Impact of organic no-till vegetables systems on soil organic matter in the Atlantic Forest biome.

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ContentslistsavailableatScienceDirect

Scientia Horticulturae

j o u r n a l ho me p a g e :w w w . e l s e v i e r . c o m / l o c a t e / s c i h o r t i

Impact of organic no-till vegetables systems on soil organic matter in the Atlantic Forest biome

A. Thomazini

^a,∗

, E.S. Mendonc¸ a

^a

, J.L. Souza

^b

, I.M. Cardoso

^c

, M.L. Garbin

^a

aDepartmentofPlantProduction,FederalUniversityofEspíritoSanto,29500-000Alegre,ES,Brazil

bResearchofINCAPER—CentroSerrano,BR-262,km94,29.375-000VendaNovadoImigrante,ES,Brazil

cSoilScienceDepartment,FederalUniversityofVic¸osa,AvenidaP.H.Rolfs,s/n,Vicosa36570-000,MG,Brazil

a r t i c l e i n f o

Articlehistory:

Received25August2014 Receivedinrevisedform 25November2014 Accepted1December2014

Keywords:

Greenmanure

Labileandstablefractions Soilhealth

SoilCbalance

a b s t ra c t

Soilorganicmatteriswidelyrecognizedasastrategyusedtoimprovesoilqualityandreducecarbon emissionstotheatmosphere.Aﬁeldstudywascarriedouttoinvestigatetheeffectsofcovercropsin organicno-tillvegetablessystemsonchangesinsoilorganicmatterandCO2 Cemissions,indryand rainyseasons.WehypothesizedthatCO2 Cemissionsarehigherinconventionaltillascomparedwith no-till,andthatno-tillincreasessoilCsink.Thecroprotationcompriseda3-yearcroppingsequence involvingtwocropsperyear—cabbage(BrassicaoleraceaL.)inwinterandeggplant(Solanummelongena L.)insummertime.Treatmentswereno-tillondeadmulchofgrass(AvenastrigosaSchreb.andZeamays L.),leguminous(LupinusalbusL.andCrotalariajunceaL.),intercrop(grassandleguminous)andconventionaltill(nodeadmulch)withrotaryhoearrangedinarandomizedblockdesignonaclayeyOxisol(Typic Haplustox)atDomingosMartins-ES,Brazil.On2012and2013,disturbedsoilsamplesatthreedifferent layers(0–5,5–15and15–30cm)andundisturbedsamplesat0–10,10–20and20–30cm,forchemical andorganicmattercharacterizationweretaken.CO2 Cemissionsandsoiltemperatureweremeasured insituonMarch,May,AugustandOctober2012andFebruary2013(after3yearsofexperiment).Con- ventionaltillsiteshowedthelowestmicroporosityvaluesandthehighestmacroporosity,followedby lowersoilbulkdensityat0–10cmlayer.TotalorganicCrangedfrom34.94to50.48gkg⁻¹inintercrop and27.11to43.74gkg⁻¹inconventionaltill.TotalNrangedfrom2.81to5.34gkg⁻¹ingrassand2.54 to4.51gkg⁻¹inconventionaltill.HighestCstockwasrecordedinintercrop.Conventionaltillshowed lowerlabileCvalueswhilerecalcitrantCwashigherintheintercroptreatment.Theannualaverageof CO2 Cemissions(␮molCO2m⁻²s⁻¹)followedtheorder:grass(15.89)>intercrop(13.77)>leguminous (13.09)>conventionaltill(11.20).Highestannualaverageofsoiltemperaturewasrecordedinconven- tionaltill(23.95^◦C).Lowestannualmeanofsoilwatercontent,microbialbiomassC,andhighestmetabolic quotientwererecordedinconventionaltill.Theseresultssuggestthattheuseofcovercropsandorganic compostinpre-plantingpromoteCincrements.Thecontributionoforganicresiduesincreasesthewater holdingcapacityandreducessoiltemperature.No-tillreducessoildisturbanceandpromotesapositive balanceofC.Organicno-tillvegetablesystemsisastrategytoincreasesoilCandshouldbeencouraged inordertoincreasesoilqualityintheAtlanticForestBiomeinBrazil.

1. Introduction

TheBrazilianAtlanticForestisnowreducedtoabout11.4to16%

ofitsoriginalcoverofapproximately150millionhectares(Ribeiro etal.,2009).Mostdeforestedareasarecomposedofagricultural

∗Correspondingauthor.Tel.:+552733593971;fax:+552835528927.

E-mailaddresses:andre.thz@gmail.com(A.Thomazini),

eduardo.mendonca@ufes.br(E.S.Mendonc¸a),jacimarsouza@yahoo.com.br (J.L.Souza),irene@ufv.br(I.M.Cardoso),mlgarbin@gmail.com(M.L.Garbin).

systemsondegradedsoils.Anthropogenicactivitiesleadtoland misuse causingchangesinthephysical,chemicalandbiological attributesofsoils(Reicoskyetal.,1999;Powlsonetal.,2011).This impliesdecreasesinthestorageoforganiccarbonandnutrientsas wellasintheproductivecapacityofsoils,sinceCisanindicator usedtoassesssoilquality(SilvaandMendonc¸a,2007;Ghoshetal., 2012).

Itiswidelyrecognizedthatsoilorganicmatterisoneofthemost importantindicatorsofsoilqualityandhealth(Lal,2004;Ghosh etal.,2012).Increasingormaintainingsoilorganicmatteriscriti- caltoachieveoptimumsoilfunctionsandcropproduction(Ghosh http://dx.doi.org/10.1016/j.scienta.2014.12.002

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etal.,2012).Whenmonitoringsoilqualityinthetropics,sensitive soilqualityindicatorsneedtobeidentified,mainlyduethecontin- uousandintensivevegetableproductionintheseareas(Moeskops etal.,2012).Soilmanagementcanleadtohigherdecomposition ratesoforganicmatterdecreasingtheconcentrationofthissoil component(SilvaandMendonça,2007).Agriculturecansignifi- cantlycontributetoelevateatmosphericCO₂ concentrationsasa consequenceofsoilmanagement(Powlsonetal.,2011).TheseC lossestotheatmospherecanbemainlyreducedbyminimizing soildisturbance,eitherwithno-tilloragroecologicalmanagement (SilvaandMendonça,2007).Itisestimatedthat89%ofthepotential formitigationofgreenhousegasesproducedbyagriculturerelies onCsequestration(Smithetal.,2008).Inaddition,increasingthe soilorganicCcontentisanimportantstrategytodealwithclimate changesdrivenbyCemissionstotheatmospherefromagricultural lands.

