Effects Of N Reduction And Variable Fertilization On Soil N Balance And Yield Of Maize And Nitrogen Fertilizer Use Efficiency

To address the problems of fertilizer wastage and reduction of N fertilizer utilization and maize yield due to the long-term input of large amounts of N fertilizer and the inability of traditional fertilization methods to apply N accurately according to the spatial differences of soil nutrients,a 2-year field experiment was conducted in the black soil area of northeast China.The experiment took maize as the research object,adopted the fertilization method of N reduction combined with variable N fertilization,used high spatial resolution remote sensing images as the data source,superimposed the spatial interpolation of soil organic matter content in the research area,normalized difference vegetation index and digital elevation model,and used the object-oriented segmentation method to carry out soil precision management zoning.The experiment set up five fertilizer application gradients based on the baseline N application(kg·hm^-2)to generate a continuous variable fertilizer application prescription map.There were seven treatments in the experiment:no N treatment（N₀）,conventional N application by farmers(N₂₃₅),conventional N application by farmers with variable N fertilization treatment(N₂₃₅V),N reduction by 10%(N₂₁₂),N reduction by 10%with N fertilization treatment(N₂₁₂V),N reduction by20%(N₁₉₀),and N reduction by 20%with N fertilization treatment(N₁₉₀V).By exploring the responses of soil N balance,maize growth differences,accumulation and allocation of maize dry matter and N,maize N transport and uptake,maize yield and seed quality,and N fertilizer utilization to N fertilizer reduction combined with variable N fertilization,we investigated the optimized N fertilizer reduction program under the appropriate variable N application technology in black soil areas,aiming to provide data support and theoretical basis for the green and precise fertilization technology of maize in northeast black soil areas.The main results of the study were as follows:（1）N reduction combined with variable fertilization reduced the spatial variation of soil nutrients,increased the mean values of alkaline nitrogen,organic matter content and p H,and slowed down the degree of soil acidification due to fertilization.Soil alkaline nitrogen and organic matter contents reached the highest values under N₂₁₂V treatment,and p H values reached the highest values under N₁₉₀V treatment.（2）The effects of soil nutrient spatial heterogeneity on maize growth spatial difference were reduced by N reduction combined with variable fertilization.Compared with conventional N application method,the mean values of SPAD and NDVI increased and the coefficient of variation decreased under N reduction combined with variable fertilization at tasseling stage,and the uniformity of maize canopy coverage improved.SPAD and NDVI reached the highest values under N₂₁₂V treatment at tasseling stage.（3）N reduction combined with variable fertilization increased dry matter accumulation in all organs of maize thus increasing the total dry matter mass.The dry matter accumulation under N reduction increased in each growth period compared with the conventional N application,and the highest increase in dry matter accumulation was observed in N₂₁₂V treatment.Dry matter accumulation of stem and leaf under N reduction increased from seedling stage to tasseling stage compared with conventional N application,and was more translocated to seeds from filling stage to maturity stage,which promoted the formation of dry matter in grain.The variation coefficient of dry matter accumulation in different organs was decreased by variable fertilization compared with conventional uniform N application.The decrease rate increased with the passage of growth period,and the decrease rate was the largest in maturity period.By increasing dry matter accumulation in stems and leaves at the early growth stage and grains at the late growth stage,variable fertilization increased total dry matter accumulation and reduced the spatial difference of dry matter accumulation in different organs.（4）N accumulation in all maize organs was increased by N reduction combined with variable fertilization.N accumulation in maize under N reduction combined with variable fertilization increased at all growth stages compared with conventional N application,and N accumulation in maize was the highest under N₂₁₂V treatment.Because N accumulation in stems and leaves at tasseling stage and maturity stage was higher than that of conventional N application,N transport efficiency of vegetative organs and contribution of N remobilization in vegetative organs to grains under N reduction were lower than that under conventional N application,but variable fertilization made up for this negative effect.In addition,the N harvest index and the N uptake rate before and after anthesis were significantly increased under N₂₁₂V treatment compared with conventional N application.（5）N reduction combined with variable fertilization increased ear number,kernel number per ear,100-kernel weight and yield of maize.Maize yield reached the highest under N₂₁₂V treatment,which increased 184.52%and 36.39%compared with conventional N application in 2021 and 2022,respectively.The coefficient of variation decreased 28.53%and 15.85%compared with conventional N application in 2021 and 2022,respectively.N reduction combined with variable fertilization increased maize yield mainly by significantly increasing grain weight.Compared with conventional N application,N reduction combined with variable fertilization also improved maize quality to a certain extent,and the contents of crude protein,crude fat and starch of maize increased,but the difference was not significant.（6）Compared with conventional N application,N fertilizer use efficiency,N agronomic use efficiency,N partial productivity and contribution rate of N fertilizer to grain were significantly increased under N reduction combined with variable fertilization.In conclusion,N reduction combined with variable fertilization were beneficial to soil N balance,promoting the accumulation and transport of maize dry matter and N,improving maize yield and quality and N fertilizer use efficiency,and could be used as an effective way to achieve agricultural green development,in which N reduction by 10%combined with variable fertilization was the best recommended scheme.