Soil quality and reforestation of the Brazil nut tree (Bertholletia excelsa Bonpl.) after laterite-type bauxite mining in the Brazilian Amazon forest

Abstract

The reforestation of the Amazon forest after mining requires the introduction of native species, such as the Brazil nut tree. However, there are incipient studies with the Brazil nut tree under these conditions. The aim of this study was to diagnose soil properties that determine the adequate growth of Brazil nut trees in bauxite mining restoration areas in the Amazon forest. Three Brazil nut tree sites in bauxite mining reforestation areas in Porto Trombetas–Oriximiná (Pará, Brazilian Amazon) were selected, two with high plant mortality and one with low plant mortality. During the mining process, the Fe–laterites layer that naturally occurs at approximately 4 m depth is broken, and the fragments are mixed into the overlying horizons of the original soil. This sterile material was scattered to reconstruct the soil profile after bauxite mining. Soil sampling was carried out for chemical (up to 50 cm depth) and physical analysis (up to 100 cm depth). The height and diameter of the trees, Fe–laterite mass on the soil surface, Fe–laterite occurrence along the soil profile and soil density were determined. The soil fertility was not the cause for the differences in tree growth among the sites. The primary cause of low Brazil nut tree growth was the physical degradation of soil. The Fe–laterites increase soil density and impairs root growth, favoring low growth and high mortality of plants. In the better-quality site, the Fe–laterite fragments were placed farther from the soil surface (∼27 cm). The negative effect of Fe–laterites in reforested areas after bauxite mining is not only a problem in Brazil, since approximately 88% of the world’s bauxite reserves are the laterite-type (Meyer, 2004).