Changes in soil carbon and nitrogen foll

(1)

Other uses, including reproduction and distribution, or selling or

licensing copies, or posting to personal, institutional or third party

websites are prohibited.

In most cases authors are permitted to post their version of the

article (e.g. in Word or Tex form) to their personal website or

institutional repository. Authors requiring further information

regarding Elsevier’s archiving and manuscript policies are

encouraged to visit:

(2)

ContentslistsavailableatSciVerseScienceDirect

Agriculture,

Ecosystems

and

Environment

j ourna l h o me pa g e :w w w . e l s e v i e r . c o m / l o c a t e / a g e e

Changes

in

soil

carbon

and

nitrogen

following

tillage

conversion

in

a

long-term

experiment

in

Northern

France

Bassem

Dimassi

a

_,

_Jean-Pierrre

_Cohan

b

_,

_Jerome

_Labreuche

b

_,

_Bruno

_Mary

a,∗

a_INRA,_Unité_Agro-Impact,_Site_de_Laon,_Pôle_du_Griffon,₀₂₀₀₀_{Barenton-Bugny,}_France

b_ARVALIS_Institut_du_Végétal,_Station_{Expérimentale,}₉₁₇₂₀_Boigneville,_France

a

r

t

i

c

l

e

i

n

f

o

Articlehistory:

Received28September2012

Receivedinrevisedform17January2013 Accepted23January2013

Keywords: Soilorganiccarbon SOC

Soilnitrogen Long-term Tillage Notill

Fullinversiontillage

a

b

s

t

r

a

c

t

Althoughcontinuousno-till(NT)isrecommendedforerosioncontrolandcarbonsequestration,itoften hasalimiteddurationsincefarmersalternatebetweenNTandfullinversiontillage(FIT)tocontrolweed infestationandavoidsoilcompaction.Inthispaper,weevaluatetheeffectofcontinuoustillageandtillage conversionofNTtoFITandviceversaonSOCandSONstocks,inalong-termexperimentatBoignevillein NorthernFrance.ContinuousNT(CNT)andFIT(CFIT)treatmentswereestablishedin1991andmaintained until2011whilehalfoftheplotswereconvertedin2005:fromCNTtonewFIT(NFIT)andCFITtonew NT(NNT).BulkdensitiesandorganicCandNcontentsweredeterminedin2001and2011downtothe oldploughingdepth(opd)whichwasalsomeasured.SOCandSONstockswerecalculatedatequivalent soilmassbycorrectingeitherbulkdensitiesortheopd.Bothmethodsproducedverycloseresultsand similarconclusions.

AtypicalgradientofSOCandSONconcentrationsvsdepthwasobservedinCNTasopposedtoarather uniformdistributioninCFIT.CNTresultedinSOCconcentrationinthetopsoil(0–5cm)higherby38% in2001and53%in2011comparedtoCFIT.Conversely,itledtoaSOCreductioninthedeeperlayer (ca.10–28cm)by14%in2001and18%in2011.TheglobaleffectwasnosignificantchangeinSOCand SONstocksbetweentreatmentsovertheoldploughedlayer(4060tsoilha−1₎_in_both_years:_43.2_and

45.0tCha−1_in₂₀₀₁_and_44.7_and_45.8_t_C_ha−1_in_2011,_in_CNT_and_CFIT,_{respectively.}

In2011,sixyearsaftertillageconversion,thestratificationofSOCandSONhaddisappearedinNFIT whereasanewonehadappearedinNNTwithasmallergradientthaninCNT.SOCorSONstocksover theoldploughedlayerdidnotdiffersignificantlybetweentreatmentsafter6yearsofconversion:SOC stockswere45.8,43.2,44.7and43.1tCha−1_in_the_CFIT,_NFIT,_CNT_and_NNT_treatments,_{respectively.}

Furthermore,SOCstocksbelowtheoldploughedlayer(ca.28–40cm)wereslightlygreaterinFITthanin NTtreatment(10.9vs8.7tCha−1_)._In_this_experiment,_continuous_or_conversion_tillage_did_not_result_in

anyCsequestrationbenefit.

1. Introduction

The adoption of conservation tillagepractices including no-till technique (NT) has considerably increased during the last decades.DerpschandFriedrich(2009)reportedthatagricultural areas under NT progressed worldwide from 45 million ha in 1999to105millionhain2008.In2006,34%ofannualcropsin Francehadbeenestablishedwithoutpriorsoilinversionagainst 21%fiveyearsearlier(Chapelle-Barry,2008).CurrentlyinEurope, there are about 1.3 million ha of arable cropland under ‘con-servationagriculturesystems’involvingnotillorshallowtillage withoutsoil inversion(ECAF, 2011).This interest for NT tech-niques maybe explained by several expected benefits suchas

∗_{Corresponding}_author._Tel.:₊₃₃₃₂₃₂₄₀₇_71;_fax:₊₃₃₃₂₃₂₄₀₇_76.

E-mailaddress:bruno.mary@laon.inra.fr(B.Mary).

soilandwaterconservation,enhancementofsoilfertility(Liebig

etal.,2004;Meleroetal.,2009),reductionoftillagecosts,

work-ingtimeandfuelconsumptionwhichremainthemajormotivation forfarmers.Comparingtheenergyrequirementsofno-till, min-imum tillage(MT)andfull inversiontillage(FIT),Sharmaet al.

(2011)foundthatNTandMTdecreasedtheenergyconsumption

by 34%and 31%,respectively, compared toFIT.However, long-term continuous NT is restricted in practiceand farmers often alternatebetweenNT and mouldboard ploughing(Pierceet al., 1994).A studyconductedbyHill (2001)intheCorn Beltofthe UnitedStatesindicated thattheaverageduration ofNTdidnot exceed1.4and2.4 yearsinMinnesotaandIllinois,respectively. Rotational tillageis appliedon about40% of agricultural fields inIndiana(Omonodeetal.,2006).InFrance,only11%ofannual cropsthat wereconductedwithoutprior soilinversionin2006 hadneverbeenmouldboardploughedsince2001(Chapelle-Barry,

2008).

(3)

Severaltermsareusedintheliteraturetodescribethistillage management:intermittent,infrequent,periodicallyoroccasional

FIT(Conantetal.,2007;Quinckeetal.,2007).Periodictillagemay

helptosolvetheproblemslinkedtoconservationtillageandNT techniquessuchaspathogensdevelopmentorinfestationof herbi-cideresistantweedsthatmaycompromisecropproductionand/or increasepesticidesuse(Chapelle-Barry,2008).Itisencouragedin Europebythedirective2009/128/CEonthesustainableuseof pesti-cides.Along-termsurveycarriedoutinNebraska,USAshowedthat FIT(mouldboardploughing)decreasedthepopulationofdowny bromeweedsincomparisonwithundisturbedNT(Kettleretal., 2000).Reducedtillagewithoutinversionseemstobemore promis-ingthanFITbuthassomedrawbacks.Forexample,Sansetal.(2011)

showedthatreducedtillageusingchiselploughincreasedbytwoto threetimestotalweedcoverandperennialcovercomparedtofull inversiontillage.AnotherinterestofperiodicFITmaybethe reduc-tionofsoilcompaction.Ferrerasetal.(2000)examinedphysical propertiesofaChernozemicloamsoilwithdegradedstructurein Argentina,foundhighersoilmechanicalresistanceunderNT com-paredtoFITandsuggestedthatthismightleadtosmallergrowth ofwheatrootsandreducewheatyield.

