Effects Of Slow Release Nitrogen Fertilizer On Soil Nitrogen Use Efficiency And Cotton Yield And Quality

【Objective】Xinjiang is the most important cotton production base in China.Nitrogen is an essential element in the process of cotton growth.There are some problems in Xinjiang cotton field,such as excessive nitrogen fertilizer application,low utilization rate and serious nitrogen loss.Nutrient release of slow-release nitrogen fertilizer is relatively slow,and combined application with urea is beneficial to nitrogen use efficiency and crop yield.In this study,the effects of different proportion of liquid slow-release nitrogen fertilizer and urea on soil physical and chemical properties,enzyme activity,nitrogen absorption and utilization,yield and quality of cotton were studied.The optimal proportion of slow-release nitrogen fertilizer and chemical fertilizer and the effect of improving nitrogen use efficiency were clarified,in order to provide theoretical reference for the rational application of nitrogen fertilizer and the popularization and application of slow-release nitrogen fertilizer in drip irrigation cotton fields in Xinjiang.【Methods】The experiment was carried out from 2020 to 2021 with cotton variety’Xinluzao 64’as the test material.The experimental design included pot experiment of screening the proportion of slow-release nitrogen fertilizer and urea,and field application effect experiment of slow-release nitrogen fertilizer combined with nitrogen reduction.According to the different nitrogen application methods and nitrogen application rates,pot experiment was set up to conventional total urea（T2）and slow-release nitrogen fertilizer with urea in different proportions（NS）.According to the nitrogen application rate,three levels were set up:no nitrogen reduction N_0.8S_0.2（T3）,N_0.6S_0.4（T4）,nitrogen reduction 20%N_0.6S_0.2（T5）,N_0.4S_0.4（T6）,nitrogen reduction 40%N_0.4S_0.2（T7）,N_0.2S_0.4（T8）,with no nitrogen fertilizer（T1）as the control,a total of eight treatments.The field application experiment was carried out in the experimental field of Shihezi University in 2021.The optimal proportion of slow-release nitrogen fertilizer combined with nitrogen reduction screened from potted plants was applied to the field to further verify its fertilizer efficiency and its influence on cotton yield and quality.Three treatments were set:no nitrogen fertilizer（H1）,conventional total urea（H2）,and slow-release nitrogen fertilizer combined with urea（H3）under20%nitrogen reduction.After treatment,soil physical and chemical properties,enzyme activity and nitrogen accumulation of cotton field at different growth stages were measured,and nitrogen absorption and utilization efficiency,cotton yield and quality and their components were calculated.【Main results】（1）Combined application of slow-release nitrogen fertilizer and urea in different proportions could improve soil physical and chemical properties,enzyme activity,cotton growth,nitrogen utilization and yield.There was no significant difference in soil water content,total nitrogen content,inorganic nitrogen content,enzyme activity,cotton growth and development index,nitrogen accumulation in various organs and yield between the treatment of 20%N reduction combined with slow-release nitrogen fertilizer T5 and T6 and the conventional urea treatment,and the nitrogen utilization rate reached the highest among all treatments.Among them,the treatment（T5）of 20%N reduction combined with 20%slow-release nitrogen fertilizer could make the plant height,dry matter accumulation,SPAD value and yield of cotton have no significant difference with the conventional urea treatment when the proportion of slow-release nitrogen fertilizer was relatively small,which was the best proportion of slow-release nitrogen fertilizer combined with urea in this experiment.（2）The results of field application experiments showed that 20%nitrogen reduction combined with slow-release nitrogen fertilizer could enhance the water and nitrogen retention ability and aggregate stability of cotton field soil,and improve the inorganic nitrogen content and soil enzyme activity of cotton field soil.The aggregate stability parameter R_0.25of 20%nitrogen reduction combined with slow-release nitrogen fertilizer treatment in 0～20 cm soil layer was higher than that of conventional total urea treatment.There was no significant difference in total nitrogen and water content in 0～60 cm soil layer between20%nitrogen reduction combined with slow-release nitrogen fertilizer treatment and conventional total urea treatment.The ammonium nitrate nitrogen content in 40～60 cm soil layer was significantly lower than that of conventional total urea treatment,which could reduce the leaching loss of nitrogen to the deep soil layer and avoid a large amount of nitrogen waste.（3）In the field application experiment,20%nitrogen reduction combined with slow-release nitrogen fertilizer treatment can effectively promote the growth and development of cotton,improve the nitrogen accumulation,nitrogen utilization rate and seed cotton yield of cotton,and reduce nitrogen input without reducing cotton yield.There was no significant difference in plant height,SPAD value,dry matter accumulation,bud and boll nitrogen accumulation and seed cotton yield between 20%nitrogen reduction combined with slow-release nitrogen fertilizer treatment and conventional urea treatment.The nitrogen use efficiency of 20%nitrogen reduction combined with slow-release nitrogen fertilizer treatment was the highest,which was 7.87%higher than that of conventional urea treatment.The treatment of 20%nitrogen reduction combined with slow-release nitrogen fertilizer was also conducive to the transfer of nitrogen in reproductive organs to cotton bolls at the late boll setting stage,and there was no significant difference in boll number per plant,single boll weight,lint percentage,breaking specific strength and mic value between the treatment and conventional fertilization.【Conclusion】Under the planting conditions of drip irrigation cotton field in Xinjiang,the soil water content and total nitrogen content in 0～60 cm soil of cotton field treated with 20%slow-release nitrogen fertilizer combined with 20%nitrogen reduction were not significantly different from those of conventional nitrogen application,which improved the stability of soil aggregates in 0～20 cm soil and the activity of catalase,and significantly reduced the residual loss of inorganic nitrogen in 40～60 cm soil of cotton field.Nitrogen reduction combined with slow-release nitrogen fertilizer can effectively promote cotton growth and nitrogen absorption and utilization,especially increase the nitrogen nutrition supply in the late growth stage of cotton,and significantly improve the nitrogen use efficiency of cotton.The application of nitrogen fertilizer was reduced and the amount of fertilizer was saved without reducing cotton yield.The results can provide theoretical reference for rational application of slow-release nitrogen fertilizer and reduction of fertilizer application in drip irrigation cotton field.