根据田间试验资料,分析研究了黄土丘陵沟壑区苜蓿地土壤水分的周年变化规律,并以休闲地和几种一年生作物地作为对照进行对比研究,得出以下主要结论:①雨季降水对苜蓿地土壤水分的补给起着重要的作用,其土壤贮水量动态与年内的降雨周期相吻合,但总体上朝着土壤不断干化的方向发展;②经过一个雨季,苜蓿地的土壤贮水量与平均含水量分别呈不同程度的下降,而休闲地与4月份持平;③相同的降水对不同作物地的补给效果不同,以3m土层计算,苜蓿地的农田蒸散量与谷子、玉米相当,比豆子地高,但要低于高粱地;④长期种植苜蓿引起的深层土壤干化问题必须引起足够的重视,干化土地的水分恢复不是一朝一夕的事情。

Soil moisture plays a critical role in crop growth and vegetation restoration in the Loess Plateau.In order to analyze soil moisture's variation of the alfalfa plot and its impact on the soil water eco-environment,field experiments were conducted in 2002.At the same time, evapotranspiration of fallow land and some other crop fields were also studied as a contrast.The main results are as follows:(1)Precipitation in the rainy season plays an important role in the supplement of soil water in alfalfa plot.The soil moisture's dynamic period was identical with the rainy season,but the trend is getting dry.(2)Through a rainy season,the soil water content and soil moisture was declined in the alfalfa plot,but to the fallow land which were equal with the levels in April.(3)The same rainy season has different replenishment results on different crop fields.Alfalfa plot's evapotranspiration calculated in the top 3m soil layer was close to the millet and maize fields,higher than bean field,but lower than sorghum field.(4)The drying layer caused by long term's alfalfa's growing should be noticed.It's hard to recover the soil moisture in the dryed layer.