EFFECTS OF CROPPING ON THE STRUCTURAL STABILITY OF SOILS RICH IN ORGANIC-MATTER

The structural stability of 32 cropped soils in the northwest lberian peninsula was compared with that of pasture and woodland soils in the same region using Emerson's test and a rain simulator. The cropped soils were found to be less stable, largely because of the reduction in organic matter content due to cropping. Stability was also favoured by high concentrations of aluminium oxides bound to organic matter, and weakened by high pH. The latter relationship is hard to explain on the basis of the data obtained in this study; it is suspected that structural stability and soil pH are influenced by some third factor linked to farming practices (applied fertilizer levels, use of heavy machinery, etc.).