Cover Crops as an Agroecological Practice on Organic Vegetable Farms in Wisconsin, USA

15 Pages·2017·0.51 MB·English

sustainability
ConceptPaper
Cover Crops as an Agroecological Practice on Organic
Vegetable Farms in Wisconsin, USA
ErinM.Silva1,2,*andVirginiaM.Moore2,3
1 DepartmentofPlantPathology,UniversityofWisconsin-Madison,1630LindenDr.,Madison,WI53706,USA
2 PlantBreedingandPlantGeneticsProgram,UniversityofWisconsin-Madison,1575LindenDr.,Madison,
WI53706,USA;[email protected]
3 DepartmentofAgronomy,UniversityofWisconsin-Madison,1575LindenDr.,Madison,WI53706,USA
* Correspondence:[email protected];Tel.:[phone];Fax:[phone]
AcademicEditor:CarolShennan
Received:6October2016;Accepted:14December2016;Published:1January2017
Abstract: Global agricultural and food systems face the challenge of feeding a growing world
population in the face of finite and diminishing resources. To guide the redesign of agricultural
systems,farmersandpolicymakersareincreasinglyturningtoagroecology. Organicagriculturehas
historicallyintegratedagroecologicalpracticeswithinitsregulatoryframework;however,questions
remain as to the extent to which organic farmers are maintaining and expanding agroecological
practices. Inthispaper,wewilladdressconvergencesanddivergencesofagroecologicalandorganic
practices. Using cover cropping as a model agroecological practice, we conduct a preliminary
assessment on the degree to which organic vegetable farms in Wisconsin, USA are integrating
agroecological concepts into their farm management, drawing upon the results of a 2013 cover
croppingpracticesurvey. Thesurveydatademonstratesvaryingdegreesofcomplexityanddiversity
incovercroppingpractices,potentiallyillustratingthedesireoforganicfarmerstopromoteahigh
degreeofagroecosystemservices. Farmers’integrationofcovercropdiversityandcomplexitywas
notcorrelatedtofarmsizeorrevenue. TheseresultsofferpreliminaryevidencethatWisconsin’s
organicvegetablefarmersareintegratingagroecologicalpracticesontheirfarms,evenasgrowthin
theorganicmarketcontinuestooccur.
Keywords: agroecology;organicagriculture;covercropping;ecosystemservices;USA
1. Introduction
Ourglobalagriculturalandfoodsystemsfacethechallengeoffeedingagrowingworldpopulation
inthefaceoffiniteanddiminishingresources. Aswelooktowardtheissuesconfrontingfarmers—soil
erosion,groundandsurfacewatercontamination,chemical-resistantweedsandinsects,diminishing
fossilfuel-derivedandminedresources—itbecomesclearthatinordertoachieveasustainablepath
forward,ourfutureagriculturalsystemsmustbebasedonadaptablepracticeswhichenhancethe
cyclingresourcesandecologicalbalance,whilemaintainingproductive,nutritionally-densecrops.
Toguidetheredesignofagriculturalsystemsonwhichtheglobalfoodsupplydepends,farmers
andpolicymakersareincreasinglyturningtoagroecology. Agroecology,theintegrationofecological
concepts to agricultural systems, arose in the early part of the 20th century as a response to the
increasingindustrializationofouragriculturalsystem[1,2]. Onebroadly-useddefinitiondescribes
agroecology as “ ... the integrative study of the ecology of the entire food system, encompassing
ecological,economicandsocialdimensions”[3]. Asasetoffarmingpractices,agroecologypromotes
more ecological strategies of management, including less dependence on monoculture systems;
avoidanceofinputsubstitution,externalinputmarkets,andcostlybiotechnologypackages;cyclingof
Sustainability2017,9,55;doi:10.3390/su9010055 www.mdpi.com/journal/sustainability
Sustainability2017,9,55 2of15
resourceson-farmorfromlocalagroecosystemterritories;protectionofenvironment;andemphasis
onlocalorregionalmarketstructuresandterritorialdevelopmentstrategies[4].
As with agroecology, the term “organic agriculture” has been used to describe a specific
agriculturalproductionsystemforalmostacentury. Lampkin(1990)definesorganicagricultureasa
farmingsystemapproachthataims“tocreateintegrated,humane,environmentallyandeconomically
sustainableproductionsystems,whichmaximizerelianceonfarm-derivedrenewableresourcesand
themanagementofecologicalandbiologicalprocessesandinteractions,soastoprovideacceptable
levelsofcrop,livestockandhumannutrition,protectionfrompestsanddisease,andanappropriate
returntothehumanandotherresources”[5]. AnotherdefinitionhasbeenofferedbytheInternational
FederationofAgriculturalMovements(IFOAM):“OrganicAgricultureisaproductionsystemthat
sustains the health of soils, ecosystems and people. It relies on ecological processes, biodiversity
andcyclesadaptedtolocalconditions,ratherthantheuseofinputswithadverseeffects. Organic
agriculturecombinestradition,innovationandsciencetobenefitthesharedenvironmentandpromote
fairrelationshipsandagoodqualityoflifeforallinvolved”[6].
