Rapid assessment of soil health in cocoa landscapes around Téné Forest Reserve, Middle-West Côte d'Ivoire

The study was conducted within and around the Classified Forest of Téné in the middle-west region of Côte d'Ivoire, with the aim of providing guidance for interventions that focus on developing resilient cocoa-forest landscapes. Two specific landscapes, Mafia and Petit Bouaké, were selected for analysis. These landscapes are located in settlements where cocoa growers reside, close to Goulikao in the Oumé district. The selected landscapes shared similar land-use patterns, including secondary forests, 26-year-old cocoa plantations, 13-year-old teak plantations, and recurrent fallow-maize fields of 5-year-old. To assess soil health, several key metrics were measured at three different soil depths: 0-10 cm, 10-20 cm, and 20-30 cm. The metrics included soil organic carbon (SOC), pH-H20, and Mean Weight Diameter (MWD). The following key findings were observed: (i) most sampling plots exhibited SOC concentrations below the sustainable threshold of 20 kg ha-1 required for cocoa farming when the soil pH values fell within the suitable range of 5.5-7.5 ; (ii) SOC concentrations and stocks can serve as indicators of soil health deterioration in the top 10 cm of soil within cocoa landscapes, due to their sensitivity to land-use changes and MWD can be used as an indicator in the depth increments of 10-20 cm and 20-30 cm ; (iii) apart from maize fields, which are recognized as the most degraded system within the landscape, soil health can be restored over a decade or more beneath teak and cocoa plantations ; (iv) teak plantations demonstrated a potential soil organic storage rate of +0.476 Mg C ha-1 yr-1 in the top 30 cm, supporting the validity of the 4 per 1,000 theory. Therefore, teak plantations can be recommended as a land-use option to combat global warming. In cocoa orchards, the carbon storage capacity varied from +0.16 to +0.54 Mg C ha-1 yr-1, with an overall carbon storage rate of +0.094 Mg C ha-1 yr-1 in the top 30 cm of soil. This finding highlights the potential of cocoa agroforestry to enhance SOC storage and suggests its use as a viable option for mitigating CO2 emissions, as advocated by the Paris Agreement (COP 21). Implementing good agricultural practices that focus on improved soil health, in conjunction with cocoa agroforestry that integrates farmer-preferred trees, should form the foundation of a new cocoa cropping model in the areas surrounding forest reserves.

Keywords: Carbon sequestration, 4 per 1000 initiative, soil degradation, resilience, tree-based systems