POROSITY CHARACTERIZATION IN 2 SPANISH SOIL PROFILES WITH HYDROMORPHIC FEATURES

Porosity and pore-size distribution were determined in the horizons of two soils located in Galicia (NW Spain), where problems attributed to a low water permeability were found. Determinations were carried out by means of mercury intrusion porosimetry and pores in the range 100-0 .007 mum were analyzed. In the more developed Castro soil, total poros ity was higher in the A horizon than in the other two. In the Croa soi l, less developed and much richer in clay, the porosity of the A horiz on was lower than that found in the ACg one. Irrespective of the patte rn of total porosity, A horizons of both soils had pores larger in siz e than those present in the deeper ones. This trend was particularly e vident for the Castro soil where the porosity given by smaller pores i ncreased progressively with depth. We have shown that laboratory measu rements carried out on small soil aggregates can reveal differences of total porosity and pore size distribution in soil profiles.