中文摘要：

通过对紫色土坡耕地地表径流、壤中流径流过程及其硝酸盐含量的长期监测,研究紫色土坡耕地硝酸盐流失特征。结果表明,径流过程对紫色土坡耕地硝酸盐流失过程影响明显。地表径流过程中硝酸盐含量随降雨历时表现为先升后降的趋势,而壤中流过程则表现为不断上升、趋于稳定的趋势。紫色土坡耕地硝酸盐流失潜在的环境风险极大,历次降雨产流事件中地表径流和壤中流NO3--N平均含量分别为0.73±0.17 mg L^-1、21.72±2.05 mg L^-1,其中,75%的地表径流NO3^--N含量超过0.5 mg L^-1,85%的壤中流NO3--N含量超过10 mg L^-1。紫色土坡耕地地表径流NO3--N年流失负荷为0.93±0.05 kg hm^-2,壤中流NO3^--N年流失负荷为33.51±2.73 kg hm-2,分别占当季施肥量的0.62%、22.34%,随壤中流淋失是紫色土坡耕地硝酸盐流失的主要途径。紫色土坡耕地硝酸盐流失不仅可能造成当地地表水富营养化,而且可能造成当地浅层地下水硝酸盐污染,将加剧长江上游水环境压力。

英文摘要：

Nitrate loss is an important route of nitrogen loss,and its mechanism in flat cropland has been documented.However,it is still unclear how nitrate loss takes place in sloping cropland.Long-term plot experiments on field runoff were performed to monitor nitrate loss with runoff process in a sloping cropland of purple soil.Results show that runoff affected the process of nitrate loss from the slope cropland.Nitrate content in runoff increased at the initial period of a rainfall event,and then declined,and in the subsurface flow,it increased steadily and leveled off gradually.The potential environmental risk of the nitrate in surface runoff from slopeland of purplish soil is extremely high.The average nitrate content in surface runoff and subsurface flows of several rainfall events was N 0.73±0.17 mg L^-1 and N 21.72±2.05 mg L^-1,respectively.In about 75% of the surface runoffs,nitrate content was above N 0.5 mg L^-1 and in about 85% of the subsurface flow above N 10 mg L^-1.It was calculated that that the annual nitrate loss with surface runoff from the slope cropland of purple soil was N 0.93±0.05 kg hm^-2,accounting for 0.62% of the fertilizer-N applied in the current crop season,while with the sub-surface flow,it was N 33.51±2.73 kg hm^-2,accounting for 22.34%,suggesting that nitrate loss via subsurface flow is the main route of nitrate loss from the sloping cropland of purple soil,not only leading to eutrophication of surface waterbodies and pollution of groundwater,but also aggravating environmental pressure in the upper streams of the Changjiang River.