灌溉条件下包气带黄土层中NO-3-N的深部运移

通过渭北黄土塬地区NO3--N的原位运移试验,测定了10 m范围内黄土超根层中NO3--N浓度随时间的变化,对NO3--N和土壤含水量的运移通量及运移速率进行了定量分析。结果表明:微孔隙渗流的水分运移速率为44~65 mm/d,优先流的运移速率可达450 mm/d以上;NO3--N在施肥灌溉及作物吸收等因素的综合影响下形成积累峰值带,并向下运移,其平均运移速率为56.3 mm/d;在作物生长缓慢的冬季大定额灌溉条件下,施入农田的尿素并不能被作物完全吸收,上层土壤吸附的NO3--N会被大量淋洗,50%以上的NO3--N随入渗水流运移到作物根层以下,成为深层土壤和地下水的NO3--N污染来源。

NO-3-N deep migration in loess layer of non-saturated zone under irrigation condition

Soil NO3^--N was measured in Weibei Loess soil under irrigation condition. The deep irrigation of NO3^- -N concentration was measured in 10m scope in the ultra root level with time changing. It quantitatively analyzed and discussed the migration flux and velocity. The result showed that the scale of soil water migration velocity in the minipore permeation is 44-65 mm/d, the velocity in preferential flow is up to more than 450 mm/d. NO3^- -N concentration is accumulated as a peak strip influenced by irrigation, fertilizer and crop absorption. The peak strip moves on and its average velocity is 56.3 mm/d. Under higher irrigation quota in the winter, the crops cannot absorb extra urea. The NO3^--N absorbed in upper layer leaches largely, and the 50% urea moves to the lower root zone with the pore water. Consequently it becomes the source of deep soil and ground water pollution.