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

a_Department_of_Plant_Production,_Federal_University_of_Espírito_Santo,_29500-000_Alegre,_ES,_Brazil b_Research_of_{INCAPER—Centro}_Serrano,_BR-262,_km_94,_29.375-000_Venda_Nova_do_Imigrante,_ES,_Brazil c_Soil_Science_Department,_Federal_University_of_Vic¸_osa,_Avenida_P.H._Rolfs,_s/n,_Vicosa_36570-000,_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

r

a

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)and conven-tionaltill(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−1_in_conventional_till._Total_N_ranged_from_2.81_to_5.34_g_kg−1_in_grass_and_2.54

to4.51gkg−1_in_conventional_till._Highest_C_stock_was_recorded_in_intercrop._Conventional_till_showed

lowerlabileCvalueswhilerecalcitrantCwashigherintheintercroptreatment.Theannualaverageof CO2 Cemissions(␮molCO2m−2s−1)followedtheorder:grass(15.89)>intercrop(13.77)>leguminous

(13.09)>conventionaltill(11.20).Highestannualaverageofsoiltemperaturewasrecordedin conven-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).Increasingormaintainingsoilorganicmatteris criti-caltoachieveoptimumsoilfunctionsandcropproduction(Ghosh http://dx.doi.org/10.1016/j.scienta.2014.12.002

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

No-tillandorganicagricultureincreasesoilCandN sequestra-tion,andreducetheoxidationofsoilorganicmatter(Bayeretal., 2009;Campigliaetal.,2014).Continuousinputofplantresidues andpaucityofsoildisturbancepromotereductionsinCO2 C emis-sions through decreasesin organicmatter decomposition rates (Lal,2004;Bayeretal.,2009).Onotherhand,conventionalcrop production intensify soil disturbanceand, consequently, break-downthesoilaggregates(Bayeretal.,2009).Conventionaltillage isthemostcommonagriculturalmanagementforvegetable pro-ductioninareasformerlyoccupiedbytheAtlanticForestinBrazil. Inaddition,vegetableproductionishistoricallymanagedbyfamily smallholders.Intensivefarmingorintensivesoilpreparationin hor-ticulturedegradesthesoil–plantenvironment,mostlyduetothe reductioninconcentrationandqualityofsoilorganicmatterand thediversityofsoilorganisms(Tianetal.,2011).Degradationofsoil organicmatterleadstolong-termdecreasesinhorticultural pro-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),municipalityof Domin-gosMartins-ES (20◦22SE41◦03W)altitudeof950mabovethe

Fig.1. Averagemonthlyprecipitationandairtemperatureofthemunicipalityof DomingosMartinsbetweenJanuary2012andFebruary2013.DatafromIncaper.

sea.TheclimateoftheregionisAw(tropicalclimateanddry sea-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(mainly let-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, althoughportionsofthepilecanbecomeanaerobicbetween turn-ings. Moreover, it provides better control of flies, more rapid and uniform decomposition rates and less problems regarding moisturecontrol(MillerandJones,1995).Thecompostwas pre-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% mag-nesium,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(totalizing24permanent experi-mentalunits)coveringatotalareaof576m2_._Therefore,_the_effects oforganicmanagementaccumulatedovertheyears.Tillage treat-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.Thisisthemainvegetable crop-pingsystemoftheBrazilianhorticulture(Souzaetal.,2012). Operationscheduleconductedannuallyintheno-tilland con-ventionaltillwerepresentedinTable1.From2009to2013,no-till wasperformedwithblack oatand whitelupinas wintercover crop, followed bycabbageaswinter vegetablecrop. Maizeand sunnhempworkedassummercovercrop,followedbyeggplantas summervegetablecrop.Blackoatandwhitelupinweresownon March2012aswintercovercrops.Covercropseedswerespread manuallyandlightlyburied.Covercropsweresowninrowsspaced 33cmfromeachotherforalltreatments.Theseedrateswere480g perplotforblackoatand660gperplotforwhitelupin.Inthe inter-croppedsamplingunits,seedswerereducedtohalfofthesevalues. OnJuly2012,covercropsweremowedbymechanicalmowingand cabbagewasplanted.Covercropresidueswereleftonthesoil sur-faceasorganicdeadmulchandtheywerenotincorporatedintothe soil.Onemontholdcabbageseedlingsweretransplantedbyhand. Thecabbageseedlingswerearrangedinsinglerowsdistant60cm fromeachother.Thedistancebetweenthecabbageplantsinthe rowswas40cm.

