Differential impacts of organic and chemical fertilization on soil organic carbon pools and stability, and soil quality in cacao agroforestry

Fertilization impacts soil organic carbon (SOC) and its stability, key factors for soil quality and climate change mitigation. This study assessed the long-term effects of chemical (CON) and organic (ORG) fertilizations on oxidizable SOC pools, SOC stability, and soil quality in cacao soils. Soils were sampled from 20 farms under ORG and CON at 0–15 ​cm and 15–30 ​cm depths, with an uncultivated field as a reference. SOC pools and their derived indices were analyzed, with soil quality being evaluated using a minimum dataset and principal component analysis. The SOC stock was significantly higher in ORG (60.2–69.8 ​Mg ​C ha⁻¹) than in CON (42.8–49.6 ​Mg ​C ha⁻¹). The SOC stock in ORG was largely in the active pool (54–68 ​%), while it was predominantly in the passive pool (73–74 ​%) in CON. The SOC stock and active SOC pool decreased with soil depth while the passive pool increased with soil depth. Unlike the recalcitrant index, the lability index was high in ORG (1.41–1.82) and low in CON (1.01–1.10). Consistent with the carbon management index, the soil quality index, based on SOC, microbial biomass C, pH, dehydrogenase activity, and bulk density, was higher in ORG (0.753–0.821) than that in CON (0.169–0.235), reflecting soil degradation in CON. Our study revealed that, while CON reduced SOC stock, it improved SOC stability, highlighting a trade-off between SOC quantity and resistance to decomposition. In contrast, ORG enhanced active SOC build-up and soil quality but was less effective in promoting long-term carbon sequestration. These findings highlight fertilization practices that enhance SOC lability and soil quality or improve SOC stability, providing appropriate strategies for the sustainable management of cacao agroecosystems.