

Precipitationanddailyairtemperatures(maximumandminimum)

measurementswererecordedatHARS(HancockResearchStation-UWExtension

AGWeather)andwereusedtocalculategrowingdegreedayaccumulationfor

boththecovercropandsweetcorngrowingseasonsandwerecalculatedas:

GrowingDegreeDays°C(GDD)=[(T°C(DailyMAX)+T°C(DailyMIN))/2]/TBASE

Whereifthedailymaximumtemperature>30°wassetequalto30°andifthe

dailyminimumtemperature<10°wassetequalto10°.TBASEisthebase

temperaturefortheorganism,wheresweetcornTBASE=10°andoatTBASE=5.5°.

Covercropstandcountsandabovegroundbiomass(AGB)werecollected

on10June2014and19June2015,withthreesamplescollectedperwholeplot

13froma0.37m2areain2014anda0.14m2areain2015.Covercropbiomass

samplesweredriedina60°Cforced-airdryerforoneweek,mechanicallyground

usinga0.5mmsieve,andstoredinplasticvialsuntilanalysis.Nitrogencontentof

covercropbiomasswasdeterminedbyre-dryingsamplesforatleast24hours

priortoanalysis,withtotalcarbon(C)andtotalnitrogendeterminedusingflash

combustion(ThermoFisherScientificFlashEA1112NCAnalyzer,ThermoFisher

ScientificInc.,Waltham,MA).Sweetcornwasharvestedatmaturity(90DAPin

2014and89DAPin2015)on11September2014and11September2015.Yield

wasdeterminedasbothfreshweightyield(Mgha-1)andearyield(asthousand

earsperhectare)byharvestingmarketableearsinrowsthreeandfourofeach

six-rowplot.Earswerecountedandimmediatelyweighed(unhusked)inthefield

forfreshweightyieldcalculation.

StatisticalAnalysis

StatisticalanalysiswascompletedusingSAS(StatisticalAnalysisSystem,

version9.2,SASInstitute,Cary,NC).Covercropbiomass,Cyield,Nyield,andC:N

ratiowereanalyzedbyyearusingProcMIXED,withblocksasarandomeffect.

Forsweetcornyields,eachstudyyearwasevaluatedseparatelyandanalysisof

variance(ANOVA)wasconductedtodeterminesignificanteffectsofcovercrop

andN-rate(ProcMIXED)withblocks(covercroptreatment)asrandomeffects.

TodetermineagronomicoptimalNrate(AONR)bycovercroptreatmentbyyear

Nresponsedatawerefittolinear,linear-plateau,quadratic,andquadratic-

14plateauusingProcREGandProcNLIN.TheNrateresponsedatawerevisually

inspectedandthemodelwiththelargestcoefficientofdetermination(R2)value

wasreported.TheAONRistheminimumrecommendedNratenecessaryto

achievethemaximumyield.

ResultsandDiscussion

Covercrops

Themonthlyairtemperaturesduringthe2014covercropgrowingseason

were1to3˚Cabove30-yearnormaltemperatures(citationfor30-yraverage?)

averaging5˚C(1˚Cabovethe30-yearnormal)inApril,14˚C(3˚Cabovethe30-

yearnormal)inMay,and20˚C(2˚Cabovethe30-yearnormal)inJune.Cover

cropswerenotirrigatedandtotalprecipitationwas196mmfromcovercrop

seedingtoterminationin2014.

In2015,themonthlytemperaturesduringtheoatgrowingseasonwereat

or4˚Cabove30-yearnormaltemperatures,averaging8˚CinApril(atthe30-year

normal),15˚C(4˚Cabovethe30-yearnormal)inMay,and18˚C(4˚Cabovethe

30-yearnormal)inJune.CovercropGDDwerehigherin2015comparedto2014;

however,thedifferencebetweenyearlyGDDnarrowedbycovercrop

termination.Totalprecipitationthroughoutthe2015oatgrowingseasonwas

191mm.

Covercropgrowth,biomassproduction,andNuptakevariedgreatly

betweenseasons,withmorebiomassandNuptakemeasuredin2015.Compared

15to2014,legumecovercrop(berseemcloverandchicklingvetch)AGBwas12-14

timesgreaterin2015.The2014chicklingvetchproduction(258kgha-1,12kgN

ha-1)wasbelowtheexpectedAGBandwithinexpectedN-uptakerange(339to

4000kgha-1and6to161kgNha-1)(ThiessenMartenetal.,2001;Boumanetal.,

1993;Buechietal.,2015;Rinnofneretal.,2008),whileproductionin2015(3717

kgha-1,134kgNha-1)wasclosetothegreatestvaluespreviouslyreported.The

C:Nratiosofchicklingvetchweresimilarbothyearsofthisstudy(9in2014and

12in2015)andtopreviouslyreportedvalues(Buechietal.,2015;Rinnofneret

al.,2008).BerseemcloverAGBproductionandNuptakein2014(71kgha-1and

3kgNha-1)waslowerthanmeasuredberseemandothercloverspeciesinthe

literature(500to200kgha-1)(Fakharietal.2015;Parretal.2011;Readetal.

2011).BerseemcloverAGBproductionin2015(891kgha-1)andC:N(17)were

withintherangeofvaluesreportedinotherpublishedstudies;howeverNuptake

waslowerthanexpected(20kgNha-1)(Fakharietal.2015;Marstorpand

Kirchmann,1991;Parretal.2011;Readetal.2011;Snappetal.2005).Berseem

clover’spoorbiomassproductionandN-uptakeinbothgrowingseasonssuggests

thatAprilthroughMayplantingdatescouplewithaJuneterminationdatemay

notallowfortheadequategrowthintheCentralSandsregionofWisconsin.

Oatandcombinedoat/berseemcloverproduction,alsovariedgreatly

betweenseasons.OatAGBin2014(272kgha-1)was21timeslowercomparedto

2015(5824kgha-1)(Table1)andcombinedtreatment(oat+berseemclover)

16AGBwas17timesgreaterthan2015.Oatbiomassinboth2014and2015was

withinrangeofotherstudiesintheregion,from7to91kgNha-1andC:N

between15and33(AndraskiandBundy,2005;Contrera-GoveaandAlbrecht,

2005).Tovaryingmagnitudes,oatAGBvariabilityhasbeendocumentedinother

upperMidwesterncroppingstudies.InaWisconsin-basedstudy,Andraskiand

Bundy(2005)noted5-folddifferencesinoatbiomass(590kgha-1to3010kgha-

1)betweenyearsfortheirfallplantedandwinterkilledcovercrop.Alsoin

Wisconsin,Contreras-GoveaandAlbrecht(2005)measuredspring-plantedoat

biomasswithameanweightof7700kgha-1following77daysofgrowth(mid-

ApriltolateOctober).Pro-rated,thisvaluescorrespondswiththebiomass

accumulationduringthe2015fieldseasonofthisstudy(100kgAGBha-1day-1).

Combinedoatandberseemclovertreatmentinboth2014and2015had

thegreatestAGB(333kgha-1in2014and5864kgha-1in2015)andNuptake(9

kgNha-1in2014and140kgNha-1in2015)ofallcovercrops,fallingwithinthe

rangeofreportedvaluesforcombinedgrassandlegumeAGBmeasurementsin

publishedliterature(177to6175kgha-1and60kgNha-1to115kgNha-1)(T.

Rinnofneretal.2008;Parretal.2011).

Sweetcorn

Meanmonthlyairtemperaturesduringthe2014sweetcorngrowing

seasondeviatedfrom-5to2°Caroundthe30-yearnormaltemperatures,

averaging20°CinJune(2°Cabovethe30-yearnormal),19°CinJuly(1°Cbelow

17the30-yearnormal),20°CinAugust(2°Cbelowthe30-yearnormal),and15°Cin

August(5°Cbelowthe30-yearnormal).GDDwerehigherthanthosein2015,

accumulating891GDDin2014.Totalaccumulatedwater(precipitation272mm

+irrigation276mm)throughoutthesweetcorngrowingseasonwas548mm.

Inthe2015sweetcorngrowingseasonmeanmonthlyairtemperatures

deviated-3to1°Caroundthe30-yearnormaltemperatures,averaging18°Cin

June(atthe30-yearnormal),21°CinJuly(1°Cabovethe30-yearnormal),19°C

inAugust(3°Cbelowthe30-yearnormal),and18°CinAugust(2°Cbelowthe30-

yearnormal).TotalaccumulatedGDDwere845in2015andtotalaccumulated

water(precipitation264mm+irrigation256mm)throughoutthe2015sweet

corngrowingseasonwas519mm.

Sweetcornyieldswereevaluatedseparatelybetweenearyield(1000ear

ha-1)andfreshweightyield(Mgha-1)inboth2014and2015andwere

standardizedtothesameplantdensity(9,720plantsha-1)).Analysisofvariance

showsthatappliednitrogenratesignificantlyimpactedsweetcornyieldinboth

2014and2015(p<0.05).Therewasaninteractioneffectbetweencovercrop

treatmentandNrateinstudyyear2014(p<0.05)(Table2).

In2014,sweetcornearyieldresponsestoincreasingNapplicationson

BC,CV,andNONEtreatmentswerequadratic(Figure1),withAONRsatornear

thehighestNrateusedinthisstudy(280kgNha-1).Sweetcornearyield

responsesin2014toOATandO+Bwerelinear(Figure2).Inthesameyear,

18sweetcornfreshweightyieldresponsestoalltreatmentswerelinear,butwith

CVandNONEplateauingatNratesof171and148kgNha-1(Figures1&2).In

2015,sweetcornearyieldresponsestoallcovercroptreatmentswerequadratic,

withAONRsof215,216,221,259,and269kgNha-1forNONE,OAT,OAT+B,CV,

andBC,respectively(Figures3&4).Sweetcornfreshweightyieldresponsesto

Nin2015werelinearto121,136,138,and138kgNha-1forNONE,OAT,OAT+B,

andBC,respectively.SweetcornfreshweightyieldresponsetoNfollowingCVin

2015wasquadratic(AONR=280kgNha-1)(Figure3).Inboth2014and2015,

regardlessofbiomassaccumulationdifferences,neitheryearsawanNcredit

fromthecovercropandN-ratetreatments.Inbothstudyyears,eachtreatment

combinationhadahigherAONRascomparedtothecontrol;therefore,

mineralizedNfromthecovercropsdidnotaffectsweetcornyieldregardlessofN

rate.Inspiteofcovercropseasonalproductiondifferences,covercropsdidnot

provideanitrogenbenefitforsweetcornyield.