Alargenumber of studieshaveassessed theimpactof con-versionfromFITtoNTonsoilorganiccarbon(SOC)andnitrogen (SON)(e.g. Deenand Kataki,2003;Hermleet al.,2008;

Blanco-CanquiandLal,2008;Christopheretal.,2009;Dalaletal.,2011)

aswellasrecentmeta-analyses(Bakeretal.,2007;Angersand

Eriksen-Hamel,2008;Luoetal.,2010; Virtoet al.,2011).

How-everfewstudieshaveinvestigatedtheimpactofoccasionalFITor completere-conversionofNTtoFITonSOCandSON(Pierceetal.,

1994;Quinckeetal.,2007;Conantetal.,2007;Yangetal.,2008).

ThesestudiesshowamarkedredistributionofSOCwithinthesoil profileafterconversionfromNTtoFITbymouldboardploughing andalargevariabilityintheresultsofstockevolutionbetween experiments.Inthispaper,weanalyzetheresultsofalong-term experiment(20years)comparingNTandFIT.Ourobjectiveswere (1)tocomparetwomethodsofcalculationofSOCandSONstocks, (2)toquantifytheimpactof20yearsofcontinuousFITorNTon SOCandSONdistributionandstocksand(3)toanalyzethe evolu-tionofSOCandSONstocksafter6yearsofconversionofNTtoFIT

andviceversa.

2. Materialsandmethods

2.1. Studysiteandexperimentaldesign

The ongoing long-term field experiment is carried out by Arvalis-Institut du Végétal at the experimental station of Boigneville, Northern France on a Haplic Luvisol, (FAO, 1998) developed onloess. It is referredas ExperimentE (48◦₁₉′₃₀′′_N,

2◦₂₃′₀₃′′_E)._Physical_and_chemical_soil_{characteristics}_are_shown

atTable1.Thesitehasanaverageannualtemperatureand

pre-cipitationof10.8◦_C_and ₆₅₀_mm,_respectively₍_Constantin_et_al.,

2012).Thefield hadbeenmouldboardploughedformanyyears and was ploughed down to about 28cm until 1991 when the experimentwasinitiated.Twotillagetreatmentswereestablished andmaintaineduntil2011:CFIT(continuousfullinversiontillage) andCNT(continuousno-till).After1991,mouldboardploughing inCFITwasrealizedeveryyeartoasmallerdepth(about25cm) thanbeforewhiletheonlytillageoperationintheCNTtreatment wassowingusingadrillequippedwithdiscs.Thetillage opera-tionsinCFITtreatmentwere:shallowcultivationwithdischarrow two timesafter harvest, mouldboard ploughingin autumn and seedbedpreparationatsowing. Cropresidueswereallreturned tosoil,eithermixedwithsoilbytillageinCFITorleftatsoil sur-faceintheCNTtreatment.Theexperimentaldesignisarandomized

Table1

Soilcharacteristicsmeasuredin2001inthe0–25cmsoillayerinthetwotreatments: CFIT=continuousfullinversiontillage;CNT=continuousnotill.

CFIT CNT

blocksystemwiththreereplicatesforeachtreatment.Eachblockis composedoftwoplotsof9m×45msize.OnNovember15,2005, allplots weresplitdownintotwo subplots,halfof thembeing managedaspreviouslyandtheotherhalfbeingconvertedtothe alternativetillagetechnique,yieldingfourtreatments:CFIT (con-tinuousFIT),CNT(continuousNT),NFIT(newFITfollowingNT)and NNT(newNTfollowingFIT).From2005to2011,themanagement ofNFIT(resp.NNT)wassimilartoCFIT(resp.CNT).

Athree yearscroprotationwasestablishedinallplots since thebeginning oftheexperiment:springpea,winter wheatand springbarley.Onlyonecropoftherotationwaspresenteveryyear inallplotstosimplifytillageandfertilizationoperations.Winter wheatandspringbarleyreceivedfertilizer-N,inaverage180and 110kgNha−1_y−1_,_{respectively,}_mainly_as_ammonium_nitrate_split

intwoapplications.Grainyieldwasdeterminedonthegrain col-lectedwiththeharvestereveryyearsince1991.Theharvestindex (graintoshootratio)wasmeasuredonseveralsubplots(1m2_size,

3replicates)andwasusedtocalculatetheamountofaerialdry matterreturnedtosoilafterharvest.

2.2. Soilsamplingandanalysis

The soilsamplingstrategy was designedfor calculating SOC andSONstocksonanequivalentsoilmassbasis(ESM)(Ellertand

Bettany,1995)overadepthgreaterthanthecurrenttillagedepth.

Oneparticularfeatureoftheexperimentwastoreducethe plough-ingdepthaftertheonsetoftheexperimentfromca.28to25cm, andtomeasuretheoldploughingdepth(calledYinthe follow-ingtext)ineachsoilsamplingdate.TheidentificationofY(cm) wasperformedbydetectingchangesinsoilcolorandstructureon thesoilcores.Weassumethattherewasnoerosion(duetogood drainageandveryweakslopeofthefield)sothatthesoilmassmust beconstantoverthedepth0–Y.

Soil sampling was performed using two methods. The first method (SM1) consisted in opening one soil trench (about 50cm×50cm×50cm) per plot.Threesoil sampleswere taken fromthreetrench walls,dividedintoseverallayers(about5cm thick)and gatheredtogetherforeachlayer.Thesecondmethod (SM2)consistedinusingahydraulicgauge(Humaxdrillinggauge, Switzerland) topull out soil cores of8cm diameterand 20cm heightinsertedinplastictubes.Soilsampleswerecollectedatthree dates.InNovember2001,twosoilcoresweretakenineachplot withSM1methoddownto35cmdepthanddividedinto5layers (0–5,5–10,10–15,15–YandY–35).InNovember2005and2006, afterthetotaltillageconversion,soilsampleswerecollectedusing SM2methoddownto20cmandthendividedintotwolayers0–5

and5–20cm(Attardetal.,2011).InOctober2011,wesampled3

(4)

downto40cmanddividedeachcoreintofivelayers(0–5,5–10, 10–15,15–YandY–40).

Coarse residues and roots were removedfrom soilcores by handpicking.Soilsampleswerethenovendriedat35◦_C_for₄₈_h_and

crushedtopassthrougha2mmsieve.Soilsubsampleswereball milledbeforeanalysis.SOCandSONconcentrationswere deter-minedbydrycombustionwithanelementalanalyserCNS2000 (LecoCorp.,St.Joseph,MI,USA)oneachofthe9replicatesofeach layer.Bulkdensitiesweredeterminedateachsamplingdatewith twomethods.Thefirstoneemployedin2001and2005consisted inpushingasteelcylinder(98.18cm3₎_into_soil_and_weighing_the

soilbeforeandafterovendrying48hat105◦_C._The_second_method

operatedin2011consistsinusingadualgammaprobe(LPC-INRA, Angers,France). Weused itfor the5–10,10–15,15–20,20–25, 25–30,35–40cmlayersandthecylindermethodfor0–5cmdepth, with6replicatesperlayer.

