紫色土地区水文特征对硝态氮流失的影响研究

采用人工降雨模拟的方法,研究水文传输途径对紫色土中NO3--N流失的影响.研究结果表明,在所有雨强中均观察到壤中流的存在.在小雨强长历时的降雨中壤中流的径流量大于大雨强短历时降雨;随着雨强的增大,壤中流的径流系数下降.在紫色土地区,氮素的流失途径不仅包括地表径流而且包括壤中流,并且壤中流是NO3--N的主要水文传输途径.无论是否受到施肥措施的影响,壤中流中NO2--N浓度均高于地表径流.在对照小区,壤中流中NO3--N平均浓度是地表径流的7倍以上;施肥后壤中流NO3--N平均浓度为26.07mg·L-1,是地表径流的20倍以上.在对照小区,壤中流NO3--N的流失量占流失总量的30%以上;在施肥小区,壤中流NO3--N流失量占总流失量的90%以上.在紫色土地区,土壤特征和降雨特征决定了该地区壤中流形式的普遍存在,而NO3--N以壤中流流失的特点与当地施肥习惯的耦合效应增大了该地区的NO3--N流失风险.

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.