Productivity, profitability and partial nutrient balance in maize-based conventional and organic farming systems in Kenya

Productivity,

pro

fi

tability

and

partial

nutrient

balance

in

maize-based

conventional

and

organic

farming

systems

in

Kenya

Noah

Adamtey

a,

*,

Martha

W.

Musyoka

b

,

Christine

Zundel

c

,

Juan

Guillermo

Cobo

a

,

Edward

Karanja

b

,

Komi

K.M.

Fiaboe

b

,

Anne

Muriuki

d

,

Monicah

Mucheru-Muna

e

,

Bernard

Vanlauwe

f

,

Estelle

Berset

a

,

Monika

M.

Messmer

a

,

Andreas

Gattinger

a

,

Gurbir

S.

Bhullar

a

,

Georg

Cadisch

g

,

Andreas

Fliessbach

a

,

Paul

Mäder

a

,

Urs

Niggli

a

,

Dionys

Foster

a

a

ResearchInstituteofOrganicAgriculture(FiBL),Switzerland

b_{InternationalCenterforInsectPhysiologyandEcology(icipe),Nairobi,Kenya}

c_{DirectorateofProductionSystemsandEcosystems,SwissFederalOfficeforAgriculture,Bern,Switzerland} d

NationalHorticulturalResearchCenter,KenyaAgriculturalandLivestockResearchOrganisation(KALRO),Nairobi,Kenya e

KenyattaUniversity,EnvironmentalScienceDepartment,Nairobi,Kenya f

InternationalInstituteofTropicalAgriculture(IITA),Nairobi,Kenya g

InstituteofAgriculturalSciencesintheTropics,UniversityofHohenheim,Germany

ARTICLE INFO

Articlehistory:

Received29February2016

Receivedinrevisedform29September2016 Accepted3October2016

Availableonlinexxx

Keywords:

Organicfarmingsystems conventionalfarmingsystems high-inputs

low-inputs nutrientexport partialnutrientbalance

ABSTRACT

In2007twolong-termtrialswereestablishedinKenyatocontributeresearch-basedevidencetothe global debate on the productivity, economic viability and sustainability of different agricultural productionsystems.Thesetrialscompareconventional(Conv)andorganic(Org)farmingsystemsathigh andlowinputlevelsattwolocations,i.e.Chuka,withHumicNitisols,highinherentsoilfertilityand rainfall,andThika,withRhodicNitisolswithlowsoilfertilityandrainfall.Thehighinputsystems(High) represent commercial-scale, export-oriented production that uses the recommended amounts of fertilisers,pesticidesandirrigationwatertogeneratehighyields,whilstthelowinputsystems(Low) representlocalsmallholderpractices,usingrelativelyfewfertilisersandpesticidesandoperatingunder rain-fedconditions.Theconventionalsystemsreceivedsyntheticfertilisersandorganicmanure,whilst theorganicsystemsonlyreceivedorganicinputs.Thetrialssofarhaveconsistedofa6-season,3-year, crop rotationwithmaize (Zeamays L.) plantedin thelongrainyseasons(March-September), and vegetables in the short rainy seasons (October – February). Generally, there were no significant differencesinthedrymatteryieldsandnutrientuptakebymaize,babycornorbeansbetweenthe conventionalandorganicsystemsateithersite.Similarmaizegrainandbabycornyieldswerealso obtainedatChuka.However,atThika,maizegrainyieldsinOrg-Highin2007(atconversion)werelower thantheyieldsinConv-High,buttheyieldsbecamesimilarin2010(afterconversion).Atthesamesite theyieldsofmaizegrainundersolecroppinginOrg-Lowwere3.2timeslowerthantheyieldsin Conv-Lowin2007and1.7timeslowerin2010.Whenintercroppedwithbeanstheyieldsofthetwosystems weresimilar.InthefirsttwoyearsprofitsfromConv-Highwere0.5–1.8timesand0.2–2.4timeshigher thaninOrg-Highwhensellingtheproduceatlocal(ChukaandThika)andregionalmarkets(Nairobi),but thereaftertheprofitfromthetwowassimilar,evenwhenorganicproducewassoldatregularmarket prices.FromthefifthyearonwardsOrg-Highattractedapricepremiumof20to50%andthismadeit1.3 to4.1timesmoreprofitablethanConv-Highwhensellingonlocalandregionalmarkets(inChuka,Thika andNairobi).ComparedtoConv-High,partialNandKbalancesatthetwositeswerepositiveandhigher inOrg-High,exceptforNatChuka.OurfindingsdemonstratethatOrg-Highisproductive,economically viable,resource-conservingandcancontributetosustainableagricultureproductioninKenyadepending onregionalconditionsandthecropscultivated.

ã2016TheAuthors.PublishedbyElsevierB.V.ThisisanopenaccessarticleundertheCCBY-NC-ND license(http://creativecommons.org/licenses/by-nc-nd/4.0/).

* Correspondingauthor.

E-mailaddresses:noah.adamtey@fibl.org,adamteynoah@gmail.com(N.Adamtey).

http://dx.doi.org/10.1016/j.agee.2016.10.001

0167-8809/ã2016TheAuthors.PublishedbyElsevierB.V.ThisisanopenaccessarticleundertheCCBY-NC-NDlicense(http://creativecommons.org/licenses/by-nc-nd/4.0/).

ContentslistsavailableatScienceDirect

Agriculture,

Ecosystems

and

Environment

1.Introduction

About80percentofAfrica’spopulationdependsonagriculture astheirprimarysourceoflivelihood.Itprovidesemploymentfor about60%oftheeconomicallyactivepopulation,andforabout70 percentof theAfrica’spoorestpeople (ADB,2010).Agriculture represents 30-40 percent of Africa’s gross domestic product (GDP)andaccountsfor60%ofitsexports(IFPRI,2004).Themain formof farminginsub-Saharan Africa(SSA),as in manyother partsofthetropics,issimultaneousmultispeciesfarming(i.e.the cultivationofavarietyof cropsonasinglepiece ofland).This systemissuitedtosmallscalefarmersseeking tocultivate for bothsubsistenceandcommercialpurposes(Dixonetal., 2001; Vandermeeretal.,1998).Fivemajorfarmingsystemshavebeen identifiedin SSA, thathave different potentialsfor agriculture growthandpovertyreduction.Theyare:maize-mixedfarming;

agro-pastoral; highland perennial; root and tuber crops and

mixedcereal-rootcrops(Aurichetal.,2014;Dixonetal.,2001). Maize-basedmixedfarmingsystemscover16%ofthelandareaof SSA(Aurichetal.,2014).InEastandSouthernAfrica,maize-based

mixedfarming is themost importantfood productionsystem,

mainly located in semi-humid to sub-humid agro ecological

zones that extend across the plateau and highland areas at

altitudesof800to1500m,stretchingfromKenyaandTanzania throughZambia,Malawi,ZimbabweontoSouthAfrica,Swaziland andLesotho(Dixonetal., 2001).Itaccountsfor246millionha (10%)ofthetotallandareainEastandSouthernAfrica,32million ha(19%)ofthecultivatedarea(ofwhichjust0.4millionha1is under irrigation) andinvolves about 60 millionpeople (Dixon etal.,2001;Jaetzoldetal.,2006).

Theproductivity(outputperunitoflandarea)ofmaize-based mixed farming in East and Southern Africa is very low and is consideredtobeonereasonforthepersistenceofruralpovertyin theregion(Akinnifesietal.,2010;Jaetzoldetal.,2006).Thelow cropproductivityhasbeenattributedtoanumberoffactorsthat include low soil fertility and long-term soil degradation (e.g. acidification,compaction,lossofsoilorganicmatterandnitrogen)

(Amede,2003;HenaoandBaanante,2006;Folberthetal.,2014) causedbydeforestation,overgrazing,continuousandintensified croppingwithinadequatereplacementof soilnutrients (Henao and Baanante,2006; Sileshi et al.,2010) and a low takeup of

sustainable resource management strategies (Omotayo and

Chukwuka,2009).Thereisaclearneedtoreversethedeclinein soilfertilityandthedegradationofthenaturalresourcebase(land, water, forest,and biodiversity).This is a key toincreasing and sustaining cropproductivity which, in turn, will increase food

security and reduce hunger and poverty. The most frequently

recommendedoptionstoachievethisaretodevelopconventional agriculture, diversify production systems or intensify existing production patterns (Dixon et al., 2001; Folberth et al., 2014). However,inmostcountriesinSSAthepotentialofconventional agriculture,basedaroundmonocultures, mechanisationandthe useofsyntheticinputssuchaschemicalfertilisersandpesticides (BeusandDunlap,1990)islimitedbythehighcostsofdoingso. Thereareotherlimitingfactorstoo:theoftenhighlyvariablesoils, highPfixationcapacity(Kwabiahetal.,2003;Nziguhebaetal., 1998) and large within-farm soil fertility gradients (Vanlauwe etal.,2006).Thesefeatureshaveledmanytoraiseseriousconcerns aboutpotentialofconventionalagriculturetoimprove productivi-tyandprovidesustainableyieldsinSSA(seeRigbyandCàceres, 2001).

Organicagricultureisanapproachthataimstoclosenutrient cycles and has the potential to improve the use efficiency of nitrogenandphosphorus(Badgleyetal.,2007).Organic agricul-turecombinesanumberofpracticesincludingtheapplicationof organic fertilisers, intercropping with nitrogen-fixing trees or

legumesor withother crops thatproduce synergies,extended crop rotations with greater phenological diversity of crops, biologicalpestcontrol, theuseof locallyadaptedseeds/breeds, andthere-integrationofanimalsonfarms.Italsoprecludesthe useofsyntheticinputssuchaspesticides,herbicides,hormones and the preventive use of antibiotics (all defined by organic standards).However,therearequestionsaboutwhetherorganic agriculturecanachieveproductionandproductivitylevelsthat arecomparabletoconventionalagriculture.Factorsthatlimitthe productivityoforganicagriculturecanincludeshortagesof,and poorquality,organicmaterialsandtheslownutrientreleaseof organicinputswhichcanbe insuf_ficienttomeetcropnutrient

demands at periods of peak demand (Murwira et al., 2002;

OmotayoandChukwuka,2009).Fromashorttermperspective, organic agricultureis generally seen as unable tosupport and sustainthehighlevelsofproductivityneededtomeetlocaland globalfooddemand(Kirchmannetal.,2008;Seufertetal.,2012). Butfroma longertermperspectiveitis believedtoholdmore prospectofbeingsustainableandstable(ReganoldandWachter, 2016).

