Effect Of Annual Optimal Nitrogen Management On Crop Yield And Nitrogen Use Efficiency In Winter Wheat-Summer Maize Multiple-Cropping System Of Guanzhong Plain

The traditional fertilization has been used up to now,which has made great contribution to the increase of crop yield.However,with the development of modern agriculture and the current agricultural situation,the traditional fertilization practice needs to be changed.The phenomenon of excessive and unreasonable use of nitrogen?N?has become one of the main problems in China.And with the rapid increase of populaton and food demand,the problem has become increasingly serious,which negatively affects the food security and the agro-ecosystem.Winter wheat-summer maize multiple-cropping system is major planting system in northern China,but the unreasonable fertilization has become the important problem in the region.Therefore,it is necessary to establish an annual optimal fertilization management for promoting sustainable development of agriculture.However,it has less research about annual optimal N management in winter wheat-summer maize rotation system.At present the majority of studies focused on a single crop or optimized N practice on a single crop.Traditionally,farmers apply a large amount of N as basal fertilizer and less N for topdressing.Obviously,this N practice lead to large amounts of N fertilizer input in the early stage of crop growth,without considering the characteristics of N demand of crop.This results large amounts of fertilizer waste.In addition,fertilizer split for several times is time-and labor-consuming.Therefore,in this research,one traditional practice N1,an annual N rate of 510 kg ha^-1with four applications and four optimized N treatments with reduced N rates[(annual N application rate of 420 kg ha^-1,N2),reduced application times and used SRF at jointing stage of maize?N3?,used fertilizer mixture at jointing stage of maize?N4?and fertilizer mixture used at jointing stage of wheat and maize?N5?,respectively]were conducted to systematic research the effects of annual N managements on crop yield,group quality of plant and N use efficiency.At the same time,¹⁵N isotope tracer technology was used to explore the effect of optimized N management on N use efficiency,N residual,N loss and its mechanism.Then to determine the optimum annual nitrogen application management.The study can provide theoretical and practical support for application in northern China.The main results of this research are as follows:?1?Compared to N1,the optimized fertilization treatments did not reduce wheat or maize yield and the annual crop yield also had no response to the reduced N.The grain quality analysis showed that in 2015-2016 and 2016-2017 annual N management had no effect on winter wheat grain quality of crude protein,starch,flour yield,wet gluten,sedimentation and test weight.There was also no effect on crude protein,starch,crude fat and crude fiber of summer maize.?2?In winter wheat and summer maize growing seasons,the total aboveground biomass gradually increased and was maximal at the mature stage.No differences were observed among the treatments.Leaf area index?LAI?showed a trend of increasing first and then decreasing and was maximal at the anthesis stage.The chlorophyll relative content?SPAD value?had a similar trend to LAI.The number of tillers of winter wheat was higher in N1treatment than the optimized N treatments before re-greening stage,but the trend was opposite after the jointing stage.Plant height and stem diameter of summer maize showed a gradually increasing trend and no differences among all the treatments.?3?compared to N1,the annual N-agronomic efficiency?NAE?of the optimized fertilization treatments increased by 6.75-27.59%and 2.53-39.87%in 2016 and 2017,respectively.The N-uptake efficiency?Nup E?,N-fertilizer productivity?Nf P?,and N-agronomic efficiency?NAE?of the optimized fertilization treatments were higher than N1treatment,particularly for treatments with a mixture of urea and slow-release fertilizer.But the N-translocation efficiency?Nt E?and N-harvest index?NHI?were not significantly affected.After harvested of wheat and maize,the soil N content analysis indicated that the contents of NO₃^--N and NH₄⁺-N of optimized treatments were lower at wheat and maize harvest than conventional treatment N1.And the optimized N treatments had no effect on soil total N and organic matter.Compared to N1,annual N treatments had no effect on total N uptake of plant.NRE of wheat and annual nitrogen recovery efficiency?annual NRE?did not differ among treatments in 2015-2016,but significantly increased in 2016-2017compared to N1.For maize,optimized N managements decreased the NRE in N3 and N4treatments of two years compared to N1and N2.The fate of ¹⁵N label urea showed that N from fertilizer taken up?Ndff?and from soil?Ndfs?by wheat were not affected by N management;however,in maize,Ndff performed differently.The total Ndff was lower in treatments N3 and N4,but the total Ndfs was not different among treatments.Optimized N practices enhanced N uptake by plant from soil.The residual ¹⁵N in the upper 0-60 cm of soil after wheat and maize harvested was lower than N1.And the Potential losses in wheat obviously decreased compared to N1,but in maize,N3 and N4 had lower residual N in the soil's top 60 cm,but resulted in higher potential losses than N1 and N2.?4?The analysis of the production cost and net income of winter wheat and summer maize showed that compared with the traditional N1 treatment,the optimized N treatments reduced the input cost and saved the labor with reducing N application rate and times.The net profit increased 12.2%-18.7%and10.7%-46.5%,respectively in 2015-2016 and2016-2017 compared with N1.