Integrating compost and biochar as climate-smart soil amendments to enhance cocoa yield, profitability, and sustainability in Ghana

Abstract Declining soil fertility constrains cocoa productivity across Ghana’s cocoa landscapes, while smallholder adoption of organic amendments remains limited. We evaluated combined applications of mineral fertilizer, compost and biochar under no-shade and medium-shade systems for cocoa productivity, soil fertility and profitability over two growing seasons (2022/2023–2023/2024) in moist and dry semi-deciduous zones of Ghana. A split-plot design comprised shade system as the main plot and five soil amendments as subplots: no amendment (T1), mineral fertilizer (T2), mineral fertilizer + biochar (T3), half-rate mineral fertilizer + compost without rock phosphate (T4), and half-rate mineral fertilizer + compost with rock phosphate (T5), replicated three times. Shade did not significantly affect pod load or bean yield, whereas all amended treatments significantly outyielded the control. By the second season, bean yield increased by 74–93% and 75–89% relative to the control in the moist and dry zones, respectively, with T5 consistently producing the highest yield. Amendments improved soil pH, organic carbon, total N, available P, cation exchange capacity and microbial biomass carbon, with the largest gains under T4 and T5. Stepwise regression identified nutrient use efficiency, nutrient release rate, cation exchange capacity, microbial biomass carbon, soil nitrogen, organic matter, and available phosphorus as key yield drivers, explaining 91% of yield variation, with soil nitrogen as the strongest predictor. Net income increased by up to 78% under T5 compared with 53% under T2. These findings suggest that partial substitution of mineral fertilizer with on-farm compost offers Ghanaian cocoa farmers a cost-effective, soil-fertility-building pathway to higher yields and profitability.