No-tillandorganicagricultureincreasesoilCandNsequestra- tion,andreducetheoxidationofsoilorganicmatter(Bayeretal., 2009;Campigliaetal.,2014).Continuousinputofplantresidues andpaucityofsoildisturbancepromotereductionsinCO₂ Cemis- sions through decreasesin organicmatter decomposition rates (Lal,2004;Bayeretal.,2009).Onotherhand,conventionalcrop production intensify soil disturbanceand, consequently,break- downthesoilaggregates(Bayeretal.,2009).Conventionaltillage isthemostcommonagriculturalmanagementforvegetablepro- ductioninareasformerlyoccupiedbytheAtlanticForestinBrazil.

Inaddition,vegetableproductionishistoricallymanagedbyfamily smallholders.Intensivefarmingorintensivesoilpreparationinhor- ticulturedegradesthesoil–plantenvironment,mostlyduetothe reductioninconcentrationandqualityofsoilorganicmatterand thediversityofsoilorganisms(Tianetal.,2011).Degradationofsoil organicmatterleadstolong-termdecreasesinhorticulturalpro- ductivity.Thus,sustainabletillageispreferabletoattainapositive netbalanceofCinthehighlyweatheredtropicalsoils(Mendonc¸a andRowell,1996).

Theuseofcovercropsrepresentapotentiallyvaluablesupply oforganicresidues(Csource) whentheyareused inno-tillage systemsandtheirresiduesareleftonthesoilsurface(Campiglia etal.,2014).No-tillsystemscanmitigateCO₂ Cemissions.Thisis becausecroprotationandorganicresiduesonsoilsurfacepromote gradualdecompositionoforganicmatter,favoringCincorporation (Bayeretal.,2009;Conceic¸ãoetal.,2013).Physicalprotectionof organicmatterprovidedbystableaggregatesunderno-tillreduce organicmattermineralizationandleadtoCaccumulation(Sixetal., 2004).However,thereisalackofinformationaboutCstoragegains and CO₂ C soil emissionsby organicno-till vegetablesystems, especiallyin theareasformerlyoccupiedbytheAtlanticForest biome,awell-knownbiodiversityhotspot(Myersetal.,2000).Here, wereporttheresultsofalongtermﬁeldexperimentconducted indryandrainyseasons.Weaimedtoinvestigatetheeffectsof covercrops inorganicno-till vegetablessystems onchangesof soilorganicmatterandCO₂ Cemissions,indryandrainyseasons.

WehypothesizedthatCO₂ Cemissionsarehigherinconventional tillascomparedwithno-till,andthatno-tillincreasessoilCsink, leadingtoimprovedsoilquality.

2. Materialandmethods

2.1. Sitelocation,characterizationandlandusespriortothe experiment

The study was carried out at the 2.5ha organicagriculture experimentalsiteofIncaper(EspíritoSantoInstituteforResearch, TechnicalAssistanceandRuralExtension),municipalityofDomin- gosMartins-ES (20^◦22SE41^◦03W)altitudeof950mabovethe

Fig.1. Averagemonthlyprecipitationandairtemperatureofthemunicipalityof DomingosMartinsbetweenJanuary2012andFebruary2013.DatafromIncaper.

sea.TheclimateoftheregionisAw(tropicalclimateanddrysea- soninwinter),precipitationrangesfrom750to1500mmperyear, andallmonthsoftheyearhaveaveragetemperaturesof18^◦Cor higher.Theregionischaracterizedbydrywinterandrainysummer (Köppen,1923).Meanmonthlyprecipitationandairtemperature are presented in Fig.1. Soilis classified asRed-Yellow Latosol, BrazilianClassificationSystem(Embrapa,2006)orasclayeyOxisol, TypicHaplustox(SoilTaxonomy,USDAclassification).From1990to 2009,thisareawascultivatedwithorganicvegetables(mainlylet- tuce,cabbageandeggplant).Organicmanagementwasperformed using15Mgha⁻¹oforganiccompost(drymass)amendments.The composting areafollowed theindore system(Miller and Jones, 1995)withalternatinglayersstackedformingcellsthatreceived manualeversionperiodicallyinordertocontrolhumidity(50%) and temperature(60^◦C).The methodreliesonaerobic activity, althoughportionsofthepilecanbecomeanaerobicbetweenturn- ings. Moreover, it provides better control of flies, more rapid and uniform decomposition rates and less problems regarding moisturecontrol(MillerandJones,1995).Thecompostwaspre- paredwithastackedmixtureof:groundedgreencamerongrass (PennisetumpurpureumSchumach.),coffeehusk,cropresiduesof maize and beans, and inoculation with chicken manure at the rate of 50kgm⁻³. Organic compost characteristics were (total amount):52%organicmatter,16:1carbon:nitrogenratio,7.3pH,2%

nitrogen,1.2%phosphorus,1.2%potassium,4.8%calcium,0.5%magnesium,54mgdm⁻³ copper, 188mgdm⁻³ zinc,12,424mgdm⁻³ iron,793mgdm⁻³manganese,25mgdm⁻³boron.Moredetailsof theorganicvegetablecropping(1990–2009)canbefoundinSouza etal.(2012).

2.2. Experimentaldesign,covercropsandcroprotation

Theorganicno-tillvegetablessystemsexperimentwasinitiated in 2009.Theexperiment comprisesfourtillagesystems,imple- mentedon4m×6mplots,accordingtoaRandomizedComplete BlockDesign,withsixreplicates(totalizing24permanentexperi- mentalunits)coveringatotalareaof576m².Therefore,theeffects oforganicmanagementaccumulatedovertheyears.Tillagetreat- mentsconsistedof:

(i)No-tillondeadmulchofgrass(grass):blackoat(Avenastrigosa Schreb)wasusedaswintercovercropfollowedbymaize(Zea maysL.)assummercovercrop.

