| With the insect resistance hybrid cultivar Nankang NO.9 as material, The field experiment was conducted to study the effect of transplanting density, ratio of nitrogen fertilizer application and chemical control times of DPC on yield, fiber quality and development of soilless seedling transplanting cotton at the Experiment Station of Yangzhou University during 2007 to 2008.The main results were as follows:1.The seed cotton yield was highest (4284kg·hm-2) at 24,000 to 30,000 plants·hm-2 under different planting density from 18,000 to 36000 plants·hm-2 for the soilless seedling transplanting cotton. and the fiber length was longer , the fiber micronair was in optimal under the planting density from 18,000 to 36000 plants·hm-2.Under planting density of 24,000 plants·hm-2 and 30,000 plants·hm-2 , the number of boll per plant and the boll weight were higher, squaring appearance and boll setting were also more rapid,dry matter weight for vegetative and reproductive organs was higher too, which was benefit for the coordination of source-sink, the maximum LAI were 4.08 and 4.18 respectively, which was in the scope of high yield cotton whose leaf area index was at 4.0 to 4.5, the amount of nitrogen,phosphorus and potassium absorption were higher, and the peak of the nutrient absorption was synchronous with the full bolling period, which was beneficial to boll set and the increase of the yield.2.The seed cotton yield was highest(4652.2kg·hm-2) at 10%, 65% and 25% of the ratio of nitrogen fertilizer application for transplanting, peak flowering and peak boll period respectively. The number of boll for the individual and the population were the highest under the nitrogen application treatment.Under the ratio of the nitrogen application for getting highest seed cotton yield, the maximum LAI was optimal and it maintained longer time, the chlorophyll content was higher, the absorption amount of the NPK was highest and the peak of NPK absorption was synchronous with the full boll period. The absorption of the P and K was higher before flowering period, which was benefit to reuse for the boll development. There were close positive correlation between the yield and the absorption of NPK, the absorption of nitrogen and potassium were higher with the yield increase.3.The seed cotton yield was highest (4854.6kg·hm-2) with DPC application at the early flowering, peak flowering and seven days after topping for the soilless seedling transplanting cotton , the yield was 7.16% more than that of the conventional nutritious bowl transplanting cotton, the difference was significant.The systematic chemical control of DPC could also increase the fiber length to 32.2mm, improve fiber micronaire at 4.18, the results suggest that the systematic chemical control of DPC for the soilless seedling transplanting cotton, which was 30g·hm-2 at the early flower, 45g·hm-2 at the peak flowering, 60g·hm-2 at seven days after the topping, was beneficial to improve fiber quality .The systematic chemical control of DPC from early flower could significantly reduce the plant height, increased the number of bolls, speeded up square appearance and boll setting,the maximum LAI was 4.38, which was in the scope of 4.0 to 4.5 for the goal of the high yield of the cotton.The systematic chemical control of DPC also increased the boll and it's opposite leaf physiological activities of the soilless seedling transplanting cotton. The chlorophyll and soluble sugar were higher in the opposite leaves,the boll volume and boll weight increased, the soluble sugar content and the boll wall weight was decrease with the boll development.
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