2.3. Calculations

Soilmassoverthedepth0–Yiscalculatedas:

M(Y)=100

soilmassmustbeconstantandequaltotheinitialsoilmass,called referencesoilmass(MR):

Soilsampleswerenotcollectedatthestartofexperimentin1991, sothat we used themeasurements made in an adjacent simi-larlymanaged field to assess bulk densities and old ploughing depth.Themeasurementsgave YR=28±0.6cmandMR equalto 4060±90tha−1_.The _measurements_of _Y _and ₍_j₎_made _at _each

samplingdate wereusedtocalculateM(Y).Since M(Y)wasnot strictlyequaltoMR,weusedtwocorrectionmethodstoobtain con-stantESM.Thefirstmethod(M1)assumedthatthemeasuredYm valuesweretruewhereasbulkdensitiesm(j)werenot.A correc-tionfactorwasappliedtothebulkdensityofeachlayerinorder tomatchthesamereferencemass:

= MR

Thesecondmethod(M2)assumedthatthemeasuredbulk den-sitiesm(j)weretruewhereasYmwasnot.ThecorrectedYvalue (YC)wascalculatedasfollows:

Yc=Ym+

MR−M(Ym)

m(Ym)

(6)

Thiscorrectionallows,aspreviously,tohavethesameequivalent soilmasssince.TheM(YC)=MRcorrespondingcalculationofSOC stock(SOC2,intha−1)is:

Similar calculations were made for a greater depth Z (varying between35and40cm)usingthefollowingequations:

SOC1(Z)=SOC1(Y)

Zcbeingcalculatedtoprovidethesameequivalentmassbetween treatments. The same calculations were made for SON stocks replacingC(j)byN(j).

2.4. Statisticalanalysis

Theeffectoftillagetreatmentontotalbiomass,grainyieldand biomassofcropresidueswasevaluatedforeachcropbyanalysis ofvariance(ANOVA)performedforthetwoperiods1991–2005 and2006–2011.WealsoconductedonewayANOVAtoexamine theimpactoftillagemanagementonSOCandSONconcentrations foreachsoillayerandtheimpactonSOCandSONstocksin2001 and2011foreachequivalentsoilmass.Thestatisticaldifferences betweengroupedmeansofSOCandSONwereassessedusingpost hocTukey’sHonestlySignificantDifference(HSD)testformultiple comparisonsatthe95%confidencelevel.Statisticalanalyseswere carriedoutusingR©version2.10.1.

3. Results

3.1. Grainyieldsandaerialcropresidues

ThegrainyieldsandaerialcropresiduesarepresentedatTable2. Wecalculatedtheaverageandtheconfidenceintervalsofthethree cropsfortwoperiods:(i)fromthebeginningofthestudyin1991 untilthetillageconversioninNovember2005and(ii)after con-version from2006to2011.Annualvariation ingrainyieldwas relatedtoclimaticconditionsandcropdamagescausedbydiseases (notshown).TheANOVAindicatedthatgrainyieldandbiomassof cropresiduesofeachcropwerenotsignificantlydifferent(P<0.05) betweensoiltillagetreatmentsonbothperiods,althoughthere wasatrendforloweryieldofspringpeainno-tillduringthefirst period(1991–2005)beforeconversion.WecalculatedtheCinputs tosoilduetothereturnofabovegroundcropresidues,knowing thatCcontentofcropresidueswas43.5%(meanofallmeasured values).ThemeanCinputvariedfrom2.07to2.26tCha−1_y−1_._No

significantdifferencewasfoundbetweentheperiodsandthetillage treatments.

3.2. BulkdensityandYmeasurements

Bulkdensitiesmeasuredin2001and2011withthetwo meth-odsmentionedaboveand forthedifferentsoillayersaregiven

atTable3.In2001,beforetillageconversion,bulkdensitieswere

(5)

Table2

Averagegrainyieldandbiomassofaerialresiduesreturnedtosoilofeachcrop(tDMha−1_y−1₎_and_mean_C_inputs_to_soil_due_to_aerial_crop_residues_(t_C_ha−1_y−1₎_during_each timeperiod.Valuesinbracketsaretheconfidenceintervals(P<0.05).

Period Crop CFIT NFIT CNT NNT

Grainyield 1991

–2005

Winterwheat 7.49(1.64) – 7.22(1.46) –

Springbarley 6.07(0.65) – 6.13(0.52) –

Springpea 5.21(0.61) – 4.34(0.72) –

2006 –2011

Winterwheat 7.02(1.43) 6.36(1.70) 6.50(1.48) 6.65(1.84)

Springbarley 6.12(1.26) 6.78(0.37) 6.31(1.79) 6.77(0.18)

Springpea 2.88(0.70) 3.04(0.60) 2.56(0.51) 2.62(0.60)

Aerialcropresidues 1991

–2005

Winterwheat 7.19(1.58) – 6.94(0.06) –

Springbarley 5.38(0.53) – 5.66(0.46) –

Springpea 4.43(0.61) – 3.55(0.73) –

2006 –2011

Winterwheat 6.75(1.54) 6.11(1.91) 6.24(1.68) 6.39(2.09)

Springbarley 6.41(0.22) 6.01(0.32) 5.58(0.98) 6.25(0.16)

Springpea 2.46(0.62) 2.18(0.20) 2.49(0.39) 2.14(0.52)

Cinputstosoil 1991–2005 Allcrops 2.23(0.14) 2.18(0.10) 2.18(0.10) 2.23(0.14)

2006–2011 Allcrops 2.26(0.13) 2.07(0.17) 2.07(0.11) 2.14(0.09)

Table3

Soilbulkdensities(gcm−3₎_measured_and_corrected_to_provide_equivalent_soil_mass_using_method₁_(Eq.₍₄₎_,_see_text)._Values_in_brackets_are_the_confidence_intervals₍_P_<_0.05). Lowercaselettersindicatesignificantdifferencesbetweentillagetreatmentsineachlayer(Tukey’sHSD,P<0.05).

Year Depth(cm) CFIT NFIT CNT NNT

Measured Corrected Measured Corrected Measured Corrected Measured Corrected

2001 0–5 1.48(0.01) 1.39(0.01) – – 1.35(0.03) 1.27(0.03) – –

5–10 1.52(0.02) 1.42(0.01) – – 1.46(0.03) 1.38(0.03) – –

10–15 1.47(0.06) 1.38(0.05) – – 1.48(0.06) 1.40(0.05) – –

15–20 1.50(0.02) 1.40(0.02) – – 1.54(0.01) 1.45(0.01) – –

20–25 1.50(0.02) 1.40(0.02) – – 1.54(0.01) 1.45(0.01) – –

25–30 1.50(0.02) 1.40(0.02) – – 1.54(0.01) 1.45(0.01) – –

30–35 1.43(0.01) – – – 1.45(0.04) – – –

2011 0–5 1.24(0.02)ab 1.21(0.05) 1.24(0.07)a 1.29(0.06) 1.29(0.04)a 1.24(0.04) 1.32(0.08)b 1.38(0.06)

5–10 1.42(0.06)a 1.39(0.04) 1.35(0.08)b 1.40(0.05) 1.47(0.04)a 1.41(0.02) 1.44(0.03)a 1.51(0.01)

10–15 1.49(0.09)a 1.45(0.05) 1.43(0.07)a 1.49(0.03) 1.50(0.05)a 1.45(0.02) 1.48(0.01)a 1.54(0.03)

