Soil Management in Indigenous Agroforestry Systems of Guarana ( Paullinia cupana Kunth) of the Sateré-Mawé Ethnic Group, in the Lower Amazon River Region

The Sateré-Mawé Brazilian indigenous people cultivate the guarana liana in biodiverse agroforests that incorporate many species, mainly trees, and produce food, medicines, fuel and income. The objective of this study was to evaluate the soil fertility in nineteen indigenous guarana agroforestry systems (AFSs) compared with areas of adjacent forests in the Andirá–Marau Indigenous Land—an ancestral territory of the Sateré-Mawé people. Soils in both locations showed low natural fertility, with levels of most macronutrients below the minimum agronomic reference levels. Higher C and soil organic matter (SOM) content was observed in the forest soils and may be related to greater vegetation cover and higher litter production. However, the maintenance of the average levels of most nutrients in the soil of the AFSs, at the same level as under the forests, suggests that efficient nutrient cycling is taking place. In these conditions, the management of organic matter seems to be essential to maintain the productivity of guarana AFSs since levels of C, SOM and organic N were not considered as low as those of most of the other soil attributes that were evaluated. The high tree diversity in the guarana agroforests, including N-fixing species, may also contribute to efficient nutrient cycling and maintenance of the soil food web. The results suggest that the addition of limestone, green manure practices and the reincorporation of organic residues from guarana processing, among other sources, can be a low-cost alternative to improve soil fertility and increase guarana production in the AFS under study.