SHORT TERM EFFECTS OF ALTERNATIVE PHOSPHATE FERTILIZATION ON THE FERTILITY OF CAMBISSOL UNDER UNBURNED PASTURE.

Brachiaria brizantha is the main species of cultivated pasture in Brazil. However, periodic burnings are triggering its degradation since the 70’s in the Amazon. The lack of information on the short-term effects of alternative phosphate on soil fertility in unburned pastures leads to the demand for research related to this topic. The effects of alternative phosphate on the chemical fertility of Cambisol under unburned pasture were evaluated one year after its fertilization to support recommendations to maintain or increase the biomass productivity of B. brizantha (cv. Marandú) pasture in the southwestern of the Brazilian Amazon. This assessment was performed in November 2016, on a field experiment carried out from September untill November 2015. The treatments were comprised by Pnb = Unburned pasture + 0 kg ha-1 of P, Pnb + 25 kg ha-1 of P, Pnb + 100 kg ha-1 of P, and Pnb + 200 kg ha-1 of P from a partially acidulated phosphate rock compared to the burned pasture. Agronomic dosis of N and K were applied to the plots without pasture burning. Soil samples were collected for the soil chemical fertility analysis one year after the treatments. The treatments with phosphate fertilization maintained the topsoil acidity attributes, saturation of basis, cation exchange capacity, organic carbon and carbon stock in similar pattern to the B. brizantha burned, but it was effective in maintain the pattern of adequate topsoil fertility with 200 kg ha-1 of phosphorus which promoted high phosphorus and sulphur availabilities.