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Crop Water Information: Groundnut

Thissectionpresentsinformationonwaterrelationsandwatermanagementofgroundnutandprovideslinkstoothersourcesofinformation.

Crop Description and Climate

Groundnut(Arachishypogaea)originatesfromSouthAmerica.Presentannualworldproductionofunshellednutsisabout35.1milliontonsfromabout25.5millionha.(FAOSTAT,2001)

Thecropisgrownbetween40NandSlatitudes.Itsgrowingperiodis90to115daysforthesequential,branchedvarietiesand120to140daysforthealternatelybranchedvarieties.Themeandailytemperatureforoptimumgrowthis22to28Careductioninyieldoccursabove33Candbelow18C.Germinationisdelayedattemperaturesbelow20C.Groundnutisconsideredadayneutralplantanddaylengthisnotacriticalfactorinfluencingyield.Forgoodyields,arainfedcroprequiresabout500to700mmofreliablerainfalloverthetotalgrowingperiod.

Thecropisbestadaptedto.welldrained,loose,friablemediumtexturedsoils.Heavytexturescauseproblemsinliftingthecropatharvest.Also,thetopsoilshouldbeloosetoallowthepegs(onwhichthefruitsareformed)toenterthesoileasily.

Beingalegume,groundnutcanfixnitrogenfromtheair.However,apreplantingnitrogenapplicationof10to20kg/haisoftenrecommendedtoassuregoodcropestablishment.Phosphorousrequirementsare15to40kg/hapotassiumrequirements25to40kg/ha.Atoohighapplicationofpotassiumcancauseadecreaseinyield.Forproperkernelformationandpodfilling,300to600kg/haofcalciumisrequiredatthebeginningofpodformationinthetopsoilwherethefruitsareformed.LimestoneisusedwhensoilacidityneedstobecorrectedandgypsumwhenonlytheCalevelneedstobeincreased.AtpHlowerthan6,limingmaybenecessarytoavoidaluminiumandmanganesetoxicity.

Groundutduringripening

Thegraphbelowdepictsthecropstagesofgroundnut,andthetablesummarisesthemaincropcoefficientsusedforwatermanagement.

Stages of Development Plant date Region

Cropcharacteristic Initial

CropDevelopment Midseason Late Total

Stage length,days

25

35

35

35

35

45

45

35

35

25

35

25

130

140

140

Dry season

May

May/June

West Africa

High Latitudes

Mediteranean

DepletionCoefficient, p 0.45 >> 0.45 0.5

Root Depth, m 0.25 >> >> 0.5

Crop Coefficient,Kc 0.4 >> 1.05 0.6

Yield ResponseFactor, Ky 0.2 0.8 0.6 0.2 0.7

Water Requirements

Dependingonclimate,thewaterrequirementsrangefrom500to700mmforthetotalgrowingperiod.Asrelatedtodevelopmentstages,thekcvaluefortheinitialstageis0.40.5(15to35days),thedevelopmentstage0.70.8(30to45days),themidseasonstage0.951.1(30to50days),thelateseasonstage0.70.8(20to30days),andatharvest0.550.6.

Water Supply And Crop Yield

Therelationshipsbetweenrelativeyielddecrease(1Ya/Ym)andrelativeevapotranspirationdeficitforthetotalgrowingperiodareshowninthefigurebelow.

Thisfigureshowstherelationshipsbetweenrelativeyielddecrease(1Ya/Ym)andrelativeevapotranspirationdeficitfortheindividualgrowthperiods.

Vegetativeandreproductivegrowthshowadefiniteresponsetowatersupply.However,excessivesoilwaterisharmfulbecauselackofoxygeninthesoillimitstheactivityoftheNfixingbacteriathisisnotedbyanunhealthygrowthpatternandyellowingoftheleaves.Excessivesoilwaterinheavysoilsatharvestcancausethepodstobetorneasilyfromthepegswiththepodsremaininginthesoil.

Thefloweringperiod(2)ismostsensitivetowaterdeficit,followedbytheyieldformationperiod(3).Ingeneral,waterdeficitsduringthevegetativeperiod(1)causedelayedfloweringandharvest,andreducedgrowthandyield.Waterdeficitsduringflowering(2)causeflowerdroporimpairedpollination,whereaswaterdeficitsduringtheyieldformationperiod(3)giveareducedpodweight.Theearlypartoftheyieldformationperiod(podsetting)isparticularlysensitivetowaterdeficit.Inthecaseoflimitedwatersupply,watersavingsshouldbemadeduringtheperiodsotherthanflowering(2)andearlyyieldformation(3).Ahighertotalproductionisobtainedbyincreasingthecultivatedareaandpartiallymeetingcropwaterrequirementsratherthanbymeetingfullcropwaterrequirementsoveralimitedarea.

Followingtablepresentsthegrowthperiodsforgroundnut

Crop stage Days

0 Establishment 1020

1 Vegetative 2535

2 Flowering1 3040

3 Yield formation (including pod setting and pod filling) 3035

4 ripening 1020

1Floweringcontinuesduringpartoftehyieldformationbutthepodsfromthelateformedflowersdonotreachmaturity.

Water Uptake

Thecrophasawelldevelopedtaprootwithmanylateralswhichmayextendtoadepthof1.Sm.Themajorpartoftherootsystemis,however,foundinthefirst0.5to0.6msoillayer.Fullgrownplantsnormallyextract100percentofthewaterfromthefirst0.5to1.0mofthesoil(D=0.51.0).Underanevapotranspirationrateof5to6mm/day,therateofwateruptakebythecropstartstoreducewhensome50percentofthetotalavailablesoilwaterhasbeendepleted(p=0.5).

Irrigation Scheduling

Dependingonthelevelofcropevapotranspirationandwaterholdingcapacityofthesoil,intervalsvaryfrom6to14daysupto21daysforloamsoils,withshorterintervalsduringflowering(2)whendepletionofavailablesoilwatershouldnotexceed40percent.Inthecaseofsupplementalirrigation,bestresultsareobtainedwhenwaterisappliedduringthefloweringperiod(2).

Irrigation Methods

Onlighttexturedsoils,sprinklerirrigationoffersadvantagesbylightandfrequentwaterapplication,sufficienttowetthefirst0.6mofthesoil.Furrowirrigationisfrequentlyusedonmediumtexturedsoils.

Yield

Underrainfedconditionsgoodaverageyieldsvaryfrom2to3ton/haunshellednutsunderahighlevelofmanagement.Underirrigationandahighlevel100ofmanagement,yieldscanbe3.5to4.5ton/haunshellednuts.Thewaterutilizationefficiencyfortheharvestedyield(Ey)forunshelled,driednutswithamoisturecontentofabout15percentis0.6to0.8kg/m3.Groundnutscontainabout30percentproteinandarerichinvitaminsBandC.TheoilcontentfortheVirginiabunchtype(alternatelybranched),isbetween38and47percentforthesmallseededSpanishtypes(sequentiallybranched),47to50percent.Oilcontentisreducedconsiderablywhenwaterdeficitsoccurduringtheyieldformationperiod(3).