Long-termfarmingsystemsexperiments(LTEs)arean impor-tantwayofevaluatingthepotentialsandlimitationsofdifferent farming systems against sustainability criteria (productivity, economic viability and resource-conservation). There is a long traditionofundertakingfarmingsystemscomparisonsin temper-ateclimates(Mäderetal.,2002;Pimentel,2005).Thesetrialsare oftenrunoverlongperiodsinordertocapturetheimpactsonsoil productivity.Yieldsintemperateregionshavebeenfoundtobe20 to25%lowerinorganicsystemsthaninconventionalones(Seufert etal.,2012),althoughnutrientandenergyefficiency,soilfertility andbiodiversitywerefoundtobeenhancedinorganicsystems (Bengtssonetal.,2005;Mäderetal.,2002;Pimentel,2005).There isverylittlelong-termdataontheperformanceof organicand conventionalsystemsinthetropicsandsubtropics(Bationoetal., 2012;Seufertetal.,2012).Moreover,inAfricasuchtrialshaveoften beenfacedwiththechallengesofinconsistencyindatacollection andmanagementorfundingconstraints,whichmakeitdifficultto evaluatetheirperformance(Bationoetal.,2012).Inadditionthe studiesthathavebeenundertakendidnotcomparethe

perfor-mance of small holder and commercial-scale farms under

multispeciesfarming,orunderdifferentgeographicalandweather conditions, features which are all typical of African farming systems.

In view of this knowledge gap, the Research Institute of

Organic Agriculture (FiBL), in collaboration with its research partnershasestablishedanetworkoflong-termfarmingsystems comparisontrialsin thetropicswithfield sitesinKenya,India and Bolivia (Forster et al., 2013). These field trials aim at comparingtheagronomic,economicandecologicalperformance

of conventional and organic farming systems under different

ecological zones, soil types, and management practices. The

hypotheses of thisstudyare that:(a)organic farmingsystems will match the productivity and profitability of conventional

farmingsystemsunder intensivecropping overthemediumto

longterm(6-20yearsormore);(b)undercontinuouscultivation, conventionalandorganicfarmingsystemshavedifferenteffects on nutrient exports and partial nutrient balance. The specific

objectives were: (i) to assess and compare the productivity

(measure ofoutput producedper unitofland area) of organic

and conventional farming under high input and low input

systems in two different sites in Kenya, (ii) to determine the profitability(themeasureof revenue lessproduction costs)of organicandconventionalfarminginhighandlowinputsystems, and(iii)toevaluatetheeffectofconventionalandorganicfarming systemsonnutrientexportsandpartialnutrientbalance.

2.Materialsandmethods

2.1.TheLong-TermSystemsComparisonTrialsinChukaandThika 2.1.1.Sitedescription

TheLongTerm SystemsComparisonTrialsitesatChukaand Thikaaresituatedinthesub-humidzonesoftheCentralHighlands ofKenya.Thetrialswereestablishedin2007andareexpectedto runfor20years.Bothareasarecharacterisedbyabimodalrainfall pattern(longrainyseasons fromMarchtoJune and shortones

from October to December). Chuka is situated in the UM 2

agroecologicalzone,alsocalledtheMainCoffeeZoneandislocated at 1,458mabove mean sealevel in Tharaka Nithi County (37 38.792'N&020.864'S),about150kmawayfromNairobi.The meanannualtemperatureatChukarangesfrom19.2–20.6Cand meanannualrainfallis1373mm.ThetrialsiteislocatedatKiereni PrimarySchool.ThikaissituatedintheUM3agroecologicalzone oftheuppermidlands,alsocalledthesunflower-maizezoneand thesiteissituatedinthepremisesoftheKenyanAgriculturaland Livestock Research Organisation, (KALRO) in Murang’a County. Thikaisabout20kmawayfromNairobi(3704.747'Nand10.231' S)andliesat1,500mabovemeansealevelwithanannualmean temperaturerangingbetween19.5and20.7Candmeanannual rainfallis840mm.ThesoilsatChukaare HumicNitisolswhile thoseatThikaareRhodicNitisols(Table1)basedontheFAOworld referencebaseforsoilresources(IUSSWorkingGroupWRB,2006; Wagateetal.,2010a,b).

2.1.2.Experimentaldesignandmanagement

Priortosettingupthetrials,soilhomogeneitytestsofthesites weredonein2006withmaizegrownasthesolecropwithoutany inputs.Dataaboutthemaizeyieldandbiomass,pHandtotalsoil

organic carbon were collected from 55m plotswhich were

usedasaguidetoblockthetrialsitesateachlocation.Basedon thedataobtainedfromthehomogeneitytest,theexperimental plots,eachmeasuring88m,werethensetup(withaninnernet plot size of 66m for data collection). Each treatment was

appliedin aRandomisedCompleteBlock Design (RCBD)which

wasreplicatedfourtimesinChukaandfivetimesinThika.Ateach siteconventionalfarming(Conv)andorganicfarming(Org)were comparedattwolevelsofinputs:highinputs(High)representing export oriented, large scale production and low inputs (Low) representingsmall holderproduction largelyfor domestic use. Thetypeofinputsandtheamountofnutrientsappliedpercropin eachcropping season (Table 2)in theconventional highinput

system (Conv-High) and the organic high input system

(Org-High) were based on the recommendations of the Kenyan

Ministry of Agriculture and the Japanese International

Co-operation Agency’slocal andexportvegetablegrowingmanual (MOA/JICA,2000).Theonesintheconventionallowinputsystem

(Conv-Low) andthe organiclowinput system(Org-Low) were

based on a survey done within a 20km radius of the two

experimentalsitesthatassessedthepracticesof35householdsin TharakaNithiCounty(ChukaArea)and25in Murang’aCounty (ThikaArea)(Musyoka,2007;Székely,2005;seesupplementary sheetAnnex1).

2.1.3.Croppingsystems

ThecropsandthecroppingpatternofthetrialsinChukaand ThikaareshowninTable2.The selectionof cropsforthehigh inputsystems(Conv-HighandOrg-High)andlowinputsystems

(Conv-Low and Org-Low) were based on reports by Székely

(2005),Musyoka(2007)andMOA/JICA(2000).Thecroprotations werebasedonfarmers’practicesintheareaandtheprincipleof croprotationrecommendedbytheKenyan InstituteofOrganic Farming (KIOF) (Székely, 2005). In Conv-High and Org-High, maize(ZeamaysL.),astaple foodcropintheareawasplanted everyyearinthelongrainsseason.InConv-Highitwasplantedas asolecrop.InOrg-Highitwasplantedasarelay-intercropwith

Mucunapruriens.Onemaize(Zeamays,var.H513)andBabycorn( Zeamaysvar.Pana14)seedwaseachplantedperholeatan inter-andintra-rowspacingof75cm30cminthehighinputsystems whilsttwo maize seedswereplantedper holeataninter- and intra-rowspacingof75cm60cminthelowinput-systems.The

low input systems was intercropped with beans (Phaseolus

vulgarisL,var.GLP92)plantedataninter-andintra-rowspacing of75cm30cm(2seedsperhole).Mucunaprurienswasplanted fourweeksafterthemaizeemerged,asarelaycropataninter-and intra-rowspacingof75cm80cmattwoseedsperhole.When maize(ZeamaysL.)isusedasavegetableitisknownas‘babycorn’

andconsistsofunfertilisedyoungearsharvested2or3daysafter silk emergence (1–2cm long). It is typically eaten whole, cob included.Thisisincontrasttomaturecorn,thecobofwhichistoo

tough for human consumption. In this paper each 6-season

(3year)rotationinallthesystemsisreferredtoasacycle.Since

the fields had been cropped for several years before the

establishmentofthetrials,the1stcyclealsocoincidedwiththe periodofconversiontoorganicmanagement(accordingtoIFOAM standards)inOrg-HighandOrg-Low.

2.1.4.Managementpracticesinthedifferentfarmingsystems

In Conv-High, farm yard manure (FYM) and Di-ammonium

phosphate(DAP)wereappliedatplantingattheratesshownin

Table2.Calciumammoniumnitrate(CAN)wereappliedwhenthe maizewasatthe8leafandtasselingstages.InOrg-Highcompost

(madefrommaizestover andfarmyard manure(FYM),Tithonia

diversifoliar (Tithonia),ashand rockphosphatewere appliedat planting.Tithoniawasappliedinaformofamulchtosupplya starter N twoweeks after themaize emerged. At6 leaves and tassellingstagesTithoniawasagainappliedinaformofplantteato supplyNasatopdressing.AteachtimeofTithoniateaapplication, 12.5kgoffreshand tenderleavesofTithoniawasusedperplot (size88m).ThetenderleavesofTithoniawaschoppedintosmall piecesandsoakedinplasticdrumsofwaterataratioof1:5(leafto water).Theopentopofthedrumscontainingthemixturewere coveredtoavoidammoniavolatilisationandkeptundershade.The

mixtures were stirred once after every 3days to allow for

mineralisation until 10 to14days when the water had turned darkbrownishgreen,anindicationthatmostofthenutrientshad dissolvedintothewater.Theplantteawassievedandthetrash removed.Thegeneratedliquidwasthendilutedwithwateratthe Table1

