Oxidação do enxofre elementar em solos tropicais

Abstract

The use of fertilizers with low content of sulfur (S), in low organic matter content soil, may result in sulfur limitation to crops. The use of elemental-S as a fertilizer, isolated or associated to commercial formula, may reduce the costs of fertilization in sulfur deficient soils. The objectives of this study were: a) to verify if two tropical soils have capacity to oxidize elemental-S; b) to evaluate if the period of incubation suggested by Janzen & Bettany (1987a) is adequate to estimate the elemental-S oxidation and c) to measure the effect on soil pH of the added elemental-S. For this, a trial was carried out with soil samples of an Typic Hapludalf and a Typic Haplustox (SOIL SURVEY STAFF, 1999). The samples of both soils were incubated with dosis of sulphur (0, 1,5, 3,0, 6,0, 9,0, and 12mg of S0 kg-1 of soil), for periods between 0 and 70 days. The temperature of incubation was 27°±1°C. Both soils showed capacity of oxidizing the applied elemental S to S-sulfate, available form to plant. In the Ultisol oxidation of elemental-S produced maximum values of 563 of S-sulfate mg dm-3 of soil and in the Oxisol soil 207 of S-sulfate mg dm-3 of soil, demonstrating the differentiated capacity of elemental-S oxidation. In both soils the pH decreased, being the diminution bigger for the Ultisol. The incubation period of six days for the evaluation of the elemental-S oxidation suggested by Janzen & Bettany seems to be insufficient.