Experimental Study On NO₃～--N Deep Migration In Loess Plateau Of Aerated Zone Under Irrigation Condition

The use of nitrogen fertilizer improves the crop quantity and meets the present demand for the food in the world. However, it brings a series of environmental problems. With the increase of population, on the one hand, we need to continue improving crop productivity; on the other hand, we must avoid destroying and polluting the ecological environment effected by high fertilizer use volume and improper using method. One key technique to solve these problems is to integrated regulate the distributing, motivation, storage and translation of water and nutrition in the soil—crop—aerated zone system and its ecological effect, and determine the reasonable fertilization and irrigation in order to get the aim of improve quantity, save water and fertilizer, and improve the environmental quality. This paper discusses the irrigation effect on the NO₃^- -N distribution and motivation in the aerated Loess Plateau, ascertain the relationship between irrigation and nitrogen leaching, and precisely predict the polluted condition of soil and groundwater. After analyzing, we got the conclusions as follows:(1)The soil moisture content changes with Loess lithology, irrigation quantity and local climate in 10m-scope depth. It changes prominently in 2m scopes, which are effected by the weather condition. In 2m deeper depths, matrix potential energy in ancient soil is larger than that in yellow soil, so the soil moisture is collected in ancient soil. There are two notably peak value strips in 1.0³.4m and 7.2⁸.0m depth.(2)Under concentrate water supply, the seepage process has prominent motivation of high soil moisture content, and its width is about 2.4m. The unsaturated irrigation supply has duality in yellow soil. The mini-pore water velocity is 5⁶.5mm/d while the preferential flow velocity can reach 450mm/d.(3)NO₃^- -N has the peak value strip under the synthesized effect of fertilizer, irrigation, and crop absorption. The concentration reduced with the depth increasing, its average velocity is 56.3mm/d. It shows that ancient and loam soil in yellow aerated zone has prominent retention and storage of seepage water.(4)NO₃^- -N concentration is apparent in upper soil. With the depth deeper, it changes mildly. Most of the NO₃^- -N is eluted to the deeper soil and got collected. It goes on moving...