Soil: acidification horizons

Because natural weathering of minerals in the upper soil horizons is not sufficient to neutralize that amount of acid, a gradual acidification takes place so that even calcareous soils can be affected, especially at the stem base of beech and red oak, both possessing high stem flow rates. In silicate soils, clay minerals can be destroyed, releasing AP " and Fe, by replacing... 

With respect to the survival of Erica arborea, acidification of a soil mass (Bw, 2Bwl and 2Bw2 horizons) containing clay from about 25 to 50% and silt from about 35 to 60%, to a pHj Q of around 3.8, appeared to have required more than the 20 0 years of age that the plants actually showed. Consequently, we hypothesized that the Erica plants became established in this soil many years ago (probably centuries), and that they had passed through periods of abundance and of decline, during which, even at different intensities, they had continuously acidified the soil. 

In the case of Erica arborea, which is an acidophilic species, the colonization of an alkaline soil derived from marine sediments had been so efficient that it had converted to acid conditions a mass of soil to about 60 cm in depth. As indicated by the absence of differences between the two soil compartments of this soil thickness, the process of acidification was able to transform all the bulk soil into rhizosphere soil. Indeed, Erica roots are now colonizing the horizon underneath, where dissolution of carbonates has already been accomplished, but where the bulk is still less acidic than the rhizosphere soil. At greater depths, carbonates persist and roots of Erica are rare. 

Andersen, S., Christophersen, N., Mulder, J., Seip, H.M. and R.D.Vogt (1990). Aluminium solubility in the various soil horizons in an acidified catchment. Surface Water Acidification Programme, Final Report, (J.Mason, ed.) The Royal Society, London, (in press). 

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