Land Use and Soil Type Exert Strongly Interactive Impacts on the pH Buffering Capacity of Acidic Soils in South China

Soil acidification is a severe environmental problem around the world. Soil pH buffering capacity (pHBC) is the intrinsic factor affecting the soil acidification rate and is intensively impacted by anthropogenic and natural conditions. However, composite assessments of the effects of land use and soil type on soil pHBC are still limited. Therefore, we collected samples of five soil types (red soil, lateritic red soil, latosol, paddy soil and acid sulphate soil) from two land use patterns of agricultural and adjacent forest fields at different depths (0–10 cm, 10–20 cm and 20–30 cm) in South China, aiming to investigate the effects of land use and soil type on soil pHBC in this region. The results show that land use, soil type and their interactions greatly influence soil pHBC and physico-chemical properties. Forest soils have a significantly higher pHBC (11.40–49.50 mmol·kg−1 soil·unit−1 pH), cation exchange capacity (CEC), exchangeable Al3+ (EAl3+) and clay content than agricultural soils. Acid sulphate soil has the highest pHBC (49.27–117.83 mmol·kg−1 soil·unit−1 pH) values and exchangeable acid (EA) content among all investigated soil types, whereas lateritic red soil has the lowest pHBC (10.56–31.71 mmol·kg−1 soil·unit−1 pH). In agricultural fields, soil pHBC is positively related to CEC, soil organic carbon (SOC) and EA, indicating that agricultural soils may be in a cation exchange buffering stage. The soil pHBC of forest fields is positively correlated with SOC and EAl3+, implying that forest soils may be in the Al buffering stage. In conclusion, soil pHBC would vary with different land use forms and soil types, in which a series of key complex physico-chemical processes and interactions would occur to regulate soil pH buffering capacity.