Nitrate-nitrogen （NO3-N） dynamics and nitrogen （N） budgets in rice （0ryza sativa L.）-wheat （Triticum aestivum L.） rotations in the Taihu Lake region of China were studied to compare the effects of N fertilizer management over a two-year period. The experiment included four N 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 （0 kg N ha-1）. The results showed that an overlying water layer during the rice growing seasons contributed to moderate concentrations of NO3-N in sampled waters and the concentrations of NO3-N only showed a rising trend during the field drying stage. The NO3-N concentrations in leachates during the wheat seasons were much higher than those during the rice seasons, particularly in the wheat seedling stage. In the wheat seedling stage, the NO3-N concentrations of leachates were significantly higher in N treatments than in NO treatment and increased with increasing N rates. As the NO3-N content （below 2 mg N L-1） at a depth of 80 cm during the rice-wheat rotations did not respond to the applied N rates, the high levels of NO3-N in the groundwater of paddy fields might not be directly related to NO3-N leaching. Crop growth trends were closely related to variations of NO3-N in leachates. A reduction in N application rate, especially in the earlier stages of crop growth, and synchronization of the peak of N uptake by the crop with N fertilizer application are key measures to reduce N loss. Above-ground biomass for rice and wheat increased significantly with increasing N rate, but there was no significant difference between N2 and N3. Increasing N rates to the levels greater than N2 not only decreased N use efficiency, but Mso significantly increased N loss. After two cycles of rice-wheat rotations, the apparent N losses of N1, N2 and N3 amounted to 234, 366 and 579 kg N ha-1, respectively. With an increase of N rate from NO to N3, the percentage of N uptake in total N inputs decreas