(ii)No-tillondeadmulchofleguminous(leguminous):whitelupin (Lupinusalbus,L.)wasusedaswintercovercropfollowedby Sunnhemp(CrotalariajunceaL.)assummercovercrop.

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(iii) No-tillondeadmulchofgrass andleguminous (intercrop):

grassandleguminousplantswereintercroppedusingthesame covercropsingrassandleguminoustreatments.

(iv)Conventional plow-based tillage (Conventionaltill): imple- mentedusingconventionaltillagewithrotaryhoeoneweek beforeplanting,withnocovercrop.Thetractorusedwasarear rotaryminitiller(YanmarMRT-650EX)withtherotarytines placedrightbehindthewheels.Thisisthemainvegetablecrop- pingsystemoftheBrazilianhorticulture(Souzaetal.,2012).

Operationscheduleconductedannuallyintheno-tillandcon- ventionaltillwerepresentedinTable1.From2009to2013,no-till wasperformedwithblack oatand whitelupinas wintercover crop, followed bycabbageaswinter vegetablecrop. Maizeand sunnhempworkedassummercovercrop,followedbyeggplantas summervegetablecrop.Blackoatandwhitelupinweresownon March2012aswintercovercrops.Covercropseedswerespread manuallyandlightlyburied.Covercropsweresowninrowsspaced 33cmfromeachotherforalltreatments.Theseedrateswere480g perplotforblackoatand660gperplotforwhitelupin.Intheinter- croppedsamplingunits,seedswerereducedtohalfofthesevalues.

OnJuly2012,covercropsweremowedbymechanicalmowingand cabbagewasplanted.Covercropresidueswereleftonthesoilsur- faceasorganicdeadmulchandtheywerenotincorporatedintothe soil.Onemontholdcabbageseedlingsweretransplantedbyhand.

Thecabbageseedlingswerearrangedinsinglerowsdistant60cm fromeachother.Thedistancebetweenthecabbageplantsinthe rowswas40cm.

Afterwintercrop,maizeandsunnhempweresownonOctober 2012assummercovercrops.Theseedrateswere600gperplotfor maizeand300gperplotforsunnhemp.Residuesweremowedon February2013followedbyeggplant(Solanummelongena)planting.

Eggplantseedlingsweregrownintubesof180cm³,usingamixture oforganiccompost/soilof1:2assubstrate.Theeggplantseedlings werearrangedinsinglerowsatadistanceof120cmbetweenthem.

Thedistancebetweenthecabbageplantsintherowswas70cm.

Cabbageandeggplantreceived15Mgha⁻¹oforganiccompost(dry mass)atplantinginallno-tilltreatments.Cabbageandeggplant seedlingswereirrigatedimmediatelyaftertransplantinginorder toavoidmoisturestress.Insidetherows,theweedswereremoved manuallywhenevernecessary.

2.3. Soilsampling

SoilwassampledinMarch2012,attheendof2011summer crop. Ineach plot,onedisturbed soilsample(atthree different layers;0–5,5–15and15–30cm,usingDutchaugers)andoneundis- turbedsoilsample(0–10,10–20and20–30cm,bythevolumetric ringmethod)weretaken(Embrapa,1997).Thesoilsampleswere airdried,groundedandsievedthrougha2-mmsievetoremove largerpiecesofrootmaterialandthestonefraction.Allsoilsam- pleswereanalyzedinthesoillaboratoryattheFederalUniversity ofEspíritoSanto,AgricultureScienceCenter.

2.4. Soilchemicalandphysicalcharacterization

SoilchemicalandphysicalcharacterizationisgiveninTable2.

ThepHwasdeterminedona 1:5soil:deionisedwaterratio;the potentialacidity(H+Al)wasextractedwithCa(OAc)₂ 0.5molL⁻¹ buffered to pH 7.0, and quantiﬁed by titration with NaOH 0.0606molL⁻¹.ExchangeableCa²⁺,Mg²⁺andAl³⁺wereextracted with1molL⁻¹KClandNaandKwereextractedwithMehlich⁻¹ (Embrapa,1997).Theelementcontentintheextractsweredeter- minedbyatomicabsorption(Ca²⁺,Mg²⁺andAl³⁺),ﬂameemission (KandNa)andphotocolorimetry(P).Theeffectivecationexchange capacity(CEC_E)wascalculatedbysumofcations(Ca²⁺,Mg²⁺,Na⁺,

K⁺andAl³⁺)andtotalcationexchangecapacity(CTCT)estimatedby thesumofbasesandpotentialacidity.Thegranulometricanalysis wasperformedbypipettemethod,50rpm,16h(Embrapa,1997).

2.5. CovercropbiomassandCinput

Covercropbiomasswascollectedinsidea1×1msquareineach plotforfreshmassdetermination.Further,itwasdriedinoven withcontinuousaircirculation(60^◦C)fordrymassdetermination.

Totalcarbonofcovercropbiomasswasanalyzedbylossinigni- tionat430^◦Cfor24hinmufﬂefurnace(Kiehl,1985).Aproportion of950gCkg⁻¹biomassforwhitelupinandsunnhemp,920gCkg⁻¹ biomassforblackoatandmaizeand935gCkg⁻¹biomassforinter- cropwerefoundafteranalysis.Thefactorof 1.724wasusedto convertorganicmatteroforganiccompostintoorganicCbasedon theassumptionthatorganicmattercontains580gCkg⁻¹biomass (CarmoandSilva,2012;SoilSurveyStaff,1996).

2.6. Soilphysicalattributes

Undisturbedsoilsamplesweresaturatedinwaterfor24hand thenplacedinasandtensiontableof−6kPa.Soilmicroporosity (M_ic)wascalculatedafterstabilizationofwaterintothevolumet- ricring(72h).Bulkdensity(BD)wasperformedbythevolumetric ringmethodandparticledensity(PD)wasdeterminedbythevol- umetric ﬂaskmethod(Embrapa,1997).Totalporosity (TP) was calculatedusingthefollowingequation:

TP=1−

_BD

PD

(1) where BD is bulk density (gcm⁻³) and PD is particle density (gcm⁻³). Macroporosity(Map) wascalculated as the difference betweentotalporosityandmicroporosity(Embrapa,1997).

