Effects Of Late Nitrogen Application On Nitrogen Utilization And Processing Quality Of Wheat

Many studies regarding on late nitrogen(N)fertilization on grain yield and processing quality of wheat have been conducted.However,the results varied among studies which led to di fferent,sometimes even reversed conclusions.One of the possible explanations for these inconsistent conclusions might result from different timings of late N application.In previous studies,the so-called 'late N fertilization' covered a wide range of wheat growth stages including stem elongation,booting,heading,anthesis,or even post-anthesis stage.Results from our previous studies indicated that there might be a critical period for late N application to alter N participation and improve the processing quality of wheat grains,while earlier or later than which might show less or no late N effect on protein and processing quality of wheat grain compared to the critical period.However,the effect of late N application at different timing on grain and processing quality of wheat grain,as well as the mechanism behind it are still not clear yet.Therefore,in order to provide some insight in better understanding of the issues addressed above,a field experiment was carried out in Ningjin County,Hebei Province from October 2017 to June 2019 using a high-gluten winter wheat cultivar 'Gaoyou 2018'.With a same dose of N application at 240 kg N/hm2,four treatments with various N application timings were conducted,i.e.N application at sowing and stem elongation stages(Ns+E),N application at sowing,stem elongation and booting stages(Ns+E+B),N application at sowing,stem elongation and heading stages(Ns+E+H),as well as N application at sowing,stem elongation and anthesis stages(Ns+E+F).The effects of late N application on grain yield,quality as well as N uptake and utilization of wheat were studied.The main results are summarized as follows:(1)Compared with NS+E,grain yield showed an increasing trend by splitting 50%of the N application at stem elongation stage to late growth stage.Particularly for N splitting application at booting stage,the grain yield was increased by 11.9%in the 2017 to 2018 season.About 54.6%-76.4%of the grain yield derived from the accumulation of dry matter after anthesis.Especially for N application at booting stage(NS+E+B),the post-anthesis dry matter accumulation and its contribution rate to the grain were both significantly improved,which were 49.3%and 31.8%higher than that of NS+E(no late N application),respectively.(2)Compared with NS+E,late N application had no significant effect on grain protein concentration of wheat,while significantly altered grain protein composition and enhanced gluten protein content.Particularly for late N application at booting stage,the concentrations of gliadin and glutenin,as well as the proportions of gliadin and glutenin in grain total protein were increased by 12.3%,8.8%,11.5%and 9.4%,respectively,compared with that of NS+E(no late N application).Furthermore,late N application significantly increased the sedimentation value of wheat flour as well.Compared with NS+E,the sedimentation value of wheat flour was increased by 2.2%-8.6%and 9.9%-14.0%by late N application in the two consecutive experimental seasons,respectively.Besides,among different late N application timings,the sedimentation value of NS+E+B treatment was significantly higher than that of other late N treatments(application at heading or anthesis stage).Compared with NS+E treatment,the enhancement of sedimentation value was 11.3%in NS+E+B treatment on average for two years.(3)Compared with NS+E,late N application increased N uptake in grains and aboveground of wheat at maturity.Besides,late N application at booting stage showed the most prominent effect among all treatments which enhanced N uptake in grains and aboveground of wheat by 16.6%and 18.3%compared to that of NS+E,respectively,in two consecutive seasons.In terms of grain N origin,around 62.9%-83.5%of N in grains derived from N accumulated before anthesis and transported post-anthesis to the grain,while 16.5%-37.1%from post-anthesis N accumulation.Besides,late N application,especially at booting stage,significantly increased post-anthesis N accumulation and its contribution to the grains,which was 111.1%and 81.6%higher than that of NS+E treatment,respectively,in two experimental seasons.Furthermore,the partial factor productivity of applied N and N uptake efficiency showed similar trends among treatments in two experimental seasons as NS+E+B>NS+E+B>NS+E+F>NS+E treatment.(4)The changes in grain protein concentration had significant impacts on processing quality related parameters.Based on results from two experimental years,wet gluten content of wheat flour was positively correlated with the grain protein concentration(R2=0.605**,P<0.01).Moreover,in terms of grain protein concentration prediction using SPAD,results demonstrated that the correlation between SPAD and grain protein concentration of the first and second leaves below flag leaf were significantly higher than that of flag leaf.Besides,the correlation between SPAD and grain protein concentration was highest in the leaves at booting stage(R2=0.438**,P<0.01)compared with that of other stages.Therefore,SPAD values of the first leaf below flag leaf at booting stage could be considered as one of the promising predictors for grain protein concentration at maturity of wheat.(5)The total residual nitrate-N and ammonium-N in the 0-100 cm soil profile at wheat maturity showed similar trends in the two experimental years among treatments as NS+E+F>NS+E+H>NS+E>NS+E+B.Therefore,the late N application at booting stage(NS+E+B treatment)could be a promising N management practice in reducing N residue in the soil at maturity stage and thus lowering the risks of N volatilization and leaching loss.Therefore,considering grain yield,quality as well as N uptake and utilization,the application of N fertilizers at sowing,stem elongation and booting stages(4:3:3)might be a suitable N fertilization management practice for achieving high grain yield,improved processing quality and high N utilization efficiency of wheat under current conditions or locations with similar soil and climatic conditions as the present study.