简介:Excessivenitrogen(N)fertilizerapplicationtowinterwheatisacommonproblemontheNorthChinaPlain.TodeterminetheoptimumfertilizerNrateforwinterwheatproductionwhileminimizingNlosses,fieldexperimentswereconductedfortwogrowingseasonsateightsites,inHuiminCounty,ShandongProvince,from2001to2003.TheoptimumNrateformaximumgrainyieldwasinverselyrelatedtotheinitialsoilmineralNcontent(Nmin)inthetop90cmofthesoilprofilebeforesowing.TherewasnoyieldresponsetotheappliedNatthethreesiteswithhighinitialsoilmineralNlevels(average212kgNha-1).TheaverageoptimumNratewas96kgNha-1forthefivesiteswithlowinitialsoilNmin(average155kgNha-1)beforesowing.ResidualnitrateNinthetop90cmofthesoilprofileafterharvestincreasedwithincreasingfertilizerNapplicationrate.TheapparentNlossesduringthewheat-growingseasonalsoincreasedwithincreasingNapplicationrate.TheaverageapparentNlosseswiththeoptimumNrateswerelessthan15kgNha-1,whereasthefarmers'conventionalNapplicationrateresultedinlossesofmorethan100kgNha-1.Therefore,optimizingNuseforwinterwheatconsiderablyreducedNlossestotheenvironmentwithoutcompromisingcropyields.
简介:Polystyrenemacromonomerswithdifferentmolecularweightwerepreparedbyradicalpolymerizationofstyrene(St)inbenzeneusingβ-methacryloxylethyl2-N,N-diethyldithiocarbamylacetate(MAEDCA)asamonomer-iniferter.Characterizationofthemacromonomerby~1H-NMRshowedthattheendgroupswereα-methacrylyoxylethyloxycarbonyl-methylandω-(N,N-diethyldithiocarbamyl).Themacromonomerwasdifficulttohomopolymerize,butitwaseasilycopolymerizedwithmethylmethacrylate(MMA)initiatedbyAIBNtoformgraftcopolymers(PMMA-g-PSt)withPStbranchesrandomlydistributedalongthePMMAbackbone.CopolymerizationreactionandthestructureofthegraftcopolymerswerestronglyaffectedbyM_nandconcentrationofthemacromonomer.ThecompositionandM_nofthepurifiedgraftcopolymerweredeterminedby~1H-NMRandGPCanalysis.
简介:AnewkindofpolysiloxanecontainingN,N’-bis(diphenylsilyl)tetraphenylcyclodisilazanewaspreparedbyanionicnon-equilibriumpolymerizationwitha"seedsolution"asinitiator.Themonomer,N,N’-bis(hydroxydiphenylsilyl)-tetraphenyl-cyclodisilazane(BHPTPC),wassynthesizedviathehydrolysisofN,N’-bis(chlorodiphenylsilyl)tetraphenyl-cyclodisilazane(BCPTPC).AnewmethodforthepreparationofBCPTPCisalsoreportedherewithhighyieldandsimplermanipulation.ThesynthesizedpolysiloxanecontainingN,N’-bis(diphenylsilyl)tetraphenylcyclodisilazanewascharacterizedby1H-NMR,29Si-NMR,gelpermeationchromatography(GPC)andintrinsicviscosity.