农业生产活动对黄土高原丘陵沟壑区坡地土壤水分动态的影响

Effect of agricultural activities on soil moisture content at slopeland in hilly and gully region of Loess Plateau

通过在坡度为20°耕地和荒草坡面对降水、土壤水密集观测,结合模拟降雨实验,从降雨入渗、蒸散发等过程分析讨论了影响黄土高原丘陵沟壑区坡地土壤水分动态的主要因素。结果表明:1)降雨入渗量△S主要受控于雨强和降雨量,坡耕地的入渗量随着雨强增加而衰减的速度快于荒坡,坡耕地有利于中等雨强大雨的下渗,雨强增大时两坡面的降雨转化率逐渐接近,且植被的再分配作用凸显,甚至使短历时暴雨时坡耕地的入渗速度低于荒坡,长历时的大、暴雨或连续降雨利于深层入渗,坡面耕作或在裸地上种植冰草后降雨转化率增约50%;2)7月～10月上旬为土壤水补给期,土壤水分在枯水年及平水年处于负平衡,在丰水年获得补给,最终以蒸散发消耗;3)荒地主要耗水层在20cm,耕地土壤水分活跃层及作物主要耗水层延伸至30cm。总体上,农作物增大蒸散发量、增加土壤水分利用深度,农业生产活动对减少降雨径流、增加土壤水资源量、强化水分小循环有重要作用。

The ecological and environmental recovery in hilly loess region of Loess Plateau is an important issue in the semi -arid Northwest China, where the agricultural activities has greatly affected the soil moisture condi- tions by influencing the hydrological processes as precipitation infiltration and soil water consumption. By inten- sively observing precipitation, soil moisture and soil water potential at 20~ cropland and grassland, combining with simulation rainfall at runoff spots, we identified the effect of agricultural activities on soil moisture at slopel- and from aspects of precipitation infiltration and evapotranspiration. The following conclusions have been summa- rized ： 1 ） The infiltration amount of precipitation is determined by rainfall intensity and amount, and the infiltra- tion amount at sloping cropland decreases faster than the wasteland under intensive precipitation. The agricultural cultivation at slopeland enhances the infiltration of median intensity rainfall, and during intensive storms, the soil water conversion coefficient declines to be close to that of wasteland and the role of vegetation on precipitation re- distribution outstands so quickly that it even slows down the infiltration speed at sloping cropland. Long -dura- tion heavy rainfall or rainstorms are beneficial to percolation. The agriculture c uhivation at slopeland or planting at sloping bareland increases the soil water conversion coefficient by about 50%. 2） Soil water storage decreases at normal year or dry year, and get recharge in wet year. The soil water mainly recovers during July and Octo- ber, and eventually consumes by evapotranspiration. 3 ） Both the active layer and dominant consumption layer of soil water at slopeland are deepened by 10cm to be 30cm layer after cultivation. In conclusion, agriculture activi- ties at slopeland not only increases the evapotranspiration and utilization of soil water, but also obviously increa- ses the soil water storage, so it is beneficial to increase soil water resources and to enhance local hydrological cy- cle.