Questions remain, however, as to the degree to which organic agriculture, with foundations
groundedwithinecologicalprocesses,alignswithagroecologicalproductionapproaches. Tobeginto
deriveananswertothisquestion,weaddressconvergencesanddivergencesofagroecologicaland
organicpractices,focusingontheintegrationofagroecologicalperspectivesintotheUnitedStates
Department of Agriculture’s National Organic Program (USDA-NOP) regulation. Then, we will
describe cover cropping as a model agroecological practice that is currently employed in varying
degrees and complexities on organic farms across the United States of America (USA). As a case
study,wewillusecovercroppingasanindicatorwithwhichtoconductapreliminaryassessment
ontheintegrationofagroecologicalconceptsintofarmmanagementonorganicvegetablefarmsin
Wisconsin,USA.
2. HistoricalOverviewofAgroecologyandOrganicAgriculture
Differences in the genesis of agroecology and organic agriculture have led to differences in
practicalapproachesthatstillremaintoday. Agroecology,whilefirstnotedbyscientistsandwriters
intheearlypartofthe20thcentury[1,7],gainedstrengthinthemiddlepartofthe20thcenturyin
responsetoenvironmentaladvocates’oppositiontotheindustrializationofglobalagriculturalsystems
anditsincreasinglyapparentnegativeimpactsonthegreaterecosystem. Intandemtotherecognition
of agroecology as an agricultural approach throughout the twentieth century, organic agriculture
achievedmorewidespreadrecognition. Unlikethetermagroecology,whichfromthebeginninghad
closertiestothefieldofecology,theoriginsoforganicagriculturearemorestronglyalignedwithsoil
enhancementandpreservation.Whilemirroringthecomplexityofecologyinmanyrespects,theschool
ofthoughtwhichshapedorganicagriculturewasrootedinthephilosophyofholism,inwhichthe
farmwasviewedasacomplexsystem(an“organism”),drivenbyprocessesthatlinkedsoilorganic
matter(referredtoas“humus”)andsoilbiologytocrop,human,andlivestockhealth[8,9].
Whilethesetwotermsareuseddistinctly,commonalitiesdoexistbetweenorganicfarmingand
agroecologyinbothpracticeandvision. Intermsofhistoriccontext,bothwereenergizedbythepublic
responsetointensivechemicalpollution—inagricultureandinotherindustries—andtherenewed
discussionsofenvironmentalismthathadfurtherturnedtofoodandfarming[10]. Bothmovements
wereenergizedbythepublicationofRachelCarson’sseminalwork“SilentSpring”(1962),highlighting
thedangersofpesticidesinourfoodsystemsandenvironment. Finally,bothpromotedclosedsystems
andresourcecycling,diverseproductionapproacheswithinafarmingenterprise,diverselandscape
elements, and reliance on biological processes for building soil fertility and controlling pests and
diseases[11]. Whiletheterms“agroecology”and“organicagriculture”haveexistedinagricultural
lexiconforalmostacentury,theterm“organicagriculture”ismorehighlyrecognizedbyconsumers,
inlargepartduetotheregulatoryandmarketcomponentassociatedwithorganicagricultureinthe
USAandglobally.
Sustainability2017,9,55 3of15
Unlikeorganicagriculture,whichisgovernedbystrictregulatorycodes,agroecologyisnotstrictly
definedbyacodifiedsetofpractices. However,broaddefinitionsdoexistthatallowfordesignation
ofcertainpracticesasagroecological. AccordingtoWezeletal.[12],“agroecologicalpracticescanbe
characterizedasagriculturalpracticesaimingtoproducesignificantamountsoffood,whichseekto
valorizeecologicalprocessesandecosystemservicesbyintegratingthemasfundamentalelements
in the development of the said practices, as opposed to simply relying on external inputs such as
chemicalfertilizerandsyntheticpesticideapplication,orontechnologicalsolutionssuchasgenetically
modifiedorganisms”. Assuch,agroecologicalpracticesarebasedonvariousecologicalprocessesand
ecosystemservicessuchasnutrientcycling,biologicalNfixation,naturalregulationofpests,soiland
waterconservation,biodiversityconservation,andcarbonsequestration,whilecontributingtothe
sustainabilityoftheagriculturalsystem[12]. Examplesofagroecologicalpracticesincludetheuseof
covercrops,greenmanures,intercropping,agroforestry,biologicalcontrol,resourceandbiodiversity
conservationpractices,orlivestockintegration[2,12,13].
As the practices to be mandated by the USDA-NOP were established, alignment with
agroecological practices is evident. The broad definition included in the USDA-NOP regulation
describesorganicproductionasa“productionsystemthatismanagedinaccordancewiththeAct
andregulationsinthisparttorespondtosite-specificconditionsbyintegratingcultural,biological,
andmechanicalpracticesthatfostercyclingofresources,promoteecologicalbalance,andconserve
biodiversity”[14]. Theregulationspecificallymentionspracticesthatcanbeconsideredagroecological,
includingtheuseofcroprotation,covercrops,andcatchcropstoprovideforpestmanagementin
annualandperennialcrops(subpart§205.206),aswellasculturalpracticesthatenhancecrophealth,
includingselectionofplantspeciesandvarietieswithregardtosuitabilitytosite-specificconditions
and resistance to prevalent pests, weeds, and diseases (subpart § 205.206). Further, the organic
regulationincorporateslandscapeelementsofagroecologymanagement,includingtheregulationof
pestinsectsthroughthedevelopmentofhabitatfornaturalenemiesofpests(§205.206).
