Chemical quality of a Yellow Latosol under pasture submitted to levels and frequency of fertilization and liming

Abstract

In the period 1996 to 2000, at Embrapa Rondônia, Porto Velho was evaluated the effects of levels and frequency of fertilization and levels of liming on the chemical attributes of a dystrophic Yellow Latosol, clay texture, under pasture of Brachiaria brizantha cv. Marandu in the process of degradation. We adopted the experiment in design of randomized blocks with three replicates, in a factorial arrangement 2 x 2 x 2 x 2 to the levels of liming (aiming at saturation V-20 and 40% - dolomitic lime with 70% PRNT), nitrogen fertilization (50 and 100 kg ha-1 of urea-N), phosphate (50 and 100 kg ha-1 P2O5 - triple superphosphate) and potassium (30 and 60 kg ha-1 of K2O, potassium chloride); and 3 x 2 x 2 x 2 for fertilization frequencies (annual, biennial and triennial), being reapplied the same doses of fertilizers, there was no replacement of lime. In the implementation of the experiment the lime and fertilizers were coverage distributed and incorporated into the soil by light disking, reapplication in the fertilizers were distributed in the same way but not incorporated. After four years, were collected representative samples of soil, at depths of 0 to 15 cm and 15 to 30 cm, which were analyzed chemically. The results obtained for each soil layer were subjected to analysis of variance and means were compared by Tukey test. Independent levels of fertilizer, when liming from 20 to 40% of V, decreased potential acidity, active acidity and Al+3, neutralizes its toxicity; happening the inverse in the pH in H2O, the sum of exchangeable bases and V, mainly in the depth 0-15 cm soil. In both depths, P fertilization had a direct effect on the levels of total P in soil; while the application of K2O did not alter the availability of this nutrient, nor the additional N was able to increase the content of soil organic matter. Only the total P was influenced by the frequency of fertilization, lower concentrations were obtained with the three year reapplication, and higher in the biennial. The application of lime in order to increase the 40% V, increases the pH in H2O, the exchangeable bases and V, reduces the ion Al+3 and neutralizes its toxicity; most notably in the topsoil (0-15 cm). The minimum levels of fertilization in kg ha-1 should be: 100, 50 and 60 of N, P2O5 and K2O, respectively. Lime and fertilizer can be distributed to haul without soil incorporation, when you want to fix and fertilize the top layer of grass (0-15 cm depth).