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paperAggregate

EffectofDifferentConservationTillageMeasuresonSoilAggregateCompositionandStabilityinSpringWheat–FieldPeaRotationSysteminSemi-aridLoessPlateauofChina

Abstract：

Recentstudieshaveshownthatconventionaltillagesystemcausedsoildisturbancesandtherebydamagingsoilstructureandformationofsoilaggregates.Therefore,thisstudywasconductedtoinvestigatetheeffectoflong-termtillagesystemsonsoilaggregatecompositionandstabilityinspringwheat−fieldpeasequenceinarain–fedsemi−aridenvironment.Experimentalworkincludedthefollowingtreatments:

conventionaltillagewithstrawremoved（T）,Notillagewithstrawremoved（NT）conventionaltillagewithstrawincorporated（TS）andNo-tillagewithstrawretentiononthesoilsurface（NTS）.Theresultsshowedthat,TSandNTSenhancemechanicalstabilityandwater-stablelargeaggregatesanditsstabilitycomparedwithTandNT.Notillagewithstrawretention（NTS）alsoimprovemeanweightdiameter（MWD）ofsoilaggregatesandincreasesoilaggregatesstability.Moreover,thewaterstableaggregateof2013and2014weresignificantlyimprovedcomparedto2006and2007.

Keywords：

Tillagesystem,Aggregates,MWD,PAD

Introduction

Soilaggregatestabilityisafundamentalpropertythatdeterminessoilproductivityandresistancetoerosionanddegradation[1,2].Aggregatestabilityisahighlycomplexparameter,influencingawiderangeofsoilproperties,includingcarbonstabilization,soilporositywaterinfiltration,compactibility,,hydraulicconductivityandresistancetowatererosion[Ref].Consequently,maintaininghighstabilityofsoilaggregateisessentialforpreservingsoilproductivity,minimizingsoilerosionanddegradationandthusalleviatingenvironmentalpollutiontoaminimumdegree.However，theLoessplateauhasbecomeoneofthemostseverelyerodedareasintheworldduetothecombinedactionoffrequentheavysummerrainstorms,steeplandscapes,long-termhumanactivitiesandhighlyerodiblesoil.TheimpactsofhumanactivitiesontheLoessPlateauhavebeenmainlycausedbyover-grazingandlargescalemonoculturesofwheatandmaize[3,4].TheregionisregardedasthecradleofagriculturalproductioninChinaandisprimarilyusedforcropping,butitisalsoseverelyaffectedbysoilerosionandhighevaporativelosses,whichthereforerestrictproductivity（YinandYin,2010）.IntensivemethodsofsoilcultivationoftenacceleratesoilerosionprocessesLal,2004,Wangetal.,2013）.

Conventionaltillagewasthelocalfarmingpracticewhichincludedmoldboardploughingforpreparationofsuitableseedbeds..Nevertheless,numerousworkershaveprovedthattheconventionaltillagesystemhasprogressivelycausedlossofsoilorganicmatter,degradationofsoilstructureandthenacceleratesoilerosion[5].Thestabilityofaggregatesattheintermediatesoilsurfacegreatlyinfluencesthesoilsusceptibilitytoerosion.Raindroponfreshlytilledsoilcausesbreakdownofsurfaceaggregatessothatinfiltration,surfacesealing[6],andsoildetachment[7]arealladverselyaffected.Resultsofsomestudiesconcernedwithsoilerosioncontrolindicatethatno-tillagesystemisaneffectivewayofcontrollingerosion[8].Andtherehavebeennumerousreportsofreducedrunoffandsoillossunderconservationtillage[9].Hence,conservationtillagesystems,ratherthanplow-basedseedbedpreparation,isapotentialtoprovidemoresustainableuseofsoilresources.

Literatureisrepletewithdataregardingtheeffectsofdifferenttillageandcroppingsystemsonarangeofsoilproperties（Tarkalsonetal.2006,Verhulstetal.2010）,buttheresearchresultsachievedareverydiverse.Inaddition,theeffectsoftillagetechnologiesandcroprotationsinvolvingcovercropsonsoilstructuralstabilityontheLoesssoilsarestilllessunderstood.

Consequently,reliedonalong-termconservationtillageexperimentestablishedin2001,thisstudywasperformedtoevaluatetheimpactsofnotillageandconventionaltillageunderspringwheat-fieldpearotationonaggregationpropertiesandaggregatestabilityofaRhodicFerralsolatvariousdepths.

Materialsandmethods

Sitedescription.

Thefieldexperimentwasinitiatedin2001atDingxiExperimentalStationofGansuAgriculturalUniversity（35°28'N,104°44'E,1971ma.s.l.）,GansuProvince,northwestChina.NorthwestChinaisatypicalsemi-aridclimate,whichischaracterizedbydroughtandnaturaldisasters.ThisareahasAeoliansoils,locallyknownasHuangmian（ChineseSoilTaxonomyCooperativeResearchGroup,1995）,whichequatetoCalcaricCambisolsbasedontheFAO（1990）description.Thissoiltypehasasandy-loamtextureandrelativelylowfertility（Table1）,andisprimarilyusedforcroppingandisthedominantsoilontheLoessPlateau.Long-term（annual）rainfallrecordsforDingxishowanaverageof391mmperyearofwhichapproximately55%fallbetweenJulyandSeptember.Dailymaximumtemperaturescanriseto38°CinJuly,whileminimumtemperaturesusuallydropto−22°CinJanuary.Annualcumulativetemperatures>10°Care2240°Candannualradiationis5930MJm-2,with2477hofsunshine.Theseconditionsarerepresentativeofthosecommonlyfoundwithinagriculturalareasofsemiaridenvironments.Theregionhasalonghistoryofcontinuouscroppingunderconventionaltillage,whichincludessoilinversionandnumeroussoilsmoothingoperationsandresidueremoval.TheexperimentsiteatDingxihasbeenmaintainedwithoutanyalterationssince2001priortothisflaxexperiment（LinumusitatissimumL.）wascropped.

