Effects of Nitrogen Application Rate on Dry Matter Accumulation and N,P,K Uptake and Distribution in Different Organs and Utilization of Hybrid Cotton under High-yield Cultivated Condition

Nitrogen application rates of 0,75,150,225,300 and 375 kg·hm-2 on dry matter accumulation and distribution as well as the N,P,K uptake and utilization of hybrid cotton were studied under high yield conditions.The results showed that the nitrogen utilization and dry matter content were significantly positive correlated with N,P,K accumulation.The nitrogen can improve the dry matter and N,P,K accumulation.But the effect that applying nitrogen was no longer significant when the nitrogen application rate increased to 300 kg·hm-2.The analysis of nitrogen content on dry matter accumulation of different organs indicated that nitrogen content was positive correlated with leaves and negative correlated with stems in the middle stage of cotton growth periods and positive correlated with stems in the latter growth stage.The nitrogen content was positively correlated with cotton bud and flower in the middle growth stage while negative in the latter growth stage.When the nitrogen application rate increased to 300 kg·hm2,nitrogen decreased the proportion of N,P,K and dry matter distributed to reproductive organs and increased the proportion of leaves and stems.The vegetative growth of the hybrid cotton was excessively vigorous.In this experiment,applying the nitrogen of 300 kg·hm-2 had the highest seed cotton yield which was 1.66% higher than the nitrogen of 225 kg·hm-2,but there was no significant difference.When nitrogen rate increased to 375 kg·hm-2,the seed cotton yield decreased by 2.23% and 3.92% compared with N 300 kg·hm-2 and 225 kg·hm-2,respectively.The nitrogen utilization decreased distinctly while the phosphorus and potassium utilization increased with the more nitrogen fertilizer added.