Optimization Of Chemical Capping Time Based On NAWF And Its Effect On Chemical Defoliation And Ripening Of Cotton

【Objective】This study aims to investigate the effect of different spraying times of the chemical topping agent"Zifengding"on the topping effect of cotton,and to clarify the changes in photosynthetic material accumulation and distribution,nitrogen distribution,and yield quality of cotton under different chemical topping times.In addition,the study looks into the optimization of chemical topping time based on nodes above white flower（NAWF）,along with its influence on the effect of chemical defoliation ripening of cotton,particularly in northern Xinjiang.The research findings can serve as a scientific basis for the promotion and application of chemical topping and chemical defoliation ripening technology for cotton.【Method】Cotton variety Xinluzao 78 was used as the material while"Zifengding"was selected as the chemical topping agent.Five chemical topping times were set based on the manual capping time（July 5）in northern Xinjiang,namely,June 25（NAWF=7.4）,June 30（NAWF=6.5）,July 5（NAWF=5.2）,July 11（NAWF=4.1）,July 16（NAWF=3.2）,with manual capping as the control.The study adopted a split-zone design,with the main zone subjected to topping treatment and the secondary zone to defoliation and ripening treatment（D₁）and water spray treatment（D₀）.Xinsaili was selected as the ripening agent.On September 4th,defoliation and water spraying were carried out in the community.The research analyzed the changes in agronomic characters,photosynthetic capacity,dry matter and nitrogen allocation,defoliation effect,yield,and fiber quality of cotton under different treatments.【Result】Compared to manual topping,the plant height,plant width and the number of fruit branches showed an increasing trend with the delay of chemical topping time.Additionally,leaf area index and net photosynthetic rate increased with delayed chemical topping time,with higher values observed in cotton under chemical topping treatment later than the manual topping treatment.Moreover,the results of dry matter accumulation and distribution and nitrogen distribution of chemical topping cotton showed an S-shaped growth curve,with the maximum accumulation obtained at NAWF4.1.The distribution of dry matter and nitrogen in plant organs was not affected.There was a close relationship between plant dry matter and net photosynthetic rate and leaf area index,and the correlation coefficients were up to 0.934 and 0.962,respectively.The effect of chemical topping time on the ripening effect of cotton defoliation showed that the flocculation rate and defoliation rate of cotton treated with earlier topping were higher than those treated with later topping（except NAWF3.2）.The boll weight of cotton under different chemical topping time was not affected,but the seed cotton yield was significantly different from that of manual topping.The treatment later than manual topping（NAWF4.1 and NAWF3.2）could increase the number of boll forming per plant and increase the seed cotton yield.Chemical topping time had no significant effect on cotton fiber quality.【Conclusion】The study concluded that delaying the spraying time of chemical capping agent can increase the number of fruiting branches,shape a more compact plant,and increase the number of boll formation per plant.The finding recommends the use of NAWF4.1 for chemical topping in northern Xinjiang to achieve higher yields while affecting cotton fabric fraction and fiber quality minimally.