Effects of nitrogen fertilization on accumulation and distribution of dry weight and nitrogen of cotton bolls

To investigate the responses of the accumulation and distribution of dry weight and nitrogen of cotton bolls to nitrogen applications and their relationships with fiber and seed quality characteristics,field experiments were carried out in Xuzhou(117°11′E,34°15′N) and Anyang,Henan(114°13′E,36°04′N) using two cotton cultivars,Kemian 1 and NuCOTN,with three nitrogen levels(N 0,240 and 480 kg/ha).The results show that the dry weights,nitrogen accumulation characteristics of cotton bolls(shell,fiber and seed) and quality of cotton bolls are affected under the N fertilization.In a single boll,at the N 240 kg/ha,its dry weight is the highest except cotton shell,its nitrogen content is in the middle,and its nitrogen accumulation amount is the highest.Thus the boll weight is the highest and the cotton boll quality(fiber and cottonseed quality) is the best.At the N 0 kg/ha,the start time of rapid dry weight is earlier,the rates of dry weight and nitrogen accumulation are slower,and the dry weight and nitrogen accumulation amounts are lower,which result in the lowest boll weight and the poorest cotton boll quality.At the N 480 kg/ha,the nitrogen content and accumulation amount are increased in cotton bolls.In mature one,dry weight distributive indices are decreased in cotton fiber,while nitrogen distributive indices are increased in cotton seeds.The seed protein content is increased,while boll weight,fiber strength and seed oil content are decreased.These results indicate that the low nitrogen rate affects the transportation of photosynthesis production and nitrogen to bolls,the high nitrogen rate affects the distribution of cotton dry weight and nitrogen in cotton bolls,and both of the rates decrease the boll weight and qualities of fiber and cotton seeds.