2.7. Soilorganiccarbonandnitrogen

Soilsubsamplesofapproximately20gwerecrushedinamortar topassa250␮mmesh,andthenanalyzedfortotalsoilorganiccar- bon(totalorganicC),totalnitrogen(totalN),labilecarbon(C_labil) andrecalcitrantcarbon(C_recal).TotalsoilorganicCwasperformed bywetoxidationwithK₂Cr₂O₇ 0.167molL⁻¹ inthepresenceof sulfuricacidwithexternalheating(YeomansandBremner,1988).

TotalNwasobtainedbysulfuricaciddigestionfollowedbyKjel- dahl distillation(Bremmerand Mulvaney, 1982;Tedesco et al., 1995).ThefractionsofsoilorganicCwereestimatedthrougha modiﬁedWalkelyandBlackmethodasdescribedbyChanetal.

(2001)using2.5,5and10mLofconcentratedH₂SO₄resultingthree acid–aqueoussolutionratiosof0.25:1,0.5:1and1:1(whichcorre- sponded,respectivelyto3,6and9molL⁻¹ H2SO4).Theamount of soilorganicC determinedusing2.5, 5and 10mLof concen- tratedH₂SO₄whencomparedwithtotalC,allowedseparationof totalCintothefollowingfourfractionsofdecreasingoxidizability:

FractionI(verylabile)organicCoxidizableunder3molL⁻¹H₂SO₄; FractionII(labile)thedifferenceinsoilorganicCextractedbetween 6and3molL⁻¹H2SO4;FractionIII(lesslabile)thedifferenceinsoil organicCextractedbetween9and6molL⁻¹H₂SO₄;andFractionIV (non-labile)residualorganicCafterreactionwith9molL⁻¹H₂SO₄ whencomparedwithtotalC.ThesumoffractionsIandIIcorre- spondstothelabile CandthesumoffractionsIIIandIVtothe recalcitrantC(Chanetal.,2001).Becauseofpossiblechangesin bulkdensityasaresultofcroppingsystemandorganicfertiliza- tion,theCandNstocks(0–30cm)werecalculatedonamassper unitvolumebasis(EllertandBettany,1995),takingthesoilmass oftheconventionaltillascontrol.

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Table1

Operationalscheduleconductedannuallyintheno-tillandconventionaltilltreatmentsfrom2009to2013.

---2012--- ----2013---

Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec Jan Feb

---Summer--- ---Fall--- ---Winter--- ---Spring--- ---Summer--- Soil sampling¹

Soil CO2-C emission and soil sampling²

Winter crop - Cabbage Cover crop sown³

Cover crop mowed Cabbage planting Plowing- Rotary hoe⁴ Organic compost Hand weeding

Summer crop - Eggplant Cover crop sown⁵

Cover crop mowed Eggplant planting Plowing- Rotary hoe ⁴ Organic compost

1DeterminationoftotalorganicCandN,recalcitrantandlabileC;²DeterminationofmicrobialbiomassC,solubleCandwatercontentofsoil;³BlackoatandWhitelupin;

4Onlyforconventionaltilltreatmentandtherewasnocovercropinconventionaltill;⁵MaizeandSunnhemp;DatesofsoilCO2 Cemissionandsoilsampling²:14/03/12;

22/05/12;10/08/12;2510/12;06/02/13.

2.8. SoilCO₂ Cemissionandsoiltemperature

MeasurementsofCO₂ CemissionsweremadeonMarch,May, August,October2012andFebruary2013.CO₂ Cemissionswere measuredusingaportableLI-8100analyzer(LiCor,EUA)coupled toadynamicchamber(LI-8100-102),knownassurveychamber, having10cmdiameterplacedonPVCsoilcollarsinsertedinthe soil(5cmdepth)beforetheexperiment.Measurementswerebased onsixreplicatesin each treatmentandlasted forover 1.5min, duringwhichtimemeasurementsofCO₂ Cconcentrationswere madeinside thechamberat 3-sintervals.AnnualCO₂ C emissions werecalculated basedon themeanof allmeasurements.

Soiltemperatures(5.0cmdepth)weredeterminedduringthegas ﬂuxmeasurements.TherelationbetweenCO₂ C(FCO₂ C)andsoil temperature(T_soil)wasdescribedbythefollowingequation:

FCO2=F0×exp(b×Tsoil), (2)

with the natural log (Ln) of the CO2 C emission we have Ln(FCO₂ C)=Ln(F0×exp(b×T_soil)), the result is Ln(FCO₂ C)=Ln(F0)+b×T_soil. A linear relationship between

Ln(FCO₂ C)andtheT_soilisexpectedwheresoiltemperatureisa limitingfactor.Basedonthebcoefﬁcientsitispossibletoderive theQ₁₀factor,whichrepresentsthepercentageincreaseinCO₂ C emissionfora10^◦Cincreaseinsoiltemperature.Thisisderivedas Q10=e¹⁰^×^b(Carvalhoetal.,2012).

2.9. SoilwatercontentandmicrobialbiomassC

Ineachplot,disturbedsoilsampleswerecollectedat5cmdepth todeterminatesoilwater content,microbialbiomass C,soluble carbon(C_sol)andmetabolic(Qmet)andmicrobialquotient(Q_mic).

SoilsampleswerecollectedinMarch,May,August,October2012 andFebruary2013.Thethermogravimetricmethod(105–110^◦C for 24h) was usedto determine soil water content (according toEmbrapa,1997).TheCcontentinthemicrobialbiomasswas determinedbytheirradiation-extractionmethod(accordingtothe methodologydeveloped byFerreiraet al.,1999).TheC content extractedby0.5MK2SO4(calibratedpH6.5–6.8)innon-irradiated sampleswasusedtoestimatesolubleC.Metabolicquotientwas determinedbytheratiobetweenthesoilCO₂ Cemissionrateper Table2

Chemicalandphysicalcharacterizationofthesoilsunderdifferentmanagementsystemsintheexperimentalsite.