Table1.Soilpropertiesatthestartoftheexperiment2001,atDingxiExperimentalStation

Soildepth（cm）

Bulkdensity（gcm−3）

pH

OrganicC（gkg−1

TotalN（gkg−1

TotalP（gkg−1

TotalK（gkg−1）

0–5

1.29

8.32

7.63

0.85

1.89

18.6

5–10

1.23

8.37

7.46

0.87

1.92

18.5

10–30

1.32

8.33

6.93

0.78

1.82

18.3

Experimentaldesignandtreatmentdescription

Theexperimentutilizedfullyphasedfactorialdesignreplicatedfourtimesunderfourtillagetreatmentsandtworotationphases.Springwheat（cv.DingxiNo.35）andfieldpea（cv.Yannong）weresowninrotationwitheachofthetwophasespresentineachyear.Phase1startedwithspringwheat,followedbyfieldpea（referredtoasW→P→Wsequence）;phase2startedwithfieldpea,followedbyspringwheat（referredtoasW→P→Wsequence）.Therefore,therewere48plotsintotal（fourtillagetreatments×twophases’×fourreplicates）.Eachplotwas4mwidex17mlonginblock1,21mlonginblocks2and3and20mlonginblock4.Table2showsdetailedtreatmentdescriptionsusedintheexperiment..Allthecropsandtreatmentsweresownwiththesameno−tillseeder（fivetosixrowsof1.2mwidth）,designedbyChinaAgriculturalUniversity.Theno-tillseeder,drawnbya13.4kW（18HP）tractor,wasdesignedtoplacefertilizersbelowtheseed-rowsusingnarrowpointopenersfollowedbyconcaverubberpresswheelsinoneoperation.

Table2.Descriptionoftillagetreatmentsintheexperiment

Treatment

Description

Code

Name

Abbrev

1

Conventionaltillage

T

Thefieldwasploughed3timesandharrowedtwiceafterharvesting.ThefirstploughwasconductedinAugustimmediatelyafterharvesting,thesecondandthirdploughsinlateAugustandSeptemberrespectively.Theploughdepthswere20cm,10cmand5cm,respectively.Thefieldwasharrowedafterthe3rdploughinSeptemberandre-harrowedinOctoberbeforethegroundwasfrozen.ThiswasthetypicalconventionaltillagepracticeinDingxiregion.

2

No-tillage

NT

No-tillagethroughouttheseason..

3

Conventionaltillagewithstrawincorporation

TS

ThefieldwasploughedandharrowedexactlyasTtreatment,butwithstrawincorporationatthefirstplough.

Allthestrawofthepreviouscropwasreturnedtotheoriginalplotimmediatelyafterthreshingandthenincorporatedintosoil.

4

No-tillagewithstrawmulching

NTS

No-tillagethroughtheseason.Allthestrawfrompreviouscropwasreturnedtotheoriginalplotimmediatelyafterthreshingandplaceonthesoilsurface

Sowingrate,fertilizationandfieldmanagement

Springwheatwassownat187kgha−1inmid-MarchandharvestedinlateJulytoearlyAugusteachyear.Fieldpeawassownat180kgha−1inearlyAprilandharvestedinearlyJulyeachyear.Nitrogenandphosphoruswereappliedat105kgNha−1asurea（46%N）andat45.9kgPha−1ascalciumsuperphosphate（6.1%P）forspringwheat,and20kgNha−1and45.9kgPha−1forfieldpea.Though,fieldpeawasnotinoculatedasappropriaterhizobiaMwasnotavailableonthemarket,indigenousrhizobiawerepresentonthesite（Ref）.Glyphosatewasusedforweedcontrolduringpostharvestfallowperiodasperproductguidelines.Duringthegrowingseason,weedswereremovedbyhandandpestsanddiseasesweremonitoredandcontrolledbyconventionalpracticesinthearea.

Measurements

Soilsweresampledfromthetop0–30cmdepth.Fivecores（25-mmdiameter）werecollectedfromeachplotandbulkedintoonesampleperplotinmid-Augustin2006,2007,2013and2014.Thesampleswereusedtomeasurethecontentofsoilaggregatewithmechanicalstability（>5mm、2~5mm、0.25~2mm、<0.25mm）.Thesamplesweremixed,airdriedandgroundto0.2mm.Thesizedistributionandstabilityofsoilaggregatesweredeterminedbydrysievingandwetsieving[11],MWDbyusingLal[12]equation;PADbyusingFanRuqinetal.[13]method.MWD（mm）andPAD（%）wereusedtorepresentthestabilityofsoilaggregate.

Atfullmaturity,allplantsintheentireplotwerecutby5cmabovegroundusingsickles.Theedges（0.5m）oftheplotweretrimmedandd