In the Brazilian savannah (Cerrados area), about 60 % of the surface area is used as pasture land and 30 % of the latter is cultivated pasture. Many studies have reported that pastures degrade quickly and degradation would be more intense when the soil was tilled prior pasture sowing. Pasture degradation (decrease in the pasture quality and yield, weed invasion) would be partly a consequence of the soil structure evolution (Balbino & Di Stefano, 1999). Origin of pasture degradation is still under discussion and analysis of the literature showed that there is a lack of quantitative data. The aim of this study is to perform a detailed analysis of the porosity in a low productivity cultivated pasture and to compare the results with the porosity of a similar soil still under native vegetation (Cerradão, i.e. Scierophylous forest).
