| In recent years,Cotton chemical topping technology research on time,frequency and dose are becoming more perfect.Chemical topping application area increased year by year,the research field also extended to the growth mechanism and so on.However,nitrogen rate on chemical topping cotton growth,yield and other aspects of the study is still less.To make clear the effect of nitrogen application on chemical topping cotton,growth and development,dry matter accumulation,photosynthetic characteristics and yield has important theoretical and practical significance.In this study,Xinluzao No 57 as the test material,we were studied under chemical topping conditions(The same amount of nitrogen applied to the manual topping as a control)on the effect of the different nitrogen rates(0、100、200、300、400 kg/hm~2)on cotton growth and development,yield formation,dry matter accumulation,nutrient accumulation and photosynthetic characteristics.The main results are as follows:With the increase of nitrogen application rate,the chemical topped cotton showed increased plant height,increased boll number,widened line width,extended growth period,increased proportion of autumn peach,reduced rate of blossom before frost and reduced effect of plant height,increased the number of bolls and the yield of seed cotton.The increase in the amount of nitrogen does not change the chemical topping for the shaping of plant type,Compared with the same amount of nitrogen applied to the manual topping,the plant height is still high,the fruit branches are many and the line width are narrow..when the nitrogen application rate was 300 kg/hm~2 Two kinds of topping method before frost Lint cotton lint yield were all the best,the chemical topping cotton was 2471.14 kg/hm~2,and the manual topping cotton was2513.42 kg/hm~2.After chemical topping cotton nitrogen rate reached 300 kg/hm~2,dry matter accumulation and nitrogen accumulation are still slightly increased.However,after manual topping cotton nitrogen rate reached 300kg/hm~2,dry matter accumulation and nitrogen accumulation decreased.The rapid accumulation of manual topping cotton is 56~100 d after emergence,chemical topping cotton is 59~109 d.At the same time,the dry matter accumulation and nitrogen accumulation of chemical topped cotton under the same nitrogen application rate were higher than that of manual topped cotton(After the top 30~60 d).Therefore,we can use the chemical topping cotton late organ dry matter accumulation and nitrogen accumulation of more features for the cotton genital organs to provide nutrients,increase yield,while avoiding cotton premature senescence.When the nitrogen content was 300 kg/hm~2,the leaf area index and SPAD value of chemical topped cotton were higher than that of manual topped cotton,and the high value duration longer than the manual topped cotton,Nitrogen fertilizer was continuously applied under this condition,manual topping cotton leaf area index and SPAD value growth was less than chemical topping cotton.At the same time,the two kinds of topping cotton can improve the photosynthetic function of cotton leaves when the nitrogen application rate is 300 kg/hm~2,making the activity of PSII,the maximum efficiency of PSII photochemistry,the proportion of the open portion of the PSII response center,apparent photosynthetic electron transport rate and PSII total photochemical quantum yield improved.And reduced non-radiative energy dissipation,so that the light absorbed by the leaves was more fully used for photosynthesis.Among them,chemical topped cotton in the late growth period better.Therefore,under the condition of chemical capping,when the amount of nitrogen applied is 300kg/hm~2.the dry matter accumulation and nutrient accumulation of cotton can be increased,the photosynthetic area is increased,the photosynthetic time is prolonged,ensuring a higher population photosynthetic capacity and long photosynthetic function duration,and the optimal yield. |
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