Theinitialsoilcharacteristics(asmeansandstandarderrors)ofthefieldreplicates ofthelong-termsystemscomparisontrialsitesatChukaandThika,intheCentral HighlandsofKenya. Chuka Thika 0–20cm 20–40cm 0–20cm 20–40cm Sand [gkg1_{] 948 803 547 627} Silt [gkg1_{] 1667 1535 14111 1028} Clay [gkg1] 7409 7675 80514 83613 pH-H2O 5.80 6.10 5.40 5.70.3 EC [mScm1] 138.73.3 1596.2 119.87.2 128.514.6 CEC [Cmolckg1] 17.50.5 14.80.4 110.3 10.10.4 Corg** [gkg1] 23.20.8 21.10.4 22.60.2 18.30.4 Ntot [gkg1] 2.080.03 1.780.09 1.60.04 1.480.06 S [mgkg1_{] 18.30.1 12.40.9 392.3 26.63} P [mgkg1] 28.91.9 12.10.8 12.20.6 20.1 K [Cmolckg1] 1.250.03 0.980.03 1.280.03 1.050.17 Ca [Cmolckg1] 8.750.29 8.60.3 3.530.19 3.80.97 Mg [Cmolckg1] 2.280.05 2.10.04 1.90.11 1.730.31 Na [Cmolckg1] 0.20 0.10 0.150.03 0.10 Al [Cmolckg1_{] 0.010 0.050.03 0.10 0.280.02}

ratioof1:2(leafteatowater)toreducetheteaconcentration.The plantteawasthenappliedequallytoalltheplantsintheplot.The

trash that was removed was also distributed in between the

plantingrowsintheplot.Inaddition,cropresiduesfromprevious cropswereretainedwithinthesystem.InConv-LowFYMandDAP wereappliedatplanting.InOrg-LowdecomposedFYMandrock phosphatewereappliedatthetimeofplanting.Inthetwostudy areasTithoniagrowsinthewildandisalsogrownasahedgeplant bythemajorityoffarmers(Annex1,supplementarysheet).Also, about77%ofthefarmershadatleastonecowthatgeneratesonthe average6tonnes(freshweight)ofmanureperyear.Thepresence andavailabilityofTithoniaandmanurehelptoaddresstheoften commonchallengethat alack,orlimitedavailability, oforganic

inputs is a barrier to the widespread adoption of organic

agriculturebysmallholder farmers.The planthealth measures that were taken are shown in Table 3. Pests (stem borer and termites)weremanagedbasedonbi-weeklyscoutingreportsanda sprayingcalendarin Conv-Highand Org-High.In Conv-Lowand Org-Lowpestsanddiseases wererandomly managed.Inallthe systemshandhoeingwasdoneateveryplantingineachseasonup toadepthof20cmfollowedbytwoweedingwithamatchet(asis generallypracticedinKenya,exceptinverylargescalecommercial productionofwheat,floricultureandpineapples).Theamountand

frequencyofirrigationwater,typeofpesticidesandtheirrateof applicationareindicatedinTable3.

2.1.5.FieldDataCollection

Agronomicdatawerecollectedusingtheentireplantsfroma netplotof66m. Thedry weightofthemaizeandbeanswas determinedatamoisturecontentof13%.Babycorn(freshgreen young cobs) data was collected at 3–4day intervals at the beginningofharvestandat6–8dayintervalsatthelaterstages ofharvest.Babycornwassortedintomarketableand unmarket-ableyields(basedonspecificationsprovidedbyexportcompanies) andthemarketableyieldswereusedtocalculatetheyieldsper hectare.Allthedataonyieldsandgrossmarginspresentedinthe paperareleastsquaremeansvalues.Economicdata(i.e.labour, inputandtransportcostsandmarketprices)atChuka,Thikaand Nairobiwerecollectedforeachseasoninallthesystems.

2.1.6.Weatherdata

Thedailyprecipitationdatausedinthispaperwereobtained fromweatherstationsthatwereinstalledatthetwoexperimental sitesatthestartoftheproject.Tohighlighttherainfalldistribution over time, cumulative precipitationthroughout theseasonwas calculatedandpresentedgraphically.Theeffectoftheamountand Table2

Recommendedapplicationratesofinputsandthecroppingpatterninthe6season-3-yearcroprotationofthelongtermsystemcomparisontrialinChukaandThika,Kenya. Farmingsystem Yearinthe

cycle

Season Crop Descriptionofinputsappliedtomaizeandbeans TotalN applied (kgha1₎

TotalP applied (kgha1₎

Conv-High 2007/10 LS Maize 7.5tha1FYM,200kgha1DAP,100kgha1CANa

96 54 SS Cabbage 10tha1FYM,200kgha1TSP,300kgha1CAN 145 64 2008/11 LS Babycorn 11.3tha1FYM,200kgha1DAP,100kgha1CANa

113 60 SS Frenchbeans 7.5tha1FYM,200kgha1DAP,100kgha1CANa

113 60 2009/12 LS Babycorn 11.3tha1_FYM,200kgha1_DAP,100kgha1_CANa _{113 60}

SS IrishPotatoes 7.5tha1FYM,300kgha1TSP,200kgha1CANa

103 83

Org-High 2007/10 LS Maize/Mucunab

7.5tha1FYM-compost,364kgha1RP,5.4tha1Tithoniamulch&3.9tha1

Tithoniafreshleavesusedastea

96 54

SS Cabbage 15tha1FYM-compost,400kgha1RP,6tha1Tithoniamulch&6tha1

Tithoniafreshleavesusedastea

145 64

2008/11 LS Babycorn/ Mucunab

11.3tha1_{FYM-compost,364kgha}1_RP,5.4tha1_{Tithoniamulch&3.9tha}1 Tithoniafreshleavesusedastea

113 60

SS Frenchbeans 11.3tha1FYM-compost,364kgha1RP,5.4tha1Tithoniamulch&3.9tha1

Tithoniafreshleavesusedastea

113 60

2009/12 LS Babycorn/ Mucunab

11.3tha1FYM-compost,364kgha1RP,5.4tha1Tithoniamulch&3.9tha1

Tithoniafreshleavesusedastea

113 60

SS IrishPotatoes 11.3tha1_{FYM-compost,581kgha}1_RP,8.2tha1_{Tithoniamulch 103 83}

Conv-Low 2007/10 LS Maizeb

5tha1offreshFYM,50kgha1DAP 31 18 SS Kales/Swisschard 1tha1offreshFYM,50kgha1TSP,60kgCAN 20 13 2008/11 LS Maizeb

5tha1offreshFYM,50kgha1DAP 31 18 SS Grainlegumes Nofertilizerapplication NA NA 2009/12 LS Maize/beansb

5tha1offreshFYM,50kgha1DAP 31 18 SS Irishpotato

Potatoes

2tha1_{offreshFYM,100kgha}1_{DAP, 27 25}

Org-Low 2007/10 LS Maizeb

5tha1FYM-basedcompost,100kgha1RP,1.36kgha1Tithoniamulch 31 18 SS Kales/Swisschard 1tha1offreshFYM-compost,1.2Tithonianmulch,90kgha1,1.2tha-1

Tithonia

freshleavesusedastea

20 13

2008/11 LS Maize/beansb _5tha1_{FYM-basedcompost,100kgha}1_RP,1.36kgha1_{Tithoniamulch 31 18}

SS Grainlegumes Noinputapplication NA NA

2009/12 LS Maize/beansb

5tha1FYM-basedcompost,100kgha1RP,1.36kgha1Tithoniamulch 31 18 SS Potatoes 2tha1FYM-basedcompost,200kgha1RP,2.72kgha1Tithoniamulch 27 25

1

Conv-High,conventionalhighinputsystem;2

Org-High,Organichighinputsystem;3

Conv-Low,conventionallowinputsystem;4

Org-Low,organiclowinputsystem. Assumptions:FYM/compost(DW):1.12%totalNand0.3%P(Lekasietal.,2003);DMofFYMisassumedtobe40%;Tithoniadiversifolia(DW):3.3%N;0.31%P;3.1%K

(Nziguhebaetal.,1998);DMofTithonia=20%;PhosphaterockfromWestAfrica(Finck):11–13%P.

a_{CAN=calciumammoniumnitrate,CANwasappliedastop-dressinginallthecrops:Intwosplitsforhighinputonlyforspecificcropsinlowinput.} b

CompostpreparationstartswiththeindicatedamountofFreshfarmyardmanure(FYM)andwasappliedatplanting.DAP=Di-ammoniumphosphate;TSP=triple superphosphate;RP=rockphosphate;LS,longrainseason;SS,shortrainseasons.TithonianmulchwasappliedaftercropgerminationasstarterN.Organichighinputsystem alsoreceivedmaizestover.

distributionofrainfallonyieldswasassessedthroughcomputing

the occurrence of dry spells that exceeded 5, 10, 15 or 20

consecutive days,usinga rainfallthreshold valueof 1mm.The selectionoftherainfallthresholdvaluewasbasedontheargument of Ngetich et al. (2014): that when there is less than 1mm of rainfallthewaterremainsonthesurfaceofthesoilorontheplant coverandreadilyreturnstotheatmospherethrough evapotrans-piration.

2.2.Soil,manure,compostandplanttissueanalysis

SoilpHwasanalysedusinga1:2.5soiltowaterratio(w/w)as

described by Okalebo et al. (2002). Soil particle size was

determined by the hydrometer method (Bouyoucos, 1962).

Potassium(K),calcium(Ca),magnesium(Mg), sulphur(S)were analysed afterextraction using 20mLof Mehlich 3 solutionas

described by Mehlich (1984). Total N was determined by the

KjeldahlmethodasdescribedbyGupta(1999)andPbytheOlsen

method according to Okalebo et al. (2002). Exchangeable

aluminium(Al)was analysedwitha spectrophotometer(model

Shimadzu1240)atawavelengthof567nmafterextractionusing potassiumchloride(Kennedyand Powell,1986).Organiccarbon was assessed by the wet oxidation method (Robinson, 1994).

Compostand manuresampleswereair-driedunder shade toa

constant weight and ground (<0.25mm, 60

m

m mesh). After-wards,0.3goftheairdriedsampleswereanalysedforN,PandK,as

describedbyOkaleboetal.(2002).ToevaluateN,P,andKuptake anddrymatteraccumulation,twoplantswereselectedatrandom fromoutsidethenetplotareaof66matharvestandtheabove

ground plant biomass samples were oven-dried at 60C to a

constantweighttodeterminethedrymatteryield(DMY).Dried plantsamplesweregroundintoafinepowderinamillandsieved (<0.25mm, 60500

m

m mesh).Afterwards, 0.3gof each of the

ground sampleswas analysed forN usingtheKjeldahl method

(Okaleboetal.,2002).ForPandK,0.5gofeachgroundsamples wasdestroyedthroughvolatilisationoroxidationbydry combus-tioninaMufflefurnaceatatemperatureof500Cfor6hours,and thesolublemineralconstituents,whichformthemainpartofthe residualash,weredissolvedindiluteacid(Hydrochloricacid,HCl). Anysilicapresentwasdehydratedandthereforemadeinsoluble. Thesamplesolution(orfiltrate)wasrunonaspectrophotometer andflamephotometertodeterminePandK(Okaleboetal.,2002).

