Study of buffering. Systems in soils from Galicia, N.W. Spain

Abstract

The effects of acid rain on surface horizons of five soils from Galicia and the buffer capacity of these soils with respect to the addition of H` were studied. Soil samples were placed in percolating tubes with a diameter of 7.5 cm. The diluted acid treatment, composed of distilled water acidified with HCl to a pH value of 3, was applied to each duplicate soil core at a drip-rate of 2.8 mL min⁻¹, for 8 hr d⁻¹ over 18 days. The acid addition produced an associated leachate of both organic and inorganic anions and cations, although behavior patterns differed: a quick leach of labile forms (probably soluble forms) and a slower leach of more retained forms (most likely to be exchangeable forms and/ or products dissolved from solid phases). The organic C decreased and the N increased as the percolates became more acidic. The neutralizing mechanisms for each of the soils used in the experiment corresponded in general terms to the buffer capacity that was to be expected given the initial chemical characteristics. An exception to this was the soil in the silicate system buffer where, because of its slow rate, the cation exchange buffer system worked preferentially.