Soil water distribution characteristics of alfalfa with different planting years in the gully region of loess plateau

The distribution characteristics of soil water of alfalfa with different planting years in the gully region of the loess plateau were studied. The results showed that the soil water content in 02m layer was affected by annual precipitation. Soil layer below 2m was drier without water supplying, forming a dry layer. Alfalfa had used the soil water of (upper) layers on first growing season years, and the soil water had been renewed from upper layers, however renewing the soil water of the lower layers was difficult. The soil water content of 10,15 and 23 years alfalfa didn't change (significantly) in 9m,10.8m and 11m soil layers respectively, and the dry layer was disappear. The variance coefficient of soil water decreased with the increase of depth. It pointed that the great water deficit caused by evapo-transpiration was significant in 09m layer, the amount of deficiency was more than annual precipitation.