A field micro-plot (labeled 15N) fertilizer experiment was conducted to investigate the use efficiency of fertilizer N and its residual features under different rice-based cropping systems (Chinese milk vetch-rice rotation, fallow-rice rotation and wheat-rice rotation) in the Taihu Lake Region. Results showed that 20.9%-49.6%of N uptake of rice was derived from the applied fertilizer N. Fallow-rice rotation system largely depended on inorganic N fertilizer to form yield. N fertilizer use efficiency of rice was 25.0%-41.5%of the labeled fertilizer N at harvest. Residual fertilizer N rate in soils was 13.4%-24.6%, over 90%of which was in the 0-20 cm soil layer. The amount of fertilizer N residue in the soil profile decreased rapidly with increasing soil depth. Only 0.2%-0.7%of the fertilizer N was in the soil layer of 30-40 cm. Fertilizer N use efficiency and soil residual N rate were largest at N application rate of 240 kg·hm-2 under Chinese milk vetch-rice rotation and fallow-rice rotation systems. This respectively exceeded by 55.6%and 66.0%over N fertilizer use efficiency under wheat-rice rotation. Fertilizer N use efficiency, soil residual rate as well as total N recovery rate were lowest while N loss rate highest under wheat-rice rotation system at N application rate of 240 kg·hm-2. As for the Chinese milk vetch-rice rotation system, the loss rate of N fertilizer was lowest, which was less than those of fallow-rice rotation and wheat-rice rotation systems by 13.9%and 39.2%, respectively. Under different rotation systems, rice yield increased with increasing urea application rate. Under straw-return application of Chinese milk vetch of Chinese milk vetch-rice rotation system, rice yield was significantly higher compared to those of wheat-rice rotation and fallow-rice rotation at N application of 240 kg·hm-2. Although rice yield under wheat-rice rotation was slightly higher than that under fallow-rice rotation, it was not significantly different. The study suggested that N application at 240 kg·hm-2 in addition to straw-return application of Chinese milk vetch of Chinese milk vetch-rice rotation not only ensured N fertilizer use efficiency and high rice grain yield, but also reduced the loss of N fertilizer and environmental risks. Considering these factors, Chinese milk vetch-rice rotation system was recommended as a suitable cropping system worthy of promotion in the Taihu Lake Region.%采用田间微区15N 示踪,研究了太湖地区稻田不同轮作模式(紫云英-水稻轮作、休闲-水稻轮作、小麦-水稻轮作)和施氮水平(0、120 kg·hm-2、240 kg·hm-2、300 kg·hm-2)下水稻对氮肥的吸收利用效率及土壤氮素残留特征。结果表明,水稻吸收的氮素来自肥料的比例为20.9%~49.6%,休闲-水稻轮作模式下水稻产量的获得更加依赖无机氮肥的大量投入。当季水稻对肥料氮的利用率为25.0%~41.5%,肥料氮的土壤残留率为13.4%~24.6%,其中90%以上的土壤残留肥料氮集中在0~20 cm土层,在土壤剖面中的残留率随土层深度增加而迅速降低,30~40 cm土层的肥料残留量仅占氮肥施用量的0.2%~0.7%。紫云英-水稻轮作和休闲-水稻轮作模式下氮肥利用率和土壤残留率均在施氮240 kg·hm-2时达到最大值,其氮肥利用率显著高于小麦-水稻轮作55.6%和66.0%。稻季施氮240 kg·hm-2时,小麦-水稻轮作模式下的氮肥利用率、土壤残留率以及总回收率显著最低,损失率显著最大；紫云英-水稻轮作模式下的氮肥损失率最小,分别小于休闲-水稻轮作和小麦-水稻轮作13.9%、39.2%。不同轮作模式下,水稻籽粒产量随施氮量的增加而增加,稻季施氮240 kg·hm-2时,紫云英-水稻轮作下水稻籽粒产量显著高于休闲-水稻轮作和小麦-水稻轮作,小麦-水稻轮作籽粒产量虽略高于休闲-水稻轮作,但没有达到显著水平。本研究认为,选择紫云英还田配施氮肥240 kg·hm-2,既可以保证水稻氮肥利用率而获得高产,又能减少氮肥损失而带来的环境风险,是一种值得在当地大力推广的耕作制度。
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