Physical and chemical properties of selected oxisols in the Brazilian cerrados

Profiles of selected very fine, allitic, isohyperthermic, Anionic Acrustox and coarse-loamy, mixed, isohyperthermic, Typic Haplustox under different management systems were analyzed chemically and physically. On each of the two substrates, a conventional crop rotation, a degraded pasture, and a tree plantation were selected. Native savanna was used as control. Exchange capacity, most exchangeable cations, and phosphorus were strongly related to soil organic carbon while pedogenic Fe and Al oxides were less related. Soil organic matter also controlled the formation of stable microaggregates and the degree of clay dispersion, and must therefore be seen as a key component in these soils. Management affected both the physical and chemical properties of the soils. Liming elevated the pH, increased the number of variable exchange sites, and altered clay flocculation. Such changes may have implications for pore-size distribution. Seedbed preparation resulted in soil compaction and reduced total pore volume. The loss was, however, restricted to macropores whereas mesoporosity even increased. Given the small amount of capillary water available to plants in Oxisols, this change may be seen as positive.