Nitrate-N loss effected by the runoff process in purple soil-a simulation study

Purple soil is well distributed near the Three Gorge Reservoir. A simulation study was conducted to evaluate the nitrogen loss effected by the runoff processes under artificial rainfall simulation. Three rainfall intensities of 0.5, 1.0 and 2.0 mm·min~ -1 , in two treatments of zero and 200kg·hm~ -2 nitrogen input levels, were tested. It was found that the subsurface runoff proportion declined with the increase of rainfall intensities. In the purple soil, the subsurface flow was the main path of nitrate loss in all treatment tests. In the control treatment with zero N input, the average nitrate concentration in the subsurface flow was 7 times as much as that in the surface flow. In the 200kg·hm~ -2 nitrogen input treatment, the average nitrate concentration in the subsurface flow was 26.07 mg·L~ -1 and it was more than twenty times as much as that in the surface flow. The nitrate load from subsurface flow accounted for more than 30 % of the total in the control treatment plot whereas the nitrate load from subsurface flow accounted for more than 90 % of the total in the 200kg·hm~ -2 nitrogen input plot. In the purple soil region, the characteristics of nitrate loss in the subsurface pathway were possibly due to the local agricultural practices and hydrological processes.