Spatial heterogeneity of soil moisture of apple base in Weibei dry highland

Soil moisture is an important variable that significantly affects the hydrological environment of a region. Weibei Upland in southern part of Loess Plateau is a commercial apple base where the increase of apple planting area has seriously affected the regional water cycle. It is necessary to better understand the effects of different land use patterns on the spatial distribution of soil water contents in order to account for the balances of water and energy at Weibei dry highland. In this paper, the principle and methods of geo-statistics were used to investigate the spatial heterogeneity in soil moisture at three soil depths(0～20 cm, 60～80 cm, and 280～300 cm)of different land use types (farmland, apple land, and clover land ) by calculation of semi-variogram at Weibai dry highland in Loess Plateau. Spherical model was used to fit the form of semi-variogram. The typical results showed that there are high degrees of spatial heterogeneity in farmland, apple land and clover land. In 0～20 cm layer, the scale of spatial heterogeneity is 9～16 m, 5～12 m in 60～80 cm layer, and that is 5～10 m in 280～300 cm layer. The degrees of spatial heterogeneity change with this scale. The distance of spatial autocorrelation in soil moisture is found within distances from 1～17 m. The spatial heterogeneities of autocorrelation in total spatial heterogeneity are 89.95%～94.15% (0～20 cm), 83.75%～97.64% (60～80 cm) and 85.16%～93.85%(280～300 cm), respectively, which are obviously more than that of random proportion. The scale of spatial autocorrelation increased gradually from clover land, apple land to farmland. There exists a stronger anisotropic structure in E 0° and N 90° directions in both farmland and clover land (0～20 cm), but apple land in the same direction is close to isotropy.