Effects Of Nitrogen Fertilizer Management On Cotton Growth,Yield And Soil Available Nitrogen

Two experiments were conducted in Baibi Town,Anyang City,Henan Province to solve the problems of unreasonable input of nitrogen fertilizer and unclear base-topdressing ratio of nitrogen fertilizer in cotton fields in the Yellow River Basin.In experiment 1,split plot design was adopted,and seven nitrogen application rates were set up in the main plot(0,60,120,180,240,300 and 360 kg·hm-2 for each plot),expressed by N0,N60,N120,N180,N240,N300 and N360 respectively,and two cotton varieties were set up in the sub-plot(Ji228 and Lumianyan 28).In experiment 2,six nitrogen-based topdressing ratios were set up by random block design(no nitrogen application,complete base application of nitrogen fertilizer).Base application,first flowering stage and top-dressing stage were 6:4:0,4:6:0,4:4:2 and 4:2:4,respectively.180 kg·hm-2 of pure nitrogen was applied in each plot.The effects of nitrogen fertilizer management on cotton growth,yield and soil available nitrogen were explored with the expressions of N0,N1,N2,N3,N4 and N5,respectively,in order to provide theoretical basis for rational nitrogen management model in the Yellow River Basin.The main results are as follows:1.Increasing N application within the range of 0-300 kg·hm-2 increased cotton plant height,SPAD value of chlorophyll in functional leaves,nitrate concentration in functional petioles and dry matter accumulation per plant.The order of dry matter accumulation per plant was N360>N300>N240>N180>N120>N60>NO between 61 d and 151 d after seedling emergence.Compared with N0,the seed cotton yield of N360 increased by 15.37%and 23.02%in 2017,14.18%and 13.31%in 2018,the boll number per plant increased by 2.69 and 2.25 respectively,and the boll weight per plant increased by 0.44 g and 0.38 g respectively.The relationship between nitrogen application rate and seed cotton yield,nitrogen accumulation and seed cotton yield showed an open downward quadratic function.The agronomic nitrogen use efficiency,physiological nitrogen use efficiency,internal nitrogen use efficiency and partial Nitrogen productivity of cotton decreased with the increase of nitrogen application rate.The agronomic nitrogen use efficiency of two varieties of N60 treatment increased by 179.5%and 193.9%in 2017,136.5%and 158.7%in 2018,respectively.N0,N60 and N120 treatments had lower ammonium and nitrate contents in 0-60 cm soil,which could not provide adequate nitrogen nutrition for cotton.N360 treatment had the highest nitrate nitrogen residue in 40-60 cm soil during harvest period,which increased by 30.1%in 2017 and 30.3%in 2018 compared with N180.2.Compared with no N application and complete N application,4:6 base-topdressing treatment significantly increased cotton plant height,SPAD value of functional leaves,nitrate concentration of functional petioles and dry matter accumulation.On 109 days after seedling emergence,dry matter accumulation per plant increased by 44.8%,boll weight increased by 2.5%-5.9%,seed cotton yield increased by 4.3%-11.0%,cotton yield increased by 4.3%-11.0%compared with other treatments.The agronomic utilization rate of flower nitrogen,nitrogen recovery rate and partial productivity of nitrogen fertilizer were significantly higher than that of complete base application of nitrogen fertilizer,and the residual nitrate nitrogen in soil with 40-60 cm harvest period was not significantly increased compared with other treatments.3.The highest seed cotton yield of Ji 228 and Lumianyan 28 cultivars in the Yellow River Basin was obtained when nitrogen application was 373.31 kg·hm-2 and 311.86 kg·hm-2.The maximum economic benefit was obtained when nitrogen application was 260.03 kg·hm-2 and 250.42 kg·hm-2.When the nitrogen application rate was 180 kg·hm-2,the highest yield of seed cotton was obtained by the treatment of 4:6 ratio of base-topdressing of nitrogen fertilizer.The cotton grew well,the utilization rate of nitrogen fertilizer was high,and the residual nitrate nitrogen in soil was reduced,which was suitable for the local nitrogen management.