Yieldresponsetocovercropsinbothyearshadacoefficientof

determination(R2)above0.5exceptforthe2014chicklingvetchtreatment(ear

yieldR2=0.39andfreshweightyieldR2=0.66),whichwascausedbyhigher

sweetcornyieldin0kgNha-1treatmentsacrossallblocks,comparedto56kgN

ha-1.In2014,chicklingvetchrequiredtwoadditionalherbicideapplicationsafter

sweetcornplanting;thisextrabiomassaccumulationwasnotmeasuredthough

itispossiblethatitcompetedwithsweetcorngrowthorcontributedtoan

19unmeasuredinteractionthatreducedyields.Inordertodetermineamore

realisticagronomicoptimalNrateandastrongerrelationshipbetweenchickling

vetchtreatmentandyieldresponse,regressionanalysiswascompletedasecond

time,removing0kgNha-1datapointsfromtheanalysis.Quadratic(R2=0.92)

andlinear-plateau(R2=0.93)modelswerefittothefreshweightyielddataand

adjustedagronomicoptimalNratesof217kgNha-1(freshweightyield=13Mg

ha-1)and77kgNha-1(freshweightyield=11Mgha-1)weredetermined.Sweet

cornearyielddatawith0kgNha-1datapointsremovedwasalsofittoquadratic

(R2=0.83)andlinear-plateau(R2=0.82)models,determiningadjusted

agronomicoptimalNratesof226kgNha-1(earyield=49,000earsha-1)and126

kgNha-1(earyield=45,000earsha-1).Uponremovalofthe0-Ndatapoints,the

newlyadjusted2014chicklingvetchagronomicoptimalNratesfluctuatedabove

andbelowthenocovertreatments’(AONR=148kgNha-1at10Mgha-1fresh

weightyieldandAONR=279kgNha-1at44,000earsha-1).Agronomicoptimum

Nrateforfreshweightyielddeterminedbylinear-plateauregressionwaslower

thanthecontrol,howeverwithsimilarR2valuesquadraticregressionofthesame

datadeterminedagreateragronomicoptimalNrate.Regardingregressionofthe

earyielddata,bothregressionmodelsdeterminedloweragronomicoptimumN

ratevaluesthanthecontrol.ThisinconsistencyinagronomicoptimumNrate

acrossregressionanalysiscouldbeattributedtothevariablemeanvaluesforN-

rates168kgNha-1(12Mgha-1&48,000earsha-1),224kgNha-1(11Mgha-1&

2038,000earsha-1),and280kgNha-1(12Mgha-1&50,000earsha-1)inthe2014

chicklingvetchtreatment.Variabilityinthe2014chicklingvetchdatasetis

responsibleforlowR2values(quadraticregression)andispotentiallybetter

describedbyhigherorderpolynomialregression(fourthorderR2=0.99&AONR

=151kgNha-1),accountingforthedataset’sabnormalpeaksandvalleys.

Thesefindingsareconsistentwithpreviousworkcomparingsweetcorn

yieldbenefitofleguminouscovercropsinsandysoils.Johnsonetal.(2012)

measuredminimalNbenefitfromspring-plantedfieldpeacovercropinthe

CentralSandsandWestetal.(2016)reportednonitrogencreditfromspring-

plantedfieldpeaalsointheCentralSands.Inthewarm-temperateenvironment

ofFlorida,Cherretal.(2007)documentednosweetcornyieldbenefitfromfall-

plantedwhitevetchinsandysoil.Parretal.(2011)alsodeterminednoNcredit

fromlegumes(berseemclover,redclover,orcrimsonclover)onsandysoilsof

NorthCarolina.Thus,ourfindingsagreewithotherstudiesonleguminouscover

crops,suggestingrapidmineralizationinsandysoilandsubsequentleachingof

plantavailableNbeyondtherootzonepreventNbenefittosweetcorncrop.

WedidnotdetermineanNcreditwithoatcovercrop,buthigheryields

wereobtainedathigherNratescomparedtonocovercropTheNbenefitsof

grasscovercropsandcombinedgrass+legumecovercroptreatmentsarenot

clearlydefinedintheliterature.AndraskiandBundy(2005)measureda

reductionineconomicoptimumNrateintwooutofthreestudyyearsfollowing

21fall-plantedoatcovercropinsandysoil.Alsoinsandysoils,Parretal.(2011)

measurednoNbenefitofcombinedgrassandlegumebiculturecovercrop

treatments;howeverSainjuetal.(2005)didmeasureanNbenefitfrombiculture

acovercroptreatmenttothesubsequentcrop.Onasiltloam,Stuteetal.(1995)

documentedanNbenefitfromanoat/legume-cornrotation.Thus,priorstudies

donotclearlycorroborateourfindings:thatspring-plantedoatcovercrop

providedzeroN-credittothesubsequentsweetcorncrop,butdidprovideayield

benefitathigherN-rates.

Conclusion

Legumeandgrassspring-plantedcovercroptreatmentsdidnotreduce

optimalNrateforsweetcornproductioninsandysoil,regardlessofbiomass

producedduringthecovercropgrowingseason.However,slightgainsinsweet

cornyieldwereobtainedfollowingacovercropathigherratesofappliedN.

Berseemclover,asasinglespeciesorpartofacovercropmix,isnot

recommendedasacovercropinthissystembecauseoflowproductivity.

Chicklingvetchmayalsobeproblematicwhengrownasaspring-sowncover

cropintheCentralSands,asterminationrequiredadditionalchemical

applicationsormechanicaltillageascomparedtotheothercovercropstrialed.

Theexisting,underlyingconcernoffarmersregardingtheintegrationofspring-

seededcovercropsintothecroppingsystemsoftheCentralSandswasrealizedin

in2014,wherecovercropgrowthwasslowandlittlebiomasswasproduced.Itis

22notclearthatgrowerswillbeabletoobtainaconsistentcovercropwhenspring

seedinginthisregion.

Whilethisstudyfocusedontheroleofspring-seededcovercropson

nitrogenavailabilitytothesubsequentcashcrop,italsoprovidesgreater

understandingofthebroaderimpactsofcovercropsplantedinthisregionfor

otherecosystemservices,specificallymitigationoftheimpactsofwinderosion.If

possiblewithintheseasonconstraintsofthetypicalcroprotationsinCentral

Wisconsin,farmerswillestablishfallplantedcovercrops,oftencerealrye,infield

cornandsoybean,allowingforadequatecovertoreliablycontrolwinderosionin

thespring.Concernsexistthathigheramountsofbiomassfromagrasscover

cropmayleadtoareductioninavailableNtothesubsequentcashcrops.

However,thisstudydemonstratedthatlargeamountsofbiomassfromagrass

covercropinthespringdisplayednonegativeeffectsonyieldoroptimumNrate.

Thus,theuseofcovercropsintegratingthemultifunctionalstrategyofa

conservationmanagementpracticewillnotaffectproductionofsweetcornin

thisregion.ThefutureofNmanagementresearchinthesesystemsshouldfocus

onimprovednitrogenuseefficiencythroughin-seasonNapplication,working

towardsoptimalNratereductions.

23

24TablesandFigures

TABLE1CovercropdrymatterbiomassandnitrogenuptakeatHancockAgriculturalResearchStationin2014and2015.Covercropsabbreviationsare:BC=berseemclover,CV=chicklingvetch,O+B=oatandberseemclover,andOAT=oat.

2014 2015

CoverCrop

PlantPop.a Biomass Total

CTotalN C:N Plant

Pop. Biomass TotalC

TotalN C:N

1000plantsha-1

kgha-1 kgCha-1

kgNha-1 %

1000plantsha-1

kgha-1 kgCha-1

kgNha-1 %

BC 1,050 71

(17)b31(8)

3(0.8)

11(0.6) 3,250 891

(678)353(273)

20(16)

17(1.4)

CV 260 258

(82)108(96)

12(3)

9(0.3) 2,090 3717

(850)1567(369)

134(24)

12(0.6)

O+B

1,920(O)970(B)

333(85)

137(36) 9(3) 15

(1.2)

8,820(O)3,070(B)

5864(1842)

2430(774)

140(59)

18(3)

OAT 4,690 272

(40)112(14)

6(0.6)

18(0.7) 13,310 5824

(845)2419(331)

119(30)

20(4)

aTargetplantpopulationwas4,409,000plantsha-1forBC,3,274,000plantsha-1forCV,2,015,000+3,674,000plantsha-1forO+Brespectively,and4,030,000plantsha-1forOAT.bNumberinparenthesisindicatesstandarddeviation.