15–20 1.43(0.14)ab 1.39(0.08) 1.38(0.06)a 1.44(0.05) 1.50(0.07)b 1.45(0.04) 1.47(0.04)ab 1.53(0.02)

20–25 1.55(0.05)a 1.52(0.03) 1.50(0.05)b 1.56(0.03) 1.55(0.04)a 1.50(0.03) 1.55(0.01)a 1.62(0.03)

25–30 1.57(0.09)a 1.53(0.07) 1.54(0.05)a 1.60(0.03) 1.55(0.05)a 1.49(0.05) 1.54(0.03)a 1.61(0.06)

30–35 1.55(0.10)a – 1.56(0.02)a – 1.49(0.06)a – 1.50(0.05)a –

35–40 1.49(0.06)a – 1.50(0.03)a – 1.45(0.04)a – 1.45(0.03)a –

or0–30cmdidnotdifferbetweentreatments(notshown). Con-sistently,therewasnosignificantdifferenceinmeasuredYvalues betweentillagetreatments(Table4).However,bothtypesof mea-surements had tobe diminishedby 5–6% (correctedvalues) in ordertomatchthereferencesoilmassof4060tha−1_,_indicating

thateithertheYvaluesorthebulkdensitieswereslightly over-estimated.

In2011,bulkdensitiesineachlayerdifferedverylittlebetween treatments,mostdifferencesbeingnotsignificant.However,the no-tilltreatments(CNTandNNT)wereslightlymorecompacted thantheploughedtreatments(CFITandNFIT)overofthe0–25cm depth,withameanincreaseinbulkdensityof4%.Thistrendwas consistentwiththemeasuredYvalueswhichwere0.8cmgreaterin theploughedtreatments,i.e.3%greaterthaninnotill.Thecorrected valuesofYorbulkdensityover0–25cmdifferedlittlefromthe measuredonesandwerenotcorrelatedwiththem,indicatingthat therewasnobiasinbulkdensityestimates.Asmaybeexpected,

giventhatthedeepesttillagedidnotextendbeyond28cminany treatment,bulkdensitiesinthe30–35and35–40cmlayerswere notdifferentbetweentreatments.

3.3. SOCandSONconcentrations

3.3.1. Effectofcontinuoustillage

In2001,tenyears afterthebeginningoftheexperiment,we observed thatthelong-termCNTtreatmentproduceda consid-erableSOCandSONstratification,whiletheCFITtreatmenthad a ratheruniformdistributionofSOCandSONoverthesoil pro-filedowntotheploughingdepth(Fig.1A).Threelayersmaybe distinguishedinthesoilprofile:(i)theuppersoillayer(0–5cm) containingabout700tdrysoilha−1 _where_SOC_and_SON

concen-trationsweresignificantlyhigher(P<0.05)inCNTthaninCFITby 38% and27%,respectively;(ii)anintermediatelayercontaining 3360tsoilha−1_{(=4060–700)}_which_corresponds_{approximately}_to

Table4

Oldploughingdepth(Y,incm)measuredandcorrectedtoprovideequivalentsoilmassusingmethod2(Eq.(6),seetext).Valuesinbracketsaretheconfidenceintervals (P<0.05).

Year CFIT NFIT CNT NNT

Measured Corrected Measured Corrected Measured Corrected Measured Corrected

2001 29.0(1.5) 27.2(0.1) – – 29.0(1.1) 27.5(0.2) – –

(6)

-6000 -5000 -4000 -3000 -2000 -1000 0

0

4

8

12

16

20 Soil mass (t/ha)

SOC

con

tent (g/kg)

CFIT

CNT

NNT

NFIT

***

NS

***

*

B

-6000 -5000 -4000 -3000 -2000 -1000 0

0.0

0.4

0.8

1.2

1.6

2.0 SON

con

tent (g/kg)

***

*

***

*

-6000

-5000 -4000 -3000 -2000 -1000 0

0

4

8

12

16

20 Soil mass (t/ha)

SOC

con

tent (g/kg)

CFIT

CNT

***

NS

**

NS

A

-6000 -5000 -4000 -3000 -2000 -1000 0

0.0

0.4

0.8

1.2

1.6

2.0 SON

con

tent (g/kg)

**

NS

**

*

Fig.1. SOCandSONconcentrationsinthesoilprofile(versuscumulativesoilmass):(A)in2001(twotillagetreatments);(B)in2011(fourtillagetreatments).CFIT=continuous fullinversiontillage;CNT=continuousno-till;asterisksindicatelevelsofsignificance(ANOVA).

thelayer5–29cmwithlowerSOCandSONconcentrationsinCNT comparedtoCFIT,of11–14%and 14–22%,respectively;(iii)the deeperlayerunderlyingtheploughingdepth(ca.29–34cm) con-taining640tsoilha−1_{(=4700–4060)}_with_no_significant_difference

inSOCconcentrationbetweentillagetreatmentsbutasignificant differenceinSONconcentration.TheC/Nratiooforganicmatter graduallydecreasedfromthesoilsurfacetothedeeperlayerfrom 11.27to9.08inCNTtreatmentand from10.36to8.77in CFIT treatment.

In2011,thedistributionofSOCandSONthroughoutthe pro-fileinthecontinuoustillagetreatments(CFITandCNT)showed a similar pattern to 2001 (Fig. 1B). Compared to 2001, there wasalmostnochangeinSOCconcentrationinCFITwhereasthe SOCand SONconcentrations of the CNTcontinued to increase inthe uppertwo layers (0–10cm, ca. 1400tha−1_)._The _relative

increasebetween2001and2011represented9%and10%ofSOC and12%and11%ofSONinthe0–5and5–10cmlayers, respec-tively.Conversely,theSOCconcentrationofCNTremainednearly stable(variation=2%)in theintermediate layer (10–Y, i.e.from

1400to4060tha−1₎_while_it_increased_in_the_CFIT_treatment_by

8%.

3.3.2. Effectoftillageconversion

Sixyearsaftertillageconversion,theSOCandSON stratifica-tionpatterncreatedinno-tillwasdisrupted(Fig.1B).Converting CNTintoNFITledtoaredistribution ofSOCandSONalongthe soilprofile.Mouldboardploughingreducedsignificantly(P<0.05) SOCandSONconcentrationscomparedtoCNTintheupper0–5cm layerandincreasedthemsignificantlyinthelayersbelow10cm (soilmass>ca.1400tha−1_)._On_the_other_hand,_SOC_and_SON

con-centrationsinNFITwereveryclosetothoseofCFITthroughout theentiresoilprofile(5500tha−1_,_ca._0–40_cm)._The_conversion_of

CFITtoNNTalsoresultedinnewstratificationofSOCandSON,but lesscontrastedthaninthecontinuousno-till.NNTtreatmenthad significantly(Tukey’sHSDtest,P<0.05)higherSOCconcentrations thanCFITinthefirstlayer(0–5cm)andlowerconcentrationsinthe 10–Ylayer(1400–4060tha−1_)._No_difference_in_SOC_was_observed

(7)

3.4. SOCandSONstocks

3.4.1. Effectofcalculationmethod

Table5summarizesresultsofSOCandSONstocksin2001,2005

and2011calculatedwiththetwocorrectionmethods(method1, bulkdensity correctionand method2,Ycorrection)onanESM basisof600,1300,4060,4700and5500tha−1_which_corresponds

approximatelyto4.5,9,29,34and40cmdepth.Wefirstnoticethat thetwocorrectionmethodsgaveverycloseresultsforall samp-lingdatesandsoildepths.Thisdemonstratesthattheexperimental errorsinmeasuringYdepthandbulkdensitywereverylimited andthatreliableconclusionscanbemadeonSOCandSONstocks. Thereforetheresultspresentedbelowwillbetheaverageofthe twomethods.

