Deriving fertiliser recommendations for cocoa: An offtake model approach

Cocoa production in West Africa has increased over the years, yet yields are stagnant due to factors such as limited fertiliser use, poor maintenance, and inadequate pest control. The existing knowledge on cocoa mineral nutrition is limited, with outdated and inconsistent fertiliser recommendations across countries and regions. This study aimed to develop and describe a cocoa N, P, K offtake model based on nutrient export (pods and beans) and immobilisation in the tree. The model was used to calculate fertiliser rates for a series of 195 on-farm trials in Côte d'Ivoire, Ghana, Nigeria, and Cameroon. We compare the cocoa yields in response to fertiliser rates derived using the offtake model with the response to national recommendations in each country. On each farm, four treatment plots were delineated. The treatments were: T1 = current farmer practice, T2 = weeding + pruning + insecticide application + fungicide application (no fertiliser application), T3 = weeding + pruning + insecticide application + fungicide application + current national fertiliser recommendation, and T4 = weeding + pruning + insecticide application + fungicide application + offtake model-based fertiliser recommendation. Yields were recorded from September 2021 to August 2022 and an economic assessment was conducted using two different scenario prices for the years 2020/2021 and 2022/2023. Our results showed a positive effect of fertiliser on cocoa yield wherein T3 (1109 kg ha⁻¹) and T4 (1227 kg ha⁻¹) had significantly higher yields than T1 (912 kg ha⁻¹) and T2 (917 kg ha⁻¹). A positive overall yield effect of T4 over T3 was also observed; however, the difference was significant only in Côte d'Ivoire. The economic assessment showed that the treatment based on the offtake model (T4) gave a higher gross return than the national recommendations (T3) in all countries. However, the benefits decreased from 20/21–22/23 due to an increase in fertiliser prices. Our findings show that using an offtake model approach could provide a more accurate approximation of cocoa's nutrient needs. Nonetheless, while the cocoa farm-gate price remains low, the investment capacity of the farmers to purchase fertiliser will remain limited.