25TABLE2SweetcornfreshyieldANOVAresultsasaffectedbycovercropandNrateatHancockAgriculturalResearchStationin2014and2015.Analysisconductedbyyear. MeanYield

2014 2015

Treatment Mgha-1 1000Earsha-1 Mgha-1 1000Earsha-1CoverCrop BerseemClover 7.45a 30.9a 14.7a 46.0aChicklingVetch 8.47a 35.3a 15.7a 47.1aOat+BerseemClover 6.77a 30.0a 14.3a 44.4aOat 5.48a 25.6a 14.1a 47.0aNoCover 6.36a 26.5a 13.2a 43.0aNrate,kgha-1 0 1.85a 11.2a 1.67a 7.09a56 1.44a 8.02a 6.76b 26.0b

112 6.30a 27.5b 18.0c 55.8c168 10.1b 40.6c 19.3c 58.3c224 10.8b 41.6c 19.2c 60.8c

280 11.5b 48.5c 22.0c 64.1c

Sourceofvariation Pvalue

CoverCrop 0.0005 0.0785 0.3022 0.3459Nrate <.0001 <.0001 <.0001 <.0001CoverCrop*Nrate 0.0235 0.0039 0.6263 0.4413

26

FIGURE1SweetcornagronomicoptimalNrate(AONR)asdeterminedbyregressionmodelingfollowingeachcovercroptreatment(berseemclover(BC),chicklingvetch(CV),nocovercrop(NONE))andnitrogen(N)ratereportedasearyield(1000earsha-1)(top)andfreshweightyield(Mgha-1)(bottom),Hancock,WI,2014.

0

10

20

30

40

50

60

0 56 112 168 224 280

EarYield(1000earsha-1 )

BCCV

BC:y=-0.394x2+294x+1461

R2=0.95 AONR:280

NONE:y=-0.608x2+339x+-2820

R2=0.95 AONR:279

CV:y=0.208x2+37.4x+24254 R2=0.39 AONR:280

0

2

4

6

8

10

12

14

16

0 56 112 168 224 280

FreshWeightYield(M

gha

-1)

NRate(kgNha-1)

BCCV

BC:y=0.160+0.053xR2=0.96AONR:280

CV:y=3.34+0.047xR2=0.66AONR:171

NONE:y=-0.895+0.073xR2=0.91y=9.93ifx≥148

27FIGURE2SweetcornagronomicoptimalNrate(AONR)asdeterminedbyregressionmodelingfollowingeachcovercroptreatment(berseemclover(BC),chicklingvetch(CV),nocovercrop(NONE))andnitrogen(N)ratereportedasearyield(1000earsha-1)(top)andfreshweightyield(Mgha-1)(bottom),Hancock,WI,2014.

0

10

20

30

40

50

60

0 56 112 168 224 280

EarYield(1000earsha-1 )

OATOBNONE

NONE:y=-0.608x2+339x+-2820 R2=0.95 AONR:279

OAT:y=730+160x R2=0.93 AONR:280

OB:y=7350+157x R2=0.93 AONR:280

0

2

4

6

8

10

12

14

0 56 112 168 224 280

FreshWeightYield(M

gha

-1)

NRate(kgNha-1)

OATOBNONE

NONE:y=-0.895+0.073xR2=0.91y=9.93ifx≥148

OB:y=-0.000006x2+0.046x+0.479 R2=0.95 AONR:280

OAT:y=-0.00001x2+0.044x+-.431 R2=0.93 AONR:280

28FIGURE3SweetcornagronomicoptimalNrate(AONR)asdeterminedbyregressionmodelingfollowingeachcovercroptreatment(berseemclover(BC),chicklingvetch(CV),nocovercrop(NONE))andnitrogen(N)ratereportedasearyield(1000earsha-1)(top)andfreshweightyield(Mgha-1)(bottom),Hancock,WI,2015.

0

10

20

30

40

50

60

70

80

0 56 112 168 224 280EarYield(1000earsha-1 )

BCCV

NONE:y=-1.27x2+546x+2761R2=0.88AONR:215

BC:y=-0.873x2+470x+5151 R2=0.94 AONR:269

CV:y=-0.919x2+477x+6747 R2=0.96 AONR:259

0

5

10

15

20

25

30

0 56 112 168 224 280

FreshWeightYield(M

gha

-1)

NRate(kgNha-1)

BCCV

NONE:y=-0.215+0.152xR2=0.97y=18.8ifx≥121

BC:y=0.567+0.146x R2=0.94 y=21ifx≥138

CV:y=-0.0002x2+0.140x+2.00 R2=0.91 AONR:280

29FIGURE4SweetcornagronomicoptimalNrate(AONR)asdeterminedbyregressionmodelingfollowingeachcovercroptreatment(berseemclover(BC),chicklingvetch(CV),nocovercrop(NONE))andnitrogen(N)ratereportedasearyield(1000earsha-1)(top)andfreshweightyield(Mgha-1)(bottom),Hancock,WI,2015.

0

5

10

15

20

25

0 56 112 168 224 280

FreshWeightYield(M

gha

-1)

NRate(kgNha-1)

OATOBNONE

OAT:y=1.66+0.135x R2=0.94 y=20ifx≥136

OB:y=0.356+0.138x R2=0.97 y=19ifx≥138

NONE:y=-0.234+0.167x R2=0.97 y=19.8ifx≥121

0

10

20

30

40

50

60

70

0 56 112 168 224 280

EarYield(1000earsha-1 )

OATOBNONE

OAT:y=-1.10x2+475x+13100 R2=0.97 AONR:216

OB:y=-1.18x2+527x+2936 R2=0.96 AONR:221

NONE:y=-1.27x2+546x+2761 R2=0.88 AONR:215

30

SASCodeYield data CC2014; input cc $ nrt blk yield; datalines; proc glimmix data=CC2014 plots=studentpanel; class blk cc nrt; model yield = cc nrt cc*nrt; random blk; lsmeans cc/diff; lsmeans cc*nrt/diff; run; proc sort; by blk cc nrt; proc print; run;

YieldRegressionproc print data=yield; data b; set yield; N = NRate; N2 = N*N; proc print data=b; DATA REG; SET b; PROC REG; MODEL Yield=N; PROC REG; MODEL Yield=N N2; OUTPUT OUT=X RESIDUAL=R; PROC NLIN; PARMS B0=8 B1=0.44 KNOT=100; AGEPLUS=MAX (N - KNOT, 0); MODEL Yield = B0 + B1*N - B1*AGEPLUS; OUTPUT OUT=B PREDICTED=YP RESIDUAL=RR; Proc Plot; plot yield*n yp*n='*' /overlay; plot rr*n; run; PROC NLIN; PARMS A=8 B=0.44 C=-.0015; N0=-145*B/C; DB=-.5/C; DC=.5*B/C**2; IF N<N0 THEN DO; MODEL Yield=A+B*N+C*N*N; DER.A=1; DER.B=N; DER.C=N*N; END; ELSE DO; MODEL Yield=A+B*N0+C*N0*N0;

31DER.A=1; DER.B=N0+B*DB+ 2*C*N0*DB; DER.C= B*DC+N0*N0+2*C*N0*DC; END; IF _OBS_=1 & _ITER_>0 THEN DO; PLATEAU=A+B*N0+C*N0*N0; PUT N0=PLATEAU=; end; OUTPUT OUT=b predicted=grainyldp residual=gyresid; proc plot; plot Yield*N grainyldp*N='*' / overlay vpos=35; plot gyresid*n; run;

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34

35Chapter3:OatCoverCropGrowthandInfluenceonNetNitrogenMineralizationinSandySoilAbstract

CovercropsarewidelyusedintheCentralSandsregionofWisconsin,but

theireffectonseasonalNcyclingisnotwellquantified.Theobjectivesofthis

studyweretoquantifyspring-plantedoat(Avenasativa)covercropgrowthand

N-uptake,determinetheeffectofoatcovercropandNfertilizeronin-situ

mineralizationandseasonalplantavailablenitrogen(PAN),anddeterminethe

effectofspringplantedoatcovercropsonsweetcorn(ZeamaysL.)Nuptake.The

studywasconductedacrosstwogrowingseasonsattheHancockAgricultural

ResearchStationintheCentralSandsofWisconsinandtheexperimentaldesign

wasarandomizedcompleteblock,split-plotdesignwithtwowhole-plot

treatments(oatandnocover)andtwosplit–plotN-ratetreatments(0and168

kg-Nha-1).In-situmineralizationcolumnswithanionandcationresinswereused

tomeasureseasonalmineralizationratesevery30daysduringthegrowing

season.OatbiomassandNuptakevariedgreatlybetweenyears(272kgha-1and

6kgNha-1in2014and5824kgha-1and119kgNha-1in2015,respectively),but

therewasnoeffectoftheoatcovercroponNmineralizationorsweetcornN

uptakeineitheryear.However,oatcovercropdidimpactsoilnitrateand

ammoniumwhenmeasuredatapproximately10-dayintervals.Thein-situ

mineralizationmethodprovidedvalueswithinrangeofotherstudies,butwasnot

36quantitativebasedonNbudgets.Thesefindingssuggestthatoatcovercropsdo

notappeartomeaningfullyeffecttheNcycleinthisregion.

Introduction

TheWisconsinCentralSandsregionischaracterizedbysandysoilsand

productionofvegetablecropsforthelocalvegetableprocessingeconomy.The

region’ssoiliscomprisedof90%course-texturedsand,glacialoutwashfromthe

WisconsinglaciationthatalteredtheNorthAmericanlandscapemostrecently

25,000yearsago(WisconsinGeological&NaturalHistorySurvey »IceAge

Geology).Giventheregion’ssandysoilandlowsoilorganicmatter,agricultural

productivityrequireshighinputsofirrigatedwaterandnutrients.IntheCentral

Sands,thecombinationofnitrogenapplicationandfrequentirrigationonsandy

soilcanresultinnitrate-Ngroundwaterloadingof77%oftotalfertilizerN

applied(KraftandStites,2003).Thisnitrate-Ncanleachintolocal,regional,and

eventuallynationalwaters,whichcancausehypoxiainaquaticecosystems(Justic

etal.,1995;BurkartandJames,1999).

