氮肥施用对黄土高原中部雨养农业区土壤硝态氮分布与累积的影响

黄土高原中部雨养农业区春小麦氮肥试验表明,氮肥施用量对土壤硝态氮的移动深度没有影响,但显著影响土壤硝态氮的含量与累积。连续施氮3年后第3季春小麦收获时,0～200cm土壤剖面中累积大量的硝态氮,其中48.96%～81.38%的总累积量和60.49%～122%的当年净累积量存在于0～110cm土层中。在确定春小麦适宜施氮量时应考虑到0～110cm土层中残留硝态氮的累积量。不施氮和氮磷比例为1:1时,连续施氮三年后土壤硝态氮总累积量最低,数量几乎相等;第3季春小麦收获后较播种时,土壤硝态氮发生亏缺。施氮量为52.5 kgN hm-2时土壤硝态氮的三年总累积率和第3季春小麦当年的净累积率居各处理之首(146.55%和138.21%)。合理的氮磷配比可有效减少土壤硝态氮的累积,不合理的氮磷配比下,低施氮量也会造成土壤硝态氮的大量累积。

Effects of Nitrogen Rate on the Distribution and Accumulation of Soil Residual Nitrate in the Rain-fed Agricultural Region of the Middle Loess Plateau

The purpose of this study was to determine the effects of nitrogen rate for spring wheat on soil residual nitrate distribution and accumulation in 0-200cm soil depth profile in the rain-fed agricultural region of the middle part of loess plateau.The experiment was conducted by using urea at five rates ranging from 0 N to 210Nkg hm-2 combined with 105 P2O5Kg hm-2 in March,2003.Before and after wheat harvest,the soil was sampled to a depth of 200cm and analyzed for nitrate nitrogen.It was found that nitrogen rate had no effect on nitrate movement in the soil after 3 years,i.e.residual nitrate did not move beyond 200cm in all treatments.However,nitrogen rate influenced the residual nitrate amount and accumulation in the soil significantly.After 3-year continuous application of nitrogen fertilizer,48.96%-81.38% of the total and 60.49%-122% of the net increase were accumulated in the 0-110cm profiles.When the nitrogen rate is 52.5Nkg hm2,all nitrate accumulation after 3 years accounted for 146.55% of the total.