Chibui bari is an edaphic oligochaeta from the Amazon region, called "minhocuçu" in view of its large size (length up to 60 cm). Their castings, in tower-shaped mounds with a height of up to 30 cm and dry weight of 2 kg, are common on the soil surface of Acre State. The objective of this study was to compare nutrient availability, organic carbon concentration and microbial activity in Chibui bari castings with soil of the surroundings under secondary forest, rubber cultivation and pasture, in areas of the Federal University of Acre - UFAC in Rio Branco, Acre. The experiment was arranged in a randomized block design, with three treatments consisting of a) Chibui bari castings and soil samples from within a radius of 10 cm from each casting from depths of b) 0-10 cm and c) 10-20 cm. The results were submitted to analysis of variance and treatment means compared by the Tukey test at 5 % probability. In addition, the simple correlation between the variables was analyzed. The pH values, available P, exchangeable cations (Ca2+, Mg2+, K+), organic carbon and microbial activity were higher in the castings than in the surrounding soil, whereas the Al3+ concentration was lower in castings in the 0-20 cm layer by 55 % (pasture), 62 % (rubber cultivation) and 70 % (forest). There was also a positive correlation of soil organic carbon values with pH, P, K+, Ca2+ and Mg2+ and negative correlations of Al3+ with soil organic carbon, pH, K+, Ca2+ and Mg2+ in the three areas.
Minhocuçu; earthworm castings; soil fertility
