BIOMASS AND NUTRIENT ACCUMULATION OF TWO LEGUMINOUS TREES IN AN IMPROVED FALLOW IN AMAZON RAIN FOREST

The fallow vegetation is the main component of sequential agroforestry systems in Amazon rain forest. The progressive removal of soil nutrient by slash/mulch agriculture involves continuing losses in carbon and nutrient stocks, leading to decline in soil productivity, low regeneration ability and decrease of species diversity of fallow vegetation. The fallow vegetation management by introducing fast growing leguminous trees has the potential to accumulate more biomass and nutrients to serve the nutrient demands of crops and its management has been considered as a sustainable technology production. This study aimed to evaluate the effect of low solubility of phosphorus fertilizer in the biomass and nutrient stocks of leguminous trees used in fallow improvement. The experiment was conducted for 23 months in a sequential agroforestry slash-and-mulch system in eastern Amazon forest. The species selected were tachi-branco-Sclerolobium paniculatum Vogel and inga-Inga edulis Mart. Biomass and nutrient stocks and nutrient concentrations of leaf, branch and trunk were estimated. Phosphorus fertilization had a positive effect on calcium concentration in the leaves and stocks of biomass and nutrient contents (phosphorus, calcium and magnesium) in the leaves of legume trees. Inga edulis showed higher levels of potassium, calcium and magnesium concentrations in leaves, while Sclerolobium paniculatuttm showed higher biomass and stocks of nitrogen, phosphorus, potassium, calcium and magnesium in leaf, branch and trunk.