3. CoverCrops: AnIndicatorAgroecologicalPracticewithinOrganicManagement
As the organic market expands and appetites for organic products increase, more hectares of
landarebeingtransitionedtocertifiedorganicmanagementtocapturemarketdemandandaccess
thehigherpricesthatorganicmarketsprovide. Withthistransitionofhectares,certifiedorganicland
maydepartfromthesmall,diversifiedandintegratedfarmshistoricallytypifyingorganicagriculture,
withtheiruseofmorecomplexagroecologicalpractices,andmovetowardlarger,morespecialized
farms,mirroringthemonoculturesofconventionalagricultureandtheirassociatedrelianceonoutside
inputs. Thisphenomenon,referredtoas“conventionalization”,wasfirstforwardedbyBucketal. in
1997[15]todescribetheCaliforniaorganicindustry,aswellasbyHallandMogyorodyin2001[16]in
theirassessmentoftheindustryinOntario,Canada. Bucketal.[15]contendthatconventionalization
canbedemonstratedbycertainfarmercharacteristics,practices,andorientationsamonglargerorganic
farmers,inparticular,thelargerfarmerswhohaverecentlymovedtoorganicfarming.
Almost 15 years after the inception of the USDA-NOP, few studies have demonstrated if
conventionalizationoftheorganicindustryhastrulyoccurred. Inpart,thisisduetothedifficulty
in identifying specific agroecological practices that would be appropriate indicators to assess a
wide range of organic farms across a wide regional distribution. As organic farming is not a
“cookbook approach”—instead encouraging farmers to use appropriate strategies for their local
climatesandagroecosystems—thedegreetowhichspecificagroecologicalpracticesareimplemented
onfarmswillvary. Thus,itcanbedifficulttorigorouslydocument,usingasingleorfewindicators,
thediversityofmanagementpracticesemployedonorganicfarmsandtheirconvergenceordivergence
withagroecologicalpracticesandprinciples.
Oneofthemorewidespreadagroecologicalpracticesobservedonorganicfarms,however,iscover
cropping. Covercroppingcanbedescribedastheuseof“vegetationplantedormanagedtoprotect
andimprovesoil,crops,orwaterquality”[17]. Covercropscanprovidenumerousecosystemservices,
Sustainability2017,9,55 4of15
includingimprovingsoilquality,nutrientcycling,pestregulation,andcropproductivity,bothinthe
samefield,andalsoacrosstime[18–21]. Thus,integratingcovercropsintocroprotationalstrategies
addsimportantfoundationalelementsofagroecologicalmanagement,includingincreasingdiversity
acrossmultiplemeasuressuchastemporal,taxonomic,andfunctionalbiodiversity[22].
Manystudieshavedocumentedthespecificagroecologicalfunctionsandimpactsofcovercrops,
ofteninamorelinearversussystems-basedcontext. AsubsetofthesestudiesareoutlinedinTable1,
organizedbytheagroecosystemserviceonwhichtheresearchisfocused. Manyofthecovercrops
describedinthistablearecommonlyusedoverwidegeographicregions,includingWisconsin,USA.
Benefitsconferredbycovercropsareoftenmulti-functional,simultaneouslyprovidingbothagronomic
andenvironmental;forexample,increasingwaterinfiltrationalsominimizessurfaceerosion,increasing
waterqualityinsurfacewaters. Thecomplexnatureofcovercrophighlightsachallengeinneatly
categorizingtheirfunctionalrolesasagroecologicalpractices,asagroecologicalperformancedoesnot
necessarilydependonspecificspeciesortechniques,butislinkedtoprocessesthatbenefitthewhole
system[23].
Table 1. Examples of agroecosystem services provided by cover crops, as documented from
peer-reviewedresearchstudies.
Agroecosystem
CoverCrop CashCropSystem StudyLocation Citation
Service
Forageradish(Raphanussativus) Notspecified Denmark [24]
Winterwheat
Hairyvetch(Viciavillosa),sunnhemp
(Triticumaestivum)andgrain Kansas,USA [25]
(Crotalariajuncea),soybeans(Glycinemax)
Reducesoil sorghum(Sorghumbicolor)
compaction
Forageradish;rapeseed(Brassicanapus);
Maize(Zeamays) Maryland,USA [26]
cerealrye(Secalecereale)
Millet(Pennisetumglaucum);sorghum; SaoPaulo,
Soybean [27]
andsunnhemp Brazil
Winterwheatand
Hairyvetch;sunnhemp;soybean Kansas,USA [25]
grainsorghum
Calopo(Calopogoniomuconoides),sunn
Improvesoil hemp,sorghum,pigeonpea
Papaya(Caricapapaya) Bahia,Brazil [28]
structure (Cajanuscajan)andjackbean
(Canavaliaensiformis)withsorghum
Springbarley(Hordeumvulgare), British
cerealrye,andannualryegrass Notspecified Columbia, [29]
(Loliummultiflorum) Canada
Tomato
Blackoat(Avenastrigose) Uraguay [30]
(Solanumlycopersicum)
Improvewater
Winterwheat Silagemaize California,USA [31]
infiltration
Bromegrass(Bromusinermis),resident
vegetation,andstrawberryclover Notspecified California,USA [32]
(Trifoliumfragiferum)
Forageradish;rapeseed;cerealrye Maize Maryland,USA [26]
Cerealrye,winterbarley
Improvesoil
(Hordeumvulgare),triticale(xTriticosecale Wisconsin,
moistureretention Soybean [33]
spp.),hairyvetch,Austrianwinterpea USA
(Pisumsativum)
Cerealryeandhairyvetch Maize Illinois,USA [34]
Cotton(Gossypiumhirsutum)
Cerealryeandhairyvetch,aloneand
andsorghum Georgia,USA [35]
inmixtures
(Sorghumbicolor)
Increasesoil
Guineagrass(Panicummaximum),Congo
organicmatterand
grass(Brachiariaruziziensis),palisade SantoAntônio
soilcarbon Rice(Oryzasativa) [36]
grass(Brachiariabrizantha),andpearl deGoiás,Brazil
millet(Pennisetumglaucum)
Cerealryeandhairyvetch, Massachusetts,
Maize [37]
rye/vetchcombination USA
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Table1.Cont.