3.4.2. Effectofcontinuoustillage

In2001,SOCstocksweresignificantlyhigher(P<0.05)inCNT thaninCFITintheuppertwolayers(ESM=1300tha−1_,_ca_._0–9_cm):

17.7vs15.3tha−1_,_{respectively.}_But_they_were_not_{significantly}

dif-ferentovertheoldploughingdepth(ESM=4060tha−1_):_43.2_and

45.0tha−1_,_{respectively.}_The_same_conclusion_also_applies_for_SON

whichrepresented4.41tha−1_in_CNT_and_4.59_t_ha−1_in_CFIT_in_the

layer0–Y.In2005,SOCandSONstockswerecalculatedonlyinthe upperlayerusingdataofAttardetal.(2011)becausesoilsampling depthwaslimitedto20cmandmostmeasurementsweremadein the0–5cmlayer.TheSOCandSONstocksweresimilartothoseof 2001inCFIT,buthadincreasedinCNTtreatment.Thisshowedthat CNTcontinuedtosequesterSOCandSONatsoilsurface.In2011,a greaterdifferenceinSOCandSONwasfoundinCNTcomparedto CFITintheuppertwolayers(0–1300tha−1_):_19.2_vs_15.0_t_SOC_ha−1

and1.87vs1.56tSONha−1_,_{respectively.}_However_no_significant

differenceswerefound,neitherintheoldploughedlayernordown toca.40cm(i.e.forsoilmassesof4060,4700and5500tha−1_).

ThetemporalvariationsinSOCandSONstocksbetween2001 and2011aregiven atTable6.Therewasnosignificantchange in SOC stocksin CFIT treatmentwhatever the depth, a signifi-cantincreaseinCNTintheuppertwolayersandanon-significant increase inCNTover theold ploughingdepth. Concerning SON stocks,bothtreatmentsexhibitedatrendforNsequestrationover time,butthetrendwasonlysignificant(P<0.05)intheCNT treat-ment.

3.4.3. Effectoftillageconversion

TheSOCandSONstocksandtheirdistributionalongthesoil profilemeasuredin2011weresignificantlyaffectedbybothtillage conversionsmadesixyearsearlierin2005(Table5).The conver-sionof CNTinto NFIT resultedin a rapid redistribution ofSOC and SONin theprofile:a marked decrease inthe upperlayers (600and 1300tha−1₎_which _was_visible_in ₂₀₀₅_soon _after_the

tillage, and an increase in the lower layers (1300–4060tha−1₎

whichwassignificantin2011.Again,thecumulativeamountsof SOCandSONoverthewholeprofile(4060,4700or5500tha−1₎

didnotdifferbetweenCNTandNFIT.Theseresultsclearlyshow thatmouldboardploughingofthepreviouslyno-tillsoildidnot induce any significant effect on SOC and SON stocks over the wholesoil profile,i.e. downtotheold ploughing depth(about 28cm)orfurtherdown(about40cm),aftersixyears of conver-sion.The conversionof CFITinto NNT increasedthe SOCstock (P<0.05)intheupperlayer(600tha−1₎_by_19%_compared_to_the

permanent CFIT but decreasedit (P<0.05) over the wholesoil profile(4060,4700or5500tha−1₎_by_6–9%._The_same_trend_was

foundforSONstocksbutwassignificantonlyforthegreatersoil

(8)

Table6

Changesinsoilorganiccarbon(tCha−1₎_and_nitrogen_stocks_(t_N_ha−1₎_from₂₀₀₁_to 2011inthe4tillagetreatmentsatvariousequivalentsoilmasses(tha−1₎_and_levels ofsignificance(Student’st-test).

Soilmass CFIT NFIT CNT NNT

SOC

4.1. Grainyieldsandcropresidues

Thegrainyieldsofwinterwheatandspringbarleywere simi-larinthetwocontinuoustillagetreatmentswhereasasignificantly greatergrainyieldofspringpeawasobservedinCFITduringthe firstperiod (1991–2005). Apossible explanationof the smaller yieldduringthefirstperiodcouldbealowerrootgrowthinthe CNTtreatmentduetotheslightlyhigherbulkdensityrecordedin 2001inthelayer15–35cm(Table3).Duringthesecondperiod (2006–2011),grainyieldsdidnotdiffersignificantlybetweenthe fourtreatmentsforanycrop.Consequently,theamountsofcarbon returnedtosoilthroughaerialcropresidueswerealmostthesame foralltreatmentsandvariedfrom2.07to2.28tha−1₍_Table₂_)._In

theliterature,cropyieldsobservedunderno-tillorfullinversion tillageareoftendifferent,suggestingthatCinputsarealsovariable betweenstudies.Intheirmeta-analysisofsoiltillageeffectsonC sequestration,Virtoetal.(2011)selected35“till–no-till”paired treatmentsderivedfrom14differentstudieswhereCinputscould beestimated.Theyfoundthatabouthalfofthemresultedinan increaseinCinputswhereastheotherhalfresultedinadecrease inCinputs.Ourresultscorrespondtothemedianvalue.

4.2. SOCandSONconcentrations

4.2.1. Continuoustillage

Asexpected,continuousno-tillmanagementledonthe long-term(10and20years)toapronouncedSOCandSONstratification throughout the soil profile as opposed to CFIT which induced a rather uniformdistributionover the soilprofile downtothe ploughingdepth.Thesefindingscanbeattributedtosmaller car-boninputsindeeperthaninupperlayersinCNTtreatment,and soilmixingin theCFITtreatment.Ourresultsareinaccordance withseveralstudies.Hernanzetal.(2009)investigatedtheSOC stratificationoveraperiodof20yearsofNTandFITtreatments underwinterwheat-legumerotationinSpainandfoundthatSOC concentrationswere75%higherinthetopsoil(0–10cm)inNTand 18%lowerinthelayer20–30cm. Astudyconductedby

Blanco-Canquietal.(2011)assessingtheSOCprofiledownto100cmin

threelong-termexperiments(>20years)intheCentralGreatPlains (USA)showedthatSOCconcentrationsinthetopsoil(0–5cm)were 57%,21%and9%greaterinNTthaninFITtreatments,whilethe SOCconcentrationsinthe5–20cmlayerweregreaterintheFIT treatmentby16%,12%and−3%,respectively.Inanotherlong-term experiment(28years)conductedinIndiana(USA),Gáletal.(2007)

alsofoundthatNThadhigherSOCandSONconcentrationsthanFIT by33%and32%inthetopsoil(0–5cm)andsmallerconcentrations

(7%and5%lower)inthelayer15–30cm.Thisorderofmagnitudeis closetoourexperimentalresultswhichgaveanincreaseof38%and 27%forSOCandSON,respectivelyinthe0–5cmlayer.Moreover

Gáletal.(2007)foundhigherSOCandSONconcentrationsbelow

theploughedlayer(30–50cm)inFITtreatment.Thisagreeswith ourresultssinceweobservedsignificantincreasesinSOC concen-trationin2011andinSONconcentrationin2001and2011.These resultsconfirmthenecessitytoexamineSOCandSON concentra-tionsatdepthsatleastequaltothedeepersoiltillageoperationand takeintoaccountdifferencesinbulkdensities,inordertointegrate resultsoverthewholesoilprofileandassessSOCandSONchanges duetotillagetreatments.

