From 1920 on, Ferralsols of the Planalto Médio region in the State of Rio Grande do Sul, Brazil, originally under forest vegetation, were converted into agricultural land, while the same soils under grassland were converted in the 1960-ies. Thereafter, chemical soil properties were affected by intense cropping, mainly of soybean and corn. To evaluate how the time of agricultural land use affected two Ferralsols in the Fortaleza dos Valos county, State of Rio Grande do Sul, pedon samples of a clay textured dystrophic Red Latosol and a medium textured dystrophic Red Latosol were collected under forest and grassland vegetation, respectively, on the top of the landscape and from soils under agricultural cultivation for eight to over 33 years. Concentrations of clay and organic matter; available and total P and K; exchangeable Ca, Mg and Al; and pH were determined. Base (V%) and aluminium (m%) saturation were calculated. Where the soil had been forested the organic matter content decreased after longer periods of agricultural use. On the other hand, the organic matter content increased as the time of agricultural use increased where the soil vegetation had been native grass. Ca + Mg contents increased while Al content and saturation decreased with the time of agricultural use. Originally Al-saturated soils under native vegetation gradually turned into soils with less than 50% of base saturation through the agricultural use. The total soil P increased notably in the surface horizons, while the total soil K also increased in deeper layers.
soil use; organic matter; nutrients