Agroecosystem
CoverCrop CashCropSystem StudyLocation Citation
Service
Washington,
Brownmustard(Brassicahirta) Potato(Solanumtuberosum) [38]
USA
Enhancenitrogen
fixation Hairyvetch Tomato Maryland,USA [39]
Hairyvetch,sunnhemp,soybeans [25]
Greenbeans
Oatandcommonvetch(Viciasativa) Oregon,USA [40]
(Phaseolusvulgaris)
Hariyvetchandcerealrye Tomato Maryland,USA [41]
Oat;hairyvetch;wintercanola
(Brassicanapus);covercropmixture1
Increasemicrobial (cowpea(Vignasinensis,V.unguiculata),
activity winterpea(Pisumsativum),millet
(Pennisetumamericanum),forageradish,
SouthDakota,
turnip(Brassicarapa);covercropmixture2 Wheatandoat [42]
USA
(wintercanola,forageoats/winterpea,
crimson(Trifoliumincarnatum)/alsikeclover
(Trifoliumhybridum),fieldpea
(Pisumsativum)/timothy(Phleumpretense),
forageradish/fieldpea)
Whitemustard(Sinapisalba),phacelia
(Phaceliatanacetifoli),annualryegrass
Notprovided Belgium [43]
(Loliumperenne),oats,cerealrye,
forageradish
Reduceerosion
Cerealryeandoat Corn-soybeanrotation Iowa,USA [44]
Sugarcane
Sunnhemp;sorghumsudangrass;oats Hawaii,USA [45]
(Saccharumofficinarum)
Cerealryeandoat Corn-soybeanrotation Iowa,USA [46]
Reducenutrient Cerealrye Lettuce(Latucasativa) California,USA [47]
leachingandloss
Phaceliaandcerealrye Broccoli(Brassicaoleraceae) California,USA [48]
Meta-analysis [18]
Mustard(Sinapisalba),forageradish,and
springvetch(Viciasativa);mixture1(spring
vetch,forageradish,berseemclover
(Trifoliumalexandrinum);mixture2(field - Germany [49]
pea,lupin(Lupinusangustifolius),blackoat
(Avenastrigose)berseemclover,phacelia,
niger(Guizotiaabyssinica)
Suppressweeds
Whitemustard(Sinapisalba),oilseedradish,
phacelia,tartarybuckwheat
Wheatandbarley
(Fagopyrumtataricum),forageradish, Germany [50]
(Hordeumvulgare)
redoat(Avenabyzantine),grainamaranth
(Amaranthuscruentus)
Illinois,
Mustard(Sinapisalba)andIndianmustard
Vegetables NewYork,and [51]
(Brassicajuncea)
Michigan,USA
Rapeseed,mediumredclover
(Trifoliumpratense),Austrianwinterpea
Enhancepollinator (Pisumsativumsubsp.arvense),andcereal
Corn-soybean-winter Pennsylvania,
andbeneficial rye;andasixspeciesmixthatincluded [52]
wheatrotation USA
habitat rapeseed,mediumredcloverAustrian
winterpea,cerealrye,forageradish
andoats
Mustard(Brassicaspp.)andbuckwheat
Broccoli California,USA [53]
Increasebeneficial (Fagopyrumesculentum)
insects
Clementinemandarin
Tallfescue(Festucaarundinace) Spain [54]
(Citrusclementina)
Okra
Sunnhempandsorghumsudangrass Florida,USA [55]
(Abelmoschusesculentus)
Suppresssoil
diseaseand Sudangrass Lettuce(Latucasativa) NewYork,USA [56]
nematodes Cowpea,sunnhemp,pearlmillet,sorghum
Tomato Florida,USA [57]
sudangrass,aloneandinamixture
Sustainability2017,9,55 6of15
SeveralofthecovercropbenefitsoutlinedinTable1involvesoilqualityandhealthenhancement,
includingimprovementstosoilfertility,soilstructure,andsoilecology.Covercropssequesterandstore
nutrientsthatmightotherwisebelosttoleachingorrunoff,maintainingfertilitywithinthesystem.
Inparticular,densely-rootedcovercropsscavengenutrientsfromdeepinthesoilprofile,providing
fertilityforfuturecrops[58–60]. Leguminouscovercropsfixnitrogenfromtheatmosphere,providing
asourceoffertilityneededbysubsequentcashcrops,withoutrelianceonoutsideinputs[58,59,61–64].