4.2.2. Tillageconversion

4.2.2.1. CNTtoNFIT. ThepermanentconversionofCNTintoNFIT

redistributed SOC and SON concentrations with an immediate impact due to the mixing effect of mouldboard ploughing. It induceda significantdecline ofSOCand SONconcentrationsin thetopsoil(0–5cm)butenrichedthelayersbelow10cmtolevels closetothoseoftheCFITtreatment.Theseresultsagreewellwith thescarcepublishedstudiesevaluatingtheconversionofCNTinto NFIT.Yangetal.(2008)examinedtheimpactofpermanent conver-sionof13yearNTtocontinuousFIT(ploughedeveryyear)during thenext8yearsinOntario,Canada.Theyfoundthatploughing sup-pressedthestratificationwithinthefirstyearbutdidnotinduce anysignificantdifferenceintheaverageSOCconcentrationinthe 0–20cmlayer.InSpain,Meleroetal.(2011)foundthatasingle mouldboardploughingofa8yearNTtreatmentledtoadecrease inSOCconcentrationof23%inthe0–5cmlayer6monthsafterthe conversionandanincreaseof8%inthe5–25cmlayer.Ina long-termno-tillexperimentinNebraska,Quinckeetal.(2007)found that,twoyearsafterasinglemouldboardploughing,SOC concen-trationdecreasedfrom8to16%inthe0–5cmlayerandonlyby3 to1%(probablynotsignificant)inthe0–30cmlayer.

4.2.2.2. CFITtoNNT. Inourexperiment,sixyearsafterthecomplete

conversionofCFITtoNNT,SOCandSONconcentrationstendedto increaseinthetopsoilbutdidnotreachthesamelevelthaninthe permanentno-till.Incontrast,theconcentrationsinthe10-Ylayer (1400–4060tha−1₎_were_smaller_than_those_found_in_CFIT

treat-ment,probablyduetosmallerCinputs.Theseresultsalsoagree withthoseofYangetal.(2008)whoreportedanetSOC enrich-mentintheupperlayer(0–5cm)andadecreaseinthe10–20cm layercomparedtothelong-termCFIT.

4.3. SOCandSONstocks

4.3.1. Methodology

WeusedtwomethodstocalculateSOCandSONstocksat equiv-alentsoilmasses.Thiswaspossiblesincebothbulkdensitiesand depthsofoldploughinglayerweredeterminedinthisexperiment. Inordertoalwaysobtainthereferencesoilmass(4060tha−1₎_over

theoldploughingdepth,wehadtocorrecteitherbulkdensities (method1)orYvalues(method2).Usingtwoindependentmethods helpedustoevaluatethepossiblesystematicerrorswhen quantify-ingSOCandSONstocks.ComparingstocksonanESMbasisisnow recognizedinsoilscienceresearchasthebestapproachtoavoid errorscausedbythespatialandtemporalvariationsofbulk den-sityinducedbytillagemanagement(EllertandBettany,1995;Gál

etal.2007;Leeetal.,2009).Wefoundthatthevariationsinbulk

densityandYwereconsistentandthetwomethodsproducedvery closeresultsandledtothesamestatisticalconclusions.

4.3.2. Continuoustillage

(9)

differentfromthosemeasuredunderCFITonanESMof4060tha−1_,

despitehigherstocksatsoilsurface(Table5).Thisresultisin con-trastwitholderstudiesandmeta-analyses.Forexample,Ogleetal.

(2005)reportedthatthe“responseratio”forCsequestration(ratio

betweenSOCcontentofCNTtoSOCcontentofCFITtreatments after20years)was1.16±0.02and1.10±0.03,undertemperate moistand dryclimates, respectively.However,themorerecent meta-analysesconductedwithsevereselectioncriteria concern-ingdepthandbulkdensityconcludedifferently.Inameta-analysis examining69pairedtillageexperiments,Luoetal.(2010)found thatthedifferenceNT-FITwaseitherpositiveornegativeandthat therewasnosignificantdifferenceonaveragebetweenthetwo tillagetreatmentsiftheSOCstockswerecalculatedonanESMbasis anddownto40cmdepth.AdoptionofNTincreasedtheSOCstock inthetopsoil(0–10cm)by3.15±2.42tha−1_and_decreased_it_by

3.30±1.61tha−1_in_the_20–40_cm_layer._These_values_agree_with

ourresultssincewefoundagainof2.42±0.57tha−1_for_an_ESM_of

1300tha−1₍_ca_._0–10_cm)_and_a_loss_of_4.20_±_0.95_t_ha−1_in_the_layer

1300–4060tha−1₍_ca._10–_Y_)._In_another_{meta-analysis,}_Virto_et_al.

(2011)showedthatthevariationinsequestrationbetweentillage treatments(eitherpositiveornegative)couldbepartlyexplained bythevariationinCinputstosoil.Our resultsfitwellwiththe linearrelationshiplinkingtheSOCdifferencetotheCinputs dif-ference(Fig.2intheirpaper)sincewedidnotfindanydifference inyieldsandCinputsfromcropresiduesbetweenthetwo treat-ments.

4.3.3. Conversiontillage

4.3.3.1. CNTto NFIT.In ourexperiment, wefoundthatthe

con-versionfromCNTtoNFITledtoa markedlossof SOCand SON stocksintheupperlayer(0–1300tha−1_,_ca_._0–10_cm)_and_a_gain

inthedeeperlayersfullyoffsettingthelossinthetopsoil.No sig-nificantdifferenceinSOCandSONstockswasobservedbetween NFITandCNToverthewholesoilprofile,i.e.from4060tha−1_(old

ploughingdepth)downto5500tha−1₍_ca_._0–40_cm)._In_the

litera-ture,thereareconflictingresultsontheeffectofsingleFIToperation or continuous conversion. In Germany, Stockfisch et al. (1999)

observed that a single mouldboard ploughing applied after 21 yearsofshallowtillage(6–8cm)resultedinanimmediatedecline in SOCand SON stocksin theupper layerwithout enrichment ofdeeperlayers. Theyconcludedthat “organicmatter accumu-lationasaresultoflong-termminimumtillagewascompletely lostbya singleapplication of inversiontillagein thecourseof onewinter”. However,therewasnocontrolintheirexperiment since theshallow tillagetreatmentwas notmaintained. In the samesite,Kochand Stockfisch(2006)investigatedSOCchanges inalong-termdeepnoninvertingtillage(0–30cm)management withshallowmixing(0–10cm)followingaone-timemouldboard ploughingevent.Theyobservedalossof4%oftheinitialstockof SOCinthe0–30cmlayerwithin6monthsafterploughingand6% loss1.5–2.5yearslater.Conantetal.(2007)conducteda model-ingstudyusingCenturymodel(Partonetal.,1987)toexaminethe impactofperiodictillageonSOCstocksinthreeagro-ecosystems inUSA.They simulateda soilC stock lossinduced byFIT after long-termNTand this lossincreasedwiththefrequency ofFIT operations.