2.3.Theproductivityandeconomicevaluationoffarmingsystems

Productivitywasmeasured astheoutput(economic market-ableyield)perplotandisgivenonaperhectarebasis.InKenyalow inputfarmersmainlyselltheirproduceonthelocalmarketorat thefarmgate,whilstthehighinputfarmersmainlyselltoregional orexportmarkets.Localinformationsourcesindicatedthatsome lowinputfarmers,especiallythoseclosetotheregionalmarkets, alsoselltheirproduceonthesemarkets.Thisledustoanalyseand Table3

TheamountandfrequencyofirrigationwaterandtypeandrateofpesticidesappliedinthelongtermsystemcomparisontrialinChukaandThika,Kenya. Farming

Systems

Year Crop Amountofirrigation waterappliedper season(m3_ha1₎

Frequencyof irrigation

Pest&diseasemanagement

Chuka Thika Chuka Thika Typeofchemicalsyandpestcontrolfortermitesandstem borer Conv-Higha 2007/ 2010 Maize * (445.50) * (**) * (8) * (**)

Bulldock(Beta-cyfluthrin) [Bulldock+Dragnet(Permethrin)] 2008/ 2011 Babycorn * (167.06) * (1698.47) * (3) * (18)

Bulldock(Beta-cyfluthrin) [Bulldock+Fungiicipeisolate30z)] 2009/ 2012 Babycorn 668.25 (365.31) 4009.50 (692.50) 12 (4) 31 (11)

Bulldock+WoodAsh

[Bulldock+Confidor(limidacloprid)] Org-Highb 2007/ 2010 Maize * (445.50) * (**) * (8) * (**)

Neem(Azadirachtaindica)oilextract

[Delfin(Bacillusthuringiensis)+Fungiisolate30] 2008/ 2011 Babycorn * (167.06) * (1698.47) * (3) * (18)

Thuricide(Bacillusthuringiensisv.Kurstaki) [Delfin(Bacillusthuringiensis)+Fungiisolate30] 2009/ 2012 Babycorn 668.25 (365.31) 4009.50 (692.50) 12 (4) 31 (11)

Aschook(A.indica)+Dipel

[Delfin(Bacillusthuringiensis)+Fungiisolate30] Conv-Lowc

2007/ 2010

Maize NA NA NA NA Woodash+soil

[Woodash+Dragnet] 2008/

2011

Maize/ beans

NA NA NA NA Woodash+soil

[Woodash+Plantextractb] 2009/

2012

Maize/ beans

NA NA NA NA Woodash+soil

[Woodash+Confidor] Org-Lowd

2007/ 2010

Maize NA NA NA NA Woodash+Soil

2008/ 2011

Maize/ beans

NA NA NA NA Woodash+Soil

[Woodash+Plantextract] 2009/

2012

Maize/ beans

NA NA NA NA Woodash+Soil

[Woodash+Plantextract]

*Therewasnoirrigationin2007and2008firstseasonbecauseirrigationfacilitywasnotinstalled.Thecropwasgrownunderrain-fedcondition;**Noirrigationbecausethere wasadequaterainfallamountanddistributionin2010atThika;Valuesinbracketsarefor2010,2011and2012;pesticidesappliedin2010,2011and2012areshowninsquared brackets;bPlantextractsareconcoctionsuppliedbyicipe.NA,notapplicablebecausethecropwasgrownonlyunderrain-fedcondition.zMetarhiziumanisopliae;yRateof chemicalforpestcontrol;Achook2Lh1_{,Buldock7kgha}1_{,Fungiicipeisolate30313kgha}1_{,Confidor1.9Lha}1_{,Neemoilextract3.3Lha}1_{,Thuricide0.5kgha}1_{,Dipel0.5kgha}1_,

Delfin0.3kgha1

,Woodash75kgha1

,Dragnet1.6Lha1

andPlantextract1171Lha1

.

a

Conv-High,conventionalhighinputsystem.

b

Org-High,Organichighinputsystem.

c

Conv-Low,conventionallowinputsystem.

d

comparetheprofitabilityofthefarmingsystemsunderbothlocal andregionalmarketconditions.Thepriceswerestandardisedby ensuringthataveragewholesalepriceswereusedforallproducts acrossthedifferentmarketsconsidered.Thiswastotakecareof any fluctuation in inputs in each year as well as to eliminate variationsthatmightoccurasaresultofretailers’interventions. MarketpriceswerecollectedfromRATIN(http:/www.ratin.net)for conventional produce on regional markets (Table 4), premium marketpricesfororganicproducewerecollectedfromfiveorganic shops for the regional market and from farmers and farmers’

groupsatThikaandChukaforthelocalmarket(Table4).Gross revenuewascalculatedbymultiplyingtheeconomicmarketable yieldsbytheprevailingsellingpricesatthelocalmarkets(Thika andChuka)andtheregionalmarket(Nairobi)(Table4).

Profitabilityisarelativetermderivedfromprofit,whereprofit istotalfarmprofits(grossrevenue)minustotalproductioncosts (Lipsey,1975).Totalproductioncostscanbeclassifiedintofixed costsandvariable costs.Therewerenofixedcostsexcept land whichwascommontoallsystems.Landwasassumedtobeowned bythefarmerandnotrented;theonlycostscalculatedwerethe

variable costs which were considered to make up the total

productioncost.Inthiscase,thegrossmarginbecomesthesameas profit.Variable costs consistedof inputs, labour, any irrigation facility and transport costs associated with the production, harvestingand marketing stages. These inputs included seeds, syntheticfertilisers,rockphosphate,farmyardmanure,compost, pesticidesandwater.Labourcostsconsistedofallfieldlabour(for preparingtheland,compostandmanure,weeding,theapplication of fertilisers, watering and maintaining the irrigation facility,

harvesting, sorting and shelling the maize), the time spent

sourcinginputsandmarketing.Thelabourwasvaluedbasedon field labourtime and thewage rate of hired farmlabourers at ChukaandThika.NomarketpricewasavailableforTithoniamulch, teaor Mucunamulch.Theirvaluations werebased onthetime takentopreparethemcalculatedattheprevailingwageratefor hiredfarm labourers atChuka and Thika(asprescribedbythe

KenyaGovernment).

A straight-line depreciation method was used to calculate depreciation expenses by spreading the cost of the irrigation facility(tank,pipes,driplinesandconnectors)overitsdepreciation periodwithequalperiodiccharges.Thesuppliersoftheirrigation facilityguaranteedthetanks,pipes,andconnectorsforaperiodof tenyears. We took this figure as the expected lifespan of the irrigationfacility and applied it tothe depreciationcalculation

(personal consultation with Irrigation Department of Kenyan

AgricultureandLivestockResearchOrganisation,KALRO). Depre-ciationwascalculatedusingthefollowingequation:

Yearlydepreciation value foreach irrigationfacility=[(Cost value-salvagevalue)/Depreciationperiod].

Transport costs include the cost of sending produce to the marketsandthecostofpurchasinginputsandirrigationmaterials forthehighinputsystems.Thepricesofinputsweredetermined for every season from local retail shops at Chuka, Thika and Nairobi.Theprofitabilityofthetwoorganicsystemswascalculated withandwithoutthepremium.Withthepremium,thecertifi ca-tioncostwasalsofactoredintothetotalproductioncosts.Thecosts ofcertificationandinspectionfororganicproductionwerebased

on prevailing national rates in Kenya. These consisted of a

registrationfee=5000 Ksh(ca.58.14$),aninspectionfee=7500 Ksh(ca.87.21$)perday,reportwriting=5000Ksh,(ca.58.14$),and issuingacertificate=5000Ksh(ca.58.14$)(personalcontactwith NESVAXcontrol,Nairobi,Kenya).Abenefit-costratiowhichshows the relationship between costs and benefits was also used to comparetheperformanceofthefarmingsystems.Inourcasethe benefitcostratiowascalculatedasthegrossmargindividedbythe totalvariableproductioncost.Theprofitabilityofbothorganicand conventional systemswasestimatedfor thedirecteffectof the fertilisersontheyieldsofmaize,babycornandbeans.Theresidual fertilisereffectwasnottakenintoconsideration.

2.4.Nutrientinput,output,exportandpartialnutrientbalance

TheN,PandKcontentsofallsoilinputsappliedineachofthe systems (Table 2) were calculated to determine the specific nutrientinputs.Similarly,thenutrientcontentsofalltheoutputs (theabovegroundbiomassformaize,babycornandbeans,grain yieldformaizeandbeans,maizecobsandhusks)werecalculated. Nutrientfluxes betweennutrient pools withinthe system (e.g. litterfall)andotherinputpathwayssuchasmineralweathering, deepsoilexploitation,biologicalN_fixation;andoutputssuchas volatilisationandleachingwerenotconsideredinthiscalculation. Outputsbyerosionorrunoffwereavoidedsincetheplotswereflat, withaslopelessthanorequalto2%.Partialnutrientbalanceswere calculatedasthedifferencebetweennutrientinputsandoutputsin eachfarmingsystem.Theexportofnutrientswascalculatedfrom theN,Pand Kcontentof allproducethatlefttheplots.In the conventionalfarmingsystemsallthebiomasswastakenfromthe Table4

Labourpricesperworkinghour,andmarketpricesofmaize,beansandbabycornintheCentralHighlandsofKenya. Year Labour(Kshh1_{) Regularpriceofcommodity(Kshkg}1₎

Location Maize Beans Babycorn

Chuka Thika Chuka Marketa Thika Marketa Nairobi Marketb Chuka market Thika market Nairobi Market Chuka market Thika market Nairobi market 2007 12.50 12.50 11.00 13.50 13.00 – – – – – – 2008 15.00 15.00 23.00 22.00 20.00 50.00 50.00 51.00 18.00 18.00 NA 2009 15.63 18.75 26.00 25.00 28.00 44.00 50.00 50.00 15.00 15.00 NA 2010 16.88 25.00 13.00 17.00 18.00 – – – – – 2011 21.88 25.00 24.00 26.00 34.00 48.00 60.00 66.00 22.00 22.00 NA 2012 31.25 41.88 30.00 30.00 34.00 44.00 55.00 67.00 25.00 25.00 NA

Priceofcommoditywithpremiumc

(Kshkg1)

2010 25.00 30.00 40.00 – – –

2011 30.00 35.00 40.00 60.00 70.00 75.00 35.00 35.00 NA

2012 35.00 35.00 40.00 60.00 70.00 75.00 35.00 35.00 NA

a_{WholesaleannualaveragepricefromfarmersandfarmergroupinChukaandThika.} b

WholesaleannualaveragepricefromRATIN(http://www.ratin.net/http://www.ratin.net/).

c

OrganicpriceisawholesaleaverageannualpricefromBridgeesOrganicshops,KalimoniOrganicShops,Greendreamsorganicshop,Zucchinigreenshop.Premium consideredonlyfrom2010(afterconversionphaseaccordingtoIFOAM).Conversionrate:1Ksh=0.015USD(2007&2008),1Ksh=0.013USD(2009),1Ksh=0.012USD(2010, 2011,2012)OANDAcurrencyconverter,22.01.2014NA,notavailable.

farm;whilstintheorganicfarmingsystemsonlythegrains,cobs andhusksweretakenaway,therestofthebiomasswererecycled backinto thesoilthroughdirect incorporationand composting

(this was based on thecommon practices of conventional and

organicfarmersinthestudyarea).