Withthecontributionofbothabove-andbelow-groundbiomass,covercropscanincreasesoilorganic
matter,whichinturnhastheeffectofimprovingsoilstructureandaggregation.
Covercropsalsoimprovesoil–hydrologicrelationshipssuchasinfiltration,drainage,andaeration.
Deep-rootedcovercropscanpenetrateandloosensubsurfacecompaction[58,59]andlivingvegetation
andsurfaceresiduesserveaprotectiverole,minimizingerosionfromwindandwater[58–60,62,65].
Improvementsinsoilstructureandreducedneedforchemicalinputsalsobothleadtoreducednutrient
leaching,whichcanultimatelyimprovewaterquality[58,62,66–69]. Whencovercropresiduesremain
onthesoilsurface,additionalhydrologicbenefitsmaybeincurred,suchasreductionsinrunoffof
sedimentandnutrientsandreducedirrigationneedsduetolowerevaporation[59,69].
Cover crops are increasingly used by farmers as a systems-based pest management tool.
Particularly when paired with high biomass reduced tillage systems, cover crops can be a highly
effectiveweedcontroloptionfororganicfarmers,asdemonstratedbycovercrop-basedreducedtillage
systems[33,58,59,61,62,70]. Beyondhighbiomassreducedtillagesystems,plantedinrotationwith
cash crop production, cover crops provide weed suppression through resource competition [58],
niche disruption through modification of light, soil temperature, and/or soil moisture [24,28],
andallelopathy[58,62,71]. Covercropscanhavepositiveornegativeimpactsonpestanddisease
problems,withcertaincoverandcashcropcombinations(eithersimultaneouslyorsequentially)either
attractingmorepestinsects,orconversely,morebeneficialpredatorsthatreducepestpopulations.
Similarly,covercropsmaydisruptadiseasecycleorpreventdiseasefromspreading,orserveasan
alternatehostforthepathogen[58,59,61,62,71].
4. Methods: CanPerspectivesfromWisconsin’sOrganicVegetableFarmersHelpGaugeTheir
AgroecologicalPriorities?
Whiletheorganicmarketcontinuestoexpandandpriceadvantagesaremaintained,morefarmers
may be motivated to enter organic production. Depending on the route taken to increase their
production—expandinghectaresonanexistingorganicfarm,ortransitioningaconventionalfarmto
certifiedorganic—farmerswillhavedifferentexperiences,motivations,andperspectives. Additionally,
theymayexperiencevaryingpressuresandopportunitiesthateitherpersuadeordissuadetheadoption
ofmorecomplexandcostlypracticeswithmultipleagroecologicalbenefits. Theattitudesofbothnew
andexistingorganicfarmers,includingtheirprioritizationofexternalenvironmentalandsocietalgoals
aswellasproductiongoals,willbeimportantdeterminantsoftheadoptionofagroecologicalpractices
totheextentthatfarmerperceptions,beliefs,andvaluesinfluencetheirdecision-making. Influenced
bypsychologicaltheory,theReasonedActionApproach(RAA)[72]considersthataperson’sbehavior
depends on their intentions, which in turn depend on their attitudes, subjective norms, and the
perceivedeaseordifficultyincontrollingthebehavior. Incorporationofperceptionsandvaluesinto
anagroecologicalpracticeadoptionframeworkresonateswiththeholontheoryofagroecology,which
proposestheconsiderationofafarmerorotheractorontheagriculturalandfoodsystemslandscape
as a holon, or an “intentional entity embedded in an ecology of contexts” [73]. As such, farmers
makedecisionsbasedonarangeoffactorsbeyondsimpleagronomicoreconomicconsiderations,
butrathertheirdecisionstoimplementagroecologicalpracticeswillbeinfluencedbyfactorsranging
frominternalvaluestosocietalandlandscape-scaleinteractions.
Wisconsin,withitsstrong,vibranthistoryinorganicagriculture,providesauniqueopportunity
toassesstrendsinconventionalizationoftheindustry—or,ataminimum,theadherenceoforganic
farmerstotheagroecologicalapproachesthatmorecloselyalignwiththephilosophyunderpinning
Sustainability 2017, 9, 55 7 of 15
entity embedded in an ecology of contexts” [73]. As such, farmers make decisions based on a range
of factors beyond simple agronomic or economic considerations, but rather their decisions to
implement agroecological practices will be influenced by factors ranging from internal values to
societal and landscape-scale interactions.
Wisconsin, with its strong, vibrant history in organic agriculture, provides a unique
Sustainability2017,9,55 7of15
opportunity to assess trends in conventionalization of the industry—or, at a minimum, the
adherence of organic farmers to the agroecological approaches that more closely align with the
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Figure 1. Location of Wisconsin, USA as highlighted by the red circle. Blue dots represent organic
Figure1. LocationofWisconsin,USAashighlightedbytheredcircle. Bluedotsrepresentorganic
hectares in the USA as documented by the 2007 USDA Census of Agriculture, with one dot
hectaresintheUSAasdocumentedbythe2007USDACensusofAgriculture,withonedotrepresenting
representing approximate 100 hectares (map obtained from the USDA National Agricultural
approximate100hectares(mapobtainedfromtheUSDANationalAgriculturalStatisticsService).
