How to Boost Cocoa Yield in Ghana? – Quantifying the Cocoa Yield Gap and Identifying its Drivers

ABSTRACT CONTEXT Global cocoa production is largely concentrated in West Africa where over 70% of cocoa is produced. Here, cocoa farming is largely a rain-fed, low-input system with low average yields, which are expected to reduce due to climate change. With increasing demand, there is a need to increase global cocoa production whilst avoiding deforestation and expansion to croplands. Thus, it is important to know how much additional cocoa can be produced on existing farmland, and what factors determine this potential for increased yield.OBJECTIVE The objective was to estimate the cocoa yield gap in Ghana. This was done by calculating water-limited potential yields for cocoa as the upper limit that can be achieved on existing land in a rain-fed system using a crop model and comparing this with farmer-based yields.METHODS We used CASE2, a physiological crop growth and production model for cocoa to simulate water-limited yields in 93 cocoa farm locations in Ghana. Yield gaps were calculated as the difference between simulated water-limited yield and average farmer yields. Both absolute and relative yield gaps were calculated. We then related the absolute and relative yield gap to environmental and management factors using mixed-effects models.RESULTS AND CONCLUSIONS There were considerable yield gaps on all cocoa farms. Absolute yield gaps ranged from 2,223 to 6,071 kg/ha across sites (mean=4,577 kg/ha) and relative yield gaps from 49 to 98% (mean= 86%). Thus, current farmer yields are only 14% of the potential under rain-fed conditions. Mixed-effects models showed that the absolute yield gaps were larger at sites with higher precipitation in the minor wet season and higher minimum temperature in the minor dry season. This model explained 22% of the variability in the yield gaps. In contrast, variation in the relative yield gaps was driven by management factors only, as normalizing water-limited yields results in a weak climate signal. The mixed-effect model showed that the relative yield gaps were reduced by increasing cocoa planting density and the application of fungicide against black pod, explaining 33% of the variability. In conclusion, the absolute cocoa yield gaps in Ghana are determined by climate with larger yield gaps in humid areas, whereas the relative yield gaps can be reduced by agronomic management practices.SIGNIFICANCE Our study is one of the first to quantify cocoa yield gaps in West Africa and shows that these can be closed by improved agronomic practices