SULPHUR AVAILABILITY IN BRAZILIAN SOILS: EVALUATION OF NITROGEN AND SULPHUR MINERALIZATION POTENTIAL BY OPEN INCUBATION

Abstract

Two open incubation experiments in laboratory conditions were carried out, using columns containing 50 g of soils, from the States of São Paulo, Minas Gerais and Goiás (Brazil). The clay contents varied from 8.0 to 60.0%, total sulphur (S) from 0.0104 to 0.0319% and carbon from 0.50 to 3.03%. In the first experiment the leachate was used for the determination of mineral nitrogen (ammonium + nitrate) and mineral sulphur (sulphate). In the second incubation trial carrier free H235S04 (0.62 microCi.g-1 soil) was applied at “zero” time of incubation. The mineralization potentials of native N and S were estimated by using hyperbolic equations. Sandy soils low in C possess small mineralization potentials, being unaffected by liming. The reverse is true in the case of clayey soils with higher C content. The half life of both N and S was modified by liming. There was not, however, a proportionality factor between the mineralization rates of the elements. The mineralization of native N and S, as well the specific activity of the added 35S tended to level off in the 8th week of incubation, no effect of liming being evident.