Afterwintercrop,maizeandsunnhempweresownonOctober 2012assummercovercrops.Theseedrateswere600gperplotfor maizeand300gperplotforsunnhemp.Residuesweremowedon February2013followedbyeggplant(Solanummelongena)planting. Eggplantseedlingsweregrownintubesof180cm3_,_using_a_mixture 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)andone undis-turbedsoilsample(0–10,10–20and20–30cm,bythevolumetric ringmethod)weretaken(Embrapa,1997).Thesoilsampleswere airdried,groundedandsievedthrougha2-mmsievetoremove largerpiecesofrootmaterialandthestonefraction.Allsoil sam-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+_and_Al3+_were_extracted with1molL−1KClandNaandKwereextractedwithMehlich−1 (Embrapa,1997).Theelementcontentintheextractswere deter-minedbyatomicabsorption(Ca2+_,_Mg2+_and_Al3+_),_ﬂame_emission (KandNa)andphotocolorimetry(P).Theeffectivecationexchange capacity(CECE)wascalculatedbysumofcations(Ca2+,Mg2+,Na+,

K+_and_Al3+₎_and_total_cation_exchange_capacity_(CTC

T)estimatedby thesumofbasesandpotentialacidity.Thegranulometricanalysis wasperformedbypipettemethod,50rpm,16h(Embrapa,1997).

2.5. CovercropbiomassandCinput

Covercropbiomasswascollectedinsidea1_×1msquareineach plotforfreshmassdetermination.Further,itwasdriedinoven withcontinuousaircirculation(60◦C)fordrymassdetermination. Totalcarbonofcovercropbiomasswasanalyzedbylossin igni-tionat430◦Cfor24hinmufﬂefurnace(Kiehl,1985).Aproportion of950gCkg−1biomassforwhitelupinandsunnhemp,920gCkg−1 biomassforblackoatandmaizeand935gCkg−1biomassfor inter-cropwerefoundafteranalysis.Thefactorof 1.724wasusedto convertorganicmatteroforganiccompostintoorganicCbasedon theassumptionthatorganicmattercontains580gCkg−1biomass (CarmoandSilva,2012;SoilSurveyStaff,1996).

2.6. Soilphysicalattributes

Undisturbedsoilsamplesweresaturatedinwaterfor24hand thenplacedinasandtensiontableof−6kPa.Soilmicroporosity (Mic)wascalculatedafterstabilizationofwaterintothe volumet-ricring(72h).Bulkdensity(BD)wasperformedbythevolumetric ringmethodandparticledensity(PD)wasdeterminedbythe vol-umetric ﬂaskmethod(Embrapa,1997).Totalporosity (TP) was calculatedusingthefollowingequation:

TP=1−

BD PD

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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,andthenanalyzedfortotalsoilorganic car-bon(totalorganicC),totalnitrogen(totalN),labilecarbon(Clabil) andrecalcitrantcarbon(Crecal).TotalsoilorganicCwasperformed bywetoxidationwithK2Cr2O7 0.167molL−1 inthepresenceof sulfuricacidwithexternalheating(YeomansandBremner,1988). TotalNwasobtainedbysulfuricaciddigestionfollowedby Kjel-dahl distillation(Bremmerand Mulvaney, 1982;Tedesco et al., 1995).ThefractionsofsoilorganicCwereestimatedthrougha modiﬁedWalkelyandBlackmethodasdescribedbyChanetal. (2001)using2.5,5and10mLofconcentratedH2SO4resultingthree acid–aqueoussolutionratiosof0.25:1,0.5:1and1:1(which corre-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.ThesumoffractionsIandII corre-spondstothelabile CandthesumoffractionsIIIandIVtothe recalcitrantC(Chanetal.,2001).Becauseofpossiblechangesin bulkdensityasaresultofcroppingsystemandorganic fertiliza-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

1_{Determination}_of_total_organic_C_and_N,_recalcitrant_and_labile_C;2_{Determination}_of_microbial_biomass_C,_soluble_C_and_water_content_of_soil;3_Black_oat_and_White_lupin; 4_Only_for_conventional_till_treatment_and_there_was_no_cover_crop_in_conventional_till;5_Maize_and_Sunnhemp;_Dates_of_soil_CO

2 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

emis-sions werecalculated basedon themeanof allmeasurements. Soiltemperatures(5.0cmdepth)weredeterminedduringthegas ﬂuxmeasurements.TherelationbetweenCO2 C(FCO2 C)andsoil

temperature(Tsoil)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×Tsoil)), the result is

Ln(FCO2 C)=Ln(F0)+b×Tsoil. A linear relationship between

Ln(FCO2 C)andtheTsoilisexpectedwheresoiltemperatureisa

limitingfactor.Basedonthebcoefﬁcientsitispossibletoderive theQ10factor,whichrepresentsthepercentageincreaseinCO2 C

emissionfora10◦Cincreaseinsoiltemperature.Thisisderivedas Q10=e10×b(Carvalhoetal.,2012).