TheCentralSandslandscapeiscomprisedofexpansiveplainsand

producersintheregionusegrasscovercropstoreducewinderosionaftercrop

harvest.However,farmersmaybeunabletoestablishcovercropsinthefall

followingcornorsoybean(Glycinemax)harvest.Spring-plantedcovercropsare

anoptionprecedinglate-summerplantedcropssuchassweetcorn,whichcanbe

plantedaslateasmid-July,buttheeffectsontheNcycleofspring-plantedgrass

37covercropsarenotwellquantified.Onsandysoil,grasscoversappeartobemore

likelytoprovideanNbenefitcomparedtolegumesaspreviousworkonfieldpea

(Pisumsativum),chicklingvetch(Viciavillosa),andberseemclover(Trifolium

alexandrinum)inthisregionhaveshownnoNcredit(Johnsonetal.,2012,West

etal.,2016,Ivancicetal.,Chapter2).Spring-seededlegumecoversresultinlow

biomassproductionandtheirlowC:Nratiobiomassappearstodecomposeand

mineralizetooquicklyandleachoutoftherootzonepriortouptakebysweet

corn(Westetal.,2016).Incontrast,grasscovercropshavebeenshownto

provideNbenefitsinthisregionintheformofeconomicoptimumnitrogenrates

(EONR).AndraskiandBundy(2005)documentedareductioninEONRofsweet

cornfollowingfall-plantedoatcovercropintwoofthreeyears.Theauthorsalso

comparedthegrowthandN-uptakeacrossthreefall-plantedgrasscovercrops,

oat,ryeandtriticale,beforesweetcornplantinganddeterminedthatoatresulted

inthegreatestabovegroundbiomassandN-uptake.Dependingonthegrowth

andC:Nratioofanoatcovercropwhenterminated,anNcreditmaybeprovided

orimmobilizationofappliedNmayoccur.InthesandysoilsofMachanga,Kenya,

Chivengeetal.(2009)quantifiedNcyclingofcombinedtreatmentsofhighC:N

ratio(60to208)plantresiduesandNfertilizer,measuringNimmobilizationand

reducedleachingwithacombinedapplication.

Mineralizationandothernitrogentransformationsvaryaccordingto

moisturecontent,microbialcommunity,soilmicroclimate,andmanagement

38practicesthatarenoteasilyrepresentedinalaboratorysetting(Binkleyand

Hart,1989).Itisarguedthatduetotheseenvironmentalvariances,in-situfield

experimentsprovidemoreaccuratemineralizationmeasurementsthan

laboratory.Variousin-situmethodshavebeenusedtoquantifyN

transformations,advancingwithtime.Eno(1960)usedburiedresinbags,

DiStefanoandGholz(1986)andBryeetal.(2002)combinedresinbagswithPVC

columnsforamoreprecisetechniquethatquantifiedsoilvolumewith

mineralizationmeasurements.Forthisstudy,weusedthecombinedsoilcolumn

andionicresintechniquetomeasurein-situmineralization.Thismethodusesa

knownsoilvolumeasausefultoolforquantifyingfield-scalemineralization.

Thisstudyquantifiedmineralizationofspring-plantedoatinasweetcorn

croppingsystemintheCentralSandstobetterunderstandoatcovercropeffect

onNcycling.Specificstudyobjectiveswereto:(i)quantifyspring-plantedoat

covercropgrowthandNuptake,(ii)determinetheeffectofoatcovercropandN

fertilizeronin-situN-mineralizationandseasonalPAN,and(iii)determinethe

effectofspringplantedoatcovercropsonsweetcornNuptake.

MaterialsandMethods

SiteDescriptionandExperimentalDesign

Atwo-yearstudywasconductedin2014and2015attheUniversityof

Wisconsin,HancockAgriculturalResearchStation(HARS)(latitude:44°8’23”N;

longitude:89°31’23”W;elevation:328m)onanoverhead-irrigatedPlainfield

39loamysandsoil(mixed,mesicTypicUdipsamments).Theexperimentaldesign

wasarandomizedcompleteblock,split-plotdesignwithtwowhole-plot

treatments(oatandnocover)andtwosplit–plotN-ratetreatments(0and168

kg-Nha-1),replicatedfourtimes.Thisstudywasconductedwithinselect

treatmentsofalargerstudy(describedinChapter2)andincludetheoat(OAT)

andnocovercrop(NONE)withoutNandwith168kgNha-1(OAT+Nand

NONE+N)treatments.Oatcovercropwasdrillseededon21April2014

andon16April2015at134kgha-1andterminatedon10June2014withan

applicationofCreditExtra®,(NufarmAmericasInc.;Alsip,Illinois)[active

ingredient(a.i.)2.3%glyphosate,mixedwithnonionic80/20surfactantand

ammoniumsulfate(AMS,21-0-0-24S)].Covercropterminationbeganon12June

2015withanapplicationofMadDogPlus®(LovelandProductsInc.;Greenley,

Colorado)[a.i.41%glyphosate,mixedwithN-(phosphonomethyl)glycine,

nonionic80/20surfactant,andAMS]andrequiredsurfacecultivationwithan

M&W®10'Dyna-Drive®(AlamoGroupInc.;Seguin,TX).On16June2015,a

secondherbicideapplicationofParallel®(AdamaUSA;Raleigh,NC)[ai.84%

metolachlor:2-chloro-N-(2-ethyl-6-methylphenyl)-N-(2-methoxy-1-methylethyl)

acetamide]wasappliedon19June2015forcompletecovercroptermination.

Theoatvarietywasnotstatedin2014andwasSaberin2015.Sweetcorn(Del

MonteFoodsHybridYellowSweetCornSeed,varietyDMC21-84)wasplantedon

13June2014and19June2015withaJohnDeereMaxEmergeTM(Deere&

40Company;Olathe,Kansas)four-rowplanterataseedingdensityof24,500plants

ha-1andharvestedbyhand11September2014and11September2015.

Fertilizerapplicationtocornwassplitbetweentwo,56kg-Nha-1duringV-4

(between0-30days)and112kg-Nha-1duringV-8(between30-60days)

growingstages.Equivalentquantitiesofurea-Nfertilizer(sixureaprillsforthe

56kgNha-1applicationrateand12prillsforthe112kgNha-1applicationrate)

wereappliedtoeachabovegroundsoilcoreareainordertoensureuniform

application.

PlantCollectionandAnalysis

Precipitationanddailyairtemperatures(maximumandminimum)

measurementswererecordedatHARSandwereusedtocalculategrowing

degreedayaccumulationforboththecovercropandsweetcorngrowingseasons

andwerecalculatedas:

GrowingDegreeDays°C(GDD)=[(T°C(DailyMAX)+T°C(DailyMIN))/2]/TBASE

Whereifthedailymaximumtemperature>30°wassetequalto30°andifthe

dailyminimumtemperature<10°wassetequalto10°.Thebasetemperature

(TBASE)foreachplantwassweetcornTBASE=10°andoatTBASE=5.5°.Data

collectedfromHARSdailytemperaturecollectionstation(HancockAgricultural

ResearchStation,2016;Table1).

Abovegroundbiomass(AGB)wascollectedon10June2014and19June

2015;threesampleswerecollectedperwholeplotfroma0.37m2areain2014

41anda0.14m2areain2015.Sweetcornwasharvestedandsubsampledon11

September2014and11September2015.Randomlyselectedsubsamplesofsix

earsandsixstalkswerecollectedfromoutsideoftheharvestrows(3and4)from

rows1,2,5,and6acrossalltreatments.Covercrops,ears,andstalkswere

weighedseparatelyinthefield.Stalkswerechoppedandonesubsamplewas

collectedperplot.Earswerecutinto2.5cmmedallionsandonesubsamplewas

collectedperear,totalingsixmedallionsubsamplesperplot.Covercropbiomass

samples,earsubsamples,andstalksubsamplesweredriedina60°Cforced-air

dryerforoneweek,re-weighedfordryweight,andmechanicallygroundusinga

0.5mmsieveandstoredinplasticvialsuntilanalysis.Nitrogencontentofcover

cropandsweetcornbiomasswasdeterminedbyre-dryingsamplesforatleast

24hourspriortoanalysisandtotalcarbonandtotalnitrogenanalysisusinga

flashcombustionprocedure(ThermoFisherScientificFlashEA1112NC

Analyzer,ThermoFisherScientificInc.,Waltman,MA).

In-situMineralizationColumnsandSoilSampleCollectionandAnalysis

Nitrogenmineralizationratesweremeasuredusingin-situincubation

coresandion-exchangeresinsachetssimilartothosedescribedbyBryeetal.

(2002).Coreswereconstructedofpolyvinylchloridepipes(30.5cmindepthand

20cmindiameter).Onthedayofplanting,twocoreswereinsertedineachplot

byhand(physicallyforcedinusingamallet),onebetweenrowstwoandthree

andthesecondcorebetweenrowsfourandfiveineachplot.Coreswereplaced

42approximately0.6minfromthesouthendofeachplotandmovedapproximately

0.6mfurthernorthwitheachnewinstallation.Afterinsertion,coreswere

carefullyexcavatedwithshovels;attentionwaspaidtoremovingthecore

withoutdisturbingthesoilwithin.Onceremoved,coreswereinverted,5cmof

thesoilwereremovedfromthebaseandaresinsachetwascurledinitsplace

coveringthecore’sentiresurfacearea.ResinsachetsweremadeofL’eggsUltra

SheerPantyhose(HanesbrandsInc.,WinstonSalem,NorthCarolina),sizelarge,

cutatthethigh,filledwith30gofRexyn300(H-OH)ion-exchangeresinbeads

andsecuredwithaknot.Aftersachetinsertion,theremainingspacebetweenthe

sachetandthebaseofthecorewasfilledwithsoil,coveredwitha23cmx23cm

squaremeshandziptiedaroundthebaseinordertosecurethesoilandresin

sachetwithinthecore.Thecorewastheninsertedbackintotheholefromwhich

itcame.Soilcoreswereincubatedin-situforthree30-dayintervals(0-30,30-60,

and60-90days)throughoutthesweetcorngrowingseason.

