Physicochemical characteristics and phytotoxicity of cocoa shell-based composts

Abstract

Composting cocoa shells is a sustainable solution for managing agricultural waste and producing organic soil improvers. This study assessed the physicochemical characteristics and toxicity of five different types of compost (C1, C2, C3, C4, and C5) made from cocoa shells and other organic waste (animal manure, rice bran, and panicum). After 8 months of composting, physicochemical analyses showed that the composts produced were mature and stable. They have adequate levels of fertilizing elements (nitrogen, phosphorus, potassium), a C/N ratio of between 15.4 and 21.7, and a basic pH, which testifies to their ability to improve soil fertility, particularly in acid soils. Germination tests (phytotoxicity) were carried out on several crops (maize, tomato, lettuce) to assess the impact of composts on plant growth. The results showed that 25% and 50% compost doses gave the best germination rates (between 60% and 90%), confirming their non-toxicity. However, higher doses (75% to 100%) resulted in a significant reduction in germination rates (30% to 40%), indicating potential toxicity. These results suggest that cocoa shell composts, used in moderate doses, are a quality organic amendment for agriculture.

Keywords: Cocoa shells, composting, waste recovery, physico-chemical analysis, phytotoxicity, soil fertility