Abstract: By using the methods of classical statistics and geostatistics, the paper studied the spatial variation of soil moisture (0-300 cm) in horizontal and vertical direction, and the effects of land use and terrain factors in a small watershed in hilly and gully Loess Plateau. The results showed that: (1) Soil moisture content in vertical direction presented a trend of decrease to increase, and the coefficient of variation ranged from 11.22% to 21.05%. There was a significant negative correlation between soil moisture content and the coefficient of variation. (2) The layered distribution of terraces and the slope terrain weakened the spatial autocorrelation of soil moisture in horizontal direction. The variation range was from 19 to 102 m. Increasing sampling density could improve the spatial structure information of soil moisture. (3) There was a strong or moderate spatial autocorrelation of soil moisture in vertical direction, with the variation range from 0.67 to 2.64 m. (4) The sill values of different environmental factors showed an opposite variation trend with the average soil water content. The increase of moisture content had certain smoothing effect on the sill value. The impacts of different land use types on the vertical variation of soil moisture were in order of grassland > woodland > abandoned farmland > cultivated land, while ridge > valley for slope position.

Key words: monsoon broad-leaved evergreen forest, non-structural carbohydrate, seasonal dynamic, forest layer