Abstract: In this paper, field experiment of different nitrogen application levels for cotton was conducted both in Nanjing of Jiangsu Province and in Anyang of Henan Province. The quantitative dynamic models of critical nitrogen uptake rate and demand of cotton after flowering were established, based on the models of crop critical nitrogen concentration dilution curve and dry matter accumulation curve. The results showed that in Nanjing and Anyang, the maximum critical nitrogen uptake rate of cotton was 5.3 kg·hm^-2·d^-1 and 4.4 kg·hm^-2·d^-1, respectively, and appeared at 42 days after flowering. The 23～59 days and 23～61 days after flowering were the periods of rapid nitrogen accumulation in cotton plant, and the critical nitrogen demand per day was higher in Anyang than in Nanjing. By comparing the nitrogen uptake rate and accumulation amount with their critical values, the appropriate N application rate for cotton was slightly lower than 360 kg·hm^-2 in Anyang, and 240 kg·hm^-2 in Nanjing. 26% and 27% of total fertilizer nitrogen should be applied as basal, and the supplemental nitrogen should be applied at 22 days after flowering. Because the model in this paper was established on the basis of critical nitrogen concentration model and linked to the cotton aerial biomass rather than time, it had a sound eco-physiological basis, and was consequently superior to other models. It also offered a tool to determinate the nitrogen application rate for cotton in different ecological regions.

Key words: Winter wheat, Photosynthesis, Transpiration, Water use efficiency