Optimizing co-composting ratios of cocoa pod husk and poultry manure for cocoa organo-mineral fertilizer formulation in the West African cocoa belt

Abstract

Cocoa is a valuable global commodity but its management results in residues such as cocoa pod husk, leaves and placenta which are under-utilised as a resource. This study sought to address this by evaluating the impacts of different mixing ratios of cocoa pod husk (CPH), placenta (PL) and locally sourced poultry manure (PM) on compost quality and which mixing ratio will enhance compost NPK stoichiometry required for cocoa organo-mineral (OMF) fertiliser formulations. Quality of compost within OMF can influence nutrient release and potentially improve soil health in cocoa farms. The composting study considered 8 treatments consisting of different combinations of PM, and CPH at ratios of 1:1, 2:1, 1:2 and 1:3, with and without addition of PL. Treatments with PL recorded the highest (32 %) organic carbon at the end of the composting period. Highest available N (5919 mg kg-1) was observed in treatments with PL and the lowest (1146 mg kg-1) was observed in treatments without PL. Treatments without PL recorded the highest available P (3843 mg kg-1) and treatments with PL yielded the lowest (2167 mg kg-1). Highest (16922 mg kg-1) available K was observed in treatments with PL and the lowest (12263 mg kg-1) observed in treatments without PL. Addition of PL to CPH and PM causes an increase in organic carbon, available N, available K but reduces available P. Compost PM+CPH (2:1) and PM+CPH (1:2) have NPK stoichiometry which aligns with nutrient requirements of young cocoa (<7 years old) and matured cocoa (≥8 years), respectively. This study demonstrates the use of circular economy to improve resource efficiency in cocoa farms. For future studies, it is important to ascertain agronomic effectiveness of the compost PM+CPH (2:1) and PM+CPH (1:2) ratios on the young and matured cocoa trees, respectively.