2.5.StatisticalAnalysis

DatavalidationatthesiteinThika,revealedthenecessityto excludesomeof thelowinputplots. In Conv-Low,plot12was

excluded between2007and 2010due toa falloweffect which

producedhighyields,aswas plot15whichexperiencederosion whichledtocropfailureintheseyears.InOrg-Lowplot10was excludedduetoafalloweffectwhichproducedexcessiveyields between2007and2011.Inthehighinputsystemsplots9and20 wereexcludedfromConv-High,andplots11and17fromOrg-High

in 2007 and 2008. This was also due to fallow effects which

producedhigheryieldsthantheotherplots.Agronomicandsoil parameterswerefirstcheckedfornormaldistributionusingthe ShapiroWilkWTest.TheBartlett’stestwasselectedtotestthe homogeneityofvariancesbetweenconventionallyandorganically managedplots. Initially, crop yieldswere analysed acrossboth locationsforeachofthethreetestcropsacrosstheyearsinallthe

cropping systems with linear mixed effect models using the

statisticspackage‘JMP’,version5.0.1(SASInstituteInc.,Cary,NC, USA).Assitehadasignificanteffectontheyieldsinmostcases,

two-wayandthree-wayANOVAwereperformedindependently

foreachsiteandthetwoinputlevels(lowandhigh).Analysesof

variance (ANOVA) were performed at a significance level of

(P<0.05,0.01and0.001),usinglinearmixedeffectmodelswith site,systemandcycleasfixedeffects,andreplicationandyearas randomintercepts.Thecyclewasincludedasafactorinthemodel toaccountforeffectsoftherotationonthesameplot.Theanalysis

was followed by a Tukey-Kramer multiple comparison test

(P<0.05)(Tukey’shonestlysignificantdifferenceHSD).A three-wayANOVAwasperformedformaizeyieldsassessedundersole

cropping at Chuka and Thika, for conventional and organic

systems, in the first and second crop rotation (factors: site, system,cycle).Afour-wayANOVAwasperformedforbabycorn (undersole cropping), and maize/beanintercrop at Chuka and Thikaforconventionalandorganicmanagementsystemsintwo consecutiveyearsofthefirstandsecondcroprotations(thefactors weresite,system,cycleandyear).Interactionsbetweenthefactors wereconsideredinalltheANOVAtests.Withtheeffectsofcycle andyearbeingsignificantin mostcases,thesystem effectwas furthertestedseparatelyineachcycleandyear(cyclebeingequal toyearinthecaseofsolecroppedmaize).Repeatedanalyseswere appliedforthetotalproductioncosts,grossrevenueormarginsof

maizeorbabycorngrownundersolecroppingandmaize-bean

underintercropping.

3.Results

3.1.Effectsofsiteandmanagementsystemsoncropyields

Soil and weather:-the two sites showed differences in soil characteristics(Table1),theamountanddistributionofrainfall (Fig.1)andtheoccurrenceofdryspells(Table5).Atbothsitesthe

rainfall over the six main seasons was erratic and unevenly

distributed.InChuka,therainfallbetween2007and2012ranged

from 279 to 557mm in the long rainy seasons and averaged

416mm.Over85%ofallrainfallgenerallywasreceivedduringthe first45daysafterplanting(DAPT)(i.e.whenthemaizereached kneeheight)(Fig.1).AtThikaduringthelongrainyseasonthe rainfallrangedfrom272to461mmandtheaveragewas322mm (Fig.1).Over82%ofalltherainfallwasreceivedduring50DAPTin

allthecroppingseasonsinThika,exceptin2011whereonly70% wasreceivedduring50DAPT.BothChukaandThikahadasimilar frequencyof totaldry spellsduring the cropgrowthperiod in

eachlong rainyseason, exceptin2009 and 2012whereChuka

recordedfewerdryspellsthanThika(Table5).In2011Thikaalso hadfewerdry spellsthanChuka. Thehighestfrequencyofdry spellsofatleast5daysdurationwasrecordedatChukainallsix

cropping seasons. By contrast Thika recorded the highest

frequencyofdryspellsofatleast10to15daysineverycropping season.

Cropyields:Yieldsofmaizegrainandcobsofbabycorninthe highinputsystemsatChukawere60and40%higherthanatThika (Table6).InthelowinputsystemsthemaizeyieldatChukawas2 to4timeshigherthanatThika.Thecomparisonsamongcropping systemswereconsistentacrossthetwositesasindicatedbythe non-significantdifference for the site x system interaction for thesecrops(Table6).Therewere,however,significantsitexcycle interactionsontheyieldsofbabycornormaizegrainasasoleora relayinter-cropinthehighinputsystems,andyieldsofmaizegrain astheinter-cropinthelowinputsystems(Table6).

3.2.Cropyieldunderdifferentmanagementoptions

Solecroppedmaize:inthelowinputsystemsatChuka,maize grainyieldsinConv-LowandOrg-Lowweresimilarin2007(inthe 1stcycle,alsoreferredtoastheconversionperiod)and2010(inthe 2ndcycle,alsoreferredtoasafter-conversioninorganicfarming) (Table 7a). However, at Thika maize grain yields increased significantly from 2007 to 2010 (P=0.001) by a factor of 3 in Conv-Lowandafactor7ofOrg-Low.TheyieldsinConv-Lowwere3 times higher than theyields in Org-Low in 2007 but this gap reducedto1.5timesin2010(Table7a).AtChuka,therewasno significantdifferencebetweenthehigh-inputsystems(Conv-High andOrg-High)onmaizegrainyieldsin2007and2010(Table7b). Maizegrainyieldsincreasedsignificantly(P<0.001)from2007to 2010inbothConv-HighandOrg-High.InthisperiodConv-High maize grainyields increasedby 28%, whilstin Org-Highyields

increased by 54%. Maize grain yields at Thika though

exceptionally low – were nearly 4 times higher in Conv-High

thaninOrg-High(P<0.05)in2007(Table7b).By2010theyieldsin Org-Highincreasedandthedifferencebetweenthetwosystems wasnolongersignificant.

Maizeintercroppedwithbeans:inthetwolow-inputsystems therewasnosystemeffectonmaizeintercroppedwithbeansat Chuka(Table8a).MaizegrainyieldsinbothConv-Lowand

Org-Low nearly doubled between the 1st cycle of 2008 and 2009

(P<0.001).AtThika,nosignificantsystemeffectonmaizegrain

yields was observedwhen they were intercroppedwith beans,

eventhoughin 2008maizegrainyieldsfromConv-Lowwere3

timeshigherthanthoseofOrg-Low(Table8a).Maizegrainyields inthe2ndcycleofConv-Lowwere2to10timeshigherandthoseof Org-Lowwere2to25timeshigher(P<0.001)thaninthe1stcycle atbothChukaandThika.BeangrainyieldsinConv-Lowand Org-Lowwerealsosimilar.

SolecroppedBabycorn:whilsttherewerenodifferencesin babycornyieldsbetweenthefarmingsystemsinindividualyears atbothsites,asanaverageoveralltheyearsOrg-Highproduced 8.6%higher(P<0.05)babycornyieldsthanConv-HighinChuka (Table8b).AtChuka,babycornyieldsduringthe1stcycle (2008-2009)increasedsignificantly(P<0.001)byafactorof3.9in Conv-Highandbyafactorof2.9inOrg-High.Cobyieldsofbabycorn remainedataroundthesamelevel duringthe2ndcycle (2011-2012).AtThika,babycornyieldsin2008wereverylowforboth Conv-HighandOrg-High,butin2009theywereexceptionallyhigh (P<0.001).In2011babycornyieldsdecreased(P<0.001)inboth systems and remained fairly stable the next year. It is worth

mentioningthatonaverage,cobsofbabycornwereharvested17 timesinOrg-Highascomparedto12timesinConv-Highatboth ChukaandThika.Also,whereasConv-Highshowedhighyieldsat theonsetof harvesting and decreasingyieldstowards theend, Org-Highshowedloweryieldsatthebeginningofharvestingthat increasedtowardstheendoftheharvestingperiod.