However,moststudiesfoundopposite resultsand similarto ours. Pierce et al. (1994) compared NT to FIT in a study con-ductedinEastLansing,USAandreportedthatasingleploughing eventmadeinalong-termNThadnoimpactonSOCcontentover

0–20cm.Kettleretal.(2000)indicatedthattheinterruptionofa

22yearNTtreatmentbyasinglemouldboardploughingdownto 15cmresulted,fiveyearslater, ina20%decreaseofSOCstocks inthe0–7.5cm layerwhich wasoffsetbya 15%enrichmentin the7.5–15cm layer.Theglobaleffectwasnosignificantchange

inSOCstocksover0–30cm.VandenBygaartandKay(2004) deter-minedthechangeinSOC(onESMbasis)whena22yearno-till fieldinOntario(Canada)wasploughedonce.TheymeasuredSOC contentsatthreedatesafterploughing(3days,7and18months) onfourplotswiththreetexturalclassesandfoundnosignificant SOCchangeinthreeplotsandadeclineonlyinthefourthplotatone date.Quinckeetal.(2007)foundnosignificantchangesintotalSOC intwofieldsinUSAonanESMbasis(2500tha−1_,_about_0–20_cm)

twoyearsafteronemouldboardploughing.Yangetal.(2008)had similarconclusionssince8yearsofpermanentconversionofNTto NFIT(mouldboardploughing)didnotcauseanysignificant differ-enceinSOCstocks(comparedtoCNT)measuredfor3000tsoilha−1

correspondingto0–20cmdepth.Ourresultsagreewiththe con-clusionofQuinckeetal.(2007):“one-timetillageconductedonce in10yearstomixthehighSOCsurfacelayerwithdeepersoilwill notresultinlargeSOClossesfollowingtillagewithanetpositive gaininSOCeventually”.

4.3.3.2. CFITtoNNT. SixyearsaftertheconversionfromCFITto

NNT,wefoundasignificantgainofSOCbutanon-significanteffect onSONstocksintheupperlayer(0–10cm)inNNTcomparedtoCFIT andNFIT.However,SOCandSONstocksdidnotreachthesame lev-elsasinCNTtreatmentindicatingthatmanyyearsarerequiredto buildupastocksimilartoCNTandreachanequilibriuminthe sur-facelayer.Ifweconsiderthewholesoilprofile(ESM≥4060tha−1_,

i.e.belowtheoldploughingdepth),theSOCstockofNNTwas sig-nificantlysmallerthanCFITbutnotsignificantlydifferentfromCNT andNFITtreatments.Yangetal.(2008)studiedthepermanent con-versionofCFITtoNNTandobservedthesametrends.Theyfound thatSOCstocks(ESM=3000tha−1₎_under_NNT_were_always_smaller

thaninCFITeventhoughtheirratiodidnotdiffersignificantlyfrom 1.TheseresultsmightbeexplainedbythelowerCinputintodeep layersinthenewno-tillsystemwhereastheCmineralizationrate couldremaincomparabletothatofCFITduringthefirstyearsafter conversion.

5. Conclusion

Severalstudiesandmeta-analysesfocusedandexaminedthe impactofconversionfromFITtoNTonSOCandSONstocksbut onlyfewstudiesinvestigatedtheimpactoftheopposite conver-sionfromNTtoFIT.Thenecessityofsuchresearchhasbeenraised becauseofthecontinuousexpansionofsuchtillagemanagements

(Hill,2001;Chapelle-Barry,2008).Theaimofourstudy,conducted

inatemperateclimateofNorthernFrance,wastoinvestigatethe impactoflong-termand permanentconversiontillage manage-mentsonSOCandSONstocksandtheirdistributionoverthesoil profile.Theoriginalityofourapproachconsistedincomparingthe permanentconversionoftwocontrastedtillagetreatments(no-till

vsdeepannualinversionploughing)withtwomethodsof calcu-lationofequivalentsoilmass.Themainconclusionsthatcanbe drawnare:

(1) thefourtillagetreatments(continuousorconvertedNTorFIT) affectedSOCandSONdistributionoverthesoilprofilewitha typicalstratificationforno-tilledtreatmentsandarather uni-formdistributionfortheploughedones;

(2) after20yearsofdifferentiation,therewasnosignificant dif-ference inC inputs tosoil and SOCor SONstocksbetween continuousno-tillandcontinuousfullinversiontillagewhen stockswerecalculatedatorbelowtheoldploughingdepth; (3) convertingno-tilltofullinversiontillagedidnotchangeSOC

(10)

(4)converting full inversion tillage to no-till lead to a slight decreaseofSOCstocksbutnosignificantchangeinSONstocks measuredatorbelowtheoldploughingdepth.

Thisstudyhighlightstheimportanceof followingchangesin SOCregularlyovertimeandinthelong-termtobeabletobetter explainC sequestration responsetochanges in tillage manage-ments.Itsuggeststhattotalsoilcarbonstocksarenotorweakly affectedbytillagepracticeintypicalarablesoilswithSOC concen-trationsaround10gkg−1_,_confirming_results_of_Virto_et_al._(2011),

andthatthesesoilscannotbesimplyturnedintoasinkfor atmo-sphericCO2byreducedtillage.Thecorollaryofsuchaconclusion

wouldbethatthenetimpactofachangeintillagepracticeboils downtothedifferenceitmakestothefluxofothergreenhouse gasesandparticularlyN2O.

Acknowledgements

This study was financed by Arvalis-Institut du Végétal and receivedsupportfromANRT(NationalAssociationforResearchand Technology),France.WeareverygratefultoD.Couture,A.Fontaine andA.Luttonfor themanagementof thelong-term fieldstudy andD.Boitez,N.Collanges,C.Dominiarczyk,E.Gréhan,F.Mahu, A.TexeiraandE.Venetandfortheirtechnicalassistance.

References

Angers,D.A.,Eriksen-Hamel,N.S.,2008.Full-inversiontillage andorganic car-bon distribution in soilprofiles: ameta-analysis. Soil Sci.Soc. Am.J. 72, 1370–1374.

Attard,E.,Recous,S.,Chabbi,A.,DeBerranger,C.,Guillaumaud,N.,Labreuche,J., Philippot,L.,Schmid,B.,LeRoux,X.,2011.Soilenvironmentalconditionsrather thandenitrifierabundanceanddiversitydrivepotentialdenitrificationafter changesinlanduses.GlobalChangeBiol.17,1975–1989.

Baker,J.M.,Ochsner,T.E.,Venterea,R.T.,Griffis,T.J.,2007.Tillageandsoilcarbon sequestration–whatdowereallyknow?Agric.Ecosyst.Environ.118,1–5. Blanco-Canqui,H.,Lal,R.,2008.No-tillageandsoil-profilecarbonsequestration:an

on-farmassessment.SoilSci.Soc.Am.J.72,693–701.

Blanco-Canqui,H.,Schlegel,A.J.,Heer,W.F.,2011.Soil-profiledistributionofcarbon andassociatedpropertiesinno-tillalongaprecipitationgradientinthecentral GreatPlains.Agric.Ecosyst.Environ.144,107–116.

Chapelle-Barry,C.,2008.Danslesillondunon-labour.AgrestePrimeur207,1–4. Christopher,S.F., Lal,R.,Mishra, U.,2009.Regionalstudyofno-tilleffectson

carbonsequestrationinmidwesternUnitedStates.SoilSci.Soc.Am.J.73, 207–216.

