The Role of Organic Matter in Soil Acidification

The pH and buffer capacity of two soils increased or remained constant after incubation with different amounts of plant material (lucerne chaff) at field capacity and when air dry. For both soils, the pH changes were greater at field capacity, whereas the buffer capacities were independent of the water treatments. The pH changes observed could be explained in terms of the organic anion concentration of the plant material. The results indicate that the initial soil pH and the anion concentration (i.e. the per cent dissociation of soluble organic acids when released into the soil) determine the acidifying effect of organic matter.