RESUMO
An experiment was carried out to study the effects of different nitrogen application rates (0, 60, 120, 150, 180 and 240 kg N · hm⻲) on the nitrogen uptake, utilization and distribution of short season cotton cultivar (CCRI-50) which was directly seeded after wheat harvest. Results showed that nitrogen application increased the nitrogen uptake of cotton at different growth stages, with the highest increment at the peak flowering-boll opening stage. Nitrogen application changed the percentages of nitrogen uptake among different growth stages. The percentages of nitrogen uptake decreased from seedling to peak flowering stage, but increased from peak flowering to boll maturing stage. In addition, nitrogen application reduced the decreasing speed of nitrogen concentration in middle and upper fruiting branches at later growth stages. Direct-seeded cotton had nitrogen and biomass accumulation in the lower and middle reproductive branches. With the nitrogen application of 150-180 kg · hm⻲, the lint yield, NARE (nitrogen apparent recovery efficiency) and the economic coefficient of biomass and nitrogen were relatively higher, and the eigenvalues of dynamic model of nitrogen content and nitrogen accumulation were relatively coordinate. Excessively high nitrogen application (over 180 kg N · hm⻲) decreased biomass and nitrogen amount of reproductive organ in lower and middle branches, narrow rise of yield, and lower nitrogen use efficiency. However, excessively low nitrogen application (lower than 150 kg N · hm⻲) also resulted in lower economic coefficient of biomass and nitrogen and yield. These results suggested the optimum nitrogen application rate 150-180 kg N · hm⻲ for direct-seeded cotton after wheat harvest in lower reaches of Yangtze River.
