前期含水量对坡耕地产流产沙及氮磷流失的影响

土壤前期含水量是影响土壤入渗、产流以及溶质迁移、淋失的重要因素之一。通过人工模拟降雨实验,对5%、9%、13%、17%和20%这5个不同前期含水量水平下的黄土高塬沟壑区黑垆土坡耕地土壤侵蚀及氮磷流失情况进行了研究。结果显示:在同一雨强和坡度条件下,随着土壤含水量的增加,坡面达到稳定入渗率的时间缩短,开始均匀产流时间也减小;在5%~17%前期含水量的范围内,径流量、泥沙量随前期含水量增加而增加,17%~20%时径流量和产沙量为递减的变化趋势;产沙量与径流量呈显著的线性关系,相关系数为0.889。前期含水量为17%时,径流中水溶性磷、硝态氮、铵态氮浓度最大,总流失量最大,3种养分在湿润层内发生积累的深度随含水量增加而减小,前期含水量17%是影响径流中养分浓度变化的一个临界值;在前期含水量范围为5%~9%时,养分流失量变化不大,且流失量较小;硝态氮平均流失总量最大,分别是铵态氮和水溶性磷的1.32和2.46倍。该项研究结果可为当地农业生产、减少水分损失、提高水分和养分利用率提供有效的指导。

Effect of Antecedent Soil Moisture on Runoff and Sediment and Nitrogen and Phosphorus Losses from Slope Cropland

Antecedent soil moisture is one of the important factors affecting soil infiltration, runoff and solute migration. In this research, soil erosion and nutrient losses of slope cropland were studied under five different antecedent soil moisture levers of 5%, 9%, 13%, 17% and 20% with artificial rainfall method in Dark Loessial soils in gully region of the Loess Plateau. Under the same rainfall intensity and slope, the time for slope soil to reach stable infiltration and to yield stable runoff decreased with the increasing antecedent soil moisture. The amounts of runoff and sediment increased with increasing antecedent soil moisture between 5% and 17%, but reduced between 17% and 20%. There was a significant linear relationship between the amounts of sediment and runoff, with coefficient of 0.889. Concentrations and total losses of soluble phosphorus, nitrate and ammonium were the greatest at 17% of the antecedent soil moisture. Antecedent soil moisture reduced the soil depth of phosphorus and nitrogen accumulation in moist layer. There is little amount of nutrient loss at antecedent soil moisture between 5% and 9%. These results indicate that 17% of antecedent soil moisture would be a critical value for nutrient runoff losses.