Influência do tratamento térmico sobre o alumínio livre do solo

Abstract

The purpose of the present work was to study the efect of heat treatments on three different oxisols and to follow the changes in free Al by chenical determinations and pot experiments with plants. Soil samples were treated in laboratory conditions for one hour at temperatures from room temperature up to 300ºC. Changes in the soil chemical properties and mineralogical composition were followed in the heat treatcd samples in order to detect any modifications in the following properties: pH taken in H KCl suspensions, organic carbon content, Fe and Al extracted with KCl and XH4 Ac pH 4.8. A compelemtary experiment was carried in order to defect any effcct of the treatment at 400ºC for 15 minutes, on dry matter production of sorgo plants grown76 on one of the oxisols. One hour heat treatment on these soils at temperatures below 100ºC caused little to no change in the above listed soil properties, where as deep changes occured when the soil was heated above 100ºC. Carbon content decreased slightly at 200°C and dropped to half its value at 300ºC. Fe(III) was sensibly reduced to Fe(II) at the expenses of carbon oxidation. This reduction caused an increase in Fe extraction in NH 4 AC reaching a maximum at 200ºC. At higher temperatures a fast dropin extratable Fe was observed with a tendency to reach zero. This observations seen to indicate that in the process of burning the vegetation cover of tropical soils, fhe heat itself can cause a benefic effect decrasing Al toxity. This effect is enhanced by the neutralixing action of the ash produced.