Acid-neutralizing capacity of Finnish mineral soils

The acid-neutralizing capacity (ANC) was determined graphically from curves obtained in HCI titration (at a constant ionic strength I = 0.1) and was expressed as a quantity of acid (meq kg-1) needed to reduce the soil pH to 3.8. The relationship between ANC3.8 g and soil characteristics was studied statistically. In 84 soil samples, ANC3.8 ranged from 12 to 184 meq kg-1. The average ANC3.8 was highest in the heavy clay soils and lowest in the non-clay soils, but the differences between the various textural soil groups were not significant. In all soil groups the initial pHCaCl2 was relatively the most important factor explaining the variation in ANC3.8. Organic C was also a significant variable; this was considered to indicate the importance of cation exchange reactions of organic matter in acid-buffering. With the exception of heavy clay soils, oxalate-soluble Al significantly explained the variation in ANC3.8, suggesting that dissolution of Al hydroxides acted as a sink for H+ ions and contributed to the neutralizing capacity at the reference pH of 3.8