| A 3-year-long field experiment was carried out to investigate the effects of nitrogen rate on nitrogen uptake and utilization of winter wheat and residual nitrate in soil under straw mulch.The experiment, including mulch (no mulch and straw mulch 4 500 kg/hm2) and N rate (0, 75, 150, 225 and 300 kg N/hm2) , had 10 treatments with 3 replicates.The results showed that there was no significant difference of N uptake by winter wheat between straw mulch and no mulch treatments.However, in the drier year, straw mulch could improve N use efficiency.No matter with straw mulch or no mulch, N uptake by winter wheat increased during 3 years.For both straw mulch and no mulch treatments, accumulated nitrate in soil didn't increase significantly when N rate increased from 0 to 150 kg/hm2, while accumulated nitrate peak was found throughout the soil profile when more than 150 kg/hm2 nitrogen fertilizer was applied.The accumulated nitrate peak of straw mulch treatment appeared at the soil depth 40cm deeper than that of no mulch. |