Nitrogen Rates Affect The Efficiency Of Harvest Aids,Yield And Quality Of Derect-Seeded Cotton

Timing of harvest is critical for mechanical picking of cotton and next crop sowing in cotton production,especially in those regions with double cropping system like Yangtze River Valley.Harvest aids is an important safeguard for cotton harvest mechanization,which can effectively promote the abscission of leaf and cracking of bolls of cotton.However the effects of harvest aids are affected by many factors,hardly meeting the demand of production.Nitrogen rates and harvest aid norms are two important factors.In order to choose the optimal nitrogen rates and harvest aid norms and speed up the process of cotton harvest mechanization,we studied the interactive effects of nitrogen rates and harvest aid norms on defoliation,boll opening,yield and quality of cotton.Field experiments were conducted in 2015 and 2016 at DaFeng Experimental Station in Dafeng(330 24' N,1200 34' E),Jiangsu Province,China.Four nitrogen rates and three harvest aid norms were used in the experiment.A split-plot design with three replications was used for this study.The main plot treatments were nitrogen with rates of 0?75?150 and 225 kg ha-1,while the harvest aids(thidiazuron+ethepon)norms of 0+0,450+1500 and 900+3000 g(a.i.)ha-1 were assigned to the subplot treatment,respectively.We studied the interactive effects of different application rates of harvest aids and nitrogen fertilizers on defoliation,boll opening and yield components of cotton.The main results were as follows:1 Effects of nitrogen rates and harvest aid norms on defoliation and boll opening of cottonSignificant interactions were observed between nitrogen rates and harvest aid norms on defoliation and boll opening of cotton.Compared to the untreated control,the percentage of leaf abscission and boll cracking were significantly increased by the application of harvest aids.However the efficiency of harvest aids was not consistent across years.In 2016,the percentage of leaf abscission and boll cracking were both greater than 90%at 20 days after application of harvest aids,meeting the demand of cotton harvest mechanization.While in 2015,the percentage of leaf abscission and boll cracking were about 70%,significantly lower than which in 2016.Under lower nitrogen rates,the percentage of leaf abscission and boll cracking had a significant increase at 5 to 10 days after application of harvest aids,while with the increase of nitrogen rates,the date of rapid increase was delayed to 10 to 15 days.Excessive nitrogen rates may delay the growth of cotton,affecting the efficiency of harvest aids.And the elevated norms of harvest aids showed better effects on over-growth cotton plant than normal one.2 Effects of nitrogen rates and harvest aid norms on cottonseed yield and qualityThere were significant interactions between nitrogen rates and harvest aid norms for defoliation and boll opening of cotton.The boll number,seed cotton weight per boll showed a significant increase as nitrogen rate increased.While compared to the 150 kg N ha-1,the cottonseed yield did not increase significantly under the application of 225 kg N ha-1.Application of harvest aids showed an inconsistent effects on seed cotton weight per boll in different branches of cotton plant.Harvest aids showed no effects on seed cotton weight per boll and fiber quality,while significantly decreased the seed cotton weight per boll in middle and upper branches of cotton plant as nitrogen rate increased,especially with the elevated norms of harvest aids.Although seed cotton weight per boll was significantly decreased by the harvest aids,cottonseed yield was increased compared to the untreated control.