Spatial analysis of soil aggregate stability in a small catchment of the Loess Plateau, China: I. Spatial variability

The intrinsic and extrinsic factors that control soil aggregate formation have been widely studied at the aggregate scale, but little is known about their roles in aggregate formation at different landscape scales. Here, a spatial analysis of soil aggregate stability and erodibility (K factors) was performed to understand the formation processes of aggregates at catchment scale. Spatial structures of the mean weight-diameter (MWD, mm), water stable aggregates greater than 0.25 mm (WSA(>0.25), %) and K factors were investigated by using classical statistics, semivariograms, Local Indicators of Spatial Association (LISA), spatial interpretation, and spatial overlay in a small catchment of the Loess Plateau, China (LPC). The results showed that MWD and WSA(>0.25) were significantly lower in farmland than in other land types, and were obviously higher in shrubland than in woodland, but it was the opposite case for K factors. Nugget/sill ratios C-0/(C-0 + C) showed a very strong spatial dependence for MWD (9.13% at 0-10 cm and 19.49% at 10-20 cm soil layer) and WSA(>0.25) (12.48% at 0-10 cm and 17.71% at 10-20 cm soil layer). These data and LISA results implied that the spatial variability of MWD, WSA(>0.25) and K factors in the Zhifanggou catchment was mainly controlled by intrinsic factors such as parent materials, terrain attributes and soil types. Besides, the effects of extrinsic factors (land use and farming practice) could not be ignored, especially for K factors. Cross-validation results illustrated that ordinary kriging (OK) performed better than inverse distance weighting (IDW) for MWD and WSA(>0.25), but it was the opposite for K factors as a whole. Land-use type, topography, vegetation, and revegetation duration showed interactive effects on the spatial heterogeneity of soil aggregate stability and K factors. Spatial analysis showed great potential to be applied in the analysis of the influencing factors of soil aggregate stability at the small catchment scale.