The Cerrado covers approximately 2 million km2, mostly in central Brazil. It consists of a gradient from grasslands (locally called campo limpo) to sclerophylous forests (cerradão) (Eiten, 1972). Between these, there are intermediate physiognomies with increasing density of woody species (campo sujo, campo cerrado, and cerrado stricto sensu). The annual precipitation varies from 600 to 2200 mm and the dry season lasts from 4 to 7 months, whereas the mean annual temperature ranges from 22°C to 27°C (Adámoli et al., 1986). Oxisols and Entisols represent approximately 46% and 15% of the Cerrado soils, respectively (Reatto et al., 1998). In general, soils are acidic, with low nutrient concentrations and high aluminum content. Under such conditions, soil organic matter (SOM) is particularly important to processes related to nutrient cycling, soil aggregation, and plant available water (Resck, 1998). Gallery forests (closed canopy with 75-95% cover) occupy about only 5% of the Cerrado but contain approximately 32% of its biodiversity (Felfili et al., 2001). They are associated with a great variety of soils, ranging from dystrophic to mesotrophic and seasonal flooded hydromorphic soils with different levels of organic matter (Reatto et al., 1998).