不同近地表土壤水文条件下雨滴打击对黑土坡面养分流失的影响

目前,土壤水分饱和和壤中流条件下,雨滴打击对养分流失的影响尚不清楚.通过3个近地表土壤水文条件(自由入渗、土壤水分饱和与壤中流)下,土槽上方架设与不架设尼龙纱网模拟降雨对比试验,研究雨滴打击对黑土坡面侵蚀过程及NO3-N、NH4-N与PO4-P随径流和侵蚀泥沙迁移的影响.结果表明,纱网覆盖消除雨滴打击后坡面侵蚀量和泥沙浓度分别减少59.4％-71.6％和57.3％ -73.0％,不同水文条件下减少量的排序为:自由入渗＞壤中流＞土壤水分饱和.消除雨滴打击后养分随径流流失的减少仅在自由入渗条件下体现较明显,该水文条件下NO3-N、NH4-N与PO4-P流失分别减少33.3％、23.1％和40.7％；3种水文条件下,消除雨滴打击均明显减少养分随泥沙的流失,其中自由人渗条件下减少效果最明显,该水文条件下,NO3-N和NH4-N流失分别减少20.9％ -54.9％和25.0％ -62.3％,而PO4-P流失减少在74.6％以上.雨滴打击增大了NO3-N的淋失,但对NH4-N与PO4-P的淋失几乎无影响.消除雨滴打击后,自由人渗条件下养分的等效径流迁移深度减少26.7％-42.6％,而土壤水分饱和与壤中流条件下基本无变化.以上研究结果为有效防治坡面土壤侵蚀和农业非点源污染提供科学理论依据,尤其是在壤中流出现的地方.

Effect of raindrop impact on nutrient losses under different near -surface soil hydraulic conditions on black soil slope

Soil erosion is largely initiated by raindrop impact on soil surface. Raindrop impact not only disperses soil material, but also enhances the disturbance of runoff, thus significantly affects soil erosion processes and nutrient losses. However, few investigations have addressed the effect of raindrop impact on soil loss and nutrient loss under soil saturated and seepage conditions. A laboratory study was designed to quantify effect of raindrop impact on soil erosion processes and nutrient losses (NO₃-N, NH₄-N and PO₄-P) of black soil in the Northeast China under different soil surface water regimes. Three soil surface water regimes were tested: freely draining soil profile with rainfall (FD), saturated soil water profile with rainfall (Sa) and seepage under 20 cm hydrologic pressure with rainfall (SP). Under each hydraulic condition, two surface cases were included with and without raindrop impact through placing nylon net over soil pan. Results showed that the elimination of raindrop impact greatly reduced soil loss and sediment concentration by 59.4%-71.6% and 57.3%-73.0%, respectively, and the reduction effect were in order FD>SP>Sa. Effect of raindrop impact on nutrient losses by runoff was only pronounced for FD treatment, and NO₃-N, NH₄-N and PO₄-P losses by runoff reduced by 33.3%, 23.1% and 40.7% after eliminating raindrop impact for FD treatment, respectively. However, the elimination of raindrop impact greatly decreased nutrient losses by soil loss for all soil surface water regimes, among the reduction effect was the most pronounced for FD treatment, NO₃-N and NH₄-N were with decrease rate of 20.9%-54.9% and 25.0%-62.3%, respectively, while PO₄-P loss reduced by above 74.6%. Raindrop impact enhanced NO₃-N leaching, while it had no obvious influence on NH₄-N and PO₄-P leaching. After eliminating raindrop impact, for FD treatment, the effective depth of transport by runoff of nutrient decreased by 26.7%-42.6%, while for Sa and SP treatments, it varied slightly. These findings supply scientific support to control soil erosion and non-point source pollution on slope, especially the place where seepage flow occurs.