[Spatial heterogeneity of soil water content under introduced shrub (Caragana korshinskii) in desert grassland of the eastern Ningxia, China].

Combined with geographic information system (GIS) data, the spatial heterogeneity of soil water in the 0-200 cm soil layer of the desert steppe with the introduction of the shrub Caragana korshinskii in eastern Ningxia was studied by classical statistical and geostatistical methods. It was found that the soil water content of each soil layer in the 0-200 cm profile was relatively low, ranging from 0.6% to 19.0% (averaged 4.4%). The coefficient of soil water content variation ranged from 49.5% to 86.3%, which indicated moderate spatial heterogeneity. The variation of soil water content at the 0-60 cm and 80-120 cm soil layers fitted the spherical model, while that at the 60-80 cm soil layer fitted the exponential model and that at the 120-200 cm soil layer fitted the Gaussian model. Soil water content at different soil layers showed different degrees of spatial autocorrelation. The nugget/sill [C/(C+C)] of soil water content in the 0-40, 60-80, and 120-200 cm soil layers ranged from 26.1% to 49.9%, with moderate spatial correlations. The nugget/sill of soil water content in the 40-60 cm, 80-100 cm, and 100-120 cm soil layers ranged from 15.5% to 22.1%, with strong spatial correlations. The scale of spatial heterogeneity in soil water content (A) varied among soil layers. The A was relatively large in the 0-20 and 20-40 cm soil layers (37.10-45.18 km) and small in the 40-200 cm soil layers (3.58-8.66 km). The results indicated that the introduction of C. korshinskii shrubs into desert grassland for vegetation recovery in recent decades have depleted soil water and accelerated the depletion of soil water in the deep layer (40-200 cm), leading to spatial heterogeneity and fragmentation of soil water (0-200 cm) with stronger effects at deep soil layer.