| Applying N at high rate year by year in maize production in China resulted in slightly grain yield increment after N fertilizer (Nf) application, decreasing nitrogen use efficiency and severe environment pollution, etc. Aming at those problems, field trials comprising of Nf rates and Nf apllication time were carried in high-yield farmland, close to Wuqiao experimental station of China Agricultural University, South-east Hebei province, Huan-huai-hai Plain. The nitrate dynamics and N mineralization in the soil of maize field, Nf effects on maize effiency absorption and utilization N, residual effects of maize Nf during wheat season, effects of NPK equilibrium on maize efficiency use of Nf, and soil-plant N analysis under maize-wheat-maize system were studied. Main results are as follows: In the zero Nf plots with plants in the 2nd maize season (2003), the nitrate content at 0~60cm profile successively decreases with soil deepening from sowing to female floret differentiation (FFD) and from ten days after dough (TDAD) to maturity while the nitrate content between soil layers isn't significantly different from FFD to TDAD. At 60~130cm profile, the nitrate content successively increases with soil deeping during maize season. The dynamics of nitrate content during maize season have two peaks (at three-leaf stage and TDAD) at 0~60cm profile and three peaks (at three-leaf, silking and dough stage) at 60~130cm profile. At silking stage, the nitrate content at 0~40cm and 40-130cm soil profile both increases with the increment of Nf rate successively. At maturity stage, the nitrate content at 0~40cm profile shows the same as at silking stage, and the difference of that at 40~130cm profile between 6kg N/mu and 0 kg N/mu is not significant; The dressing N at silking stage (DNAS) has the least nitrate content among treatments of dressing N (TDN) in the 0~40cm, 40~130cm and 0~130cm profile, respectively. In the 0~130cm profile, the total amount of soil N mineralized during maize season successively increases with both the increment of Nf rate and the postponing of Nf dressing time. In comparison with zero Nf, the root length per plant in the 0~130cm profile increases by 4.9% at 17 days after silking in 2002. The DNAS increases more root length and root surface area than zero Nf by 6.6% and 9.6%, respectively. Nf dressing time mainly affects root activity at 0~40cm soil profile. At maturity stage in 2003, the plant N amount successively increases with increment of Nf rate. Nf rate of 18kg N/mu has the highest grain N amount among Nf rates but has no significant difference from 6kg N/mu. The grain N amount of TDN is in the order of: DNAS>dressing N at 10-unfolded leaf stage (DNAT)>dressing N at dough stage (DNAD). The Nf rate of 6kg N/mu significantly increases more maize grain yield than zero Nf but when Nf rate is more than 6kg N/mu maize yield slightly increases with the increment of Nf rate. The DNAS has the highest gain yield among TDN. N physiological efficiency (NPE), N transferring efficiency (NTE), Nf efficiency (NfE) and grain N use efficiency (NUE) of 6kg N/mu are all signicantly higher than zero Nf, but when Nf rate is higer than 6kg N/mu those indexes decrease successively with the increment of Nf rate. Plant N amount isn't apparently affected by K fertilizer during maize season but successively increases with the increment of P rate. Maize grain N amount, grain yield, NfE and NTE allsuccessively increase with the increment of P rate and K rate. K rate of 8kg K^O/mu has the highest NPE among K. rates and increases more than zero K by 5.3%. NPE successively decreases with the increment of P rate, but that of 7kg P2O5/mu isn't apparent different from that of zero P. In comparison with the check (K8P7), K and P both increase NUE. In the 0~200cm profile, Nf applied to maize increases more soil nitrate content than zero Nf during wheat season. At maturity, the nitrate content both at 0~40cm and at 40~130cm soil profile shows no significant difference between DNAS and no dressing N. T...
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