Abstract/Summary

For over forty years, research to improve the fertility of cocoa soils in Ghana has focused on getting the right combination and application rates of mineral fertilisers to increase yield without considering the long-term maintenance of soil health. A nationwide fertiliser formulation and rate is therefore recommended. Cocoa pod husks (CPHs) are currently discarded as a waste but could be major source of organic matter and soil nutrients. They contain 1000 mg N kg-1 , 3000 mg P kg-1 , and 48571 mg K kg-1 . This study aimed to assess the effects of land management practices on chemical and physical properties of the soils across the different cocoa growing regions of Ghana and to investigate the scope for using CPHs to increase the sustainability of cocoa plantations. Field observations indicated that about 80% of farmers apply fertiliser, fungicides and insecticides to increase yield. About 50% of farmers perceive CPHs to benefit soil fertility and therefore spread husks on their farms. To study and compare the effects of land management practices on chemical and physical properties of the soils, soil nutrient levels of plots managed by farmers with their business as usual practices were compared with plots managed by the Cocoa Research Institute of Ghana (CRIG) researchers strictly according to their recommended management practices. Results showed that there were no significant differences in soil nutrients between the farmer managed and researcher managed plots and soils on both sites were inherently acidic and low in nutrients, particularly N and K. In the laboratory, CPHs were co-composted with different rates of NPK mineral fertiliser (equivalent to 0%, 25%, 50% and 100% of the recommended rate of NPK 50- 100-50 for a single seedling) within bench-scale bioreactors. There were no significant differences in available K between any treatments, suggesting that CPH does not require mineral K amendment during composting. Co-composting CPH with 25%, 50% or 100% N and P fertiliser additions will all produce a high-quality amendment for cocoa soils, but lower additions (i.e. 25%) of N and P are more efficient in terms of minimising nutrient losses during the composting process. CPH co-composted with NPK amendments were applied to cocoa seedlings and compared to CPH composts co-amended with NPK in terms of soil nutrient availability, plant nutrient uptake and seedling growth. Findings indicated that CPH, co�composted with mineral N and P, is a promising soil amendment for increasing the health and fertility of Ghanaian cocoa soils.