2.9. SoilwatercontentandmicrobialbiomassC

Ineachplot,disturbedsoilsampleswerecollectedat5cmdepth todeterminatesoilwater content,microbialbiomass C,soluble carbon(Csol)andmetabolic(Qmet)andmicrobialquotient(Qmic). 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 Conventionaltill 6.52 1445.38 235.80 20.40 6.71 1.40 0.00 12.51 69.80 473.19 140.62 386.19 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 Conventionaltill 6.45 672.14 143.80 5.20 3.92 1.00 0.00 9.78 53.56 468.34 129.77 401.88 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).Asvegetablescrophadsimilaryieldsandthus sim-ilarvaluesofcropresidues,theCinputaccountedreferstotheC ofgreenmanuresandorganiccompost.Theequivalencebetween CandCO2wasbasedonthemolecularweightsoftheelements,in whichonemolofCO2contains12.011gC.

2.11. Dataanalysis

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

3. Results

Meanvaluesoffreshmass,drymassproduction andCinput ofcovercropsaregiveninTable3.Duringthewintercrop,fresh massproductionofwhitelupinwassignificantlylowerthanblack oatandintercrop.Nosignificantdifferenceswererecordedin win-ter cropfordry massproductionand C input.Insummercrop, freshmassproductionofmaizewassignificantlyhigherthanthat ofsunnhemp.Thisresultwasalsoobservedfordrymass produc-tion.TheCinputwassignificantlyhigherinmaizeplotsthanthe sunnhempplotsinsummercrop.

Microporosity(Mic), 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,ClabilandCrecaltendedtodecrease.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−1ingrasswhilein conven-tionaltillitrangedfrom2.54to4.51gkg−1.TheC/Nratiotendedto increasewithincreasingsoildepth.IntercropshowedhigherC/N ratioforallsampledsoillayers.Conventionaltillshowed signiﬁ-cantlylowermeansofClabilascomparedwithgrassupto15cm soildepth.HigherCrecalwasrecordedfortheintercropwhen com-paredwithgrass at0–5and15–30cmlayer.Crecal 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

m3_m−3 _g_cm−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.Cstocksweresigniﬁcantlyhigherinthe inter-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-tillondeadmulcheof legu-minous.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 C emis-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)andhighermean val-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,showinglesssensitivitytoincreasesinsoil tempera-ture.

3.5. SoilwatercontentandmicrobialbiomassC

Soilwatercontent,microbialbiomassC,solublecarbon(Csol), metabolic (Qmet) and microbial quotient (Qmic) 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, micro-bial 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,intercropand conven-tionaltill,respectively.For allstudyperiods,signiﬁcantlylower (exceptFebruary2013)microbialbiomassCwasrecordedin con-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.

Cbalancebetweenannualinput(covercropandorganic com-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 emis-sions)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%higherthaninwinter crop-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).Ourresultsareconsistentwithotherrecordsinthe litera-tureforcovercropbiomassproductionintropicalzones(Amado etal.,2006;Bayeretal.,2009).

Conventionaltillagepromotedincreasesinmacroporosityand decreasesinmicroporosityandbulkdensityattopsoil.Thisleadto highersoilaerationcapacityandlowerwaterholdingcapacity.The macroporositywasabovethecriticallevelforgaseousexchange, whichwasof0.10m3_m−3₍_Xu_et_al.,₁₉₉₂_)._Despite_the_reduction 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,ourresultssuggestthattherearenolimitationsonsoil aera-tionandrootgrowthintheno-tilltreatments.Themicroporosity increasedforallno-tilltreatments,signiﬁcantlycontributingtothe waterstorageandplantgrowth.

