Fracionamento de fósforo em pastagem solteira e consorciada adubada com fontes de fósforo

Abstract

Phosphorus is an indispensable nutrient for the entire plant cycle, being part of photosynthesis, respiration and, especially, of root formation. However, it is sometimes unavailable for plant absorption. The objective of this work was to evaluate the reactivity and availability of soil phosphorus forms, in the short and medium term, in a pasture of mombaça grass (Panicum maximum Jacq.) In a consortium with legumes. The experiment was conducted at the Experimental Farm of Universidade do Oeste Paulista - UNOESTE, in Presidente Bernardes-SP. In the experimental design, randomized blocks were used, in a 4x3 factorial scheme in subdivided plot, with four replications. The plots are: mombaça (Panicum maximum cv. Mombaça) single with absence of nitrogen fertilization coverage; single mombaça with nitrogen fertilization coverage (150 kg ha-1 of N per year); mombaça consorciado with Macrotyloma axillare cv .; Java and mombaça consorciado with dwarf pigeon peas (Cajanus cajan). The subplots are composed of absence of P, application of P with soluble source (triple superphosphate) and application of P with natural reactive source (Bayóvar). The soil was sampled annually at depths of 0 - 10 cm and 10 - 20 cm for the fractionation of P, which consists of the sequential determination according to the method proposed by HEDLEY. After the analysis of the fractionation there was interaction of the Forage Systems and the sources of P with the contents of the extractors Pi Hid 0,1, Pi HCl and Pi Hid 0,5. For Pi Hid 0.1 and Pi HCl, because they are moderately labile extractors, it is important to keep them at a high level in the soil, and they can act as P repositories. The presence or not of a P source is directly linked the presence of N, due to its interaction within the soil, demonstrating a movement of the P within its utilization and its redistribution. As for Pi Hid 0.5 because it is a non-labile extractor, its reduction in a deeper layer of soil in the first year suggests that P may have been transformed into more labile forms. It is evidenced that in sandy soils the use of sources of P together with its consortium with forage legume or nitrogen fertilization generate a redistribution of P less labile to more labile in the soil profile.