Manure or biodigester effluent as fertilizer for duckweed

摘要

Anexperimenttocomparethegrowthresponseofduckweed(Lemnaminor)toincreasingconcentrationsofNfromtwosourcesofsubstrateswasconducted.Thesubstrateswererawcowmanure(M)andeffluentfrombiodigesterschargedwithcowmanure(E).TheexperimenttookplaceinAnGiangUniversity,LongXuyendistrict,AnGiangprovince,Vietnam.RawcowmanureandbiodigestereffluentwereusedasthefertilizerswithfivelevelsofN(0,50,100,150and200kg/ha),accordingtoa2x5factorialarrangementwith2replicationspertreatmentwiththesplit-plotdesign.Averageairandwatertemperatureduringthetestwere26to31oCand25to27oCwiththehighestinthemidday,whentemperaturewas38and29oC,respectively.Plasticsbasketslinedwithplasticfilmwereusedasexperimentalponds.Thesurfaceofwaterineachbasketwas0.16m2with10cmdepth,andthevolumewas16liters.Duckweed(Lemnaspp)wasinoculatedatarateof200g/m2(30g/basket).Theyieldofduckweedwascalculatedbysubtractingtheinoculumfromthetotalbiomassproductionmeasuredevery48hoursandwasexpressedasfreshduckweedyieldg/m2/day.Thefertilizerswereappliedfivetimesinequalamountsduringtheexperiment(20days),accordingtothelevelsineachtreatment.Therewasnosignificant(P=0.85)interactionofnbsp;Nlevel*fertilizersourceforbiomassproduction.DuckweedyieldincreasedlinearlywithlevelofNinthefertilizerandwashigherforeffluentthanformanure.Rootlengthwasshorterwhenthepondswerefertilizedwiththeeffluent,rootlengthbeingnegativelycorrelatedwithproteincontentoftheduckweed(R2=0.82forEandR2=0.71forM)andwithbiomassyield(R2=0.54forEandMcombined).CrudeproteincontentinduckweedincreasedwithNlevelappliedandwashigherforeffluentthanformanure.ItissuggestedthatbiodigestereffluentisabetterNfertilizerthantherawmanureforduckweedproductioninsmallponds.nbsp;Rootlengthcanbeusedasasimpleandcheapindicatorofbiomassyieldandcrudeproteincontentinduckweed.FurtherstudiesconcerningthesourcesofNforincreasingtheNcontentofduckweedproductionaresuggestedtoimprovetheefficiencyofintegratedfarmingsystemsindevelopingcountries.