Soil acidification induced by intensive agricultural use depending on climate

Soil acidification is a major issue in agricultural ecosystems. However, how agricultural land uses shape the soil pH pattern and affect soil acidification on a regional scale are still poorly understood. The research aims to investigate the influences of typical agricultural practices on soil acidification across different climate zones of eastern China. Soil samples were collected from 240 sites and 3 land uses per site (uplands, paddies, and adjacent woodlands) across four climate zones (mid-temperate, warm temperate, subtropical, and tropical regions) of eastern China. Soil pH was quantified for each soil samples. The mean annual temperature (MAT) and mean annual precipitation (MAP) at each site were also analyzed. Climate was significantly associated with soil acidification. The differences in soil pH between adjacent land use types ranged from 0.02 to 1.12, whereas those between climate zones ranged from 0.34 to 2.22. Alkaline soils (cooler climates) exhibited a stronger acidification pace than acidic soils (warmer climates). Uplands resulted in alarming decrease in soil pH by 1.12 units relative to adjacent woodlands in mid-temperate zone, which may be induced by the dramatic loss of soil carbon. Acidification of uplands was stronger than that of paddies, owing to higher soil nitrification and carbon mineralization. Croplands had higher soil pH than adjacent woodlands only in the subtropics, indicating that agricultural practices in this zone were effective to retard soil acidification. We demonstrated, for the first time, the direction and intensity of the differences in soil pH levels among adjacent agricultural lands and woodlands depending on climate. As the two common agricultural croplands across eastern China, uplands have stronger acidification relative to paddies, particularly in the mid-temperate zone. Proper agricultural management practices to avoid carbon losses and preserve the flooding status of paddies should be considered to resist acidification of cropland soils.