Mineral Nutrition of Cocoa : A Review
Vliet, J.A. van; Giller, K.E.
Cocoa is an important global commodity. It is mostly grown on small farms by millions of cocoa farmers who depend on the crop for their livelihood. Although potential yields exceed 6000. kg/ha, average farm yields are often around 400. kg/ha. Among the production constraints met by farmers is nutrient limitation. In this review, we compile current knowledge on nutrient cycling in cocoa production systems, nutrient requirements of cocoa, and yield response to fertilizer application in relation to factors such as management, climatic, and soil conditions. Large amounts of nutrients are cycled within cocoa systems, mostly through 5-10. t/ha/yr litter fall. Still, harvesting and small nutrient losses such as leaching lead to nutrient exports causing gradual soil nutrient depletion. Exact nutrient requirements of cocoa are unknown. Leaf and soil test interpretation to identify additional nutrient needs remain ambiguous. Recommended nutrient application rates vary more than 10-fold. In several trials fertilizer application more than doubled cocoa productivity; in other cases response is minimal. Differences in response between regions, fields and even trees have yet to be explained. Interactions with agroecology and management (especially shade) are poorly understood. Without this fundamental knowledge, farm level recommendations have a weak scientific base. Different types of research are recommended to complement current knowledge. Existing data and trials can be exploited through additional analysis and more detailed measurements. Cocoa farms are highly diverse and on-farm trials offer opportunities for understanding variability in production and fertilizer response. Finally, multifactorial shade-fertilizer response trials will be essential to address some of the fundamental knowledge gaps.