| 摘 要： |
Cropland soil has a higher acidification risk, with the driving factors and the soil buffering capacity controlling the degree of soil acidification. However, the relative importance of the main driving factors at broad geographic scales remains unclear, and the evidence on the acid-buffering process is rarely examined by large-scale observations. Using 4101 soil samples obtained in 1980s and 4348 soil samples collected in 2010s, this study explored topsoil pH changes of cropland across the Sichuan Basin of China and identified the relative importance of the main affecting factors. The results showed that topsoil pH (20 cm) has decreased by an average of 0.30 units (p < 0.001). Spatially, soil pH decline mainly occurred in the periphery of the Sichuan Basin where the initial pH (1980s) were less than 7.5. The magnitudes of soil pH decline were positively correlated with precipitation, base cation removal by crops and nitrogen fertilizer rates. Precipitation was identified as the most important factor in driving soil acidification. Moreover, the soil pH decrease was primarily buffered by soil carbonates and secondarily by soil CEC, and this study identified a critical level of 36.76 g kg(-1) for soil carbonates, above which the acid-buffering capacity was mainly provided by soil carbonates, otherwise by soil CEC. These findings emphasize the importance of formulating precipitation-based optimizing agronomic management practices for preventing or mitigating cropland soil acidification, and also provide a regional observation-dependent evidence for the changing acid-buffering process during the soil acidification process. |
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