Soilwassampledfromtheareaoutsideofthecoreonthefirstdayof

incubationtodetermineinitialNO3-NandNH4-Nconcentrations.Soilwas

extractedbycombining1.5g(±0.05)ofsoilwith15mlof2MKCLand

mechanicallyoscillatingthesamplesfor15minutes.Sampleswerethenfiltered

andtheextractantwasanalyzedforNO3-Nusingavanadiumchloridereactionas

describedbyDoaneandHorwath(2003)andforNH4-Nusingacolormetric

BerthelotmethodasdescribedinHood-Nowontyetal.(2010).After30-daysof

43incubation,coreswereexcavatedandthesoilwithineachcorewasextracted.

Thesoilcoresampleswereweighedinthefieldandsubsampledforsoilmoisture

determinationforbulkdensitycalculations.Soilmoisturesubsampleswere

placedinaluminumtinsanddriedina105°Covenfor24hours.

Resinsachetswereimmediatelystoredoniceafterincubationand

extractedwithinaweek.Onceinthelaboratory,resinwasremovedfromthe

nylonsachetandweighed.Resinwasplacedinscintillationvialswith40mL2M

KCLandmechanicallyoscillatedfor60minutes(Wolf,2010).Extractantwas

filteredandsenttotheUniversityofWisconsin,MadisonSoilandPlantAnalysis

LaboratoryforNO3-NandNH4-NanalysisbyflowinjectiononaLachat

QuickChem8000.Onthesamedayofsoilcolumnremovalnewsoilcolumnswith

freshresinsachetswereinserted.

Soilsampleswerecollectedoutsideoftheincubatedcoreseverytendays

throughoutthesweetcorngrowingseasonandanalyzedforNH4-NandNO3-N

concentrations.In2014thetensamplingtimepoints(TP1toTP10)were:13

June,23June,2July,10July,21July,31July,8August,18August,29August,and

14September.In2015the9samplingpoints(TP1toTP9)were:19June,30

June,9July,17July,29July,6August,17August,26August,and11September.

Samplesweretakentoa30cmdepthatapproximately30cmonthenorth,south

andeithereastorwestsidesofeachsoilcore,dependinguponsoilcolumn

placementwithintheplot.Sampleswerenottakenbetweenharvestrowsthree

44andfour.Samplesweredriedinaforcedairdrierforatleastoneweekand

groundtopassthrougha2mmsieve.SoilsampleswereanalyzedforNO3-Nand

NH4-NusingtheDoaneandHorwath(2003)andHood-Nowontyetal.(2010)

procedures,asdescribedabove.

CalculationsandStatisticalAnalysis

ThetotalamountofNtakenupbyplantsthroughoutthegrowingseason

wascalculatedasTotalNuptake(TNU)usingthesummationofplant-availableN

concentrationinthesweetcornearsandsweetcornstalks.

TNU=NEAR+NSTALK

Partialnutrientbalance(PNB)istheamountofNthatispresumablylost

totheenvironment,andiscalculatedhereasaratioofNremoved(ear)overthe

amountofNapplied.

PNB=NEAR/NAPPLIED

TheNuptakeefficiency(NUE)ofurea-Nforsweetcornproductionwas

calculatedperunitNappliedasthedifferencebetweenTNU(Applied-N)and

TNU(Control)overtheovertotalNapplied.

NUE=(TNU(Applied-N)–TNU(Control))/Applied-N

Netmineralizationcalculationswereconductedforeachyearand30-day

timeperiod.SimilartoNoe(2011),wesummedthedifferencesbetweenstarting

andendingNO3-NandNH4-Nconcentrationsofincubatedsoilsandaddedending

resinNO3-NandNH4-Nconcentrations.

45

Analysisofvariance(ANOVA)wasconductedtodeterminetheeffectof

covercropandNrateonNmineralization,sweetcornNuptake,PNB,andNUE.

Forsimplicity,statisticalanalysiswasconductedwithfourmainplottreatments

(NONE,NONE+N,OAT,andOAT+N).ProcMixedwasusedwithblockasarandom

effectandtimeperiodsandstudyyearswereanalyzedseparately.SoilNdata

werelogtransformedinordertosatisfythehomogeneityofvariancestatistical

assumptionandanalyzedwithProcMIXEDwithblockasarandomeffectand

REPEATED=samplingtimeandSUBJECT=block×treatment.Modeltype

(compoundsymmetry=CS,heterogeneousCS=CSH,antedependence=

ANTE(1),orspatialcovariancepower=SP(POW))wasdeterminedbythelowest

akaikeandbayesianinformationcriterionscores.The2014datawereevaluated

usingSP(POW)modeltypeandthe2015datasetswereevaluatedusingtypeCSH

forNH4-Ndata,typeCSforNO3-N,andtypeANTE(1)forPAN.Meancomparisons

wereconductedusingLSMEANSforallanalyses,exceptfornitrate,ammonium,

andPANwhereLSMEANSwasusedwithSLICEtoidentifysignificanttreatment

effectsateachsamplingtime.AllstatisticswereconductedinSAS(Statistical

AnalysisSystem,version9.2,SASInstitute,Cary,NC)andNmineralization

treatmentsignificanceisreportedatthealpha=0.10significancelevelandsoilN

andsweetcornN-uptake,PNB,andNUEtreatmentsignificanceisreportedat

alpha=0.05significancelevel.

46Results

OatTemperature,Precipitation,andSeasonalGrowth

Themonthlyairtemperaturesduringthe2014oatgrowingseasonwere1

to3˚Cabove30-yearnormaltemperatures,averaging5˚C(1˚Cabovethe30-year

normal)inApril,14˚C(3˚Cabovethe30-yearnormal)inMay,and20˚C(2˚C

abovethe30-yearnormal)inJune(Table1andFig.2).Covercropswerenot

irrigatedandtotalprecipitationwas196mmfromcovercropseedingto

terminationin2014(Fig.1).

OatGDDwerehigherin2015comparedto2014(Fig.3).In2015,the

monthlytemperaturesduringtheoatgrowingseasonwereator4˚Cabove30-

yearnormaltemperatures,averaging8˚CinApril(atthe30-yearnormal),15˚C(4

˚Cabovethe30-yearnormal)inMay,and18˚C(4˚Cabovethe30-yearnormal)in

June(Table1).Totalprecipitationthroughoutthe2015oatgrowingseasonwas

191mm(Fig.1&Fig.2).

OattotalAGB(5824kgha-1)was183%greaterin2015than2014.

Accordingly,2015totalCwas2,419kg-Cha-1,182%greaterthan2014,andtotal

Nwas119kg-Nha-1,180%greaterthan2014(Table2).Covercropbiomass

variedgreatly(272kgha-1in2014and5,824kgha-1in2015)betweenstudy

years.

Mineralization

47

Meanmonthlyairtemperaturesduringthe2014sweetcorngrowing

seasonandmineralizationcoreincubationdeviatedfrom-5to2°Caroundthe30-

yearnormaltemperatures,averaging20°CinJune(2°Cabovethe30-year

normal),19°CinJuly(1°Cbelowthe30-yearnormal),20°CinAugust(2°Cbelow

the30-yearnormal),and15°CinSeptember(5°Cbelowthe30-yearnormal)

(Table1).Totalaccumulatedwater(precipitation271mm,irrigation314mm)

throughoutthesweetcorngrowingseasonwas585mm(Fig.1,Fig.2).The2014

growingseasonaccumulated891GDDin2014(Fig.3).NetNmineralization

duringthefirst30daysofthe2014sweetcorngrowingseasonwere13and16

kgha-1intheOATandNONEand25and27kgha-1intheN-appliedtreatments

(OAT+NandNONE+N),respectively.Mineralizationwithinthe0-30dayinterval

wassignificantlygreaterintheNONE+NandOAT+Ntreatmentscomparedtothe

NONEandOATtreatments(Fig.4).Mineralizationinthe30-60daytimeperiod

was38and49kgha-1inOATandNONEand81and101kgha-1inOAT+Nand

NONE+N,respectively.Therewasnosignificanttreatmentdifferencebetween

covercroptreatmentsandtheircontrols(e.g.OATvs.NONEandOAT+Nvs.

NONE+N).Duringthe60-90daytimeperiod,mineralizationwas4and6kgha-1

inNONEandOAT,respectively,andwas31kgha-1inbothNONE+NandOAT+N.

Mineralizationpatternremainedthesameduringthistimeperiod,therewasno

significanttreatmentdifferencebetweenthecovercroptreatments(OAT+Nand

OAT)andtheircontrols(NONE+NandNONE)(Fig.4).

48

Inthe2015sweetcorngrowingseasonandmineralizationcore

incubation,meanmonthlyairtemperaturesdeviated-3to1°Caroundthe30-

yearnormaltemperatures,averaging18°CinJune(atthe30-yearnormal),21°C

inJuly(1°Cabovethe30-yearnormal),19°CinAugust(3°Cbelowthe30-year

normal),and18°CinSeptember(2°Cbelowthe30-yearnormal)(Table1).Total

accumulatedGDDswere845in2015andtotalaccumulatedwater(precipitation

263mm,irrigation312mm)throughoutthe2015sweetcorngrowingseason

was575mm(Fig.1,Fig.3).Mineralizationvaluesin2015duringthe0-30day

timeperiodwere3and12kgha-1inNONEandOATand31and40kgha-1in

NONE+NandOAT+N,respectively.Therewasnosignificantdifferencebetween

covercroptreatmentscomparedtotheircontrols(NONEandNONE+N)(Fig.5).