Theresultssuggestthatover20yearsoforganicmanagement contributedtoincreasesinsoilorganicCpools.Anorganic com-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 com-post additionlead to increases in soil organicC through more intensifiedcroppingsequenceafterno-tilladoption.However,the maintenanceofsuperficialplowinginconventionaltillinducedsoil organicCdepletionduetooxidationofthelabilefractionsoforganic matter(seealsoSilvaandMendonça,2007).

IntercropsystemfavoredsoilCstoragemorethanother vegeta-blescroppingsystems.ResultsshowedthatC/Nratiosforalllayers andplantingsystemsdidnotexceed20/1,suggestinga predomi-nanceofsoilNmineralization.SoilhumustypicallyhasaC/Nratio from10/1to12/1(Grifﬁn,1972).Inthiscontext,intercropprovides aninputoforganicmaterialwithanintermediateC/Nratio,leading toalongerperiodofgroundcoverandsynchronizationbetween thesupplyanddemandofNbythecrops(Camposetal.,2011). IntermediateC/Nratiosfavortheorganicmatterhumiﬁcation pro-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 emissionsoccuratthetimeimmediatelyfollowingtillage opera-tions(Al-KaisiandYin,2005).Thus,itmayleadtounderestimation ofannualmeanofCO2 Cemissionsintheconventionaltill treat-mentinthepresentstudy.

Overall,ourresultssuggestthatinwarmerperiodsplowingis moreharmfulthanincolderperiods,increasingCO2 Cemissions inthevegetablescropping,regardlessofatendencyofreductionon CO2 Cemissionsinthenotilltreatments,especiallyinthe sum-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. Soilwatercontentisastronglimitingfactorforvegetable crop-pingsystems,anditisthemostimportantfactorinﬂuencingthe rateofgrowing,especiallyintropicalzoneswithhigh tempera-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 tototalsoilrespirationasCO2efﬂuxmeasurementsdonot distin-guishbetweenCO2 Cemissionsfromthesetwosources(Hanson etal.,2000).Theconstantaccumulationandsupplyofaboveground organicmattercanleadtoincreasesinthemicrobiologicalactivity andCO2 Cemissionrates(Costaetal.,2008;Netoetal.,2011)in theno-tilltreatment.Overall,theseresultspointtoahigh capac-ity oforganicno-till vegetablessystemstoincreasesoil-quality indicatorsalongtheyears.

EcosystemproductivityandsoilorganicCturnoverarestrongly inﬂuenced by climatic and environmental conditions, where changesonCO2 Cemissionsratesmayoccurduetovariationsin soiltemperatureunderplausibleclimatechangescenarios.Lower lossesofCwithincreasesinsoiltemperaturewererecordedinthe grassandintercroptreatments.Inthesesystems,thestabilityof organicmatterishigherthanintheotherstreatments.Such behav-iorissupportedbythehigherQ10valuesinconventionaltilland leguminoustreatments.ThesetrendssuggestthathighCsolfrom conventionaltillandleguminouscancontributetotheincreased sensitivityofCO2 Cemissionstosoiltemperature.LabileC frac-tionsarerapidlymineralizedbymicroorganisms,increasingCO2 C emissionsrates(Lal,2004).Thus,intercropismoreeffectivetostore Cunderpossiblesoiltemperatureelevationthanconventionaltill. Ingeneral,no-tilltreatmentswereassociatedwithanincrease in microbialbiomassC.MicrobialbiomassCconstitutesa small portionofsoilorganicmatter,butitismoredynamicandﬂuctuates moreovertimethanthetotalsoilorganicC,beingareliablesoil

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qualityindicatorintropicalzones(Balotaetal.,2004).Thehigher microbialbiomassCinno-tilltreatmentswasprobablyrelatedto thegreaterresidueinputsandconsequentlythehigherproportion ofreadilymetabolizedmaterials,suchassugars,aminoacidsand organicacids,enhancingmicrobialbiomassC(Tianetal.,2011).

