Effects Of Nitrogen Fertilizer Topdressing Time Stages On Nitrogen Metabolism And Yield And Quality Of Two Spike-Type Wheat Cultivars

The objectives of this study were to investigate the effects of nitrogen(N) fertilizer topdressing time on N metabolism and winter grain yield and quality.Two years of field experiments were conducted at the experimental farm of Henan Agricultural University with Lankaoaizao 8,a large spike-type cultivar,and Yumai 49-198,a small spike-type cultivar,in both 2004-2005 and 2005-2006 growth seasons,respectively.The main results are summarized as bellow:1.Effects of N fertilizer topdressing time on N metabolismThe nitrate reductase(NR)activity,glutamine synthetase(GS)activity and soluble protein increased with the delay of N fertilizer topdressing time.The correlation coefficient between NR activity,on one hand,and grain yield,protein content,and protein yield,on the other hand,reached significant levels(P＜0.05)in both investigated cultivars.The same result was found in GS activity.Compared to that at reviving stage,N topdressed at jointing and heading stage improved the N content and N accumulation in all vegetative organs at both anthesis and maturity.However,N transfer efficiency and the contribution rate of N in vegetative organs to grain decreased with the N topdressing postponed.2.Effects of N fertilizer topdressing time on photosynthetic parameters in flag leafThe photochemical efficiency(Fv/Fm),PSⅡactual quantum yield(φPSⅡ)in flag leaf of both the investigated cultivars showed their highest values in the treatments of N topdressed at jointing stage,followed by at heading stage,then at reviving stage.3.Effects of N fertilizer topdressing time on winter wheat grain yield and qualityAmong the three topdressing time,N topdressed at jointing stage showed the highest grain yield because it increased the spike number per unit area and the kernel number per spike.The grain yield of topdressing at heading stage and at reviving stage ranked second and third,respectively.However,topdressing at heading stage had the highest 1000 kernel weight.Winter wheat grain quality was also influenced by the N topdressing time.Nitrogen topdressed at heading stage increased the grain protein content greatly and that at jointing stage had the highest grain protein yield.With the N topdressing postponed,both the content of glutenin and the ratio of glutenin to gliadin increased correspondingly.In addition,the amylase content and the ratio of amylase to amylopectin decreased with the application topdressing postponed.Treatment with N topdressed at jointing stage showed highest amylopectin content,starch content and peak viscosity.Same trends were found in the trough viscosity,final viscosity,breakdown and setback. Overall,N fertilizer topdressed at both jointing and heading stages increased activities of key enzyme of N metabolism in flag leaves and grain,accelerated plant N accumulation and transfer,and improved photosynthesis capacity in flag leaves,then enhanced winter wheat grain yield and quality.