Duringthe30-60daygrowingperiodmineralizationwas12and17kgha-1in

NONEandOATand35and40kgha-1inNONE+NandOAT+N,respectively.There

wasnosignificanttreatmentdifferencebetweencovercroptreatments(OAT+N

andOAT)andtheirnocovercontrols(NONE+NandNONE).Duringthe60-90day

timeperiodnetmineralizationwas3and25kgha-1inOATandNONEand-7and

7kgha-1intheOAT+NandNONE+Ntreatments,respectively.TheOAT+N

treatmentduring60-90daysdisplayednegativenetnitrogenmineralization;

howeverthestandarderroris8.6andoverlapszero,suggestingthatthemeanis

notdifferentthanzero.In2015,throughouttheentire90-daygrowingseason

mineralizationpatternsremainedthesameamongsttreatments.

49SweetCornN-Uptake

The2014sweetcornstalkNuptakewassignificantlygreaterinNONE+N

comparedtoNONEandOAT,whileearNwasgreaterinNONE+NandOAT+N

comparedtoNONEandOAT.TheTNUinNONE+NwasgreaterthaninNONE.

TherewerenotreatmentdifferencesforPNBbuttheNUEofNONE+Nwas

significantlygreaterNthanOAT+N(Table3).In2015,stalkNuptakewas

significantlygreaterintheNONE+NtreatmentcomparedtoNONE,whileearN

uptakewassignificantlygreaterintheN-appliedtreatmentscomparedtoall

others.TheTNUwassignificantlylowerintheNONEtreatmentcomparedto

NONE+NandOAT+NandOAThadsignificantlylessTNUcomparedtoNONE+N.

In2015,therewasnosignificanttreatmentdifferenceinPNB,andNUEwas

significantlygreaterinNONE+NcomparedtoOAT+N(Table3).

SoilNH4-NandNO3-N

AnalysisofsoilNH4-NandNO3-Ninboth2014and2015wasconducted

onlog-transformeddata.In2014OATNH4-Nwassignificantlygreaterthan

NONEintimepoint3,buttherelativedifferencebetweenthehighestandlowest

valuewasonly0.4mgkg-1andNhadnotbeenappliedatthattimepoint.In2014,

NONEhadsignificantlygreaterNO3-NcontentthanOATatTP7andTP10and

OAT+NhadsignificantlygreaterNO3-NcontentthanNONE+NatTP7andTP8.

Thissuggeststhattheremaybedifferentmineralizationpatternsofoatbiomass

lateinthegrowingseasondependingonthepresenceorabsenceofNfertilizer.

50TreatmentsignificancewasalsodeterminedforNO3-NatTP3andTP4andfor

PANatTP2,TP5,TP7,andTP10,howeverthesetreatmentsdifferenceswereonly

betweenN-appliedtreatmentsandno-Ntreatments.

In2015theonlysignificantdifferencebetweenanoattreatmentandano

covercroptreatmentwasmeasuredatTP1,whereNONEhadsignificantly

greaterNH4-NthanOAT.Alsoin2015,thereweresignificanttreatment

differencesforNO3-NatTP7andforPANatTP4,TP7,andTP9,butonly

representdifferencesbetweenN-appliedtreatmentsandno-Ntreatments(Fig.

7).

Discussion

OatBiomass

Oatcovercropgrowth,biomassproduction,andNuptakeare

substantiallydifferentbetweenseasons.Coolertemperaturesduringthe2014

oatgrowingseasonreducedgerminationandledtolowerbiomassin2014(272

kgha-1)adifferenceof21timeslowerproductioncomparedto2015(5824kgha-

1)(Table2).OatAGBvariabilityhasbeendocumentedinothernorthernMidwest

croppingstudies,howeveratdifferingmagnitudes.Inasix-yearstudynearAmes,

Iowa,fall-plantedandwinter-killedoatbiomassproductionincreased22times

fromthelowestproduction(70kgha-1)tothehighest(1540kgha-1)(Kasparet

al.2012).Similartoourstudy,greaterbiomasswasassociatedwithwarmer

temperaturesduringtheoatgrowingseason(Kasparetal.2012).InaCentral

51Sands-basedstudy,AndraskiandBundy(2005)alsonotedoatbiomass

variabilityintheirfallplantedandwinterkilledcovercrop,howeverthe

differencewas5-foldbetweenyears,590kgha-1to3010kgha-1.Alsoin

Wisconsin,Contreras-GoveaandAlbrecht(2005)measuredspring-plantedoat

biomasswithameanweightof7700kgha-1following77daysofgrowth(mid-

ApriltolateOctober).Pro-rated,Contrera-GoveaandAlbrecht(2005)reported

thesamebiomassaccumulationaswedidinour2015fieldseason(100kgAGB

ha-1day-1).

OatC:Ndidnotdisplaylargedifferencesbetweenyears,thoughthese

valueswerelowercomparedtootheroatstudies.Ourstudy’sC:Nvaluesaremost

similartothosecitedinAndraskiandBundy(2005).AlsointheCentralSands,

thisstudymeasuredC:Nbetween15and33(1570kgha-1AGB)after

approximately12weeksofgrowth(August–November).HigherC:Nratioshave

beenreportedwithgreaterbiomassproduction.Radicettietal.(2016)

documentedC:Nof47(5680kgAGBha-1)andBaggsetal.(2000)measuredC:N

of38(140kgNha-1inAGB).AsimilarC:N(24.8)wasmeasuredbyKumaretal.

(2009),howevertheyproducedgreaterAGB(9700kgAGBha-1)onasiltloam

comparedtoourstudyandAndraskiandBundy’s(2005).Spatially,thethree

studieswerecompletedinsimilarclimatesandlatitudes,N44˚intheCentral

SandsofWisconsinandN42˚attheKumaretal.(2009)studysite,inNewYork.

However,plantingdatesdifferedbetweenthestudies,AndraskiandBundy

52(2005)andKumaretal.(2009)bothplantedoatinthefallaftercashcropharvest

andourstudywasspringplanted.Additionally,Kumaretal.(2009)moldboard

plowed,disked,andfertilizedtheirfieldswith51kgha-1ofNjustbeforecover

cropplanting,thisfieldmanagementwaspotentiallyresponsibleforimproving

oatyield.Inourstudyin2015residualsoilNconcentrationswerelikelyhigher

priortooatplantingduetothepreviousseason’spotatocrop.Additionally,our

2015oatcovercropwasterminatedatthestartofreproductivegrowth,

potentiallycontributingtolowC:N.

MineralizationandSoilNH4-NandNO3-N

Ascomparedtoothermineralizationstudiesutilizingasimilarin-situsoil

columnandion-exchangeresinprocedure,ourseasonalmineralizationratesfall

withintherangeofreportedvalues.Wuetal.(2007)measuredmineralizationin

acorncroppingsysteminsandysoilbetween51to75kgNha-130days-1.The

authorscompletedthisstudyinOntario,Canadaandalsodocumenteda

mineralizationpeakduringthe30-60daytimeperiod.Inanothersandysoil

covercroppingstudy,O’Conelletal.(2015)documentedmineralizationingrass

andlegumecovercroppingsystemsonasandyloambetween-70and155kgN

ha-130days-1.Bryeetal.(2002)documentedmineralizationfrom-20to59kgN

ha-130days-1inasiltloamno-tillcorncroppingsystem.Withsimilarcourse-

texturedsoils,forestecosystemshavelowermineralizationcomparedtoour

measurementsortheotherreferencedcroppingsystems’,measuring0.6to4.6kg

53Nha-130days-1(Wilhelmetal.,2013)and4.2kgNha-130days-1(Raisonet

al.,1987).Ourstudy’snetmineralizationwasgreaterthanthosemeasuredin

forestecosystemsand,whileonthelowendoftherange,comparedtoother

similarcroppingsystem’sstudies.

SoilNO3-NandNH4-Nfindingswereincongruencewith2014and2015

netmineralizationfindingsbetweenN-appliedtreatmentsandno-Ntreatments;

howeversignificantdifferencebetweentreatmentsatapproximately10-day

intervalsin2014wouldsuggestthatoatcovercropdidimpactmineralizationon

anarrowertimescalethanwasdetectablewiththein-situmethod.Specificallyin

2014atTP7(56daysafterplanting)therewasgreaterNO3-NinOAT+N

comparedtoNONE+NwhileatthesametimetheNONEtreatmenthadgreater

NO3-NthanOAT.ThismaysuggestaprimingeffectoftheNfertilizeron

decompositionandmineralizationofoatbiomasslaterinthegrowingseason.

ThiseffectcanalsobeseenatTP8,whereOAT+NhadgreaterNO3-Ncomparedto

NONE+N,andatTP10,whereNONEhadgreaterNO3-NcomparedtoOAT.Results

fromthein-situmineralizationcolumnsduring60-90daysin2014didnotresult

intreatmentdifferencesbetweenanyoatandnocovercroptreatments(Figure

4).

SweetCornNUptake

OatcovercropdidnotsignificantlyincreasesweetcornNuptake.The

onlysignificanttreatmentdifferenceintotalNuptakebetweencovercrop

54treatmentandtheircontrolswasinthe2014OATtreatmentcomparedtothe

NONEtreatment.Thisdifferencewasnotseeninthe2014mineralizationdata

howeveritwaspresentinthesoilNdata.In2014and2015therewasno

statisticalsignificancebetweenpartialnutrientbalance(PNB)treatmentsand

theircontrols,therefore,whiletheamountofNthatwasunaccountedforinthe

2015PNBwaslowerintheOAT+Ntreatmentscomparedtothecontrol,the

reductionwasnotsignificantenoughtoimpactseason-longN-losspatterns.The

Nuptakeefficiency(NUE)of2015NONE+Nwassignificantlygreaterthanthe

control,meaningthattheoatnegativelyimpactedfertilizerNuptakeincorn

comparedtotheNONE+Ntreatment.Theoattreatmentdidnothaveasignificant

enoughimpactonmineralizationtosynchronizeplantavailableNwithplant

growthneedsanddidnotprovideanNcredit(seeChapter2).Inafallplanted

grasscovercropstudyonsandysoilOlesenetal.(2009)measuredlowerNUEin

wintercerealsoncoursesandysoilascomparedtoaloamysandorsandyloam

soil.ThesefindingsarealsosimilartoWestetal.(2016),whereinnosweetcorn

NcreditwasmeasuredfromspringplantedfieldpeaintheCentralSands.

