Effects Of Different Nitrogen Application Rates On Nitrogen And Carbohydrate Concentrations In The Boll Leaf System Of Upland Cotton And Its Relationship With The Yield Of Cotton Boll

The carbon and nitrogen metabolism in cotton “boll-leaf” system has an important influence on cotton growth and final yield. The main purpose of this study is to explore the difference relationship of subtending leaf nitrogen content?carbohydrate content's dynamic variations in leaves subtending the cotton boll?seed embryo?fiber and boll traits in different nitrogen application with the growing process of cotton boll, to provide a theoretical basis for rational application of nitrogen to improve cotton yield. Cotton line with high fiber quality A001 was chosen in this study, which was bred by Jiangxi Agricultural University. A field experiment was conducted at the Agricultural experimental station, Jiangxi Agricultural University Nanchang in 2013 and 2014.we studied the effects by applying three different level of nitrogen fertilizer(480kg/hm2,high nitrogen;240kg/hm2,medium nitrogen;0kg/hm2,low nitrogen) in the year of 2013 and(520kg/hm2,high nitrogen;260kg/hm2,medium nitrogen;65kg/hm2,low nitrogen) in the year of 2014.The results were showed as below.(1)the boll weight, boll seed weight, fiber weight per boll, boll shell heavy were the highest Under the medium nitrogen level, no differ was observed between high nitrogen and medium nitrogen. There was a significant difference between low and medium nitrogen or high nitrogen, there is no significant difference among the three nitrogen rates for lint index.(2)Different nitrogen levels affected the carbon and nitrogen metabolism in the leaves subtending the cotton boll With the development of cotton boll. The order of their nitrogen content in the subtending leaves of cotton boll was high-nitrogen>mid-nitrogen>low-nitrogen, the C/N was low-nitrogen>mid-nitrogen>high-nitrogen, starch concentration and glucose concentration was low-nitrogen>mid-nitrogen>high-nitrogen, no differ was observed between high-nitrogen and med-nitrogen, the larger difference between low-nitrogen and mid-nitrogen or between low-nitrogen and high-nitrogen, indicating that low-nitrogen level inhibited the boll fruiting branch leaf sucrose to the output of the subtending boll, leading to the accumulation of starch and glucose in leaves, carbon and nitrogen ratio increased, cotton nutrition poor growth, boll development suffocate, cotton boll traits deterioration.(3)the glucose concentration in cotton embryos by mid- nitrogen treatment was highest in 17 DPA,but,in 31 DPA was lowest, indicating that it is the use of the glucose of cotton embryo used for the synthesis of protein or fat in the med-nitrogen level;in17-38 DPA,The order of sucrose concentration in cotton embryos was mid-nitrogen>low-nitrogen>high-nitrogen, after 38 DPA, The starch content of the three treatments was basically the same, indicating that compared with the low nitrogen and high nitrogen, in mid-nitrogen treatment the early stage was beneficial to the accumulation of starch, which was beneficial to the decomposition of starch in the middle and later stage; During the late stage of the embryo, the accumulation of sucrose, which is the most beneficial to the accumulation of sucrose, to the maturity of the embryo(52d),the highest sucrose content in the treatment of mid-nitrogen, followed by high nitrogen, low-nitrogen;(4)The glucose content was slightly higher than that of medium and high nitrogen in 17 DPA,and the other stages were lower than that of middle and high nitrogen, and, it were significantly lower than in nitrogen and high nitrogen in 24 DPA and 31 DPA, indicating that in low nitrogen level, the cotton fiber is in short supply of glucose, which affected the elongation of cotton fiber and the thickening of secondary wall, leading to the lowest single boll weight. The starch content in different nitrogen levels of cotton fiber with the boll development showed downward trend, which low-nitrogen treatment starch content of fiber in 31 DPA were significantly lower than in mid-nitrogen and high-nitrogen, then with mid-nitrogen treatment had no significant difference, but it was significantly lower than that of high-nitrogen treatment, indicating that low-nitrogen stress is not conducive to the starch accumulation of cotton fiber in early stage.