[Economical nitrogen application rate of winter wheat under rice-wheat rotation in the Yangtze River basin of China]. / 长江流域稻麦轮作条件下冬小麦适宜施氮量.

To promote the rational application of nitrogen fertilizer for winter wheat under rice-wheat rotation in the Yangtze River Basin, we examined the effects of nitrogen application rates (0, 120, 210, 300 kg·hm-2, expressed as N0, N1, N2, and N3 respectively) on soil nitrate content, nitrogen balance of soil-plant system and yield. The results showed that soil nitrate content increased with increasing nitrogen application rates. Under different nitrogen application treatments, all the nitrate was significantly transfered to the 60 cm soil layer till jointing stage. After jointing stage, topdressing nitrogen significantly increased nitrate content in 0-40 cm soil layer under N1 and N2 treatments and that in the 0-60 cm soil layer under N3 treatment. Soil nitrate mainly accumulated in the 0-40 cm soil layer in the mature stage. Results from nitrogen balance analysis showed that nitrogen absorption, residue and loss varied across different growth stages of wheat, with the period from overwintering to jointing being the principal time of apparent nitrogen loss. The amount of plant nitrogen accumulation, inorganic nitrogen residue and soil nitrogen apparent loss all positively correlated with the nitrogen application rate. Based on the comprehensive analysis through Coase principle and marginal revenue of environmental economics, the optimum nitrogen application rate for production, ecology and economic benefits of winter wheat under rice-wheat rotation was 250 kg·hm-2, and the ratio of base fertilizer to jointing fertilizer was 5:5, while the corresponding grain yield was 6840 kg·hm-2.

[Characteristics of uptake, residual and loss of nitrogen fertilizer in winter wheat after rice stubble]. / 稻茬冬小麦氮肥吸收、残留和损失特性.

To promote the rational application of nitrogen fertilizer in winter wheat after rice stubble, the effects of nitrogen application rate (0, 150, 225, 300 kg·hm-2, expressed as N0, N150, N225, N300) on nitrogen recovery, residue, loss and grain yield were examined using field 15N tracer technology. The results showed that with the increases of application rate, nitrogen accumulation from different sources significantly increased while nitrogen recovery significantly decreased. The accumulation of basal nitrogen in plants reached the peak during overwintering stage to jointing stage, while the accumulation of topdressing nitrogen peaked between jointing to flowering stage. At maturity, nitrogen accumulation of the top fertilizer was higher than that of the base fertilizer. Plant nitrogen accumulation from soil under N150 was higher than that from nitrogen fertilizer, but with an opposite tendency under N225 and N300. With the increases of nitrogen application rate, the residual nitrogen in the 0-100 cm soil layer in the maturing stage significantly increased, while the residual nitrogen ratio in the 60-100 cm soil layer gradually increased. In the whole growth period of wheat, both nitrogen loss and loss ratio were positively correlated with nitrogen application rate. The nitrogen loss of base fertilizer reached the highest during sowing to overwintering stage, while the nitrogen loss of top fertilizer was at the peak from jointing to flowering period. Taking grain yield into consideration, N225 treatment was the proper application rate for winter wheat after rice stubble, with grain yield being 6735 kg·hm-2, and the nitrogen fertilizer recovery rate, soil residue rate and loss rate being 42.6%, 34.0% and 23.3%, respectively.