Cocoa based agroforestry systems enhance carbon storage in deep horizons of Amazonian soils

Cocoa-based agroforestry systems have the capacity to increase carbon storage in areas degraded by pasture in the Amazon. Therefore, we evaluated the soil carbon storage capacity down to 150 cm depth in cocoa-based agroforestry systems in a deforested Amazonian landscape of Colombia. Each shade tree species (Abarco Cariniana pyriformis, Capirón Calycophyllum spruceanum, Caracolí Anacardium excelsum, and Huito Genipa americana) were independently combined with cocoa. The performance of these systems was compared with mature forests and degraded pastures taken as references. Soil carbon content was evaluated at five depths (0–30, 30–60, 60–90, 90–120, and 120–150 cm). Carbon fractions were extracted with acid solutions of increasing concentrations and classified accordingly into very labile (VL), labile (L), less labile (LL), and non-labile (NL). The C stock down to 150 cm was maximum in forest (209.6 ± 3.5 Mg C ha⁻¹) and decreased from Caracolí (190.2 ± 6.2 Mg C ha⁻¹) to Abarco (162.9 ± 2.9 Mg C ha⁻¹), Huito (150.5 ± 4.6 Mg C ha⁻¹), Capirón (137.1 ± 4.5 Mg C ha⁻¹), Full-sun cocoa (135.6 ± 3.5 Mg C ha⁻¹), and pasture (110.3 ± 3.9 Mg C ha⁻¹). In the 15-year experimental period, cocoa based agroforestry systems enhanced soil carbon contents to values up to 2.73 times the content in the initial degraded pasture, close to the performance of the forest (× 2.96). Huito and Caracolí shade trees were the most efficient at storing carbon in deep soil layers.