中文摘要：

以宁夏青铜峡灌区水稻田三氮（总氮、氨氮、硝氮）作为研究对象，从田间运移、土壤剖面中的变化以及在排水沟内受到的消解作用方面进行了分析。结果表明：（1）水稻田间，排水中总氮浓度大于其在引水中浓度；5、6月份田间积水中总氮浓度小于其在引水、排水中浓度，7、8月份刚好相反。引水中氨氮浓度小于其在田间积水、排水中浓度。5—7月排水中硝氮浓度〉其在引水中浓度〉其在田间积水中浓度，8月份变化没有明显规律。（2）土壤剖面中0-20 cm土层三氮含量最高，随着土壤剖面加深，呈递减趋势，总氮在灌溉后的含量高于灌溉期间，氨氮、硝氮灌溉后的含量低于灌溉期间。（3）排水沟内三氮均受到消解作用，消解幅度呈氨氮〉总氮〉硝氮的趋势，且与植被覆盖度、沟道长度、水流速度等因素关系密切。

英文摘要：

With strict controlling of point source pollution, how to understand and control non-point source pollution scientifically and effectively has become the important pressing research. Agricultural non-point source pollution due to wide application of fertilizers and pesticides is becoming the major cause of the environment deterioration. It has been researched in 1980s in our country, and now it becomes a research hotpot. An experiment was done to asses the loss of nitrogen in paddy field in Qingtongxia irrigation area, Ningxia. Based on this experiment, this paper tried to find out TN, NH4＋-N and NO3-N transportation and transformation law in paddy field, in soil profile and in drainage ditch. The result showed that： （ 1）In paddy field, the concentration of TN in discharging water was higher than that in introducing water. TN in accumulating water was lower than that in discharging and introducing water from May to June, the case was the contrary from July to August. The concentration of NH4＋-N in introducing water was lower than that in accumulating and discharging water. From May to July, the concentration of NO3-N was in the order of discharging water 〉introducing water 〉accumulating water, and which had no obvious characteristics in August. （2）Three kinds of nitrogen were in the highest content at the range of 0-20 cm soil layer, and tended to decrease with depth. The content of TN after irrigation was higher than that during irrigation periods and the case of NH4＋-N and NO3-N was just on the opposite. （3）The vegetation in drainage ditch had degradative effect on three kinds of nitrogen, and the rate was in the order of NH4＋-N〉TN〉NO;-N, which also had a close link with vegetation coverage, the length of ditches, water flow and other factors.