BEHAVIOR OF BRACATINGA (Mimosa scabrella) AND SESBANIA (Sesbania sesban) IN DEGRADED AREAS BY DISPOSAL RESIDUE FROM BAUXITE PROCESSING

Abstract

Topsoil return in mining activities is a common and extensively used procedure. But, for some companies this operation may represent around 70-80% of all costs to reclaim degraded areas. This study evaluated the contribution of two leguminous species to improve the initial colonization of a damaged land by bauxite residue disposal after processing in Poços de Caldas-MG. Plants of Mimosa scabrella ("bracatinga") e Sesbania sesban ("sesban") were planted in January of 1999. Plants were spaced in 2 x 1,5 m and each plot received 25 plants. The statistical alignment was of randomized blocks in the factorial proportion (3 x 4 x 2), with three of the gypsum dosage, four for the thickness layer of superficial soil laid over the residue and two species. Four repetitions were done, with five plants each. Measurements of total height were made and mortality rates were calculated. The results showed that the residue presented similar properties to a sodium-salt soil, with high pH value and electric conductivity. It was also observed that the gypsum doses, the layer thickness, and the species has significant influences in the average values registered for the variables studied. An inversely proportional relation was observed between the mortality rate and the variable gypsum dosage and layer thickness of the utilized soil, in which the increase of gypsum dosage and layer width corresponded to decreased mortality rate for the species. For all the variables studied, "sesban" showed better performance than "bracatinga".