[en] Land-use change, particularly the conversion of forests to agriculture, is a major factor contributing to soil degradation in tropical regions. This study aims to investigate the long-term effects of converting natural forests to cocoa agroforestry systems on soil organic carbon (SOC) and nutrient pools in the Oxisol of South Cameroon, addressing the issue of soil degradation due to agricultural land-use change. Using a chronosequence approach, we compared soils from natural forest with those from cocoa plantations that were 7, 41, and 52 years old. Soil samples were collected from three depths: 0–10 cm, 10–20 cm, and 20–30 cm, and were analyzed for SOC, total nitrogen (TN), available phosphorus (AP), and exchangeable bases (K⁺, Ca²⁺, Mg²⁺, Na⁺), alongside their respective stocks. The results indicated a significant decrease in SOC concentrations and stocks following the conversion from forest to cocoa cultivation, with a total loss of 18% in the 0–30 cm depth profile after 52 years. Conversely, TN and AP stocks showed increases of 44% and 11%, respectively, predominately in the deeper soil layers over the same time frame. Exchangeable potassium (K⁺) levels rose with the age of the plantations, while calcium (Ca²⁺) and magnesium (Mg²⁺) initially peaked but then experienced a notable decline. We found strong positive correlations between SOC and TN, as well as among the exchangeable cations. The finding suggest that converting forests to cocoa agroforestry without sustainable practices can lead to substantial long-term reductions in SOC and base cation availability, ultimately compromising soil health. To mitigate soil carbon and nutrient depletion, we highlight the importance of conserving existing forests and advocate for enhanced agroforestry practices with organic amendments in established cocoa systems, thereby promoting sustainable agricultural production in these highly weathered soils.
This study was partially supported by the Modernization Grant 2023\u20132024 for University Research in Cameroon and the key project of Natural Science Foundation (2022AAC02050) of Ning Xia province.
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