中文摘要：

为探讨太湖地区稻麦轮作农田适宜施氮量及氮素对干物质转运与氮肥利用的影响,于2007—2009年间在中国科学院常熟农业生态实验站建立田间定位试验。设置4个氮肥处理水平,分别用N0、N1、N2和N3表示。水稻各处理的施氮量分别为0、125、225和325kghm^-2;小麦相应处理施氮量分别为0、94、169和244kghm^-2（为稻季相应处理施氮量的75%）。结果表明,水稻施氮量超过225kghm^-2,小麦施氮量超过169kghm^-2后,产量增加不显著。水稻、小麦开花期干物质积累量均随施氮量的增加而增加,但花前营养器官干物质转运对籽粒贡献率均随氮肥用量增加而降低;氮肥农学效率与氮肥生理效率均随氮肥用量增加而降低,且N2与N3处理之间差异不显著;边际产量均随施氮量增加而下降,N3处理边际效益水稻平均低于3.1kgkg^-1,小麦平均低于2.4kgkg^-1。综上所述,无论水稻还是小麦,N2处理既能保证较高物质转运率,又能保证较高的氮肥利用效率与经济效益。

英文摘要：

Excessive application of nitrogen-fertilizers often results in low nitrogen use efficiency and high nitrogen losses in Tai Lake region. Many studies on wheat （Triticum aestivum L.） or rice （Oryza sativa L.） pliysio-ecology have been carried out aiming at high yield with reasonable amount of nitrogen fertilizer. However, most experiments have been focused on single crop. Also, assimilate accumulations before flowering play an important role on grain yield. In order to disclose the mechanism of dry matter translocation, optimum amount of nitrogen application and utilization of nitrogen under rice-wheat rotations, a field experiment was conducted under different nitrogen application rates from 2007 to 2009 at the Changshu Agroecological Experiment Station, Chinese Academy of Sciences. The treatments included four nitrogen fertilizer rates for rice and wheat, respectively： N1 （125 and 94 kg N ha^-1）, N2 （225 and 169 kg N ha^-1）, N3 （325 and 244 kg N ha^-1）, and NO control （no nitrogen）. The results showed that no significant increase in crop production was found when nitrogen application rate of rice and wheat was in excess of 225 kg ha^-1 and 169 kg ha^-1 respectively. The dry matter accumulations at anthesis of rice and wheat increased with the nitrogen rate increment, while the contribution of dry matter translocation from vegetative organs to grains before flowering decreased with increasing the nitrogen application rates. The nitrogen agronomic efficiencies and physiological efficiencies in rice and wheat were reduced with increasing the nitrogen rates, and these was no significant difference between N2 and N3 treatments. The marginal productions were declined with the increase of nitrogen applications, with lower than 5.5 kg kg^-1 in N3 treatment for both rice and wheat. Therefore, whether for rice or for wheat, the N2 treatment could maintain higher translocation rate of dry matter, higher nitrogen use efficiency and higher economic benefit.