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2001至2004年,在甘肃庆阳黄土高原定位研究了施氮和不施氮对比条件下,4龄苜蓿后茬冬小麦对氮素的响应。结果表明,4龄苜蓿后茬冬小麦产量对氮连续3年有响应,至第3茬,施氮显著增加籽粒产量(P<0.05),促进了第1茬冬小麦对氮的吸收,与产量的变化趋势一致;第2茬冬小麦对氮肥的利用率最高,达47%,不施氮下土壤氮素处于亏缺状态,第1年的亏缺量最大、第2年最小;施氮明显增加第2茬冬小麦0~60cm土层中硝态氮的含量,且硝态氮的累积峰从2003年的0~60cm土层,转移到2004年的60~200cm,表明氮有一定程度的向下淋溶。在黄土高原,4龄苜蓿后茬种植头茬作物可不施氮肥。
From 2001 to 2004, the responses of winter wheat after 4 years old Medicago sativa to nitrogen application were studied in Loess Plateau of Qingyang, Gansu Province under nitrogen and non-nitrogen application conditions. The results showed that the winter wheat yield of the fourth instar alfalfa after winter wheat responded to nitrogen for three consecutive years. By the third crop, nitrogen application increased the grain yield significantly (P <0.05), promoted the nitrogen absorption and the change of yield The second crop of winter wheat had the highest nitrogen utilization rate of 47%, the soil nitrogen was in a deficit condition without nitrogen application, the largest deficit occurred in the first year and the second year was the lowest. The content of nitrate nitrogen in 0 ~ 60cm soil layer of winter wheat and the accumulation of nitrate nitrogen shifted from 0 ~ 60cm soil layer in 2003 to 60 ~ 200cm in 2004, indicating a certain degree of downward leaching of nitrogen . In the Loess Plateau, the fourth crop of alfalfa after the first crop planted stubble crop can not apply nitrogen fertilizer.