| To coordinate the soil inorganic nitrogen release and the maize nitrogen requirement and to heighten nitrogen fertilizer use efficiency, field trial with the maize hybrid "Zhengdan 958" (with population of 9 plants/hm2) and four treatments (i.e., zero N, sowing N+10 leaf N, sowing N+silking N, and sowing N+milking N, with the rate of 90 kg/hm2 at each application time) was carried out at Wuqiao experimental station of CAU in 2002. The results are follows: (1) The nitrate concentration (NC) at 0~200 cm soil profile is ten fold of the ammonium concentration (AC) during maize season. They show differences both in aspects of dynamics and vertical distribution and in effects of nitrogen fertilizer (Nf). (2) The dynamics of NC is more violent and more sensitive to Nf than that of AC. The NC at profile 020 cm descends before big horn stage and hereafter ascends, but the NC below 20 cm profile descends before silking and ascends henceforth; The AC at 0200 cm profile descends before silking while after this the AC at 020 cm ascends during silking-milking and slightly descends after milking, but the AC dynamics below 20 cm shows irregular. (3) The vertical distribution of NC at 0~200 cm profile is apparent during maize season and Nf application can significantly increase the NC above 20 cm and below 80 cm. Postponing of Nf application can dramatically increase NC in 80~200 cm profile during milking-maturity. The vertical distribution of AC at 0~200 cm is rather even before silking and becomes apparent after this. Nf application can only increase AC at 0~20 cm profile. (4) The net soil nitrogen mineralization takes place before silking and most of the net mineralized N appears during sowing-big horn. The net soil nitrogen fixation occurs after silking, and half of the net fixed amount appears before milking. The fluctuation of soil inorganic nitrogen in Nf application treatments is milder than that in zero N treatment, and is affected remarkably by application time. |