Spatial variability of soil nutrients on hillslope in typical karst peak-cluster depression areas

The geostatistics method was used to determine and quantify spatial variability of surface soil nutrients (0～15 cm) in a typical Karst peak-cluster depression area in northwest of Guangxi province. Using line sampling method (10 m space), 95 sampling points were fixed in total. Soil organic carbon (SOC), total nitrogen (TN), total phosphorus (TP), total potassium (TK), available nitrogen (AN), available phosphorus (AP), available potassium (AK), pH value were measured. The results show that SOC, TN, AN and AK have the similar spatial variability structure, and their variability distances varied between 212～251 m, which corresponded to the average range of fields with the same land use types. TP and TK had relatively small variability distances of 141.2 m and 120.6 m, respectively. Due to the application of P-fertilizer, the variability distances of AP is the smallest in the research area. Excepted for pH value, all soil nutrients are strongly spatially dependent. The ordinary Kriging method shows that SOC, TN, AN content increases with the increasing of altitude, which indicate that the spatial pattern of soil nutrients on hillslope in typical Karst peak-cluster depression area is mainly controlled by hydrography conditions and land use types.