3.3.Aneconomicevaluationofconventionalandorganicfarming systems

The production costs in Org-Low in 2007 were12% higher

(P<0.001)than thosein Conv-low(Fig.2a–b)atThikaand 17% higheratChuka.In2008and2009,however,theproductioncosts Fig.1.Cumulativerainfalldistributionduringthecropgrowthperiod(March/ApriltoAugust/September)forsixconsecutiveyearsinthelongtermsystemscomparisontrial sitesatChukaandThika,KenyanCentralHighlands.

betweenthetwolowinputsystemswerearoundthesameatboth sites.Withtheinclusionofcerti_ficationcostsfrom2010to2012,

the production costs in Org-Low at Chuka in 2010 were 100%

higherthanthecostsinConv-LowandthoseatThika31%higher

(P<0.001).Thishugedifferencehoweverreducedin2012,with Org-Lowrecording10%higherproductioncoststhanConv-Lowin Thikaand47%higherproductioncostsinChuka.Theproduction costsin2007ofmaizeinOrg-Highwere36%higherthanin Conv-Table6

EffectsofthesitesonaveragemaizeandbabycornyieldsinconventionalandorganicfarmingsystemsatChukaandThika,intheCentralHighlandsofKenya. Croppingsystems Maize,solecropping Babycornsolecropping Maizeintercropping

Highinputsystem Lowinputsystem Highinputsystem Lowinputsystem Site Yield(tha1_{) Yield(tha}1_{) Yield(tha}1_{) Yield(tha}1₎

Chuka 5.01a 3.13a 9.93a 3.74a Thika 3.12b 1.25b 7.1b 0.91b

ANOVAsoflinearmixedeffect modelsSourceofvariation

Prob>F Site 0.0001 0.0036 0.0005 0.0001 Cycle 0.0001 <0.0001 0.7424 <0.0001 Sitexcycle 0.0001 0.0192 0.03 0.4293 System 0.9595 0.3221 0.0631 0.9748 Sitexsystem 0.1968 0.0839 0.1339 0.9032

Significantdifferences(P<0.05)betweensitesareindicatedbytheletteraandb.

Table7

a-bMeangrainyields(13%drymatter)ofmaizegrownundersolecropping/relay-intercroppinginhighandlowinputconventionalandorganicfarmingsystemsatChukaand ThikaintheCentralHighlandsofKenya.

a)Maize b)Maize

Lowinputsystems,solecropping Highinputsystems,solecropping/relayintercropping

Chuka Thika Chuka Thika

Farmingsystem (tha1₎w _semx _ny _(tha1_{) sem n (tha}1_{) sem n (tha}1_{) sem n}

Cycle1(2007)u Conventional 2.56a 0.34 4 0.73a 0.09 3 4.30a 0.36 4 0.77a 0.23 3 Organic 3.13a 0.32 4 0.23b 0.03 4 4.05a 0.26 4 0.21b 0.08 4 Cycle2(2010) Conventional 3.54a 0.58 4 2.36a 0.23 3 5.49a 0.48 4 5.86a 0.27 5 Organic 3.30a 0.59 4 1.70b 0.24 4 6.23a 0.26 4 5.81a 0.23 5

Average(cycle1&2)v

Conventional 3.05a 0.36 8 1.55a 0.42 6 4.89a 0.36 8 3.26a 0.95 8 Organic 3.22a _{0.31 8 0.97}b _{0.30 8 5.14}a _{0.44 8 2.99}a _{0.99 9}

ANOVA(Cycle1&2)

Sourceofvariation Pvalue Dfz

Pvalue Df Pvalue Df Pvalue Df

System(S) 0.627 1 0.010 1 0.423 1 0.305 1

Cycle(C) 0.120 1 <0.001 1 <0.001 1 <0.001 1

SxC 0.250 1 0.278 1 0.129 1 0.397 1

Significantdifferences(P<0.05,0.001)betweenfarmingsystemsareindicatedbytheletteraandb.

u _{ANOVApercycle:One-wayanalysisofvarianceincludingthefactorSystem.} v

ANOVAbothcycles:Two-wayanalysisofvarianceincludingthefactorsSystemandCycle.

w

Turkey-test:Valuesnotconnectedwiththesameletterdiffersignificantly(P<0.05).

x

Sem=standarderrorofmeans.

y

n=numberofobservations.

z_{Df=degreeoffreedom.} Table5

Frequencywithwhichdryspellsexceeded5,10,15and20consecutivedaysduringcropgrowthperiodinthelongrainyseasonsatthelong-termsystemscomparisontrialat ChukaandThika,intheCentralHighlandsofKenya.

Year Occurenceofdryspell

Chukasite Thikasite

>5days >10days >15days >20days Total >5days >10days >15days >20days Total

2007 4 1 1 2 8 4 1 1 2 8 2008 4 2 1 7 2 1 3 1 7 2009 2 0 0 1 3 4 1 1 1 7 2010 4 0 0 2 6 2 1 1 1 5 2011 5 0 3 1 9 1 0 1 2 4 2012 1 0 1 1 3 4 1 3 0 8 Total 20 3 5 8 17 5 10 7

HighatThika,and65%higheratChuka(P<0.0001)(Fig.2a–b).In 2008thedifferenceincostsreducedto1.6%inThikaand53%in Chuka.In2009thecostinConv-Highwas7%higher(P<0.05)than Org-HighinChukaand17%higherinThika.Withtheinclusionof certificationcostsbetween2010and2012theproductioncostsin Org-HighexceededthoseofConv-High,by2.4timesinChukaand by 89% in Thika (P<0.0001). This huge difference, however,

reduced in 2012, with Org-High recording 41 and 44% higher

(p<0.001)coststhaninConv-HighatChukaandThika.

A similar trend was observed when production costs were

calculatedfor the regionalmarket (inNairobi, seeAnnex 2a-b,

supplementary sheet). However, purchasing inputs from, and

transporting farm produce to, Nairobi’s markets increased the productioncostsslightlyabovethoseincurredwhenbuyingand sellinglocallyatChukaandThika.Ontheaveragetheproduction costsofConv-Highin2007were1.7timeshigher(P<0.0001)than forConv-LowatChukaand2.3timeshigher(P<0.0001)atThika. In2012theywere1.8to2.3timeshigher.Similarly,theaverage productioncostsforOrg-Highin2007were2.5timeshigherthan forOrg-LowatChukaand2.9timeshigheratThika.In2012,when certification costswerealsoafactor,thecostswere1.8 and2.5 timeshigheratthetwosites(P<0.0001).

Thecumulativetotalrevenueobtainedforsellingproduceat localandregionalmarketsisshowninFigs.3a–dandAnnex3a-d ofthesupplementarysheet.Therewasnosignificantdifferencein thetotalrevenueobtainedfromConv-LowandOrg-Loworfrom Conv-HighandOrg-High whensellingtheproduceata regular

pricesoneitherthelocal(Fig.3a&c)orregionalmarkets(Annex3a &c).ThetotalrevenueobtainedfromOrg-Lowwas1.2to1.4times higherthanthatobtainedfromConv-Low.Between2009and2012

the total revenue from Conv-High and Org-High was higher

(P<0.05,0.001)thanthetotalrevenuefromConv-LoworOrg-Low atbothsites.Withapremiumpricefororganicproducefrom2010 onwardsthetotalrevenueobtainedfromOrg-Highin2011and 2012was1.4to1.5timeshigher(P<0.05,0.0001)thanfrom Conv-High at both sites(Fig.3b& d).The cumulative grossmargins (profits)forthedifferentfarmingsystemsareshowninFigs.3e–h andAnnex3e-h,supplementarysheet.Exceptin2007,whenthe profitfromConv-Highwas2.1to3.8higher(P<0.0001)thanfrom Org-High(underbothlocalandregionalmarkets),therewasno significantdifferenceintheprofitmadefromConv-Highand Org-Highwhentheorganicproducewassoldatregularprice(Figs.3e& g,Annex3e&g).Withthepremiumpriceonorganicproducefrom 2010to2012,theprofitobtainedin2011fromOrg-Highonthe localmarketwas1.3timeshigherthantheprofitfromConv-High atChukaand3.2timeshigheratThika(P<0.001)(Figs.3f&h).In 2012theprofitfromOrg-Highwas1.5timeshigherthanthatfrom Conv-HighatChukaand4.1timeshigheratThika.Similarly,the profitfromOrg-Highin2011onthemarketinNairobiwas40% higherthantheprofitfromConv-HighatThikaand60%higherat Chuka(P<0.01,0.001)(Annex3f&h).In2012theprofitfromthe samemarketforOrg-Highwas60%and90%higherthanfor Conv-High.WhereastherewasamarginallylargerprofitfromConv-High

than Conv-Low in 2012 at the Nairobi market, when organic

Table8

a-bMeancobyields(freshmatter)ofbabycorngrownundersolecropping/relay-intercroppingandmaizegrainyields(14%drymatter)grownunderintercroppinginhigh andlowinputconventionalandorganicfarmingsystemsatChukaandThikaintheCentralHighlandsofKenya.

a)MaizeandBeans b)Babycorn

Lowinputsystems,intercropping Highinputsystem,solecropping/relay cropping

Chuka Thika Chuka Thika

Maize Beans Maize Beans Babycorn Babycorn

Farmingsystem (tha1)w _semx _(tha1_{) sem (tha}1_{) sem (tha}1_{) sem (tha}1_{) sem (tha}1_{) sem}

Cycle1(2008&2009)t Conventional 8.52a 2.02 6.40a 2.19 Organic 8.90a 1.7 6.20a 2.18 Year2008u _{Conventional 2.48}a _{0.77 0.23}a _{0.09 0.21 0.12 na na 3.45}a _{1.15 0.31}a _0.01 Organic 1.98a 0.55 0.25a 0.10 0.07 0.02 na na 4.50a 0.71 0.14a 0.05 Year2009 Conventional 4.23a 0.76 1.03a 0.14 0.14 0.09 0.18a 0.07 13.60a 0.69 12.23a 0.28 Organic 3.77a 0.27 0.82a 0.20 0.14 0.01 0.20a 0.08 13.30a 0.16 12.00a 0.32

Cycle2(2011&2012) Conventional 10.51a _{0.48 7.63}a _0.19

Organic 11.78a _{0.42 7.93}a _0.2 Year2011 Conventional 3.92a 0.56 0.62a 0.13 2.16 0.49 0.21 0.10 10.73a 0.22 7.63a 0.21 Organic 5.48a 0.39 0.73a 0.24 2.75 0.63 0.32 0.12 11.03a 0.18 8.40a 0.19 Year2012 Conventional 4.33a 1.07 0.70a 0.17 1.12 1.12 0.11 0.06 10.29a 0.99 7.63a 0.34 Organic 3.56a _{0.73 0.78}a _{0.11 0.84 0.84 0.11 0.06 12.52}a _{0.64 7.46}a _0.19