Treatment pH P K Na Ca Mg Al CECT V Sand Silt Clay

H2O mgdm⁻³ cmolcdm⁻³ % gkg⁻¹

0–5cm

Grass 6.40 2774.80 324.00 35.33 4.15 1.56 0.00 11.86 56.45 580.34 122.04 297.61

Leguminous 6.44 2882.95 328.67 22.83 4.61 1.42 0.00 11.48 61.32 524.07 139.98 335.95

Intercrop 6.43 3243.03 490.00 92.33 4.76 1.74 0.00 8.16 100.00 497.24 144.25 358.51

Conventionaltill 6.51 3224.14 360.50 68.00 8.04 2.43 0.00 16.25 72.22 461.87 138.25 399.87

5–15cm

Grass 6.37 1676.10 347.67 20.50 4.11 1.13 0.00 11.09 55.85 583.38 113.82 302.80

Leguminous 6.35 1293.10 304.83 14.83 4.11 1.10 0.00 9.83 63.14 557.35 117.05 325.60

Intercrop 6.32 1389.63 285.50 22.33 4.87 1.14 0.00 6.83 100.00 485.70 130.17 384.12

15–30cm

Grass 6.35 778.96 230.67 11.67 3.12 0.89 0.00 9.08 51.11 616.70 89.44 293.87

Leguminous 6.48 661.15 285.50 6.83 3.44 0.75 0.00 4.95 100.00 580.98 106.35 312.67

Intercrop 6.23 475.30 247.33 3.33 2.87 0.77 0.00 4.29 100.00 495.64 127.69 376.68

Grass:no-tillondeadmulcheofgrass;leguminous:no-tillondeadmulcheofleguminous;intercrop:no-tillondeadmulcheofgrassandleguminous;pH:activeacidity;P:

phosphorus;K:potassium;Na:sodium;Ca:calcium;Mg:magnesium;Al:aluminum;CECT:totalcationexchangecapacity;V:saturationofbases.

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Table3

Meanvaluesoffreshmass,drymassproductionandCinputduringwinterand summercovercrop.

Greenmanure Freshmass Drymass Cinput

Mgha⁻¹ Wintercrop

Blackoat 37.86a 9.09a 4.85a

Whitelupin 28.54b 6.61a 3.65a

Intercropping 37.33a 8.34a 4.52a

Summercrop

Maize 63.51a 21.80a 11.64a

Sunnhemp 28.64c 10.69b 5.90b

Intercropping 46.21b 16.48ab 8.94ab

Meansfollowedbythesameletter,inthesamecolumn,donotdifferbyTukey’stest (p<0.05).Cinput=Cdrymassofcovercrop+Coforganiccompost.

microbialbiomassCunit.Microbialquotientwascalculatedbythe ratiobetweenmicrobialbiomassCandtotalsoilorganicC(Ferreira etal.,1999).

2.10. CbalanceandCO2equivalent

Carbonbalancewascalculatedbydifferencebetweenannual averageof CO₂ C emissionsand C input(organiccompost and greenmanure).Asvegetablescrophadsimilaryieldsandthussim- ilarvaluesofcropresidues,theCinputaccountedreferstotheC ofgreenmanuresandorganiccompost.Theequivalencebetween CandCO2wasbasedonthemolecularweightsoftheelements,in whichonemolofCO₂contains12.011gC.

2.11. Dataanalysis

PearsoncorrelationswereperformedbetweensoilCO₂ Cemis- sions, soil water content and soil temperature between no-till andconventionaltill.Dataweresubmittedtoanalysisofvariance (ANOVA)andmeansbetweentreatmentswerecomparedusingthe leastsigniﬁcantdifferenceofaTukeytest(p<0.05)intheSAEGsoft- ware(Funarbe,2007).Split-plotanalysisofvarianceforsoilCO₂ C emission,soiltemperature,soilwatercontent,microbialbiomass C,solubleC,metabolicquotientandmicrobialquotientwereper- formed.Standarderrorwascalculatedfromthestandarddeviation ofthedatasetofallreplicates.

3. Results

Meanvaluesoffreshmass,drymassproduction andCinput ofcovercropsaregiveninTable3.Duringthewintercrop,fresh massproductionofwhitelupinwassignificantlylowerthanblack oatandintercrop.Nosignificantdifferenceswererecordedinwin- ter cropfordry massproductionand C input.Insummercrop, freshmassproductionofmaizewassignificantlyhigherthanthat ofsunnhemp.Thisresultwasalsoobservedfordrymassproduc- tion.TheCinputwassignificantlyhigherinmaizeplotsthanthe sunnhempplotsinsummercrop.

Microporosity(M_ic), macroporosity (Mac), total porosity(TP), bulk density (BD) and particledensity (PD)values aregiven in Table4. Highermicroporosityvalues wererecordedat0–10cm layer for all plots. Conventional till showedsigniﬁcantly lower (p<0.05)microporosityandhighermacroporosityascomparedto theno-tilltreatment.Therewerenodifferencesbetweenno-till andconventionaltillupto20cmdepthfortotalporosity.Theratio betweenmacroporosityandtotalporosityindicatesthatno-tillhas higherwaterholdingcapacity.Bulkdensitytendedtoincreasewith soildepth.

MeanvaluesoftotalorganicC,totalN,C/Nratio,labileCand recalcitrantCaregiveninFig.2.Ingeneral,asdepthincreased,total organicC,totalN,C_labilandC_recaltendedtodecrease.The0–5cm layer had the highest C and N contents. Higher (p<0.05) total organicCwasrecordedintheintercroptreatment(50.48gkg⁻¹)as comparedtoconventionaltillat0–5cmlayer(43.74gkg⁻¹).There wasnostatisticaldifferencefortotalNamongalllayersevaluated.

TotalNrangedfrom2.81to5.34gkg⁻¹ingrasswhileinconven- tionaltillitrangedfrom2.54to4.51gkg⁻¹.TheC/Nratiotendedto increasewithincreasingsoildepth.IntercropshowedhigherC/N ratioforallsampledsoillayers.Conventionaltillshowedsigniﬁ- cantlylowermeansofC_labilascomparedwithgrassupto15cm soildepth.HigherC_recalwasrecordedfortheintercropwhencom- paredwithgrass at0–5and15–30cmlayer.C_recal tendedtobe higher at5–15cm layerfortheintercrop whencompared with grass. However, nostatistical signiﬁcance wasobserved. C and Table4

Meanvaluesofmicroporosity(Mic),macroporosity(Mac),totalporosity(TP),bulkdensity(BD)andparticledensity(PD)amongdifferentvegetablecroppingsystems.

