Soil acidification and factors controlling topsoil pH shift of cropland in central China from 2008 to 2018

Soil acidification can negatively impact the sustainability of agricultural systems. Spatially explicit estimations of soil acidification and the identification of local factors driving soil pH change are prerequisites for formulating and implementing site-specific measures to prevent and mitigate cropland soil acidification. Based on pairwise comparisons between 1443 pairs of topsoil pH observations at colocated sites in 2008 and 2018, this study revealed the spatial variability of cropland soil acidification and its influencing factors across Henan Province, central China. The results showed that the topsoil pH of cropland in Henan Province decreased by an average of 0.36 units, and more than 94% of the cropland in the study region suffered from varying degrees of topsoil pH decline from 2008 to 2018, demonstrating a large range in soil acidification. The most serious soil acidification of croplands occurred in the southern part of the province, while in the northern part of the province, the topsoil pH decreased to a lesser extent or even slightly increased. The topsoil pH shift of cropland was found to be closely associated with the N fertilizer application rate, base cation removal by crops, and factors influencing the soil response to acidification, i.e., soil calcareousness, initial acidity, clay content, moisture regimes and temperature regimes. Among the various factors, the N fertilizer application rate was identified as the most important factor related to soil acidification. Croplands face the risk of accelerating soil acidification due to continuous excessive nitrogen application, increasing the removal of base cations while promoting crop yield, and decreasing or even disappearing carbonate material in the soil.