Adubação fosfatada e frações inorgânicas de fósforo em um latossolo do Trópico Úmido

Abstract

Agricultural production in tropical soils depends on the supply of doses of phosphate fertilizers, but the efficiency of fertilization is associated with the choice of source and mode of application. We investigated whether different proportions and modes of application of the mixture of FNR (Arad Reactive Natural Fostatto) with SFT (Super Triple Phosphate) influence the inorganic fractions and the availability of P in a Dystrophic Yellow Latosol, cultivated with Pera-Rio orange for three years. A factorial 5 x 2, distributed in randomized blocks was used, combining five proportions (00-100; 25-75; 50-50; 75-25 and 100-00%) of the mixture of FNR with SFT at the dose of 150 kg ha-1 of P2O5, and two modes of application (total application of the dose in the first year and split dose application, with 50 kg of P2O5 ha-1 year-1 for three years). Soil samples were taken after 12, 24 and 36 months after application of the treatments, in layers 0-10 and 10-20 cm deep. There was a significant effect (P < 0.05) of the interaction mode of application x proportions of the mixtures of the sources on the inorganic fractions of P, at both depths and in all years, and isolated effect of these factors on the availability of P-resin in the first year after application of the treatments. The results indicate that the use of the total application combined with proportions with higher amounts of FTS for the first year, or split application combined with higher amounts of FNR for the second and third year, provided greater terrors both of P-resin and, in part, of the P- Al, P-Fe and P-Ca fractions. Thus, the residual effect of the natural source helped to keep the stock in the soil in the long term. We also identified that the largest fractions in these soils are in the following order of concentration: P-Fe > P-Ca > P-Al.