Soil Carbon Sequestration in Cacao Agroforestry Systems: A Case Study from Bahia, Brazil

Abstract

Agroforestry systems (AFS) based on cacao (Theobroma cacao L.) may play an important role in capturing carbon (C) aboveground and storing it belowground (soil) through continuous deposition of plant residues. Cacao AFS in Bahia, Brazil, are comprised of cacao planted either with woody species such as Erythrina spp. and Gliricidia spp. or under tree canopies in natural forest, the latter being known as "cabruca". The large amounts of leaf litter, roots, and woody material from shade species as well as cacao represent a substantial addition of C into these systems, most of which, following decomposition, is stored in the soil. The total C storage in the weathered Oxisols under cacao AFS in Bahia is estimated as 302 Mg ha(-1) to 1 m depth. Occlusion of C in soil aggregates could be a major mechanism of C protection in these soils. Therefore it is important to know the amount of soil C storage across different soil aggregate classes at different soil depths and identify the extent of the sequestered C that is occluded in the soil aggregates. Furthermore, the deep-rooted nature of cacao and shade trees makes it imperative to look below the surface soil, where most conventional soil studies are focused. Carbon sequestration potential of cacao and other shaded-perennial-crop-based AFS could be a source of income for the farmers of these crops, the majority of whom are smallholders. Understanding the mechanisms of soil C sequestration could lead to proper realization of this potential through better management options.