Abstract

To estimate the sensitivity of soils to naturally and anthropogenic induced acidification we measured Acid Neutralizing Capacities (ANC) of typical soils in West Germany. Measured values of ANC are strongly dependent on the procedure employed. We conducted three kinds of experiments to distinguish between 1. Short-Term Acid Neutralizing Capacity (STANC) due to exchange processes and dissolution of easily weatherable non-silicate minerals, on the scale of days to years, 2. Medium-Term Acid Neutralizing Capacity (MTANC) due to dissolution of easily weatherable silicate minerals, on the scale of decades and 3. Long-Term Acid Neutralizing Capacity (LTANC) considering the buffer capacity of stable minerals, on the scale of centuries. The experiments have been applied on soil profiles at forest and agricultural sites with soil parent material ranging from Holocene sediments, Pleistocene loess, and Devonian sedimentary rock (greywacke/shale). Calculated acid neutralizing capacities ranged from 12.9meq kg^-1 to 747meq kg^-1 (STANC) depending on target pH, 580meq kg^-1 to 3680meq kg^-1 (MTANC) and 2841meq kg^-1 to 12233meq kg^-1 (LTANC). Only 11% to 19% of the MT- and LTANC can be explained by a release of basic cations (Ca, Mg, K, Na) and Mn. Thus, the remaining buffer capacity is associated with Al and Fe. These elements do not buffer protons until pH <4.8 (Al) and <3 (Fe), respectively. Because of the beginning Al-toxicity below pH 4.8 only the basic cation fraction of MTANC and LTANC should be taken into consideration when assessing soils in terms of acidification endangerment.

Keywords: Soil acidification; Soil degradation; Acid neutralizing capacity; Resilience; Buffer capacity