Biological activity of soils under systems of organic farming, agroforestry and pasture in the Amazon

The aim of this work was to evaluate biological indicators of soils used under the systems of organic farming, agroforestry and pasture in the south western part of the Amazon region of Brazil. The experiment was carried out at the Seridó Ecological Site, located in Rio Branco, in the state of Acre, Brazil. The experimental design was completely randomised, with five treatments (land-use systems) and six replications, with each replication consisting of four single samples. The systems of land use evaluated were: 1) native forest (control); 2) agroforestry (AFS); 3) pasture; 4) intercropped passion fruit, maize, cassava, pineapple and forage peanut; and 5) intercropped passion fruit, maize, cassava, pineapple and tropical kudzu. It was found that organic farming systems intercropped with kudzu resulted in smaller losses of C-CO2 through edaphic respiration, and a greater accumulation of microbial biomass carbon. The intercropped organic farming system which included the forage peanut resulted in a greater loss than retention of carbon in the soil at a depth of 5-10 cm. Soil under the agroforestry system was equivalent to the soil of the control (native forest) in relation to the release and retention of carbon through biological activity. At a depth of 5-10 cm, soils under pasture presented similar microbial biomass to those under organic cultivation intercropped with tropical kudzu. However, at that depth, soils under pasture presented greater microbial biomass than those under natural forest, agroforestry or organic cultivation intercropped with forage peanut.