Conant,R.T.,Easter,M.,Paustian,K.,Swan,A.,Williams,S.,2007.Impactsofperiodic tillageonsoilCstocks:asynthesis.SoilTill.Res.95,1–10.

Constantin,J., Beaudoin, N.,Launay, M., Duval,J., Mary, B.,2012. Long term nitrogen dynamicwithvariouscatch cropscenarios: testand simulations with the STICS modelin temperateclimate. Agric. Ecosyst. Environ. 147, 36–46.

Dalal,R.C.,Allen,D.E.,Wang,W.J.,Reeves,S.,Gibson,I.,2011.Organiccarbonand totalnitrogenstocksinavertisolfollowing40yearsofno-tillage,cropresidue retentionandnitrogenfertilisation.SoilTill.Res.112,133–139.

Deen,W.,Kataki,P.K.,2003.Carbonsequestrationinalong-termconventionalversus conservationtillageexperiment.SoilTill.Res.74,143–150.

Derpsch,R.,Friedrich,T.,2009.Developmentandcurrentstatusofno-tilladoption intheworld.In:Proc.18thISTROConf.,Izmir,Turkey,T1-041,pp.1–16. ECAF,2011.ConservationAgricultureandtheCAP2020MakingSustainable

Agri-cultureReal2011–2012.ECAF,Brussels,p.34.

Ellert,B.H.,Bettany,J.R.,1995.Calculationoforganicmatterandnutrientsstoredin soilsundercontrastingmanagementregimes.Can.J.SoilSci.75,529–538. FAO,ISRIC,ISSS,1998.WorldReferenceBaseforSoilResources.FAO,Rome. Ferreras,L.A.,Costa,J.L.,Garcia,F.O.,Pecorari,C.,2000.Effectsofnotillageonsome

soilphysicalpropertiesofastructuraldegradedPetrocalcicPaleudollofthe southern“Pampa”ofArgentina.SoilTill.Res.54,31–39.

Gál,A.,Vyn,T.J.,Michéli,E.,Kladivko,E.J.,McFee,W.W.,2007.Soilcarbonand nitrogenaccumulationwithlong-termno-tillversusmoldboardplowing over-estimatedwithtilled-zonesamplingdepths.SoilTill.Res.96,42–51. Hermle,S.,Anken,T.,Leifeld,J.,Weisskopf,P.,2008.Theeffectofthetillagesystem

onsoilorganiccarboncontentundermoist,cold-temperateconditions.SoilTill. Res.98,94–105.

Hernanz,J.L.,Sanchez-Giron,V.,Navarrete,L.,2009.Soilcarbonsequestrationand stratificationinacereal/leguminouscroprotationwiththreetillagesystemsin semiaridconditions.Agric.Ecosyst.Environ.133,114–122.

Hill,P.R.,2001.Useofcontinuousno-tillandrotationaltillagesystemsinthecentral andnorthernCornBelt.J.SoilWaterConserv.56,286–292.

Kettler,T.A.,Lyon,D.J.,Doran,J.W.,Powers,W.L.,Stroup,W.W.,2000.Soilquality assessmentafterweed-controltillageinano-tillwheat-fallowcroppingsystem. SoilSci.Soc.Am.J.64,339–346.

Koch,H.J.,Stockfisch,N.,2006.Lossofsoilorganicmatteruponploughingundera loesssoilafterseveralyearsofconservationtillage.SoilTill.Res.86,73–83. Lee,J.,Hopmans,J.W.,Rolston,D.E.,Baer,S.G.,Six,J.,2009.Determiningsoilcarbon

stockchanges:simplebulkdensitycorrectionsfail.Agric.Ecosyst.Environ.134, 251–256.

Liebig,M.A.,Tanaka,D.L.,Wienhold,B.J.,2004.Tillageandcroppingeffectsonsoil qualityindicatorsinthenorthernGreatPlains.SoilTill.Res.78,131–141. Luo,Z.,Wang,E.,Sun,O.J.,2010.Canno-tillagestimulatecarbonsequestrationin

agriculturalsoils?Ameta-analysisofpairedexperiments.Agric.Ecosyst. Envi-ron.139,224–231.

Melero,S.,López-Garrido,R.,Madejón,E.,Murillo,J.M.,Vanderlinden,K.,Ordón˜ez,R., Moreno,F.,2009.Long-termeffectsofconservationtillageonorganicfractions intwosoilsinsouthwestofSpain.Agric.Ecosyst.Environ.133,68–74. Melero,S.,Panettieri,M.,Madejón,E.,Macpherson,H.G.,Moreno,F.,Murillo,J.M.,

2011.Implementationofchisellingandmouldboardploughinginsoilafter8 yearsofno-tillmanagementinSWSpain:effectonsoilquality.SoilTill.Res. 112,107–113.

Ogle,S.M.,Breidt,F.J.,Paustian,K.,2005.Agriculturalmanagementimpactsonsoil organiccarbonstorageundermoistanddryclimaticconditionsoftemperature andtropicalregions.Biogeochemistry72,87–121.

Omonode,R.A.,Gal,A.,Stott,D.E.,Abbey,T.S.,Vyn,T.J.,2006.Shorttermversus continuouschiselandno-tilleffectsonsoilcarbonandnitrogen.SoilSci.Soc. Am.J.70,419–425.

Parton,W.J.,Schimel,D.S.,Cole,C.V.,Ojima,D.S.,1987.Analysisoffactors control-lingsoilorganicmatterlevelsinGreatPlainsgrasslands.SoilSci.Soc.Am.J.51, 1173–1179.

Pierce,F.J.,Fortin,M.C.,Staton,M.J.,1994.Periodicplowingeffectsonsoilproperties inano-tillfarmingsystem.SoilSci.Soc.Am.J.58,1782–1787.

Quincke,J.A.,Wortmann,C.S.,Mamo,M.,Franti,T.,Drijber,R.A.,2007.Occasional tillageofno-tillsystems:carbondioxidefluxandchangesintotalandlabilesoil organiccarbon.Agron.J.9,1158–1168.

Sans,F.X.,Berner,A.,Armengot,L.,Mäder,P.,2011.Tillageeffectsonweed commu-nitiesinanorganicwinterwheat–sunflower–speltcroppingsequence.Weed Res.51,413–421.

Sharma,P.,Abrol,V.,Sharma,R.K.,2011.Impactoftillageandmulchmanagementon economics,energyrequirementandcropperformanceinmaize-wheatrotation inrainfedsubhumidinceptisols,India.Eur.J.Agric.34,46–51.

Stockfisch,N.,Forstreuter,T.,Ehlers,W.,1999.Ploughingeffectsonsoilorganic matterafter20yearsofconservationtillageinLowerSaxony,Germany.SoilTill. Res.52,91–101.

VandenBygaart,A.J.,Kay,B.D.,2004.Persistenceofsoilorganiccarbonafterplowing along-termno-tillfieldinsouthernOntario,Canada.SoilSci.Soc.Am.J.68, 1394–1402.

Virto,I.,Barré,P.,Burlot,A.,Chenu,C.,2011.Carboninputdifferencesasthemain factorexplainingthevariabilityinsoilorganicCstorageinno-tilledcompared toinversiontilledagrosystems.Biogeochemistry108,17–26.