| In order to study the effect of nitrogen application on the dynamic change of soil nitrogen in the wheat-maize rotation system in the semi-humid region of the Loess Plateau,the dynamic changes of soil mineral nitrogen in 0-200 cm soil layer during different growth stages of wheat and maize were compared and analyzed. The result show that after two-year experiment,compared with the soil total nitrogen amount before the experiment,the soil total nitrogen stocks in the 0-60 cm layer was significantly increased with the increase of nitrogen fertilizer application rate,and the increments of 0 kg·hm-2(N0),100 kg·hm-2(N100),200 kg·hm-2(N200),300 kg·hm-2(N300) and 400 kg·hm-2(N400) were -293,-245,288,673 and 709 kg·hm-2,respectively. Nitrogen application significantly increased the content and amount of soil nitrate,while there was no significant effect on the content and amount of soil ammonia. After the two-year experiment,the nitrate amount under N0 and N100 treatments in the 0-200 cm soil layer showed a decreasing trend,without significant nitrate leaching in the soil. N200 treatment showed no significant increase of nitrate and no significant nitrate leaching in the soil. However,compared with N0 treatment,the nitrate amount under N300 and N400 treatments in soil layer 0-200 cm was increased significantly,and the content of nitrate moved down to deep soil(100-200 cm) significantly. Therefore,200 kg·hm-2 of nitrogen application can reduce the nitrate accumulation in deep soil. |
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