Statistics Service).
Toapplythisapproachtoapreliminaryinvestigationofthedegreeofadherenceandcommitment
To apply this approach to a preliminary investigation of the degree of adherence and
ofWisconsin’sorganicvegetablefarmerstoagroecologicalmanagementapproaches,weusedcover
commitment of Wisconsin’s organic vegetable farmers to agroecological management approaches,
croppingasamodelindicatorpractice. Thesurveydatausedforthisworkwascollectedin2014,inan
we used cover cropping as a model indicator practice. The survey data used for this work was
efforttoassessthecovercroppingpracticesofWisconsin’sorganicvegetablefarmersin2013aswell
collected in 2014, in an effort to assess the cover cropping practices of Wisconsin’s organic vegetable
asinprioryearsoffarming(moredetailsonthesurveydesignandsummaryofresultscanbefound
farmers in 2013 as well as in prior years of farming (more details on the survey design and
inMooreetal., 2016[77]). Thissurvey, intendedtoassesstheextent, diversity, andcomplexityto
summary of results can be found in Moore et al., 2016 [77]). This survey, intended to assess the
whichorganicvegetablefarmerswereemployingcovercrops,wasdesignedanddistributedusingthe
extent, diversity, and complexity to which organic vegetable farmers were employing cover crops,
tailoreddesignmethod[78]. ThesurveywasmailedthroughtheUnitedStatesPostalServicetoeach
was designed and distributed using the tailored design method [78]. The survey was mailed
ofthe322certifiedorganicvegetablegrowersinthestateofWisconsin,usingaddressesacquiredfrom
through the United States Postal Service to each of the 322 certified organic vegetable growers in the
theUSDA-NOP.Farmerswerecontactedatotaloffivetimes,includingthreemailingsofthesurvey
state of Wisconsin, using addresses acquired from the USDA-NOP. Farmers were contacted a total
questionnaireandtwomailingsofreminderpostcards,betweenJanuaryandMarch2014. Atotalof
of five times, including three mailings of the survey questionnaire and two mailings of reminder
152completedsurveyswerereturned,constitutingaresponserateof47%. Questionsincludedcover
postcards, between January and March 2014. A total of 152 completed surveys were returned,
cropuse,relatedmotivationsandperceptions,andfarmdemographicinformation(size,numberof
y earsfarming,education,amongothers). Withthisinformation,wewereablederivecovercropping
trendswithinthisorganicagriculturalsectorovertime,aswellastheagroecologicalgoalsoffarmers
usingcovercrops.
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To investigate the primary factors related to the farmers’ use of cover crops to maximize
agroecologicalfunction(asindicatedbyextentofcovercropuse,covercropdiversity,andcovercrop
complexity),differenteconometricmodelsandregressionanalyseswereperformedasdetermined
by the type of dependent variable. The two-limit Tobit model was used to perform regressions
to investigate explanatory variables related to the extent of cover crop adoption, with continuous
variablesrepresentingtheproportionofvegetableacresplantedtocovercropsforsomepartofthe
2013productionseason. Thecovercropdiversityregressionwasperformedusingnegativebinomial
regression,withthedependentvariableasthenumberofcovercropspecies. Lastly,astheindicator
variablesforcomplexityofcovercropusewerebinaryandcorrelated(yesornoastotheuseoftwo
practices,underseedingandintercroppingofcovercropswithcashcrops),abivariateprobitregression
wasusedtodeterminerelatedfarmdemographicfactors. STATA14.0wasusedtoestimateregressions,
using the tobit command for the two-limit Tobit regression, the nbreg command for the negative
binomialregression,andthebiprobitcommandforthebivariateprobitregression. Moreinformationon
thespecificregressionapproachescanbefoundinthemoreextensivesummaryofthesurveyresults
publishedbyMooreetal.[77].
5. Results
Survey responses demonstrated that cover cropping was routinely integrated into organic
vegetablefarmmanagement.Ninety-twopercentofrespondentshadusedcovercropsatsomepointin
theirfarmingcareer,and78%plantedthemduring2013[77]. Additionally,diverseportfoliosofcover
crops were used by respondents, including barley, buckwheat, clovers, cowpea, millet, mustards,
oats, peas, cereal rye, annual ryegrass, sorghum sudangrass, tillage radish, turnip, hairy vetch,
andwinterwheat.
Resultsofthesurveyfurtherindicatedthatcovercroppingwasincreasingasapracticewiththe
growthoforganicvegetablefarmsinWisconsin. Acloseranalysisoftherespondentswhousedcover
cropsinaparticularfarmingseasonshowsanincreasingutilizationofthispracticeoverthe20years
priortothesurveyyear(1983–2013),risingfromalowoflessthan10%oforganicvegetablefarmers
usingcovercropsin1983,toover90%oforganicvegetablefarmersusingthispracticein2013[77].
Onagivenfarm,theextenttowhichcovercropsareplantedonthelandvaries,from25%offarmers
plantingnoneoftheirvegetablelandincovercrops,25%plantingalloftheirvegetablelandincover
crops,andtheremainingfarmersplantingaportionoftheirvegetablelandincovercrops.
