紫色土坡耕地硝酸盐流失过程与特征研究

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。

Nitrate loss from sloping cropland of purple soil

Nitrate loss is an important route of nitrogen loss, whose mechanism in flat cropland has been documented. However, it is unclear how nitrate loss takes place in sloping cropland. Field runoff plot experiments were performed to monitor nitrate loss with runoff process in sloping cropland of purple soil. Results showed that runoff affected the process of nitrate loss from slope cropland of purple soil. Nitrate content increased in the beginning of surface runoff, then decreased step by step. However, nitrate content increased in the beginning of subsurface runoff, then it inclined to steady with the rain time. Average nitrate content of surface runoff and subsurface runoff was respectively 0.73±0.17 mg.L-1 and 21.72±2.05 mg.L-1 in every rain event, in which 75% of nitrate content of surface runoff was above of 0.5 mg.L-1 and 85% of nitrate content of subsurface runoff was above of 10 mg.L-1. It could be concluded that nitrate loss from slope cropland of purple soil could affect water quality around it. The annual nitrate loss load of surface runoff from slope cropland of purple soil was 0.93±0.05 kg.hm-2 accounted for 0.62% fertilizer in a grow season, while the load of subsurface runoff was 33.51±2.73kg.hm-2. accounted for 22.34% fertilizer in a grow season. It is obvious that nitrate loss with subsurface runoff was the main approach of nitrate loss from slope cropland of purple soil. Water eutrophication and groundwater nitrate pollution could be generated attributed to nitrate loss from slope cropland of purple soil and the environmental problem in the upriver of the Changjiang river.