旱作农业土壤矿质态氮随地表径流迁移特征研究

Migration characteristics of mineral nitrogen with surface runoff in dry farmland soil

为了了解旱作农业土壤中氮素随地表径流的流失水平及规律,于野外夏玉米试验田中进行了模拟降雨与自然降雨条件下的对比试验,并通过对水量和水质的同步监测,研究了不同施肥水平下氮素的流失效应.其中,模拟降雨采用的两个降雨强度分别为40和70mm.h-1,3个尿素施肥水平分别为287、431和575kg.hm-2(以N计),每次自然降雨的试验小区布置相同.试验期间,共有20次降雨事件(包括模拟降雨),其中,4次降雨过程中产生了地表径流并有氮素流失.结果表明,次降雨径流过程中硝态氮流失浓度先迅速增大后逐步降低,而铵态氮流失浓度变化平稳,且流失浓度较低.次降雨间氮素流失平均浓度相差较大,尤其体现在硝态氮浓度上更为明显.此外,研究发现,次降雨径流过程地表氮素流失初期效应明显,且受降雨强度影响显著.通过氮素流失水平的计算发现,研究区大于25mm的降雨类型会有明显的地表径流产生及氮素流失.

To understand the process of nitrogen loss with runoff in dry farming land,a field study of nitrogen loss under different fertilization levels was conducted during cultivation of summer maize. In order to investigate the degree of soil nitrogen loss with surface runoff in dry farmland,the water quantity and quality were monitored simultaneously. Simulated rainfall was conducted at 2 rainfall intensities：40 mm·h-1 and 70 mm h-1; and 3 urea fertilizer levels：287 kg·hm-2,431 kg·hm-2 and 575 kg·hm-2. The same fertilizer treatments were used for a natural rainfall trial. During the experimental period,there were four runoff and nitrogen loss events among twenty total rainfall events （including the simulated rainfall）. In the rainfall runoff,the concentration of nitrate increased rapidly at first,and then decreased gradually,whereas the ammonium nitrogen concentration was stable,and the loss of lower concentration during a rainstorm event. Large differences were observed among different rainfalls in event mean concentration,especially in nitrate. The first flush effect of nitrogen loss with runoff was obvious and was found to be significantly affected by rainfall intensity. According to the calculated nitrogen loss,runoff and nitrogen loss in the study area always occurred during rainfall events of more than 25 mm.