Effects Of Different Nitrogen Application Rates On Cotton Yield And Environmental Effects Under "kuanzaoyou" Mode

Xinjiang is an important raw cotton production base in China.The traditional cotton planting mode of"Aimizao"has some problems,such as the excessive amount of water and fertilizer,unclean leafing,high impurity content of cotton,and deterioration of cotton fiber quality.Nitrogen fertilizer is an important material input in agricultural production.The excessive input and low utilization efficiency of nitrogen fertilizer inhibit the green development of agriculture in China and responsible for environmental pollution.Therefore,optimizing cotton planting patterns and nitrogen fertilizer input is the most effective strategies to reduce greenhouse gas（GHG）emissions and increase crop yield.This research was conducted in 2019-2020 using CCRI 109 as planting material and studied the“Kuanzaoyou”model（"Aimizao"mode was the control with the same amount of nitrogen application）under different N application to understand the cotton leaf photosynthetic characteristics,dry matter accumulation,and distribution,N₂O emission,carbon footprint,nitrogen accumulation,cotton yield,and yield components,etc.Exploring cotton planting technology with high yield and high efficiency in Xinjiang,in order to provide theoretical basis and technical support for cotton production in Xinjiang to achieve low carbon emission reduction,high yield and good quality,and environmental friendliness.The results of this study are as follows:Increasing the application of nitrogen fertilizer could improve the photosynthetic capacity and the total light interception rate of canopy.The net photosynthetic rate,stomatal conductance,and transpiration rate of cotton leaves were the highest when the nitrogen application rate was 240 kg/hm².The dry matter accumulation of cotton increased gradually,and there was no significant difference between N240 and N360.Nitrogen application could increase cotton yield,but the difference between nitrogen treatments was not significant（in 2019）.In 2020,the seed cotton yield of N240 treatment was the highest,which was 2.2%,2.4%and 14.7%higher than that of N360,N120 and N0,respectively.The boll number and lint percentage per plant increased first and then decreased with the increase of nitrogen application rate.Compared with N0 treatment,N application significantly increased boll weight,and there was no significant difference between N240 treatment and N360 treatment.Nitrogen application significantly increased the nitrogen accumulation of cotton plants,but decreasing nitrogen application appropriately did not significantly reduce the nitrogen accumulation of cotton plants.Nitrogen application significantly increased the N₂O emission from cotton fields,and the total annual N₂O emission under N360 treatment was 196.4%,113.6%,and 33.3%higher than that under N0,N120,and N240,respectively.Reducing nitrogen fertilizer application can significantly reduce farmland carbon footprint.In the carbon footprint of"Kuanzaoyou"cotton planting mode in Xinjiang,the amount of irrigation electricity,agricultural film use,and chemical fertilizer input accounted for 47.4%,25.2%,and 24.3%of the total carbon footprint,respectively.To increase the net photosynthetic rate（Pn）of cotton leaves at the full flowering stage,the"Kuanzaoyou"mode（M2）was used to expand row spacing and reduce density.At the end of the growth period SPAD value of cotton could be significantly increased,which was 1.6%higher than that of"Aimizao"mode（M1）.It is beneficial to dry matter accumulation in the later period of cotton.The nitrogen accumulation in leaf,stem,reproductive organ and whole plant was significantly increased by35.7%,11.6%,21.5%,and 23.5%in the"Kuanzaoyou"planting mode compared with the"Aimizao"planting mode.After 121 days of seedling emergence,the reproductive organ allocation ratio of"Kuanzaoyou"mode was 2.7%higher,and the dry matter allocation ratio of vegetative organs was 4.5%lower as compared to the“Aimizao”mode.The Elongation of"Kuanzaoyou"mode was significantly increased by 0.48%compared with that of"Aimizao"mode.the"Kuanzaoyou"mode increased production by 2.5%（2019）and 6.5%（2020）as compared to the“Aimizao”modeIn conclusion,Increasing nitrogen application can improve cotton photosynthetic performance,dry matter accumulation,N₂O emission,carbon footprint,nitrogen accumulation,and cotton yield.The"Kuanzaoyou"mode could improve the net photosynthetic rate at the full flowering stage thatfacilitate dry matter accumulation and improve the reproductive organs.It also enhances nitrogen accumulation in cotton plants and finally increase the seed cotton yield.Under the condition that the yield is not affected,reducing the nitrogen application rate can reduce the carbon footprint and N₂O emissions of"Kuanzaoyou"cotton field,so as to achieve a higher yield at a smaller environmental cost in Xinjiang.