Spatial Variation in Soil Available Potassium and Temporal Changes due to Intrinsic and Extrinsic Factors: a 10-Year Study

The objective of this study was to shed light on spatial variation in soil available potassium (SAK) and the spatial dependence of temporal changes in SAK after 10 years in relation to climate, topography, soil properties, vegetation, and land use. Such information would be helpful in predicting both spatial and temporal distributions of SAK to ensure efficient land use, food security, and resource sustainability. Spatial variation of SAK in Shanxi Province, China, in 2007 and 2017 and temporal changes after 10 years were determined. The effects of qualitative factors on spatial variation and temporal changes in SAK were then analyzed using one-way analysis of variance. The relationships between SAK and quantitative factors were explored, and the relative effects of climate, topography, vegetation, soil, and their combinations were assessed using stepwise multiple linear regression. After 10 years, SAK had increased in 65% of the study area and decreased in 35% of the area. The average SAK increased by 22.25 mg/kg, and SAK changed from a low level to a sufficient level in around 12% of the study area between 2007 and 2017. Qualitative factors had a more significant effect on the spatial distribution of SAK in 2017 than in 2007, whereas quantitative factors had a more significant effect on spatial variation in SAK in 2007 than in 2017 (p < 0.05). Quantitative factors explained variation in SAK at approximately 41% of the study sites in 2007 and 19% of the sites in 2017. In terms of the relative importance of these factors, climate was the most important factor influencing spatial variation in SAK, followed by topography, vegetation, and soil properties. However, these intrinsic factors had little control on temporal changes in SAK, with extrinsic factors having the greatest effect. The results indicated that intrinsic and extrinsic factors controlled spatial and temporal variability in SAK with different intensities. These findings are of great significance for future studies in predicting spatial and temporal changes in SAK in response to the soil forming environment at the provincial scale.