Influence of cocoa farm age and slope, and shade rate on cocoa soils fertility

Under a positive, nature-first cocoa farming development scenario, this study aimed to highlight the multifactorial influence of cocoa tree age, shade rate, and farm slope on soil fertility in cocoa agroforestry systems of the forest-savanna transition zone and tropical rainforest in Cameroon. Using a factorial design, 108 plots were selected, with 54 in each agroecosystem zone. Thirty soil samples were randomly collected from each plot (experimental unit) at depths of 0 to 30 cm to create composite samples. Nutrient availability was significantly impacted by the age-slope-shade interaction (P), age-slope interaction (Mg, CEC), age (C/N, P, Zn, Cu, Mn, and TP), slope (TN, Mg, Fe, CEC, and ECEC), and shade rate (Om, TN). In the forest-savanna transition zone, soils with high fertility were found under cocoa trees aged 10 to 30 years with high shade, while the lowest fertility levels were observed in soils under cocoa trees over 30 years old with low shade. In the dense tropical forest zone, most soils had very low fertility, including soils under cocoa trees over 30 years old on slopes of <5° or 5 to 15° with low shade. Soils with average fertility were identified in cocoa plantations with trees aged 10 to 30 years on slopes over 15° with high shade. Precision nutrient management in cocoa agroforestry systems is crucial and should consider farm age, slope, and shade rate, rather than following fertilization models typically recommended for annual crops.