| Taihu Lake region is one of the most high yield agriculture areas of China, the nitrogen application rate in the farm land is always higher. In order to find out the effects of nitrogen application rate (NAR) on wheat and the inorganic nitrogen in soil profile (INISP) of southern China wheat region, the optimal nitrogen application rate and the located nitrogen fertilizer experiment in the rotation of rice and wheat were studied in the experiment station of Farming and Forestry Bureau of Wujiang County, Suzhou city, Jiangsu province, China. The treatments of different nitrogen application rate were 0, 75, 150, 225, 300 and 375 kg·hm-2, and were respectively indicat by N75, N150, N225, N300 and N375. The nitrogen fertilizer was divided in two times application with the proportion of 60% as basal fertilizer and 40% as broadcasting in jointing stage. On the NAR located experiments in rice wheat rotation of three seasons in two years in Taihu Lake region, the relationships between NAR, nitrogen accumulation in wheat, the changes of INISP and the nitrogen balance and the cumulate effect of INISP in different growth stages of wheat were measured after the wheat season. The result showed that: with the NAR increasing, wheat yield, dry matter accumulation and nitrogen accumulation all increased, but NARE, NPUE and NAUE all decrease, the NAR from 225 kg·hm-2 to 300 kg·hm-2 would get high yield, and were the optimum NAR when nitrogen was relatively higher effects; the INISP mostly concentrated in 0~30 cm soil and increased with the NAR increasing at different growth stages of wheat, the inorganic nitrogen in 30~100 cm soil obviously responded to the NAR from 300 kg·hm-2 to 375 kg·hm-2, it had obviously eluviations after jointing stage; the INISP of NAR from 300 kg·hm-2 to 375 kg·hm-2 was always higher, compared with the INISP in maturity stage and in sowing stage, it increased only in the treatment of NAR 375 kg·hm-2, but all decreased when the NAR was below 300 kg·hm-2; the nitrogen apparent losses increased with the NAR increasing in wheat and soil system, the nitrogen apparent losses and the proportion of nitrogen apparent loss to nitrogen application rate in treatment with NAR 75 kg·hm-2 and 375 kg·hm-2 were respectively 26.20 kg·hm-2, 34.93 % and 168.64 kg·hm-2, 44.97 %. The nitrogen application rate of 225 kg·hm-2 was the critical NAR of wheat which was ecologically safe in Taihu Lake region. |
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