The handweeding that occurredin August/September 2012 promotedincreasesinthemetabolicquotientintheconventional tilltreatmentinOctober2012.Thisshowsthepotentialofno-till toreducesoildisturbance, sincehandweedingwasnotapplied becausecovercropalsoseemstobeasuitableapproachfor con-trollingtheweeds(Campigliaetal.,2014).LowQmetratesunder no-tillindicatestheestablishmentofanefficientmicrobial popula-tion,promotingCincorporation.Thisisveryimportanttomaintain soilCstorage.HighQmetratesareindicativeofagriculturalsystems subjectedtohighstressconditions(AndersonandDomsch,2010), asisthecaseoftheplotssubjectedtoconventionaltill.Indisturbed systems,microbialbiomassrequiresmoreC toitsmaintenance. Microbialquotientindicatestheamountofmetabolicactive car-boninthetotalsoilorganicmatterandthus,reflectsthemicrobial Ccyclingandstabilization(AndersonandDomsch,2010).LessC wasimmobilizedinmicrobialbiomassinconventionaltillsystem, resultinginlowCandnutrientcyclingrates,asindicatedbythe lowerannualaverageofmicrobialquotient.Microbialquotientof <1%isareliableindicatorofreducedCturnoverinsoils(Joergenson etal.,1994).Themicrobialquotientrecordedunderdifferent treat-mentsvariedfrom4.2to10.3%(Fig.4e)whichisslighthigherthan thefindingsofBalotaetal.(2004)fortropicalzones.Highvaluesof microbialquotientinthepresentstudyareexpectedduethe long-termorganicmanagementinthestudiedsite.Theresultsindicatea highCturnoverintheno-tilltreatments,asitisexpectedinsoilsof tropicalzonesaroundtheworld(Ghoshetal.,2012).Thus,organic no-tillvegetablessystemsprovidedamorefavorableenvironment forrapidmicrobialgrowth,amoreeffectiveCstorageonmicrobial biomass,andactedasasourceofnutrientsforvegetablegrowth.

AlthoughtherearesubstantialincrementsinCO2 Cemissionin theno-tillsystems,itisextremelyimportanttotakeintoaccount theCbalancebetweeninput,lossesandpotentialofsoilCstorage. Jia et al. (2012) reported that theC entered into organic veg-etablesystemsweremainlythroughorganicamendmentandcrop residue,andtheyaccountfor23–73%and11–16%,respectively,of thetotal Cincrease.Theconventionaltillsystempresented ele-vatedClossesthroughCO2 Cemissionand incorporatedlessC tothesoilthantheno-tillsystem.NegativeCbalance(Fig.5)was recordedintheconventionaltill,evenwiththeannualinputof 30Mgha−1year−1oforganiccompostinthewinterandsummer. AssumingaCpriceof$42perMgofCsequestered(Takimotoetal., 2008),CO2 equivalentin thisstudycan correspondto$1484.7; $846.72and$1345.68sellingCcreditsamonggrass,leguminous andintercrop,respectively.Souzaetal.(2012)reportedanincrease of 86.62tCO2 equivalentin 10 years due organicmanagement ofvegetablesatthesameexperimentalsite.Theirvalueislower thanthepresentedinthisstudyduethecontributionofcovercrop andorganiccompostafterno-tilladoption.Theseresultsshowthat organicno-tillvegetablessystemsmayalsopromoteﬁnancial sus-tainabilitytothefarmerbyCsequestration,whichisnotevidenced inconventionaltill.

5. Conclusions

Organicno-tillvegetablessystemscouldincreaseC sequestra-tionandimprovesoilqualityintropicalzones,especiallywithinthe domainoftheAtlanticForest.Themaintenanceofconventionaltill

reducedsoilorganicmatter,adverselyimpactingsoilorganicC sta-tus.CO2 Cemissionswerehigherinno-tillthaninconventional tillage.However,immobilizationofCinthemicrobialbiomasswas moreefﬁcientunderno-till,promotingapositiveCbalanceinthe soilleadingtoaCsink.Organicno-tillvegetablessystemsshould beencouraged onvegetablescropping systemsto improvesoil qualityoftheagriculturallandwithinthedomainoftheAtlantic Forestbiome.Implementationofgrass/leguminousintercropping shouldbestimulatedonorganicvegetableproduction.However, thispreliminaryﬁndingneedstobefurtherinvestigatedby includ-ingenergybalanceanalyses,sincetheoperationscarriedoutinthe covercroptreatmentsdemandedseveralworkhoursandhuman power.Thiscanbeadisadvantageofno-tillmanagement. Never-theless,croppingsystemsintropicalareasshouldattainabalance betweensoilconservationandeconomicalgains.

Acknowledgments

The authors thank INCAPER (Espírito Santo Institute for Research,TechnicalAssistanceandRuralExtension)forthestudy in partnership, the Brazilian sponsors CAPES (Coordination of Improvement of Personal Higher Education), CNPq (National CounselofTechnologicalandScientiﬁcDevelopment)andFAPES (FoundationforResearchSupportoftheStateofEspíritoSanto)for grantingﬁnancialsupportandscholarships.

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