Treatment Mic Mac TP Mac/TP BD PD

m³m⁻³ gcm⁻³

0–10cm

Grass 0.47a 0.16b 0.63a 0.25b 0.98a 2.70a

Leguminous 0.48a 0.16b 0.64a 0.25b 0.98a 2.71a

Intercrop 0.48a 0.14b 0.61a 0.22b 0.99a 2.57b

Conventionaltill 0.41b 0.24a 0.65a 0.36a 0.95a 2.72a

10–20cm

Grass 0.42a 0.16a 0.57a 0.27a 1.15a 2.72ab

Leguminous 0.42a 0.16a 0.58a 0.28a 1.12a 2.65b

Intercrop 0.42a 0.19a 0.61a 0.31a 1.15a 2.92a

Conventionaltill 0.41a 0.18a 0.59a 0.31a 1.14a 2.81a

20–30cm

Grass 0.41a 0.13b 0.54b 0.24b 1.19ab 2.61b

Leguminous 0.42a 0.13b 0.55ab 0.24b 1.21a 2.73ab

Intercrop 0.42a 0.16ab 0.58ab 0.27ab 1.19ab 2.83a

Conventionaltill 0.42a 0.18a 0.60a 0.31a 1.13b 2.83a

Grass:no-tillondeadmulcheofgrass.Leguminous:no-tillondeadmulcheofleguminous.Intercrop:no-tillondeadmulcheofgrassandleguminous.Meansfollowedby thesameletter,inthesamecolumn,donotdifferbyTukey’stest(p<0.05).

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Fig.2.Meanvalues(n=6)oftotalorganicC(a),totalN(b),C/Nratio(c),labileC(d)andrecalcitrantC(e)inthedifferentplantingsystems.Meansfollowedbythesame letter,didnotdifferbyTukey’stest(p<0.05).Horizontalbarsrepresentstandarderrorofthemean.Grass:no-tillondeadmulchofgrass.Leguminous:no-tillondeadmulch ofleguminous.Intercrop:no-tillondeadmulchofgrassandleguminous.

N stockvalues in thedifferentvegetablesplantingsystems are giveninTable5.Cstocksweresigniﬁcantlyhigherintheinter- crop(131.2Mgha⁻¹)whencomparedwiththeothertreatments.

Conventional till showed C stock of 105Mgha⁻¹. N stock was 12.2Mgha⁻¹ingrassand10Mgha⁻¹inconventionaltill.

3.4. SoilCO₂ Cemissionandsoiltemperature

CO₂ CemissionsandsoiltemperaturevaluesaregiveninFig.3.

LowestCO₂ CemissionswererecordedinallplotsduringMay Table5

Carbonandnitrogenstocksvaluesinthedifferentplantingsystems(Mgha⁻¹)inthe sampledsoilproﬁle(0–30cm).

Treatment Grass Leguminous Intercrop Conventionaltill

Carbonstock 115.8b 110.9b 131.2a 105b

Nitrogenstock 12.2a 10.4a 10.4a 10a

Grass:no-tillondeadmulcheofgrass.Leguminous:no-tillondeadmulcheofleguminous.Intercrop:no-tillondeadmulcheofgrassandleguminous.Meansfollowed bythesameletter,inthesamerow,donotdifferbyTukey’stest(p<0.05).

and August2012(Fig.3a).Meanannual CO₂ C emissionswere 4.2; 3.64; 3.46 and 2.96␮mol CO2m⁻²s⁻¹ in grass, intercrop, leguminous andconventional till,respectively. Thesevaluesare equivalenttoanannualefﬂuxof15.89;13.77;13.09and11.20Mg C CO₂ha⁻¹year⁻¹,respectively.SigniﬁcantlylowerCO₂ Cemis- sions were recorded in the conventional till treatment during March2012,ascomparedwithothertreatments.CO₂ Cemission valuesgraduallyincreasedfromMay2012toFebruary2013.Dur- ingFebruary2013,theaverageCO2 Cemissionswerehigherinthe conventionaltill,withnodifferencesamonggrassandintercrop.

Soiltemperature showedsimilarseasonaldynamics,presenting loweraveragesinthewinter(August2012)andhighermeanval- uesin thesummer (March 2012and February 2013) (Fig. 3b).

Annual average soil temperature was 21.18; 21.15; 20.93 and 23.95^◦C for grass, leguminous, intercrop and conventional till, respectively. Signiﬁcantlyhighersoiltemperature wasrecorded in conventional till for all study periods (except for October 2012), when compared with no-till treatments. The Q₁₀ factor waslowerintheintercropwhencomparedwiththeconventional till(Table6).Thelowestbparameterwasrecordedinintercrop

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Fig.3. CO2 Cemissions(a)andsoiltemperature(b)inthedifferentplantingsystems.Samecapitallettersindicatenosigniﬁcantdifferencesamongmonthsandsame lowercaselettersrepresentnosigniﬁcantdifferenceswithinmonthsforthedifferenttreatmentsbyTukey’stest(p<0.05).Verticalbarsrepresentstandarderrorofthemean.

Grass:no-tillondeadmulchofgrass.Leguminous:no-tillondeadmulchofleguminous.Intercrop:no-tillondeadmulcheofgrassandleguminous.

treatment,showinglesssensitivitytoincreasesinsoiltempera- ture.

3.5. SoilwatercontentandmicrobialbiomassC

Soilwatercontent,microbialbiomassC,solublecarbon(C_sol), metabolic (Q_met) and microbial quotient (Q_mic) are given in Fig. 4. The annual averagesoil water content (gg⁻¹) followed the order:intercrop (0.28gg⁻¹)>grass (0.27gg⁻¹)>leguminous (0.27gg⁻¹)>conventionaltill(0.20gg⁻¹).Significantlylowersoil water content wasrecorded in theconventional till,compared with those of no-till for all study periods (Fig. 4a). There was a significantassociation among soil water content, microbial biomass C, soluble C, metabolic and microbial quotient in the five periodsstudied. Microbialbiomass C decreased in the coldermonths(fromMaytoOctober2012)andincreasedinthe warmer period (after October 2012), which coincided with the highersoiltemperatures(Fig.3b)andsoilwatercontentvalues (Fig.4a).