In addition to the extent of cover crop adoption over years farming as an agroecological
practices indicator, the complexity to which cover crops are managed can serve as another gauge
as to the farmer’s commitment to agroecological farming approaches. On the simplest level, if a
farmermaintainstheirprimarymotivationtoplantcovercropsasadherencetotherequirementsof
certificationagencies,themostbasicsolutionwouldbetoplantacleanfieldinasinglecovercrop.
However,morecomplicatedstrategies—underseedingintoacashcrop,interplantingcovercropsat
the time of cash crop planting, using more complex mixtures and cover crop “cocktails”—speaks
tothedesireofthefarmertousecovercropswithmoremultifunctionalintentions. TheWisconsin
survey results indicated that 25.7% of respondents under-seeded cover crops before the cash crop
washarvestedfromthefield,and29.4%inter-plantedcovercropsinpathwaysbetweentheircash
crops[77]. Additionally,farmersplantedmultiplecovercropspeciesbothwithinsinglefieldsand
acrosstheirfarms,benefittingfromthemultipleagronomicandecosystemservicetraitsprovideby
differentcovercropspecies. Resultsofthesurveyindicatedthatfarmersintegratedmorethanone
cover crop species into their management plans, using an average of two species every year and
threespeciesatleastinsomeyearsforatotalaverageoffivecovercropspeciesusedperfarm[77].
Achieving even greater levels of complexity and diversity, a large number (64.0%) of respondents
plantedcovercropspeciesmixturesinsomefields.
Survey respondents were also asked to rank the reasons why they used cover crops, given
the options of the following agroecological functions: adding organic matter; improving fertility;
Sustainability2017,9,55 9of15
improvingsoilstructure;suppressingweeds;erosionprotection;preventingnutrientleaching;reducing
pestsanddiseases;increasingbiodiversity/habitat;andimprovingwaterinfiltration. Increasingsoil
organicmatterhadthemostvotesinthetop3(97),withimprovingsoilfertilityrankingcloselybehind
(90)[77]. Athirdsoilfunction,improvingsoilstructure,wasthethirdhighestfactorrankingthetop
three (66). Other non-soil related agroecological functions, such as reducing pest and disease and
increasingbiodiversityandhabitat,rankedmuchlower,withonlysixrespondentsrankingeachinthe
topthree.
Interestingly, these rankings did not conform closely with farmers’ perceptions of cover crop
benefits. Respondentswereaskedtorespondtoaseriesofstatementsonafive-pointLikertscale,
from“stronglyagree”,“agree”,“neutral”,“disagree”,and“stronglydisagree”. Statementsincluded:
cover cropping improves farm profitability; cover cropping improves soil health, cover cropping
improvessoilfertility;covercroppingdecreasesweedandpestpressure;andcovercroppingincreases
biodiversity/habitat. Mostfarmersmoststronglyagreedwithstatementsaboutsoilbenefits: 98%
of respondents agreed or strongly agreed that “cover cropping improves soil health”, and 99%
agreedorstronglyagreedthat“covercroppingimprovesfertility”[77]. However,respondentsalso
agreed (albeit less strongly) that cover crops offer other benefits (88% agreed or strongly agreed
that “cover cropping decreases weed/pest problems”, and 82% agreed or strongly agreed that
“covercroppingincreasesbiodiversity/habitat”). Thesevaluesindicatethatasignificantlygreater
proportion of farmers held beliefs that broader agroecological benefits existed as compared to the
number of farmers planting cover crops with the intention of deriving those ecosystem benefits.
However,asignificantnumberoffarmersalsofeltthatcovercropsbenefittedtheeconomicaspectsof
sustainabilityontheirfarm,with87%agreeingorstronglyagreeingthat“covercroppingimproves
farmprofitability”[77].
Regressionanalysesdemonstratedseveralrelationshipsbetweencovercropadoptionandfarm
characteristics. Covercroppingextentwasfoundtobestronglycorrelatedwiththefarm’sdependence
onvegetablerevenue;themoredependentafarmwasonrevenuefromvegetablecrops,thesmaller
the proportion of vegetable hectares were planted in cover crops [44]. Extent of cover cropping,
however,wasnottotalfarmhectarage. Neithervegetablerevenuenorfarmsizewascorrelatedwith
complexityordiversityofcovercropsused. However,negativebinomialcountdataregressionof
thenumberofspeciesplanteddemonstratedthatthecomplexityofcovercropplantings—andtheir
relatedmultifunctionalbenefits—werelinkedtotheeducationandexperimentalnatureoffarmers.
Additionally,farmersweremoreaptatusingcovercropsinmorecomplex,multifunctionalwaysif
theyknewotherfarmersthatalsousedcovercrops.
6. Discussion
AnalysisofthissurveyprovidespreliminaryevidencethatWisconsin’sorganicvegetablefarmers
areintegratingagroecologicalpracticesontheirfarms,evenasgrowthintheorganicmarketcontinues
tooccur. However,theanalysisissomewhatsimplifiedandlimitedinitsabilitytodealwiththefull
scopeandrationaleforpracticeadoption. Inadditiontoeconomicandfarmphysicalandbiological
drivers,adoptionofanytechnology,includingcovercropping,intertwineswithpersonalvalues,social
norms,availableknowledge,andothercomplexfactors,andthesefactorsarechallengingtoadequately
assessinthecontextofasurvey.
