Tropical soils play an important role in the carbon (C) cycle of the earth. Human clearing of tropical forests for agriculture has the potential to alter soil C storage. These changes may make soils significant sources of C to the atmosphere (Houghton et al., 1983; Detwiler and Hall, 1988). They are also important indicators of soil fertility and agricultural sustainability (Tiessen et al., 1994). In recent decades, tropical forests have replaced temperate forests and grasslands as the region on Earth experiencing the most rapid land cover conversion. The Brazilian Amazon Basin—the world’s largest region of intact tropical forest—is being deforested at the rate of approximately 11,000 to 29,000 km y−1 (INPE, 1998; Skole and Tucker, 1993). Cattle pastures now represent the largest single use of deforested lands Basin-wide, and more than half of deforested land is used for cattle pasture at some time (Fearnside, 1987; Serrão, 1992). In some regions, such as central Rondônia or eastern Pará, that figure may be even higher.