Effects Of Continuous Fixed-Point And Quantitative Nitrogen Application On Cotton Growth And Nitrogen Use Efficiency

In order to explore the effect of continuous fixed-point and quantitative nitrogen application on cotton growth and nitrogen utilization,and provide an important theoretical basis for rational fertilization of continuous cropping cotton field in alar region of Southern Xinjiang.This experiment was a single factor randomized block experiment,in which the single factor was nitrogen fertilizer.In 2018,six nitrogen application treatments were set at 0,90,180,270,360 and 450kg/hm~2respectively,and the above experiments were repeated in situ in 2019 and2020 to study the effects of different nitrogen application on cotton growth and nitrogen fertilizer utilization in 2019 and 20201.With the increase of nitrogen application rate,cotton plant height increased significantly.With the increase of cumulative effect,the difference between 0kg/hm~2and 90kg/hm~2 treatments became more and more obvious.The effect of fixed-point and quantitative nitrogen application for two consecutive years on stem diameter was not great.With the accumulation of nitrogen application effect,the difference between 0 kg/hm~2and 90 kg/hm~2 treatments was significant in2020.According to the temporal and spatial distribution of cotton bolls,the proportion of dry matter in different parts of the plant and the fitting curve of plant dry matter logistic equation,it was concluded that the growth period of cotton bolls was advanced in two years of continuous no nitrogen application in 2019,and in 2020,the growth period of cotton bolls was advanced in 0 and 90 kg/hm~2 treatments,and there was no significant difference among 270,360 and 450kg/hm~2 treatments.2.The dilution curve of critical nitrogen concentration in alar region of Xinjiang is determined by two-year positioning test,a=3.91 and b=0.28.The results show that RMSE is2g/kg,and n-rmse is 11.11%,which indicates that the function is better fit performance,and the maximum biomass and nitrogen concentration on the upper ground conform to the power function relationship.3.Through the diagnosis of nitrogen utilization parameters and nitrogen nutrition,cotton growth is limited without nitrogen or 90 kg/hm~2,which is insufficient nitrogen supply,and the yield will always decrease with the increase of years.The nitrogen application amount reached270 kg/hm~2,which showed the phenomenon of excessive nitrogen application.4.There was no significant difference in the yield of seed cotton in 2019.In 2020,when the nitrogen application rate reached 270 kg/hm~2,the yield would decrease with the increase of nitrogen application rate.Therefore,the most reasonable amount of nitrogen was 270 kg/hm~2.5.Through three consecutive years of positioning experiments,it is concluded that the harvested seed cotton yield reached the highest when the NNI was 1.05 in 2019,which was4780kg/hm~2,and the harvested seed cotton yield reached the highest when the NNI was 0.98 in2020,which was 5310 kg/hm~2.Conclusion:With the increase of nitrogen accumulation effect years,no nitrogen application and 90 kg/hm~2nitrogen application had obvious effects on cotton growth and development,and the effects would be more and more serious.Compared with other treatments,270 kg/hm~2of nitrogen fertilizer had the best growth and yield.Therefore,the most reasonable amount of nitrogen application was 270 kg/hm~2.