Effects Of Chemical Topping On Photosynthetic Production And Defolianting Of Cotton

【Objective】Exploring the chemical capping technology of cotton instead of manual topping,which is of great significance to promote the whole process mechanized management of cotton production in Xinjiang.In this paper,the chemical topping agent of mepiquat-chloride,which is widely used in mechanical cotton picking field in Xinjiang,is taken as the object.The effects of different topping methods and different concentrations of chemical topping agents on cotton topping results were studied.The change characteristics of chemical capped cotton population,photosynthetic capacity of single leaf,substance accumulation and distribution were defined.Combined with the application of defoliating ripening agent in late growth stage,the influence of chemical top sealing on the effect of cotton defoliation was discussed,and the research results provided reference for mechanized management of cotton.【Method】Under field conditions,the study planted different cultivars in a large area of cotton in northern Xinjiang,including Xinluzao 72,Xinluzao 61 and Xinluzao 67.DPC⁺was selected as chemical topping agent,and three concentration gradients of chemical topping agents were set,among which the low concentration was 90g·hm^-2+60ml·hm^-2（dactyl amine+additive）;Medium concentration:180g·hm^-2+120ml·hm^-2;High concentration:270g·hm^-2+180ml·hm^-2,with no topping and manual topping as control.It was determined under different treatments,that were the changes of agronomic characters,photosynthetic capacity,dry matter distribution,defoliation effect,yield and fiber quality.【Result】Compared with manual topping,plant height,internode number of main stem and leaf number of chemical topping cotton still increased,but it was effectively controlled compared with no topping cotton.Plant width,fruit branch length and internode length in the upper part of the plant were significantly lower than those in the treatment of no topping and manual topping.It means that the growth of the upper part of the plant was inhibited.Compared with the artificial topping treatment,the plant height,the number of fruit branches,the number of internodes of main stem and the plant width of high concentration treatment increased by 4.4～2.3 cm,0.8～1.93,1～1.4,and 1.4～4.8 cm.As the concentration of chemical topping agent increases,the length of upper fruit branch and upper internode decreased,and the control effect of new part increased.The leaf area index（LAI）and leaf chlorophyll content of chemically topping cotton were higher,and the high value lasted for a long time.Compared with no topping and manual topping cotton,the net photosynthetic capacity of chemical topping cotton was high in later growth stage.The net photosynthetic rate of leaves of medium and high concentrations was always higher than that of other treatments,and the photosynthetic rate of top leaves increased with the increase of concentration.And the canopy apparent photosynthetic rate of medium and high concentrations was also higher than that of the two control treatments.The matter distribution of chemically topping cotton changed.The material distribution of boll in the middle and upper part of the plant was not affected,and the dry matter distribution rate of boll in the lower part of the plant was higher under medium and high concentration treatments.After chemical topping,the new fruit branches of main stem did not have enough nutrients and did not produce low quality cotton bolls.The defoliation rate and bolls opening rate of chemically topping cotton were higher than that of manual topping cotton,and the ratio of impurity leaves was lower than that of manual topping cotton.The boll number per plant of chemical topping cotton was significantly higher than that of no topping and manual topping,but boll weight of upper fruit branches was lower than that of manual topping,so the yield increase was limited.【Conclusion】DPC+as chemical topping agent can effectively control the growth of top fruit branches of cotton under high concentration conditions,and the cotton plant type is more compact,and the topping effect is excellent.After chemical topping,the leaf area index（LAI）and leaf photosynthetic capacity of cotton were higher and the photosynthetic capacity of single leaf was stronger than before,but the LAI and photosynthetic value of cotton decreased slowly in the late growth stage,the canopy apparent photosynthetic of cotton population was high and the accumulation of dry matter was more accumulated,and the distribution of various organs was coordinated,and the cotton bolls accumulate more dry matter,which laid a foundation for the formation of high yield.Chemical topping of cotton is beneficial to the application of defoliating and ripening agent,but has no adverse effect on the quality of cotton fiber.