A recent study by Chinese and Australian soil scientists elucidated different drivers of soil acidification along a 3,600-kilometer north-south transect through northern China. There were two general types of soil in this transect: 1,900 kilometers of carbonate-containing soils and 1,700 kilometers of non-carbonate-containing soils.
Soil acidification as a phenomenon occurs when acid, often represented as hydrogen ions, is deposited onto soil that has some inherent capacity to buffer the change in pH. This study examined how various soil parameters are correlated with its pH buffering capacity.
In carbonate-containing soils, carbonate content was found to be positively associated with, and the main determinant of, soil pH buffering capacity, while in non-carbonate-containing soils, this was true of the soil’s cation exchange capacity.
In the carbonate-containing soils, the carbonate (a base) neutralizes the acid, buffering the change in pH. In soils without carbonate present to neutralize the acid, the soil particle must exchange a cation for one or more hydrogen ions. This removes the hydrogen ions from solution, thereby decreasing the acidity of the soil, and effectively buffering the change in pH.