AnnualaveragemicrobialbiomassCwas433.00;378.67;380.63 and246.77mgkg⁻¹ forgrass,leguminous,intercropandconventionaltill,respectively.For allstudyperiods,signiﬁcantlylower (exceptFebruary2013)microbialbiomassCwasrecordedincon- ventionaltill,comparedwiththoseoftheno-tillsystems(Fig.4b).

LowersolubleC contentswererecordedinAugust andOctober 2012(Fig.4c). AnnualaverageofsolubleCwas133.04;147.87;

126.75and 148.42mgkg⁻¹ forgrass,leguminous, intercropand conventionaltill,respectively.Therewerenodifferencesamong treatments for soluble C in August and October 2012. Lowest metabolicquotientwasrecordedduringMarch,MayandAugust, graduallyincreasingfromMay2012toFebruary2013(Fig.4d).

Annualaveragemetabolicquotientwas1.58;1.50;1.60and2.01 forgrass,leguminous,intercropandconventionaltill.Signiﬁcantly highermetabolicquotientwasrecordedintheconventional till

treatmentinOctober2012,comparedwiththeno-tilltreatments.

Signiﬁcantlylowermicrobialquotient(exceptFebruary2013)was recordedinconventionaltill.Annualaveragemicrobialquotient was9.69;7.84;7.54and5.64%forgrass,leguminous,intercropand conventionaltill.

3.6. CbalanceandCO₂equivalent

Cbalancebetweenannualinput(covercropandorganiccom- post) and annual losses(CO2 C emissions) are given in Fig. 5.

High C input in no-till is contributing to positive C balance.

The difference between C input and C emitted (CO₂ C emissions)was9.65;5.50and8.74Mgha⁻¹ inthegrass,leguminous and intercrop treatments, respectively. C balance was negative in conventional till (−2.15Mgha⁻¹), even withannual inputof 30Mgha⁻¹ organic compost. Carbon balance represents 35.38;

20.16 and 32.04Mgha⁻¹ year⁻¹ of CO₂ equivalent sequestered forgrass,leguminousandintercrop,respectively.Conventionaltill showednegativebalanceofCO2equivalent(7.88Mgha⁻¹year⁻¹).

4. Discussion

Cover cropbiomassproduction wassigniﬁcantlyaffected by theseason,reasonablyduetothevariationofclimaticconditions (Fig.1).Theaveragerainfallduringthesummercropping cycle (December–March)wasindeed85%higherthaninwintercrop- pingcycle(June–September).Theresultssuggestthathigherwater availabilityandincreasesintemperature(Fig.1)contributedtothe highcovercropbiomassproductionduringthesummercropby maize andsunnhemp, aswellasCinput.Theamountof above ground biomass produced is probablydue to moresuitable air temperaturesand rainfallwhichoccurredthroughoutthecover Table6

ParametersofthemodelbetweenCO2 Cemissionsandsoiltemperature,andQ10factorinthedifferentplantingsystemsduringthestudiedperiod.

Treatments Ln(CO2 Cemission)=a+(b×Tsoil)

a b R p Q10

Grass 1.070±0.184 0.016±0.008 0.341 0.065 1.170±0.189

Leguminous 0.494±0.193 0.034±0.009 0.582 <0.001 1.404±0.198

Intercrop 0.947±0.200 0.015±0.009 0.297 0.111 1.160±0.209

Conventionaltill 0.398±0.263 0.027±0.010 0.424 0.020 1.310±0.289

n=120,aandb:linearandangularcoefficients,respectively.R:correlationcoefficient.p:Significancelevel.Grass:grass:no-tillondeadmulcheofgrass.Leguminous:no-till ondeadmulcheofleguminous.Intercrop:no-tillondeadmulcheofgrassandleguminous.

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Fig.4.Watercontentofsoil(a),microbialbiomassC(b),solublecarbon(c),metabolic(d)andmicrobialquotient(e)inthedifferentplantingsystems.Samecapitalletter indicatenosigniﬁcantdifferencesamongmonthssampledandsamelowercaserepresentnosigniﬁcantdifferenceswithinmonthsforthedifferenttreatmentsbyTukey’s test(p<0.05).Verticalbarsrepresentstandarderrorofthemean.Grass:no-tillondeadmulchofgrass.Leguminous:no-tillondeadmulchofleguminous.Intercrop:no-till ondeadmulchofgrassandleguminous.

cropgrowingperiod.Grassespromotedhigherbiomassproduction andCinputthanleguminoustreatments.Itiswell-knownthatthe mostwidelyusedcovercropsaregrasses,whichareconsideredthe mostsuitablecovercropsandleguminousareappreciatedfortheir nitrogensupplytothevegetablecroppingsystem(Campigliaetal., 2014).Ourresultsareconsistentwithotherrecordsinthelitera- tureforcovercropbiomassproductionintropicalzones(Amado etal.,2006;Bayeretal.,2009).

Conventionaltillagepromotedincreasesinmacroporosityand decreasesinmicroporosityandbulkdensityattopsoil.Thisleadto highersoilaerationcapacityandlowerwaterholdingcapacity.The macroporositywasabovethecriticallevelforgaseousexchange, whichwasof0.10m³m⁻³(Xuetal.,1992).Despitethereduction insoilbulkdensityandincreasesinmacroporosityinconventional

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Fig.5.CBalancebetweenannualinput(covercrop+organiccompost)andannual losses(CO2 Cemissions)amongdifferentvegetablescroppingsystems.Grass:no- tillondeadmulchofgrass.Leguminous:no-tillondeadmulchofleguminous.

Intercrop:no-tillondeadmulcheofgrassandleguminous.

till,ourresultssuggestthattherearenolimitationsonsoilaera- tionandrootgrowthintheno-tilltreatments.Themicroporosity increasedforallno-tilltreatments,signiﬁcantlycontributingtothe waterstorageandplantgrowth.

Theresultssuggestthatover20yearsoforganicmanagement contributedtoincreasesinsoilorganicCpools.Anorganiccom- positionrichinC(302gCkg⁻¹organiccompost;correspondingto 9.06MgCwasaddedtothesoilonanannualbasisandincreased soilorganicCstorage.Souzaetal.(2012)reportedthat,atthesame site,totalorganicCcontentsat0–20cmwere10.1and20.3gkg⁻¹ in1990and2009,respectively.Thisresultisprobablyduetothe organicmanagementsystempracticedfor19yearsbefore2009.

