Effect Of Different Water Nitrogen Treatment On Soil N₂O Emission And Yield In The Flowering Period Of Drip Irrigation Cotton Fields

Under-membrane drip irrigation cropping pattern is the main cropping pattern of cotton in Xinjiang region,which has the advantages of water saving,maintaining soil temperature and regulating soil physical properties.How to reasonably regulate water and nitrogen dosage to effectively reduce soil nitrous oxide（N₂O）emissions while improving cotton yield is an important scientific issue for energy conservation and emission reduction in drip irrigated farmland in Xinjiang.In this study,the soil gas flux measurement system was applied to monitor the soil N₂O emission characteristics of cotton during the period of heavy fertilizer and nitrogen demand（boll stage）,and the data of N₂O gas emission and soil environmental factors were collected to investigate the soil N₂O emission characteristics of cotton fields under drip irrigation in Xinjiang.The effects of different levels of water and nitrogen treatments on N content,dry matter quality and yield of above-ground parts of cotton plants in sub-membrane drip irrigated cotton fields were analyzed.The main findings were as follows:（1）Soil temperature in the 0～60 cm soil layer of different levels of water and nitrogen treatments showed a gradual decrease with the advancement of cotton fertility.The treatment of 240 kg/hm²of N application and 4200 m³/hm²of total irrigation water combined 0～20,20～40 and 40～60 cm soil layers showed a lower range of temperature variation and could maintain a higher soil temperature in the soil layer,which was more favorable for cotton growth and development.Soil volumetric water content showed periodic changes with the irrigation cycle,and after each irrigation cycle,soil volumetric water content increased to the peak and then started to decrease until the next irrigation cycle.The soil water content of different irrigation quota treatments showed 5400 m³/hm²>4800 m³/hm²>4200 m³/hm²>3600 m³/hm².The nitrate-nitrogen content of soil from 0 to 30 cm under different levels of water N treatment was larger and the fluctuation trend was significantly larger than that of soil from 30 to 60 cm.The ammonium nitrogen content in the0～60 cm soil layer under each level of nitrogen application increased significantly,and after chasing fertilizer at the early flowering stage,the soil ammonium nitrogen content in the 0～60 cm soil layer of each nitrogen application treatment showed a fluctuating trend of increasing and then decreasing as the fertility period progressed,and finally the ammonium nitrogen content in each treatment decreased to the low content level.（2）The highest dry matter quality,yield and above-ground N content of cotton plants were achieved at240 kg/hm²N application level and 4200 m³/hm²irrigation level.Both excessive fertilizer application and excessive irrigation had inhibitory effects on cotton yield,and reasonable N application could effectively improve cotton dry matter quality.Nitrogen content of cotton organs was mainly influenced by the level of N application.（3）The peak of soil N₂O emissions occurred mainly at the end of the fertilization and irrigation cycle,and the higher the irrigation amount,the lower the N₂O emission fluxes.N₂O emission fluxes were positively correlated with N application level,comparing 240 kg/hm²and 360 kg/hm²N treatments,the average N₂O emission fluxes of 360 kg/hm²N treatment were higher than that of 240 kg/hm²N treatment at the same irrigation level,which was 1.60-2.27 times higher than that of 240 kg/hm²N treatment.The average N₂O emission flux of 360 kg/hm²N treatment was 1.60-2.27 times higher than that of 240 kg/hm²N treatment.（4）Considering all the factors,the local optimum irrigation and fertilization management measures were240 kg/hm²of N application and 4200 m³/hm²of total irrigation water.