ThisincreaseincovercropadoptionmaybedueinparttotheimplementationoftheUSDA-NOP
regulation in 2002, which encourages use of cover crops as part of organic farmers’ nutrient
management and soil building strategies, and increased scrutiny of this practice by the certifiers
most active in Wisconsin. However, according to survey responses, this does not seem to be the
primarydriverforincreasedfarmeradoptionofcovercropping. Inresponsetothequestion“Iuse
covercropsbecauseIamsupposedto”,only10%ofrespondentsansweredagree,with0%ranking
stronglyagree. Theother90%ofrespondentsrankedthisasneutral,disagree,orstronglydisagree.
Thisimpliesthatfarmersareusingcovercropsduetotheirrecognizedproductionandagroecological
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benefits. However,itisimportanttonotethateconomicpressuresimposedbyalimitedlandbasemay
limitfarmer’sabilitytoemploycovercroppingasanagroecologicalpractice,despitetherecognition
oftheirbenefitstothemanagementsystem.
Theinformationcollectedinthesurveyfurtherdemonstratesvaryingdegreesofcomplexityand
diversityincovercroppingpractices,potentiallyillustratingthedesirebyfarmerstopromoteagreater
degreeofagroecosystemservices. Respondentsusedanaverageoftwospecieseveryyearandthree
speciesatleastinsomeyears(so,anaverageoffivecovercropspeciesinthefarm’sportfolio).However,
afewfarmsusedhighlydiversecovercropselections,withtwelveormoretotalcovercropspecies
intheircovercropportfolios. Intermsofspecificpractices,farmerscommonlyusedmixesofcover
cropspeciesinasinglefield,andmanyalsousedoverwinteringcovercrops. Lesscommonwerethe
potentiallymoremanagement-intensivepracticesofintercroppingandunderseeding. Covercropping
complexityalsoappearstoincreasewhenfarmersknowothersusingcovercrops,whichhighlights
thepotentialimportanceofsociallearning,networking,andfarmer-to-farmereducation.
Perhaps most interesting, in light of the conventionalization debate, remains the finding that
covercropdiversityandcomplexitywasnotcorrelatedfarmsizeorrevenue. Thisiscountertothe
conventionalizationargumentdescribedpreviously,whichstronglyemphasizedthegrowthoforganic
farm size as a risk factor for conventionalization [79]. Within the context of the organic vegetable
industryinCalifornia,Guthman[80]posedtheargumentthatwhenlargervegetablefarmscontinueto
farmwithagroecologicalmethods,theyareunabletocompeteinthemoreindustrializedmarketdueto
itspricestructure,pushingthesefarmerstowardinputsubstitutionapproachesandcropspecialization.
Alternatively,shepositsthatthosefarmersoperatinginalternativemarkets,suchasfarmers’markets
andCommunitySupportAgriculture,areabletobenefitfromastructurethatrewardsdiversecrop
offeringsandprovideshigherrevenuemargins,whichsupporttheadoptionofagroecologicalpractices.
WhiletheWisconsinsurveydatadidnotsupportthesetrends,itisimportanttonotethatthesetwo
regionsoftheUSAhavesubstantialdifferencesinotherfactorsthatmayimpactafarmer’schoices
infarmingpractices,suchaslandprices,availabilityofirrigationwater(eitherrainfedorirrigated),
andseasonalcostsofinputs. Additionally,overall,themeanandmediansizesoffarmsinWisconsin,
whereover50%oforganicvegetableoperationsareunder5hectaresinsize[81],maybesubstantially
differentthanthosefoundontheCalifornialandscape.
Furtherresearchisneededtoincreaseourunderstandingofthemultiplefunctionsofcovercrops
andthewaythesefunctionsinteractinordertoenhancetheabilitytodesignagroecologicalsystems.
Schipanski et al. [22] advocate for a systems-based approach to cover crop research, integrating
knowledge from different disciplines and development of a framework for weighing different
management priorities. Increased use of ecological- or bio-economic modeling, which integrates
biophysicalandsocioeconomicdataintoasinglemodel[82,83],couldalsobeusedtoassessfeasibility
anddesirabilityofvariouscovercroppingpractices.
7. Conclusions
Cautioniscertainlywarrantedwhenextrapolatingtheresultsoftheassessmentpresentedinthis
paper,whichusesasinglepracticeindicatorinorganicvegetablesystemswithinalimitedregionto
begintoassesstheextenttowhichorganicfarmersareemployingagroecologicalpractices. Studies
conductedacrosstheglobehaveposedthequestionofthemovementoforganicagriculturetoward
conventionalizationandawayfromitsmoreagroecologicalfoundations[84–87]. Fromourassessment
usingcovercroppingasamodelagroecologicalindicator,thisphenomenondoesnotappeartobe
occurringonWisconsin’sorganicvegetablefarms. Itisimportanttonotethatmanyotherstudieshave
beenconductedfromasocialscienceperspective,focusedonmotivations,scale,andmarkets,rather
thaninvestigatingtheactualpracticesemployedonorganicfarmsacrossdifferentsizeranges[88].
With a lack of interdisciplinary studies approaching this question from both social and applied
productionperspectives[89,90],thetrendsnotedbysocialscientistshavenotbeenwell-correlated
with agronomic practices employed by organic farmers [88]. The ability of organic agriculture to