The spatial variability of temporal changes in soil pH affected by topography and fertilization

Abstract

Understanding the spatial–temporal variation of soil pH is essential for agricultural production. However, studies on the spatial–temporal variation of soil pH in arable soils in areas of complex terrain are still limited. In this work, 143 and 232 topsoil samples (0 ∼ 20 cm) were collected in 2012 and 2017, respectively, in a typical hilly and mountainous area (235.35 km2) of southwestern China. Descriptive statistics, semivariance analysis, and boosted regression trees (BRT) model were used to analyze the spatial–temporal distribution characteristics of soil pH and their relationships with environmental factors (topography, parent material, and soil type) and fertilization. Samples were randomly divided into calibration (80%) and validation (20%) sets. Model performance was assessed by mean absolute error (MAE), root mean square error (RMSE), coefficient of determination (R2), and Lin’s concordance correlation coefficient (LCCC). Results indicated that BRT models could explain approximately 75% and 51% of soil pH variability in 2012 and 2017, respectively, with topography significantly influencing the spatial variation in soil pH. Spatial autocorrelation analysis showed a more homogeneous spatial distribution of soil pH in 2012 (range = 16180 m) than in 2017 (range = 588.9 m). Additionally, the BRT model was used to analyze the relationship between pH changes (2017–2012) and environmental factors and fertilization. The values of MAE, RMSE, R2, and LCCC of BRT for pH changes were 0.36, 0.44, 0.61, and 0.73, respectively. This model explained 61% of the spatial variation in soil pH changes. Elevation, organic fertilizer, slope, valley depth, and slopelengthand slope steepnessfactor were the most important factors affecting the spatial variability of soil pH changes. From 2012 to 2017, the average soil pH increased significantly by 0.63 (p < 0.001) with an increase in the northern and northeastern parts and a decrease in the southwestern areas due to the differences in organic fertilizer application and topography.