Mineralogy, size, morphology and porosity of aggregates and their relationship with soil susceptibility to water erosion

Soil erosion has been considered as the main process related to losses of s oil mass and decrease of productivity in cultivated lands as well as one of the most important processes in landscape evolution. Attention has been pa id to many pedological variables affecting intensity of erosion, but little to the influence of iron compounds on the type, size, shape and porosity o f soil aggregates. In the present study, three lithopedodomains which were assumed to be closely related to the dominant lithology of the soil parent material, varying in the degree of water erosion intensity, were selected f or further analysis which focused mainly on the influence of iron oxide min eralogy on the soil aggregation. Powder X-ray diffractometry, 80 K Mossbaue r data and SEM images are used to correlate all these variables with observ ed erosion activity in the field. The present data indicate that the more t he soil is rich in iron (hematite and/or goethite) or aluminium (gibbsite) (hydr)oxide, the smaller are its aggregates and is porous. Soils derived fr om metabasic rocks are much more susceptible to collapse under wetting than those from other lithologies. They have the highest iron and clay content. Schist-derived soil is richer in muscovite, has bigger aggregates and poro us and are less prone to collapse, while the granite-derived soil presents relatively intermediate resistance, when humid.