Average(cycle1&2)v

Conventional 9.52b 1.03 6.99a 0.94 Organic 10.34a 0.92 7.04a 0.94

ANOVA(Cycle1&2) Sourceofvariation Pvalue Df Pvalue Df Pvalue Df Pvalue Df Pvalue Df Pvalue Df System(S) 0.905 1 0.098 1 0.913 1 0.106 1 0.042 1 0.774 1 Cycle(C) 0.012 1 0.28 1 <0.0001 1 0.854 1 0.659 1 0.8 1 Year[C] 0.0004 3 <0.001 3 0.0001 3 <0.0001 3 <0.01 2 <0.001 2 SxY[C] 0.088 3 0.733 3 0.302 3 0.07 3 0.115 2 0.127 2 Significantdifferences(P<0.05,0.001)betweenfarmingsystemsareindicatedbytheletteraandb.

t

ANOVApercycle:Two-wayanalysisofvarianceincludingthefactorsSystemandYear.

u

ANOVAperyear:One-wayanalysisofvarianceincludingthefactorSystem.

v_{ANOVAbothcycles:Three-wayanalysisofvarianceincludingthefactorsystem.} w _{Tukey-test:Valuesnotconnectedwiththesameletterdiffersignificantly(P<0.05).} x

producewas soldat a premium the profitfrom Org-High was significantlyhigher(P<0.05,0.001)thantheprofitfromOrg-Low in all themarkets. There was noappreciable benefit in selling producegrownunderanyofthesystemsatThikaateithermarket. OnthelocalmarketatChuka,theseasonalbenefitcostratio(BCR) forConv-Lowwas0.3in2007and1.2in2012.In2009itreached 2.2.TheBCRforOrg-Lowstartedat0.5in2007andincreasedto2.3 in2009,beforefallingbackagainto0.2in2010and0.5in2012.In thehighinputsystem,theBCRforConv-Highrangedfrom0.1to0.5 between2007and2012,exceptin2011whenitwas1.4(Fig.4a–b). InOrg-High,theseasonalBCR(withnopremiumprice)was0.2in 2008and1.2in2009,butthendeclinedto0.1in2010and0.4in 2012.OntheregionalmarkettheseasonalBCRforproducefrom theConv-HighsystematChukarangedfrom0.3in2007to1.0in

2011 (Annex 4a-b, supplementary sheet). In Org-High the BCR

rangedfrom0.4in2007to1.1in2011.AtThika,theBCRforallthe systemsunderboth localandregionalmarketswasless than1 (Figs.4c&d,Annex4a&dsupplementarysheet).

3.4.Theeffectoffarmingsystemsonnutrientexportandpartial nutrientbalances

Thecumulativenutrientinputsandexportsfromthedifferent farmingsystemsareshowninFig.5.Attheendofsixyears,540 and562kgNha1,337and901kgKha1wereexportedfrom Conv-High,more(P<0.05)thantheamountexported fromOrg-High (147and224kgNha1;94and149kgKha1).Onaverage,135and 138kgNha1, 15 and 13kg P ha1,113 and 192kgKha1 were

exported seasonally from Conv-High at Thika and Chuka,

significantlymorethanthe37and42kgNha1,5.3and5.7kgP ha1,31and36kgKha1exportedseasonallyfromOrg-High.In Conv-Low, 48 and 119kgNha1, 3 and 10kg P ha1, 38 and

93kgKha1 were exported seasonally compared to 23 and

55kgNha1, 3 and 8kg P ha1, 6 and 22kgKha1 exported seasonallyfromOrg-Low(Table9).AtChuka,similarNandPwere

exportedfromConv-Lowand Conv-High,whilsthigherN andP

wereexportedfromOrg-LowcomparedtoOrg-High.Incontrast,at Thika,Conv-HighexportedhigherNandPcomparedtotheother systems.InConv-Low,theKexportedfrombothsitesandtheN fromChukawassignificantlyhigherthanthoseexportedfrom Org-Low.WiththeexceptionofNatChuka,Org-Highshowedpositive andhigher(P<0.05)partialNandKbalancesatbothsitesthanthe otherthreesystems(Fig.6).AllthesystemsshowedapositiveP partialbalancewiththepartialPbalanceinthehighinputsystems beinghigher(P<0.05)thaninthelowinputsystems.Similarly,the Pbalanceintheconventionalsystemswashigher(P<0.05)than thePbalanceinorganicsystems.

4.Discussion

4.1.Effectsofsite,croppingsystemsandtheirinteractionswiththe environmentoncropyields

Therewas nodiscernableinteractiveeffectbetweensite and farmingsystemsoncropyields(Table6).Therewashowever,a significant(P<0.0001,0.0005)siteeffectoncropyieldsinallthe differentcroppingsystems(Table6)whichcanbeattributedtothe differencesinenvironmental(weatherandsoil)conditionsatthe twosites.AtThikatheinitiallylowsoilfertilitystatus(Table1), unfavourableweatherconditions(lowrainfall,unevendistribution andmoisturestressduetointermittentandprolongeddryspells) (Fig. 3, Table 5), the late introduction of irrigation (2009) and scarcityofirrigationwaterin2011(duetoabrokenoverheadtank)

and 2012 (due to a shortage of water supply to the Thika

community)werethemajorsite-specificfactorsaccountingforthe loweryieldsofallcropsunderallsystems.Waterstressinducedby lowrainfallaccountedfor12and20%ofthevariationinyieldsof themaizeintercroppedwithbeansin theunirrigatedlowinput systems.ThesiteatThikahadalowersoilpH,lessorganiccarbon (org-C), total N, and very low available P and cation exchange capacity(CEC)comparedtoChuka(Table1).Thesefactorsallaffect nutrientavailabilitytocrops,theirgrowth,nutrientuseefficiency and ultimatelyyields(SubedeandMa,2009;Westermanet al., 1999).

4.2.Theeffectoffarmingsystemsoncropyields

Solecroppedmaize:atChukain2007allfoursystemsachieved similarmaizeyields(Table7a-b).Thisisinlinewiththeresultsof

Lotter et al. (2003), who in the early years of their trials in

Pennsylvania (US) reported that organic and conventionally

managed systems gave similar maize yields, as well as

Mucheru-Muna et al. (2014) in Meru South in the Central Highlandsof Kenya.Thesimilarity inmaize yieldsbetweenthe systemsduringthe1stcycle(2007)couldbeattributedtoinitial inherentlyhighsoilfertility(Table1)andrelativelyabundantand fairly evenly distributed rainfall during the cropping seasons (Fig.1a).The initialsoil pH,CEC,org-C, Nandavailable Pwere similarforbothsitesand,togetherwiththerelativelyhighrainfall (318-335.5mm) it’s fairly even distribution during the critical growthperiod 46 to80days afterplanting(DAPT) shouldhave enhancednutrientavailabilityforplantuptake(especiallyPandK,

Table9a-b),growthanddevelopmentinallthesystems.Thefairly highmaizegrainyieldsduringthe2ndcyclein2010(Table7a-b) can beattributedtotheeffectof increasedsoilnutrient inputs Fig.2.a–b:Productioncostsforconventionalandorganicfarmingsystemsinthe

Fig.3.Totalrevenue(a–d)andprofit(e–f)obtainedinthelocalmarketfromconventionalandorganicfarmingsystemsinthelong-termsystemcomparisontrialsatChuka andThika,CentralHighlandsofKenya.

(Fig.5)onsoilfertility(datareportedseparately)aswellhigher rainfallandbetterdistribution(whichwouldhavehadmoreofan effectonthelowinputsystemswhichhadnoaccesstoirrigation,

Fig.1d).BycontrastatThikathemaizeyieldsin2007forthetwo organicsystemswere3to4timeslower(P=0.001)thanintheir respectiveconventionalcounterparts(Table7a-b).Thisisinline withtheobservationsofClarketal.(1999)who,inaneight-year studyofsunflower-tomato-corn-wheat/beanrotationinCalifornia (US),foundcornyieldsfromtheorganicallymanagedsystemtobe 1.2timeslowerthanthoseinconventionalsystemsinthefirstyear. Kibunja(2012)whousedacontinuousmaize-beansrotationinthe firstsixyearsofcultivationintheKabetelongtermtrialinKenya, reportedmaizecropsfromtheorganicallymanagedsystem(FYM)

to be about 50% lower than those from the conventionally

managedsystems(whenappliedasNPorNP+FYM).Inourtrial weappliedalmostequalamountsofnutrientstotheconventional andorganicsystemsbutirrigationinthehighinputsystemsfor maizewasonlyintroducedin2009.Themostlikelyexplanationfor thetwoorganicsystemshavingsignificantlylower(3to4times lowerP=0.001)maizegrainyieldsthantheirconventionalonesin

2007 at Thika is a slower take up of nutrients from organic

fertilisersthanfromconventionalones(unpublisheddatafrom on-goingPhDstudy).Thereasonsgiventoexplainthehighyieldsat Chukain2010alsoapplyforthehighermaizegrainyieldsinall systemsin2010atThika.

Maize intercropped withbeans: maize grain yields in both

Conv-LowandOrg-LowatChukadoubledbetween2008and2009

and then stayedfairlystable until2012(Table 8a). Thiscanbe attributedtoimprovementsinsoilmanagementpracticesandthe effectsofthecroprotation.Thecroppingpatternsintherotation, i.e.maizeintercroppedwithbeansin2008,2009,2011and2012, and thecultivationofothergrainlegumesinthe2ndseasonof 2008and2011(Table2)contributedtoimprovingthesoilfertility (datareportedseparately).Theincorporationandmineralisationof decayinglegumeleavesandrootbiomassincreasedtheavailability ofmineral-Ntomaizecrops(Adeboyeetal.,2005; Evansetal., 2001).However,thefairlylowmaizegrainyieldsinOrg-Lowin 2012couldnotbeexplained(Table8a).Thepotentialof cereal-cowpea-and/orlegumerotationstosignificantlyincreaseyieldsof cerealcropshasbeendocumentedbyseveralauthors(Adeboye etal.,2005;RaoandMathuva,2000;Sakalaetal.,2004).AtThika, relativelylowmaizeyieldswereobtainedin2008and2009inboth Conv-LowandOrg-Lowandthiscanbeattributedtotheeffectof theweather(asexplainedin4.1).Moisturestressalsoaffectedthe floweringandpodfillingstagesofbeans,therebylimitingyields, hence theexclusionofbeandata inthe2008 yieldcalculation. SomeofthemaizegrainyieldsinourtrialunderConv-Highand Conv-Low (0.73-5.49tha1) and Org-High and Org-Low (0.23-6.25tha1)atChukaandThikasiteswerebelowthevalues (1.6-6.5tha1)reportedbytheEmbulongtermtrial(1993–2005)and Fig.4.BenefitcostratioobtainedfromconventionalandorganicfarmingsystemsinthelocalmarketsatChukaandThika,CentralHighlandsofKenya.

