Labile and stable organic carbon in soils of cacao agroforestry systems compared to forest and pasture in the Colombian Amazon

Abstract The study analyzed labile and stable SOC fractions in different land use systems in the Colombian Amazon. The research included cacao-based Agroforestry Systems (cAFS), full-sun cocoa plantations, forests, and pastures, using a factorial design with land use and soil depth as factors. Land use significantly affected carbon fractions, explaining 51% of variance ( P < 0.01). In the surface layer (0–15 cm), fulvic acids were highest in Huito (7.32 g C kg −1 ) and lowest in Pasture (2.76 g C kg −1 ). For humic acids, full-sun cacao showed the highest values (9.55 g C kg −1 ) followed by Capiron (7.75 g C kg −1 ). Total Humic Extract was maximum in full-sun cacao (27.68 g C kg −1 ) and minimum in Pasture (18.99 g C kg −1 ). The polymerization index was higher in Pasture (1.87) and full-sun cacao (1.46). The degree of humification was highest in full-sun cacao (64.78%), while the humification ratio showed maximum values in full-sun cacao (84.9%) and minimum in Forest (36.86%). These patterns generally persisted at deeper soil layers, demonstrating the potential of cAFS as a sustainable alternative for land use and carbon sequestration.