Spatial variability of soil total nitrogen, phosphorus and potassium in Renshou County of Sichuan Basin, China

Understanding soil nutrient distributions and the factors affecting them are crucial for fertilizer management and environmental protection in vulnerable ecological regions. Based on 555 soil samples collected in 2012 in Renshou County, located in the purple soil hilly area of Sichuan Basin, China, the spatial variability of soil total nitrogen (TN), total phosphorus (TP) and total potassium (TK) was studied with geostatistical analysis and the relative roles of the affecting factors were quantified using regression analysis. The means of TN, TP and TK contents were 1.12, 0.82 and 9.64 g kg−1, respectively. The coefficients of variation ranged from 30.56 to 38.75% and the nugget/sill ratios ranged from 0.45 to 0.61, indicating that the three soil nutrients had moderate variability and spatial dependence. Two distribution patterns were observed. TP and TK were associated with patterns of obvious spatial distribution trends while the spatial distribution of TN was characterized by higher variability. Soil group, land use type and topographic factors explained 26.5, 35.6 and 8.4% of TN variability, respectively, with land use being the dominant factor. Parent material, soil group, land use type and topographic factors explained 17.5, 10.7, 12.0 and 5.0% of TP variability, respectively, and both parent material and land use type played important roles. Only parent material and soil type contributed to TK variability and could explain 25.1 and 13.7% of TK variability, respectively. More attention should focus on adopting reasonable land use types for the purposes of fertilizer management and consider the different roles of the affecting factors at the landscape scale in this purple soil hilly area.