RESPONSE OF SOME SOILS OF GALICIA (NW SPAIN) TO H2SO4 ACIDIFICATION

This paper presents the results of an acidification experiment, consisting of seven consecutive equilibrations of repesentative soils of Galicia with a H2SO4 solution (pH 3). Different responses to soil acidification, such as SO4 retention and cation release, were evaluated. In soils derived from gabbro and amphibolite, SO4 retention and Al release were the principal acid neutralization mechanisms, whereas in soils derived from granite, schist, shale and sandstone Al release was the main process. The SO4 retention was significantly correlated with Al and Fe extracted with dihionite-citrate-bicarbonate and crystalline Fe. The released base cations came mainly from exchange sites, though sometimes also from other sources, probably by mineral weathering. The major sources of Al in these soils were metal-organic complexes and weatherable minerals. Solutions with pHs close to 4 are in equilibrium with gibbsite, kaolinite, jurbanite and alunite; at lower pH values, with jurbanite and alunite.