黄土区荒草地和裸地土壤水分的循环特征

Water cycling characteristics of grassland and bare land soils on Loess Plateau

在人工、天然降雨条件下,研究了黄土高原地区荒草地和裸地土壤水分循环特征.结果表明,干旱年(天然降雨条件),荒草地和裸地剖面内土壤水分变异系数随土层深度的增加而降低,基于标准差和变异系数两个指标,采用聚类分析可以将土壤剖面水分垂直变化划分为4层.丰水年(人工降雨条件),由于持续降雨入渗和强烈的蒸发蒸腾作用,荒草地和裸地剖面内土壤水分变异系数随土层深度的增加呈现“降-升-降”的变化趋势,且表层土壤水分变异程度明显降低.与裸地相比,荒草地土壤水分循环深度和强度加剧,表现为活跃层、次活跃层深度和蒸散量增大.土壤水分的动态变化主要受降雨和蒸散过程的影响,尤其是浅层,而深层具有相对滞后性.土壤水分的动态变化具有明显的季节性,一般可划分为3个主要时期,如春季失墒期、夏秋增失交替期和冬季相对稳定期.干旱年,土壤水分收支负平衡,入渗雨量全为蒸发蒸腾所消耗;丰水年,土壤水分收支正平衡,但入渗雨量的大部分(>80%)为强烈蒸发蒸腾所消耗.

The study under natural and simulated rainfall conditions showed that the variance coefficient of soil water in the grassland and bare land on Loess Plateau decreased with increasing soil depth, and the vertical change of soil water in drought year in the profile could be divided into four layers. In rainy year, the variance coefficient of soil water decreased first, increased later, and decreased lastly with the increase of soil depth, due to the continual rainfall infiltration and intensive evapotranspiration. The variance coefficient at surface soil layer was obviously smaller in rainy year than in drought year. Compared with that in bare land, the soil water cycling in grassland was deeper in depth and greater in intensity, as well as higher in evapotranspiration. The temporal change of soil water mostly depended on rainfall and evapotranspiration, especially in surface soil layer, and the change of soil water lagged behind gradually from low to deep layers in the profile. Soil water storage had a seasonal change, and could be divided into three main periods, i. e., decreasing in spring, alternatively decreasing and increasing in summer and autumn, and relatively stable in winter. In drought year, soil water storage decreased, and infiltrated rainfall was all consumed by intensive evapotranspiration. In rainy year, soil water storage increased, but most infiltrated rainfall （more than 80 % ） was consumed by intensive evapotranspiration.