Abstract: With Bt-transgenic hybrid cotton variety CCRI29 as material, the study on effects by applying different level of nitrogen fertilizer (225.0kg·hm-2, high; 112.5kg·hm-2, middle; 0kg·hm-2, low) in the field in 2002-2003. The plant density is about 53336/hm2. The main results are as follows: (1) The results showed that changing nitrogen application amount had some effects on cotton growth and development. Compared with mid-nitrogen and low-nitrogen, high-nitrogen promoted chlorophyll accumulating in leaf growth anaphase on fruit branch, which extended leaf function period. The dissoluble protein content of leaf was the lowest under the treatment of low-nitrogen, and the chlorophyll content decreased rapidly in leaf growth anaphase, which accelerated the leaf's senescence. (2) Different nitrogen level affected the carbohydrate metabolism in various organs of cotton plant evidently. The carbohydrate synthesis was inhibited under high-nitrogen level, but low-nitrogen level promoted carbohydrate accumulation in leaf on reproductive branch. Different nitrogen levels had no significant effect on carbohydrate concentration in seed cotton. (3) Nitrogen can enhanced activity of SOD and POD to some extent. The order of their activity of leaf born around June 1 was mid-nitrogen>high-nitrogen>low-nitrogen, but the order of leaf activity born around June 22 was high-nitrogen>mid-nitrogen>low-nitrogen.

Key words: Nitrogen, Cotton, Bolls-leaves System, Physiological Characteristics