Effects of N Management on Yield and N Uptake of Rice in Central China

Efficient N fertilizer management is critical for the economic production of rice and the long-term protection of environmental quality. A field experiment was designed to study the effects of N fertilizer management practices on grain yield and N uptake of rice. The experiment was laid out in the randomized complete block design with four replications in Central China during 2008 and 2009. Five N treatments denoted as N-0, N-15A, N-150B, N-240A, and N-240B, respectively, were studied. N-0 represented no N application and served as a control, N-150A and N-150B indicated the total N application of 150 kg N ha(-1) but with two different application schedules (A and B) across the early stage of rice growth. Schedule A was applied as follows: 40% basal, 30% at 10 d after transplanting (DAT) and 30% at 36 DAT (nearly at the panicle initiation stage), while schedule B was as follows: 30% at basal, 20% at 10 DAT, and 50% at 36 DAT. Similarly, N-240A, and N-240B indicated the total N application of 240 kg N ha(-1) with schedules A and B as described above. To quantify N uptake from fertilizer and soil, a N-15 experiment was also conducted within the main experimental field, with micro-plots. Grain yields were significantly increased as N rates increased from 0 to 240 kg N ha(-1). At the same rate, splitting N application as schedule B significantly increased the grain yield, spikelets per panicle, percentage of ripened grain, and 1 000-grain weight, compared with the N application according to schedule A. Mean rice recovery of N fertilizer by N-15 tracing method ranged from 25.39% at N-240A to 34.89% at N-150B, however, N fertilizer residual rate in the soil ranged from 12.40% at N-240A to 16.61% at N-150B. About 31.5 and 28.5% of total uptake of N-15 derived from basal fertilizer was absorbed at panicle initiation and heading stages, respectively. However, 65.6-92.5% of total uptake of N-15 derived from topdressing fertilizer was absorbed at the heading stage. Based on yield and nitrogen recovery efficiency, splitting N application according to schedule B at the rate of 240 kg N ha(-1) will be more profitable among the tested five N treatments in Central China.