AssessingtheQuantitativePrecisionoftheIn-situMethod

Thein-situsoilcoreandresinbeadmineralizationmethodmaylack

quantitativeprecision.Wesummedtherelativedifferencebetweentreatmentsin

soilcolumnNandtherelativedifferencebetweentreatmentsinresinN(leached

N)andsubtracteditfromtotalNapplied,calculatingover101kgNha-1as

55unaccountedforinthenocovertreatmentsand91kgNha-1intheoattreatments

in2014.In2015,143kgha-1wasunaccountedforinthenocovertreatmentsand

142kgNha-1intheoattreatments.Inbothfieldseasonsafractionofthe

fertilizer-Nisaccountedfor,thisdiscrepancyhasalsobeenpresentedinother

mineralizationandmassbalancestudies.In1991Errebhietal.(1998)

documentedamassbalancediscrepancyrangingfrom-36to85kgNha-1ina

sandyloampotatocroppingsystem.Inthisstudytheycalculatedthedifference

betweentotalNin(initialsoilN,fertilizerN,irrigationN,mineralizedN)minus

totalNout(plantN,leachedN,finalsoilN).Saffingaetal.(1977)inaCentral

Sands-basedpotatostudycalculatedamassbalancedifferencebetween-20to95

kgNha-1ofNapplied(fertilizerNandirrigationN)minusNoutofthesoilprofile

(leachateandplantuptake).

ThemajordifferencesinNmineralizationbetweenyearscanbeattributed

tolargedifferencesintheamountofNcapturedontheresins.Weanalyzedthe

amountofappliedNthatwasleachedoutofthesoilcolumnbycalculatingthe

relativedifferencebetweenN-appliedtreatments(NONE+NandOAT+N)and

theircontrols(NONEandOAT)ontheresin.In2014,theyearwithlowbiomass,

theNONE+Ntreatmenthad33%oftotalNappliedcapturedontheresin,56kgN

ha-1.TheOAT+Ntreatmentin2014had30%oftotalNappliedcapturedonthe

resin,50kgNha-1.In2015,theyearwithgreaterbiomass,NONE+Ntreatment

onlyhad1%ofthetotalNappliedcapturedintheresins,2kgNha-1.TheOAT+N

56treatmentonlyhad3%ofthetotalNappliedcapturedontheresinN,leaching5

kgha-1.Similarleachingstudiesconductedinirrigatedsandysoilcropping

systemsfoundarangeofvalueshigherthanourleachingvalues,howeverwithin

range.Thefollowingstudiescalculatedleachingonsandysoilsinirrigatedpotato

croppingsystems;Venetereaetal.(2011)documented21.1kgNha-1,Zvomuyaet

al.(2003)80kg-Nha-1,andDelgadoetal.(2001)94kgNha-1.

Denitrification,immobilization,andvolatilizationarethreepotential

causesofimprecisequantificationofsoilN.Highratesofdenitrificationare

unlikelyinthesesandysoils(StrongandFillery,2002).Nitrogenimmobilization

wasmeasuredinourstudyandwasonlypresentin2015at5kgNha-1.

GroundwaterNO3-N(18mgL-1NO3-N,approximately52kgNha-1)(Bundyand

Andraski,2005)appliedthroughirrigationwasnotaccountedforinthesepost-

evaluations,includingthemwouldlowerNuptake.Theotherpotentialcauseof

nitrogenlosscouldbeattributedtoammoniavolatilization.Thismaybe

responsibleforaportionoflostN,howevervolatilizationwasminimizedthrough

postfertilizerirrigationandaverageureavolatilizationrangesbetween3–40%

oftotalNapplied.Holcombetal.(2011)measured15–40%lossonsandysoil,

Rawluketal.(2001)measured20–26%lossonaclayloam,andThapaetal.

(2015)measured3–4%lossonasiltloam.In2014thefertilizerwasirrigated

within4hoursofapplication,however,in2015,theyearwithgreatercolumnN

unaccountedfor,ureawasirrigatedwithin24hoursoffertilizationandcouldbe

57responsibleforsomeNlossthroughammoniagas.Giventhattheleachedvalues

inbothyearsaresimilartothoseintheliterature,itisunlikelythattheremaining

fertilizerNbalancewasleachedthroughthesoilprofileanduncapturedbythe

in-situresinandsoilcolumnmethod.Plantuptakewasnotafactorhereeither;

methoddesignexcludedrootsfromthesoilcolumn.

TheunaccountedforNinthesoilcolumnandresincouldbetheresultof

lackofprecisioninthein-situcolumnmethod.Soilcolumnprocedureswerethe

samebetweenbothstudyyearsandresinsachetinsertionwascompletedbythe

leadscientistsonthisproject,KateIvancicandMatthewRuark,andthe

laboratory’sseniortechnician,MackNaber.Perhapsadditionaldesignchanges

canbefurtherrefinedinthefutureinordertoimproveconsistencyinresinN

captured.TheseimperfectsoilNbudgetsindicatethatthein-situsoilcolumnand

resinbeadprocedureisnottherighttoolforprecisequantificationofnutrients;

howeveritisavaluabletoolusefulforcapturingmineralizationtreatment

differencesandtrendsovertime.

Conclusion

Spring-plantedoatswereineffectiveatalteringnitrogencyclingona

seasonal(30day)scaleintheCentralSands.Overa10-daytimescale,soilNH4

andNO3displayedsmallchangesinNcyclingpatterns,suggestingthatoatdoes

impactmineralizationinthesesystems,howeverthetransformationistoorapid

toimpactseasonal-scale(30day)netmineralizationusinganin-situ

58mineralizationcolumn.Thein-situmethodprovidedmineralizationtrends

consistentwiththesoilNmeasurementsandothermineralizationstudies,

howeveriswasnotausefultoolforquantitativeNbudgetcalculation.While

therewasnoapparentNcreditoftheoat,itisimportanttonotethattheoatdid

notslowdownmineralizationinanymeaningfulwayregardlessofbiomass

amount.Thus,theuseofgrasscovercropsforwinderosioncontrolintheCentral

SandsofWisconsinwillhavelittleeffectonthenitrogencycle.Futureeffortsto

improveNuseefficiencyinthisregionwillneedtocomethroughin-season

managementofN.

59

60TablesandFiguresTable1.MeanmonthlyairtemperatureatHancock,WI2014and2015.Meansforairtemperaturefor2014and2015arepresentedasdeviationsfrommean30-yearnormaltemperatures(1985-2015).

AirTemperature Deviationfrommean

Month 30-yrnormal 2014 2015˚C

Jan. -8 -6 -1Feb. -6 -7 -7Mar. -3 -1 3Apr. 4 1 4May. 11 3 4Jun. 18 2 0Jul. 20 -1 1Aug. 22 -2 -3Sep. 20 -5 -2Oct. 12 -4 -1Nov. 4 -7 -4Dec. -3 -1 3

Table2.Oatcovercropbiomassandnitrogenuptake.Alldataarepresentedonadry-matterbasis.Year Biomass TotalC TotalN C:N kgha-1 kgCha-1 kgNha-1 %

2014 272(40)+ 112(14) 6(0.6) 18(0.7)2015 5824(845) 2419(331) 119(30) 20(4)

+Numberinparenthesisindicatesstandarddeviation.

61Table3.Nitrogenuptakeinsweetcornstalkandearin2014and2015.Concentrationsdeterminedunderfourtreatments(NONE,NONE+N,OAT,OAT+N).Nitrogentreatmentswere0kgNha-1and168kgNha-1.FertilizerappliedduringV4andV8growthstages56kgha-1(between0-30days)and112kgha-1(between30-60days),respectively.Partialnutrientbalance(PNB)andNuptakeefficiency(NUE)werecalculatedforeachcovercroptreatmentseparately.Withineachcolumnforeachstatisticallysignificanttreatmentfactor,meansfollowedbythesameletterarenotsignificantlydifferent(α=0.05).

2014 2015Treatment Stalk

NEarN

TNU PNB NUE StalkN

EarN

TNU PNB NUE

kgNha-1 kgNha-1NONE 29b 0.4b 29c 42b 2c 45c NONE+N 51a 30a 82a 0.2 0.3a 119a 50a 169a 0.7 0.7aOAT 39ab 11b 50b 76ab 9b 85bc OAT+N 51a 26a 78a 0.2 0.2a 90a 59a 149a

b0.4 0.4b

62

Fig.1.WeeklyaccumulatedrateofprecipitationandirrigationforsweetcorngrowingseasonatHancockWI,2014and2015.Planting24April2014and17April2015forcovercropand13June2014and19June2015forsweetcorn.Termination10June2014and16June2015forcovercropand11September2014and11September2015forsweetcornharvest.

0

20

40

60

80

100

120

Apr May Jun Jul Aug Sep

Water(m

m)

0

20

40

60

80

100

120Water(m

m)

Precipitation(weeklytotal)

Irrigation(weeklytotal)

TotalPrecipitationOatGrowingSeasonApril13–June18=191mmofprecipitationSweetCornGrowingSeason(Precipitation+Irrigation)0-30days=72+100mm30-60days=52+112mm60-90days=139+100mm

2014

2015

TotalPrecipitationOatGrowingSeasonApril21–June17=196mmofprecipitationSweetCornGrowingSeason(Precipitation+Irrigation)0-30days=98+100mm30-60days=33+113mm60-90days=141+101mm

63

Fig.2.MaximumandminimumdailyairtemperaturesatHancock,WIin2014and2015.

-20

-10

0

10

20

30

40Apr.

May.

Jun.

Jul.

Aug.

Sep.

