Effects Of Nitrogen Drip-Fertigation Scheduling On Growth,Water-Nitrogen Productivity And Greenhouse Gas Emissions Of Winter Wheat In The North China Plain

Irrational application of nitrogen（N）fertilizer was the main reason for low nitrogen use efficiency（NUE）in winter wheat production in North China Plain（NCP）.The excess of applied nitrogen is usually lost through volatilization,leaching and greenhouse gas emissions,which not only affects the yield and quality of agricultural products,but also causes environmental problems such as groundwater pollution and increase in global warming potential.Rational fertilization is necessary for effective management to improve NUE,reduce nitrogen losses and ensure high and stable wheat yield.A study was conducted to evaluate the effects of various nitrogen scheduling on the growth,nitrogen uptake,yield,NUE,water use efficiency（WUE）,and greenhouse gas emissions of drip-irrigated winter wheat in the NCP during the2019/2020 and 2020/2021 seasons.This study consisted of six treatments,with the same total nitrogen amount of 240 kg ha^-1,five with different nitrogen fertilizers（urea,45-46%）application schedules and one with slow release fertilizer（SRF,43%N）.The five nitrogen application schedules were N0-100（0%base and 100%topdressing）,N25-75（25%base and 75%topdressing）,N50-50（50%base and 50%topdressing）,N75-25（75%base and 25%topdressing）and N100-0（100%base and 0%topdressing）,while SRF was applied only as base（at sowing）fertilizer.There was also control with no nitrogen fertilization throughout the period of the experiment.The topdressing application was done at the jointing and booting stages of the winter wheat growth.The two-year field experiment also determined the leaf area index,plant height,yield compositions（spike per unit area,kernel per spike and 1000-grain weight）global warming potential（GWP）,and emission intensity of the winter wheat field.The main results obtained were as follows:1.The effects of splits nitrogen application on grain yield,yield compositions,aboveground biomass（ABM）,water use efficiency（WUE）and nitrogen partial factor productivity（NPFP）of winter wheat were significant（P<0.05）.The N50-50 and SRF treatments had the highest yield of 8.84 and 8.85 t ha^-1 in two growing seasons,respectively.Under the two treatments,ABM was the highest,20.67 t ha^-1 and 20.83 t ha^-1,respectively.WUE was the highest,2.28 and 2.17 kg m^-3,respectively.NPFP was also the highest,36.82and 36.88 kg kg^-1,respectively.The results showed that applying urea at a 50:50 ratio of base and topdressing could achieve comparable results as the expensive slow release nitrogen fertilizers.While single dose at sowing could reduce operational costs,it however resulted in poor yield and low productivity of water and fertilizer.On the other hand,the SRF provided a viable option to the farmers because of it high yield,but its high initial costs could be discouraging.The drip fertigation technique will support multiple applications of the cheaper urea fertilizer at reduced operational costs as compared to the traditional method of manual spreading.2.Urea applied in the N50-50 schedule significantly increased grain yield by 11.24%,8.27%,9.00%and 22.13%,as it is respectively compared with N0-100,N25-75,N75-25 and N100-0 treatments,indicating that applying urea in several times was better than any single application,and there was a weak trend that yield increases with the rise in the proportion of late nitrogen application.The total nitrogen uptake in N50-50 schedule was higher than those in other treatments,and the increase range was 6.54%（N25-75）,（9.36%）N75-25,17.73（N0-100）and 32.96%（N100-0）,respectively,which had a similar trend to the effects on yield.Agronomic efficiency,apparent recovery efficiency and partial factor productivity were the highest under the N50-50.A principal component analysis（PCA）showed that the N50-50schedule recorded the highest rank in the two years of study,with an average score of 91.20%.Applying50%of total nitrogen(240 kg ha^-1,urea)at sowing,25%at jointing,and 25%at booting stages could achieve the best coordination between high yield and rational use of nitrogen in terms of nitrogen uptake and NUE indices.Drip fertigation can be a viable strategy for reducing losses and ensuring nitrogen productivity of winter wheat fields.3.Different nitrogen application scheduling significantly affected the yield and greenhouse gas emissions of the winter wheat fields.The effects on crop yield,greenhouse gas emissions（CO₂,CH₄ and N₂O）,GWP and greenhouse gas emission intensity（GHGI）all reached significant level（P<0.05）.The N25-75 treatment had the lowest GWP(125.34 kg CO₂ eq.ha^-1)and GHGI(15.01 kg CO₂-eq.Mg^-1),but there were no significant differences between N50-50 and N25-75 treatments（P>0.05）in GWP and GHGI.Compared with N100-0 treatment,the GWP of N25-75 and N50-50 treatment significantly decreased（P<0.05）by 67.67%and 63.48%,respectively.A TOPSIS analysis results showed that the N50-50 schedule can minimize the GWP while maintaining high grain yield.The risk of global warming could be effectively reduced,high yield and improved NUE could be achieved in winter wheat production systems under the optimal nitrogen fertilizer application schedule that applies 50%of total amount of urea of 240 kg ha^-1 as basal fertilizer and topdressing doses of 25%via fertigation at jointing and booting stages,respectively.