Effect Of Optimized Nitrogen Application On Soil Nitrate Nitrogen Cotton Yield And Fertilizer N Use Efficiency

[Objective]Unreasonable application of nitrogen fertilizer will affect the supply of nitrogen nutrients in the soil,resulting in reduced crop yields and Fertilizer N use efficiency,which in turn leads to waste of resources and aggravation of environmental pollution.By studying the effects of the amount of nitrogen fertilizer,the frequency and proportion of dripping application on soil nitrate nitrogen,cotton yield and nitrogen fertilizer use efficiency.Compare the degree of correlation between soil nitrate nitrogen and cotton yield in each growth period,determine the critical value of soil nitrogen supply capacity at a certain depth in different periods.Use the polyphenol-chlorophyll meter(Dualex-4)and SPAD chlorophyll meter to diagnose the nitrogen nutrition of cotton,and compare the measured nitrogen balance index(NBI),chlorophyll(Chl)and SPAD values with the total N of cotton leaves and soil nitrate nitrogen.Perform correlation analysis and comparison.Screen the appropriate diagnostic indicators and establish a nitrogen fertilizer recommendation model for drip irrigation cotton at different growth periods.It provides a theoretical basis for the rational regulation and control of cotton nitrogen fertilizer under drip irrigation in Xinjiang.[Methods]The research adopted field plot experiment:1.Nitrogen application rate experiment:The experiment set up 6 nitrogen application levels:0,202.5,270,337.5,405,540 kg/hm~2(respectively:N0,N1,N2,N3,N4,N5).2.Nitrogen fertilizer application frequency and distribution ratio test:The experiment set up 7treatments:(1)No nitrogen fertilizer(N0);(2)Fertilization 6 times+light before and heavy(N6-L);(3)Fertilization 6 times+Heavy before and light(N6-M);(4)6 times of fertilization+light before and light+3%fertilizer for emergence(N6-M1);(5)8 times of fertilization+light before and heavy(N8-L);(6)8times of fertilization+light before and light(N8-M);(7)8 times of fertilization+light before and light+fertilizer for emergence(N8-M1).3.Different nitrogen fertilizer optimization comparison test:The experiment has 4 treatments:(1)No nitrogen fertilizer(N0);(2)Farmers’habit of applying nitrogen(NF);(3)Nitrogen application frequency and distribution optimization(NY);(4)Based on NBI recommends model nitrogen optimization(NT).[Main results](1)When the nitrogen application rate is 337.5 kg/hm~2,the residual nitrate nitrogen is concentrated in the upper layer(0-40cm)soil;under the conditions of high nitrogen(405 kg/hm~2 and 540 kg/hm~2),the deep layer(60-100 cm)Residual nitrate nitrogen in the soil.In the range of 0-270 kg/hm~2,increased application of nitrogen fertilizer can significantly promote cotton total dry matter weight and nitrogen nutrient uptake.When the nitrogen application rate was 337.5 kg/hm~2-540 kg/hm~2,cotton yield and Fertilizer N use efficiency were significantly reduced.Under the conditions of this study,there was a significant quadratic curve relationship between nitrogen application rate and cotton yield:Y=-0.0362x~2+22.062x+2507.4;the optimal nitrogen application rate was 304.7 kg/hm~2.(2)The total dry matter weight and nitrogen absorption of cotton of the first-heavy and late-li ght treatment(M)were significantly higher than that of the first-light and late-heavy treatment(L).Under the conditions of 6 times and 8 times of nitrogen application,the cotton yield of the first heavy and the light treatment increased by 13.7%and 11.7%on average compared with the first light and the light treatment.Cotton nitrogen utilization rate increased by 12.4%and 16.0%respe ctively.Increasing the number of fertilization significantly improved cotton yield and nitrogen utiliz ation efficiency.N8 treatment increased cotton yield and nitrogen utilization efficiency by an avera ge of 10.7%and 16.1%compared with N6 treatment.At the same time,0-1m soil nitrate nitrogen residues decreased by 15.3%on average.N8-M1 treatment significantly reduced the residual nitrat e nitrogen in deep soil.(3)Nitrogen nutrition diagnostic indicators NBI,Chl and SPAD have extremely significant pos itive correlations with cotton leaf N content and 0-40cm soil nitrate nitrogen(P<0.01).In each gro wth period of cotton,the determination coefficient R~2 of NBI and cotton leaf total N content diag nostic models were higher than Chl and SPAD models.Correlation model verification results show that the correlation coefficient r between the measured and predicted values of cotton leaf N are NBI(0.9143),Chl(0.8639),and SPAD(0.6526).And the mean square error(MSE),root mean square error(RMSE)and mean absolute error(MAE)of the NBI model are better than Chl and S PAD models;mean absolute percentage error(MAPE)and standard root mean square error(n RMS E)are respectively These are:6.64%and 7.46%.The verification results of the 0-40cm soil nitrate-nitrogen diagnostic model show that the verification and evaluation indicators of the NBI model a re better than the Chl and SPAD models.Therefore,the Nitrogen Balance Index(NBI)can be use d as a suitable diagnostic index of nitrogen nutrition for drip irrigation cotton.(4)There is a very significant quadratic curve relationship between soil nitrate nitrogen and c otton yield between 0-40 cm soil at the bud and flower stage;the critical values of soil nitrogen supply are 129.90 kg/hm~2 and 194.44 kg/hm~2,respectively.However,there is a very significant lin ear and plateau relationship between 0-60 cm nitrate nitrogen and cotton yield in the full flowerin g and boll stage;the critical values of soil nitrogen supply are 213.47 kg/hm~2 and 183.74 kg/hm~2,respectively.And on this basis,the bud stage,the first flowering stage,the full flowering stage a nd the boll stage were established respectively;NBI-based nitrogen fertilizer recommendation model for cotton was established.(5)Nitrogen fertilizer optimization(NT)treatment based on NBI recommended model significa ntly promoted cotton growth and nitrogen uptake compared with NF treatment;yield and Fertilizer N use efficiency increased by 18.4%and 27.7%,respectively,the 0-1m soil nitrate nitrogen resid ue was reduced by 35.3%.Compared with the NY treatment,there were no significant differences in cotton yield,Fertilizer N use efficiency,and total soil nitrate nitrogen residues,but the amount of nitrogen fertilizer was reduced by 8.4%.[Conclusion]When the nitrogen application rate was 337.5 kg/hm~2-540 kg/hm~2,the cotton yield and nitrogen utilization efficiency were significantly reduced.Among them,at 405 kg/hm~2 and 540 kg/hm~2,the residual nitrate nitrogen in the deep soil was mainly increased.Increasing the number of drops of nitrogen fertilizer and the distribution ratio in the early stage can not only increase cotton yield and Fertilizer N use efficiency,but also reduce the residual nitrate nitrogen in deep soil.Using NBI to recommend cotton nitrogen fertilizer,cotton yield and Fertilizer N use efficiency increased by18.4%and 27.7%,respectively,compared with farmers’habitual application of nitrogen;and 0-1m soil nitrate nitrogen residue was reduced by 35.3%,and the deep soil was effectively reduced Nitrate nitrogen remains.