The objective of this experiment was to study the effects of soil management systems on the bulk density, chemical soil properties, and on the soil microbial activity on a Latossolo Vermelho distrófico (Oxisol). Soil samples were collected from plots under the following management conditions: a) natural dense "cerrado" vegetation (savanna); b) degraded Brachiaria decumbens pasture, 20 years old; c) no-tillage treatment with annual crop sequence (bean, corn, soybean and dark-oat in continuous rotation), 8 years old; d) conventional tillage treatment with crop residues added to the soil, and annual crop sequence, 10 years old. The continuous use of no-tillage system resulted in an increase in microbial biomass and decrease in soil basal respiration, therefore displaying evident long-term effects on the increase of soil C content. The no-tillage system also provided an improvement in bulk density and chemical properties of the soil. Hence, the no-tillage management system could be an alternative for the conservation and maintenance of physical and chemical conditions and the productive potential of "cerrado" soils.

The influence of reforestation was evaluated during two season periods (February and October) in sites planted with Corymbia citriodora and Leucaena leucocephala through microorganism counts (bacteria, fungi, actinomycetes, and nitrite oxidizers) and microbial activity (respiratory and urease activities). An Atlantic forest and a bare soil site were used as controls. The general trends of the variables in the different soils were: Atlantic forest or L. leucocephala > C. citriodora > bare soil. The microbial populations in L. leucocephala and C. citriodora soils were significantly higher (P < 0.05) than that found in the bare soil. Similar results were obtained for respiratory and urease activities. The microbiological variables of the soil under L. leucocephala were comparable or even superior to that found under Atlantic forest. An improvement in the microbiological soil variables was observed in the soil under C. citriodora when compared to the soil without vegetation. These results can be attributed to an increasing amount of total organic C of the soils under L. leucocephala and C. citriodora in relation to the soil without vegetation.