Fig.5.Cumulativenutrientinputandexportfornitrogen,phosphorusandpotassiuminthefirstseasonsof2007to2012inthelongtermsystemcomparisontrialsatChuka andThika.(Significantdifferences(P<0.05)areindicatedbythelettersa,b,candd).

Table9

AverageseasonalnutrientexportandpercentageofnutrientinputexportedintheLongTermSystemComparisonTrialsatChukaandThikaintheCentralHighlandsofKenya. Site Farming

system

Nexport Pexport Kexport

Seasonal Average

Expressaspercentageofnutrient input

Seasonal Average

Expressaspercentageofnutrient input

Seasonal Average

Expressaspercentageofnutrient input (kgNha1) (%N) (kgP ha1) (%P) (kgKha1) (%K) Chuka Conv-High 137.7a ₁₀₁a _13.2a ₁₂b _192.2a ₁₇₈b Org-High 42.4b ₂₆b _5.7b ₇b _35.5c ₁₄c Conv-Low 118.9a ₂₆₀a _10.2ab ₄a _92.6b ₂₄₆a Org-Low 55.1b 302a 8.2ab 49a 22.2c 58c Thika Conv-High 134.9a 91ab 15.2a 13 112.3a 115a Org-High 36.8a 19c 5.3b 6 31.3b 9c Conv-Low 48.0b ₁₂₀a _2.8b _{10 38.3}b ₅₃b Org-Low 23.5b _55bc _3.2b _{17 5.9}b ₉c

Fig.6.Cumulativenutrientbalancesfornitrogen,phosphorusandpotassiuminthefirstseasonsof2007to2012inthelongtermsystemcomparisontrialsatChukaand Thika.(NA,dataforcroppingyearisnotavailableduetolossofgrainsamplesasaresultofrelocationofthelaboratory.Significantdifferences(P<0.05)areindicatedbythe lettersa,b,candd).

theKenyanAgricultureResearchInstitute’s(KARI)longtermtrial (1976-todate)attheNationalAgricultureResearchLaboratories (NARL)inKabete(Bationoetal.,2012;Kibunjaetal.,2012).

SolecroppedBabycorn:cobyieldsofbabycorninOrg-Highat ChukaandThikaweresimilartotheyieldsinConv-High(Table8b). ThisresultcontrastswiththeexperiencesofSahaetal.(2007)who reportedthatconventionallymanagedplotsproducesignificantly higheryieldsofbabycorncobsthanorganicones.Thedisparity

between these two results may be due to improved nutrient

availability(datareportedseparately)anduptake(especiallyNand Pin2011and2012,Table12,supplementarysheet)leadingtohigh yieldsofcobsperunitareainOrg-HighatChukain2008,2011and 2012 (Table 8a-b). This may also explain the observed higher frequencyofprolongedharvestsinOrg-HighthaninConv-High. Differencesin theamountand patternsofNrelease byorganic inputsandsyntheticfertilisers(Adamtey,2010)mayalsoexplain whyConv-Highobtainedhigheryieldsatthebeginningofharvest thanOrg-High.In2008thetwohighinputsystemsatbothsites recordedlowercobyieldsofbabycornthantheydidinsubsequent years (Table 8b). This can largely be attributed to an erratic distributionofrainfall(Fig.1b),astheirrigationfacilitieswerenot yetinstalled (Table 3) anda croprotation effect(Table2).The croppingpatternandrotationeffectalsoaccountforthesignificant increase(P<0.01)incobyieldsofbabycornin2009(Table8b)at bothsites.Intherotationmaizeandcabbagewereplantedinthe 1stand2ndseasonsof2007beforebabycorninthe1stseasonof 2008 (Table 2). Maize and cabbage are both crops with high nutrientdemand(Muriukietal.,2002;Schnieretal.,1997)andare likelytohaveremovedmorenutrientsfromthesoilpriortothe babycornbeingcultivated.Assuchin2008thebabycornwould havebeenmoredependentonappliednutrients.In theorganic systemlessthan10%ofthetotalNappliedfromcompostwould havebeenavailabletothefirstcrops(Adamtey,2010).Conversely, therelayintercroppingofmaizewithMucunainthe1stseasonof

2008, followed by legumes (French beans) in the 2nd season,

wouldhaveaddedavailableNtothesoilforthefollowingcropof babycornin2009(Wortmannetal.,2000;Flores-Sanchezetal., 2013). This, together with the introduction of supplementary irrigationinthesecondseasonof2008,wasexpectedtoincrease cobsandkernelyields,whichdidoccurin2009(Adamtey,2010; Hammadetal.,2011).Osie-BonsuandBuckles,(1993),Hauserand Nolte(2002)haveestimatedthatwhenMucunapuriensisgrownas an intercrop or as sole crop, it provides an equivalent of 87–

171kgNha1(throughNfixation)and138–218kgNha1(through Nretainedinresidues)tothesucceedingcropofmaize.Bationo et al. (2011) also reported that, with efficient soil fertility

management, cowpea can fix up to 88kgNha1 and this can

increasethenitrogenuseefficiencyofthesucceedingcerealcrop from20%undercontinuouscerealmonocultureto28%.Thecob yieldsofbabycornobtainedfromConv-HighandOrg-Highwere withinthevaluesreportedbyGoladaetal.(2013),Loneetal.(2013)

and Muthukumar et al. (2005) in India. At both sites the

productivity of baby cornwas similar in both Conv-High and

Org-High.

4.3.Aneconomicevaluationofconventionalandorganicfarming systems

4.3.1.Productioncosts

Thehigherproductioncostsincurredinproducingmaizeand babycorninOrg-HighthaninConv-High(Fig.2a–bandAnnex2a–

b)isincontrastwiththeexperiencesofDelbridgeetal.(2011)who

reported similar production costs between the two types of

systemsina4-yearcorn-soybean/alfafacroprotation.Ina10year trial in Minnesota (US), Mahoneya et al. (2004) reported the organicsystemtohavelowerproductioncosts.Thedisparityinthe

resultsfromourcasecanmainlybeattributedtobothhighlabour costsandthesubsidiesforsyntheticfertilisersthatwereofferedby theKenyanGovernmentin2010(Sheahanetal.,2013).Thelabour costsofproducingmaizeandbabycorninOrg-Highwerehigher everyyear(P<0.05)thaninConv-Highatbothsites(Fig.2a–b, Annex2a–b)asthepreparationanduseoforganicmaterialsand themanagementoforganicfarmswasmorelabourintensive.In

the organic system there were higher labour costs for land

preparation,mulching,Tithoniateapreparation,compostingand

more frequent weeding. In Conv-High the labour costs were

associatedwithlandpreparation,weeding,andtheapplicationof pesticides.TheseresultsareconsistentwiththoseofKipsatetal. (2004) who reported higher labour costs (75% of the total

production cost) in western Kenya when using organic inputs

and technologies rather thansynthetic inputs(61% of thetotal productionin conventionalfarming).The highproduction costs associatedwiththeadditionallabourinputrequiredfororganic farmingimplytheneedtolookforwaystoreducelabourcosts, particularlythoseassociatedwithproducingandapplyingorganic fertilisers.Thedevelopmentofsimplemachineryandtechniques forproducingandapplyingorganicinputsthatcanbeusedbyboth

small and medium-to-large scale farmers could help relieve

farmers of the high labour investments needed in organic

production.Alternatively,theestablishmentofcommunity-level compost-making facilities in areas close to organic farms that could supply high quality compost or organic fertilisers at an affordablecostisanotherpotentialsolutionfororganicgrowers.

4.3.2.Grossmargin(Profit)

Despitethehigherproductioncostsinthehighandlowinput organicsystems,Org-Highachievedsimilargrossmargins(profits) perhectareatChukatoitsconventionalcounterpartbetween2008 and2012whenproducingmaizeandbabycorn(Fig.3e,&Annex3e

of supplementarysheet).The sameheld trueforOrg-Lowwhen

maizewasinter-croppedwithbeansatChuka.Thisindicatesthat, inthesecondyearofconversionandthereafter,organicfarming (withproducesoldataregularprice)yieldedsimilarprofitsasits conventional counterpart. This contradicts the reports of Clark etal.(1999)andSetboonsarngetal.(2008)whoarguethat,inthe

absence of price premium, the returns to organic production

systemarelowerthanthosetoconventionalproductionsystems andcorroboratetheassertionofWelsh(1999)andMahoneyaetal. (2004)thatpricepremiumsarenotalwaysnecessaryfororganic systemstobecompetitivewithconventionalsystems.Delbridge etal.(2011)reportedona4yearcorn-soybean/alfafacroprotation organicinputsystem(withoutpremiumprices)thathadasimilar netreturntochemicalinputsystems,butwhenapremiumwas available for the organic produce, the organic system yielded considerablyhighernetreturnsthantheconventionalsystem.This iscorroboratedbyourfindings.In2011and2012organicproduce frombothsiteswasabletoachieveanaveragepremiumpriceof 20-50%onthelocalandregionalmarkets(Table4).Thisinturn meantthatOrg-Highwasabletoachievea1.3to4.1timeshigher (P_<0.01)grossmargin(pro_fit) thanConv-High.Thisprovidesa strongindication thatorganic highinputsystems canbe more

profitable than conventional high input systems when the

premium priceis available. In ourtrials this occurredbetween thefifthandsixthyearoforganiccultivation.IFOAM(2013)has alsoreportedthatfarmersthatengagedincertifiedorganicexport productioninEastAfricamakesignificantlymoreprofitthanthose engagedinconventionalproduction.Theseresultsandtrendswill needregularmonitoringinthecomingyearstoseewhetherthey continue. At Thika, all thefarming systems had negative gross

margins (losses) from 2007 to 2009 when selling produce at

regularprice(Figs.3g,&Annex3gofsupplementarysheet).This can beattributed topoor cropperformance in all the systems