Aftertheadoptionofno-tillin2009totalorganicChasincreased, reaching34.9gkg⁻¹at15–30cmlayerattheintercroptreatment in 2012. The biomass-Cinput by cover cropand organic compost additionlead to increases in soil organicC through more intensifiedcroppingsequenceafterno-tilladoption.However,the maintenanceofsuperficialplowinginconventionaltillinducedsoil organicCdepletionduetooxidationofthelabilefractionsoforganic matter(seealsoSilvaandMendonça,2007).

IntercropsystemfavoredsoilCstoragemorethanothervegeta- blescroppingsystems.ResultsshowedthatC/Nratiosforalllayers andplantingsystemsdidnotexceed20/1,suggestingapredomi- nanceofsoilNmineralization.SoilhumustypicallyhasaC/Nratio from10/1to12/1(Grifﬁn,1972).Inthiscontext,intercropprovides aninputoforganicmaterialwithanintermediateC/Nratio,leading toalongerperiodofgroundcoverandsynchronizationbetween thesupplyanddemandofNbythecrops(Camposetal.,2011).

IntermediateC/Nratiosfavortheorganicmatterhumiﬁcationpro- cess,resultinginaccumulationofrecalcitrantCandimprovingsoil ecologicalfunctions.VachonandOelbermann(2011)reportedthat intercrop plots hadintermediate rates of cropresidueC and N inputs,showingslowrateofdecayandaccumulatingsoilorganic matterintime.

4.4. SoilCO₂ Cemission,soiltemperature,soilwatercontent andmicrobialbiomassC

The results showed that, after plowing in summer crop (February2013),therewasanincreaseinCO2 Cemissionsinthe conventionaltillplots.Thismeasurementoccurred20daysafter plowing,whilethewinter measurementoccurred50days after

plowing. Thisobserved increase canindicatesthat there wasa period immediatelyafterplowingwhen CO₂ C emissionswere higherintheconventionaltilltreatmentthaninno-till,whichwas notquantiﬁed.ItisrecognizedthatthegreatestdifferencesinC emissionsoccuratthetimeimmediatelyfollowingtillageopera- tions(Al-KaisiandYin,2005).Thus,itmayleadtounderestimation ofannualmeanofCO₂ Cemissionsintheconventionaltilltreat- mentinthepresentstudy.

Overall,ourresultssuggestthatinwarmerperiodsplowingis moreharmfulthanincolderperiods,increasingCO₂ Cemissions inthevegetablescropping,regardlessofatendencyofreductionon CO2 Cemissionsinthenotilltreatments,especiallyinthesum- mercrop.Thisisrelatedtotheconstantinputoforganicresidues thatcoversthesoil,reducingsoiltemperatureandincreasingsoil watercontent.Whencovercropresiduesareincorporatedintothe soil,theyaresubjectedtomoresuitableconditionsofsoilwater contentandtemperatureformineralizationthantheresiduesleft onthesoilsurface(Al-KaisiandYin,2005;Campigliaetal.,2014).

Inaddition,thenon-incorporationofresiduesisakeyfactortoa slowoxidation(Ghoshetal.,2012).Thus,itmayleadtoanincrease insoilwatercontentandareductionofsoiltemperatureforlonger periodswhencomparedwithresiduesincorporatedintothesoil.

Soilwatercontentisastronglimitingfactorforvegetablecrop- pingsystems,anditisthemostimportantfactorinﬂuencingthe rateofgrowing,especiallyintropicalzoneswithhightempera- turesandevapotranspirationrates(Tianetal.,2011;Ghoshetal., 2012).Vegetableshaveahighdependenceofsoilwatercontentfor theirdevelopment,especiallyinwarmerperiods.Ourresultspoint toahigherannualsoilwatercontentintheno-till,whencompared totheconventionaltill(0.28vs0.20gg⁻¹).Thisprovidesbettersoil conditionsand reducestheneedfor irrigationinthevegetables ﬁelds.

The high CO₂ C emissions in the grass treatment can be explained by thehigher C/N ratio (higher C availability) when compared totheleguminoustreatment.Also,long-termorganic managementcanleadtosoilconditionswhereNisnotalimiting factorfororganicmattermineralizationbymicroorganisms(Sakai etal.,2011).No-tillandconventionalsystemusingblackoatand maizeinpre-plantingcanshowsimilarvaluesofC/Nratios(Costa etal.,2008).Rootrespirationandmicroorganismscancontribute tototalsoilrespirationasCO2efﬂuxmeasurementsdonotdistin- guishbetweenCO2 Cemissionsfromthesetwosources(Hanson etal.,2000).Theconstantaccumulationandsupplyofaboveground organicmattercanleadtoincreasesinthemicrobiologicalactivity andCO2 Cemissionrates(Costaetal.,2008;Netoetal.,2011)in theno-tilltreatment.Overall,theseresultspointtoahighcapac- ity oforganicno-till vegetablessystemstoincreasesoil-quality indicatorsalongtheyears.

EcosystemproductivityandsoilorganicCturnoverarestrongly inﬂuenced by climatic and environmental conditions, where changesonCO2 Cemissionsratesmayoccurduetovariationsin soiltemperatureunderplausibleclimatechangescenarios.Lower lossesofCwithincreasesinsoiltemperaturewererecordedinthe grassandintercroptreatments.Inthesesystems,thestabilityof organicmatterishigherthanintheotherstreatments.Suchbehav- iorissupportedbythehigherQ₁₀valuesinconventionaltilland leguminoustreatments.ThesetrendssuggestthathighC_solfrom conventionaltillandleguminouscancontributetotheincreased sensitivityofCO₂ Cemissionstosoiltemperature.LabileCfrac- tionsarerapidlymineralizedbymicroorganisms,increasingCO₂ C emissionsrates(Lal,2004).Thus,intercropismoreeffectivetostore Cunderpossiblesoiltemperatureelevationthanconventionaltill.

Ingeneral,no-tilltreatmentswereassociatedwithanincrease in microbialbiomassC.MicrobialbiomassCconstitutesa small portionofsoilorganicmatter,butitismoredynamicandﬂuctuates moreovertimethanthetotalsoilorganicC,beingareliablesoil