DailyAirTem

perature(̊C)

2014(high) 2014(low) 2015(high) 2015(low)

64

Fig.3.Accumulatedgrowingdegreedaysduringthecovercropandsweetcorngrowingseasons2014&2015,calculatedusingmodifiedmethod.Covercropplanting(OAT)24April2014and17April2015andtermination10June2014and16June2015.Sweetcornplanting(SC)13June2014and19June2015andharvest14September2014and11September2015.

0

100

200

300

400

500

600

700

800

900

1000GrowingDegreeDays

2014:OAT

2015:OAT

2014:SC

2015:SC

May.Jun.Jul.Aug.Sep.

65

Fig.4.Nitrogenmineralizationin30dayincrements(0-30,30-60,and60-90)underfourtreatments(NONE,NONE+N,OAT,OAT+N)attheHancockAgriculturalExperimentStationin2014.Nitrogentreatmentswere0kgNha-1and168kgNha-1.FertilizerappliedduringV4andV8growthstages56kgha-1(between0-30days)and112kgha-1(between30-60days),respectively.ANOVAcompletedacrosstreatmentswithintimeperiods,columnswiththesameletterarenotsignificantlydifferent(P<0.1).

-5

15

35

55

75

95

115

NitrogenMineralization

(kgha

-130days-1)

0-30days

30-60days

60-90days

NONE NONE+N OAT OAT+N

a

ab

a

b

a

a

b

b

a

b

a

b

66

Fig.5.Nitrogenmineralizationin30dayincrements(0-30,30-60,60-90)underfourtreatments(NONE,NONE+N,OAT,OAT+N)attheHancockAgriculturalExperimentStationin2015.Nitrogentreatmentswere0kgNha-1and168kgNha-1.FertilizerappliedduringV4andV8growthstages56kgha-1(between0-30days)and112kgha-1(between30-60days),respectively.ANOVAcompletedacrosstreatmentswithintimeperiods,columnswiththesameletterarenotsignificantlydifferent(P<0.1).

-15

-5

5

15

25

35

45

NitrogenMineralization

(kgha

-130days-1)

0-30days

30-60days60-90days

a

a

b

b

ab

b

c

a ab

ab

bc

a

NONE OAT OAT+NNONE+N

67

Fig.6.Soilammonium-N,nitrate-N,andplantavailablenitrogen(PAN)concentrationscollectedapproximatelyevery10daysthroughoutthesweetcorngrowingseasonattheHancockAgriculturalResearchStationin2014.Treatmentincludenocovercrop(NONE),nocovercropwith168kgha-1ofN(NONE+N),oatcovercrop(OAT),andoatcovercropwith168kgha-1ofN(OAT+N).ArrowsindicatetimingoffertilizerapplicationsattheV4(56kg-Nha-1)andV8(112kg-Nha-1)growthstages.Timepointsareevery9–13daysstartingon13Juneandthelasttimepointwasatsweetcornharvest(11September).

1 2 3 4 5 6 7 8 9 10

NO3-N

*

*

* *

*

*

0

2

4

6

8

10

12

14

16

18

20

22

1 2 3 4 5 6 7 8 9 10

NitrogenConcentration(mgkg

-1) NH4-N

*

*

* *

1 2 3 4 5 6 7 8 9 10

NONE

NONE+N

OAT

OAT+NPAN

TimePoint

68

Fig.7.Soilammonium-N,nitrate-N,andplantavailablenitrogen(PAN)concentrationscollectedapproximatelyevery10daysthroughoutthesweetcorngrowingseasonattheHancockAgriculturalResearchStationin2015.Treatmentincludenocovercrop(NONE),nocovercropwith168kgha-1ofN(NONE+N),oatcovercrop(OAT),andoatcovercropwith168kgha-1ofN(OAT+N).ArrowsindicatetimingoffertilizerapplicationsattheV4(56kg-Nha-1)andV8(112kg-Nha-1)growthstages.Timepointsareevery9–13daysstartingon19Juneandthelasttimepointwasatsweetcornharvest(11September2015).

*

9

1 2 3 4 5 6 7 8 9

NO3- N

*

0

2

4

6

8

10

12

14

16

1 2 3 4 5 6 7 8 9

Nitrogen

Con

centratio

n(m

gkg

-1)

NH4-N

*

*

*

1 2 3 4 5 6 7 8 9

PAN

NONE

NONE+N

OAT

OAT+N

TimePoint

69SASCodeNMineralizationdatamin1;inputintblktrt$nmin;datalines;procglimmixdata=min1plots=studentpanel;classblktrt;modelnmin=trt;randomblk;run;procsort;byblktrtint;procprint;run;procmixed;byint;classblktrt;modelnmin=trt;randomblk;lsmeanstrt/diff;run;procsort;byblktrtint;procprint;run;procglimmixdata=min2plots=studentpanel;classblktrt;modelnmin=trt;randomblk;run;procsort;byblktrtint;procprint;run;datamin22;setmin2;lognmin=log(nmin);run;procglimmixdata=min22plots=studentpanel;classblktrt;modellognmin=trt;randomblk;run;procmixed;byint;classblktrt;modellognmin=trt;randomblk;lsmeanstrt/diff;

70run;procsort;byblktrtint;procprint;run;SweetCornBiomassprocglimmixdata=ear15plots=studentpanel; classtrtblk; modelear=trt; randomblk;procprint;run;dataear151;setear15;logear=log(ear);run;procglimmixdata=ear151plots=studentpanel; classtrtblk; modellogear=trt; randomblk;run;procglmdata=ear151;classtrtblk;modelear=trt; randomblk;meanstrt/LSDLINESalpha=0.1;lsmeanstrt/PDIFFadjust=Tukeyalpha=0.1;run;procmixeddata=ear151;classtrtblk;modelear=trt; randomblk;lsmeanstrt/PDIFFadjust=Tukeyalpha=0.1;odsoutputdiffs=ppplsmeans=mmm;odslistingexcludediffslsmeans;run;%include'z:Kate\pdmix800.sas';%pdmix800(ppp,mmm,alpha=.1,sort=yes);run;SoilNO3andNO4procglimmixdata=bplots=studentpanel; classblocktrttime; modelammonium=trt|time;

71 randomblockblock*trt;run;procsort;byblocktrttime;procprint;run;databb;setb;logammonium=log(ammonium);run;procglimmixdata=bbplots=studentpanel; classblocktrttime; modellogammonium=trt|time; randomblockblock*trt;run;procsort;byblocktrttime;procprint;run;procmixed;classblocktrttime;modellogammonium=trt|time;randomblockblock*trt;repeated/subject=block*trttype=sp(pow)(t);lsmeanstrt*time/diffslice=time;run;procsort;byblocktrttime;procprint;run;procmixed;classblocktrttime;modellogammonium=trt|time;randomblockblock*trt;repeated/subject=block*trttype=ante(1);lsmeanstrt*time/diffslice=time;run;procsort;byblocktrttime;procprint;run;procmixed;classblocktrttime;modellogammonium=trt|time;randomblockblock*trt;repeated/subject=block*trttype=cs;lsmeanstrt*time/diffslice=time;run;procsort;byblocktrttime;procprint;run;procmixed;

72classblocktrttime;modellogammonium=trt|time;randomblockblock*trt;repeated/subject=block*trttype=csh;lsmeanstrt*time/diffslice=time;run;procsort;byblocktrttime;procprint;run;

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79Chapter4:OverallConclusionsandFutureWork

ThefindingsofthisstudydemonstratenoNbenefitfromspringplanted

covercropsonirrigatedsandysoil.Ourresultsalsoshowtherapid

mineralizationandNlosspotentialinthesesystems,framingfutureN

managementfocusaroundin-seasonapplication.Mineralizationofoatcover

cropswasnotsignificantlydifferentfromnocovercroptreatmentsona30-day

scaleandourfindingssuggestthatenvironmentalconditionsandvariable

biomassaccumulationbetweenyearscanspeedmineralizationtofewerthan10-

daycycles.Additionally,legumeandoatcovercropcombinationsgavezeroN

credittothesubsequentsweetcorncrop.Thesefindingsreiteratethenarrow

timeframeinirrigatedsandysoilsystemswhereinbothcovercropNis

mineralizedandsweetcornplantuptakeisgreatest.

Asevidentfromourfindings,mineralizationinfieldconditionsis

challengingtopredict.Fluctuationsinsoilmicrobialpopulationsinresponseto

soilmoisture,temperature,organicmattercomposition,pH,andresidualsoil

nutrientsarejustaportionofthefactorsimpactingmineralization.Measuring

theentirebiologicalprocessingpictureisnearlyimpossibleinthese

environments,andthenaturalprocessesarejustonepartofthesolution.The

socialaspectofNmanagementalsoneedstobeconsideredfortruly

comprehensivenutrientmanagementrecommendations.

80

Optimizingyieldswhileminimizingnutrientlossisagoalforall

producers.However,withchangesinproductionrecommendationscome

questionsofeconomicviability,socialresponsibility,humanhealth,policy

implicationsandahostofotherconsiderationsimpactedinthiscomplexsystem.

Thebroader,agroecologicalimplicationsofthisstudyhavenotbeenfully

exploredandwarrantfurtherinvestigation.Applicationofthesefindingsand

considerationoftheirsocialandlandscapeimpactsiscritical.

Reductionofnitrateleachinganditsimpactongroundwaterisa

multifacetedissue.WisconsinisatopvegetableproducerintheU.S.andnutrient

managementrecommendationsplayacrucialroleinnationalwaterquality.

Recommendationdeterminationshouldbemadebyateamofmultidisciplinary

expertsratherthanafewenvironmentalscientists.Understandingthebiological

processingbehindNmanagementisjustoneofmanyfactors.Inordertoensure

thehealthofournation’swatersandthelivelihoodsthatdependonthem,policy

andmanagementrecommendationsshouldconsiderenvironmentalandsocial

impacts,alike.