Age-dependent variations in soil carbon stocks and biogeochemical attributes under cocoa agroforests in Bono, Ghana

Abstract

Cocoa agroforestry systems (CAS) are widely advocated for their numerous benefits such as food security, soil productivity, and carbon sequestration. However, the role of CAS of various ages in soil organic carbon (SOC) storage and nutrient processes remains poorly understood, particularly in Ghana. Therefore, this study was conducted to assess the impact of different ages of CAS on soil carbon stocks and soil fertility attributes in the semi-deciduous forest zone of Ghana. Based on availability and similar management practices, cocoa agroforestry systems aged 5, 10, 15, 20, and 25 years were sampled for soil data collection. In each CAS, three 30 m × 30 m quadrats were randomly laid, and soil samples were taken. The SOC content in the 25-year-old CAS was 1.11–1.25 times higher than that of the other CAS. We observed a 16% increase in SOC stocks in the 25-year CAS compared to the 5-year CAS, highlighting the buildup of SOC over time. The 25-year-old CAS exhibited a higher capacity to store microbial biomass carbon (MBC) and nitrogen, mineralizable nitrogen, available phosphorus, and exchangeable cations, as evidenced by the cluster analysis. The principal component analysis revealed a strong influence of twelve soil attributes, including nitrate and ammonium nitrogen, SOC contents and stocks, and MBC, emphasizing their critical role in soil fertility in CAS. The study underscores the importance of CAS as a climate regulator through its role in soil organic carbon storage. Consequently, these results have important implications for sustainable land management and climate change mitigation and adaptation strategies.