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INTRODUCTION Nitrogen (N) is a key factor in the production of Corn ( Zea mays L.) because of its

Biosciences, Biotechnology Research Asia. Vol. 7 (1), 93-100 (2010). Corn ( Zea mays L.) yield and nitrogen efficiencies as affected by different nitrogen rates and redroot pigweed ( Amaranthus retroflexus L.) densities ALI VAHEDI¹*, SAEED VAZAN¹, HAMID RAHIMIAN MASHHADI²,

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INTRODUCTION Nitrogen (N) is a key factor in the production of Corn ( Zea mays L.) because of its

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  1. Biosciences,BiotechnologyResearchAsia Vol.7(1),93-100(2010) Corn(ZeamaysL.)yieldandnitrogenefficiencies asaffectedbydifferentnitrogenratesandredroot pigweed(AmaranthusretroflexusL.)densities ALIVAHEDI¹*,SAEEDVAZAN¹,HAMIDRAHIMIANMASHHADI², MAJIDAGHAALIKHANI³andALIKASHANI¹ ¹DepartmentofAgronomy,FacultyofAgricultureandNaturalResources, IslamicAzadUniversity,KarajBranch(Iran). ²DepartmentofAgronomy,FacultyofAgricultureandNaturalResources,UniversityofTehran. ³DepartmentofAgronomy,FacultyofAgriculture,TarbiatModarresUniversity,Tehran(Iran). (Received:March12,2010;Accepted:April20,2010) ABSTRACT FieldexperimentswereconductedattheAgriculturalFacultyresearchfieldoftheIslamic AzadUniversity,Astarabranch(NorthwesternIran)in2007and2008.Themaingoalwastoexamine theeffectsofredrootpigweeddensity(AmaranthusretroflexusL.)onredrootpigweedleafareaindex at50%Corn(ZeamaysL.)tasseltimeandcorngrainyield,nitrogenrecoveryefficiency,nitrogenuse efficiencyandnitrogenutilizationefficiencyunderdifferentnitrogenrates.Theexperimentswere establishedassplitplotsarrangedinrandomizedcompleteblockdesignwiththreereplicates.The mainplotwasnitrogenrateatfourrates0,100,160and220kgNha-1.Thesubplotwasredroot pigweeddensities,whichwereconsideredatfourlevels0,5,10and20weedsm-2inanextendedform tothecornfarm.Theresultsindicatedthatnitrogenapplicationupto160kgNha-1with5and10weeds m-2didnothaveanysignificanteffectonleafareaindexofredrootpigweed.However,thischaracteristic increasedwiththeweeddensityatupper160kgNha-1.Leafareaindexoftheweedwasincreased when220kgNha-1wasapplied,anditsamountsinmoredensitieswasgreateraswell.Thehighest levelofredrootpigweedleafareaindex,in20weedsm-2andapplicationof220kgNha-1wascalculated tobe1.82.Corngrainyield,nitrogenrecoveryefficiency,nitrogenuseefficiencywere13.0tha-1, 46.2%and60.5kggrain/kgNapplied,under160kgNha-1inweed-freecorncondition.Eventually,it wasfoundthatthepresenceof5weedsm-2upto160kgNha-1didnothaveanysignificanteffecton corncharacteristics;however,theyweredecreasedbyincreasingweeddensity.Thehighestdecrease wasobservedwhenwasappliedthehighestamountofnitrogenunderthehighestweeddensity. Although,20weedsm-2insteadof10weedsm-2causedmoredecreaseincornnitrogenuseefficiency, theeffectoftheseweeddensitiesdidnothaveanysignificantdifference,statistically. Keywords:Corn,Competition,Yield,Nitrogenefficiency,Weed. INTRODUCTION Nitrogen(N)isakeyfactorinthe productionofCorn(ZeamaysL.)becauseofits incorporationintomanyofthekeycompounds necessaryforplantgrowth1.Itismostoften associatedwiththeestablishmentofbothplantyield andphotosyntheticactivity2.Manyresearchers3,4 reportedrelationshipbetweencropsgrowth,grain yieldanddrymatterwithnitrogenrate.Researches showthatNitrogenRecoveryEfficiency(NRE), NitrogenUseEfficiency(NUE)andNitrogen UtilizationEfficiency(NUtE)wereinfluencedby differentNrateapplication5,6.ItisreportedthatNUE incorncroppingsystemsareonly37%7,and 33%8forcerealcropsgrownworldwide.IfNfertilizer couldbemanagedtoreflectdifferencesintheability ofcornplantstocapturescarceresources9,itcould leadtoahigherNUEincorncroppingsystems.Field andyear10canvarytheeconomicoptimum fertilizationrates.

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