Harmonizing procedures for the evaluation of compost maturity in two compost types in Ghana

Composting is one of the most favoured options for municipal solid waste recycling for waste streams with high content of biodegradable materials. Compost has many uses including its use in agriculture for soil structure and fertility improvement. However, non-mature composts when applied to soils could present inimical phytotoxic problems to crops. Despite this reality, many developing countries including Ghana, lack simple and reliable compost maturity tests, and run the risk of producing and/or using composts that have not reached maturation stage. This study was conducted to validate some chemical and biological procedures for testing the maturity of composts prepared from agricultural residues (AR) and municipal solid wastes (MSW) in Ghana. Three maturity indices - humus colour, CO2 respirometry, and germination index - were considered for this validation study. For composts produced from crop residues, the optimal values for humus colour test, CO2 evolution test, and germination index were 0.36-0.59, 1.24-1.80 gCO2 kg-1 day-1, 159.5-259.4, respectively. Similarly for the MSW composts the optimal maturity index ranges were 0.41-0.51 for humus colour test, 0.43-0.56 g CO2 kg-1 day-1 for CO2 evolution test and 0-59.1 for germination index. The MSW composts appeared mature under humus colour and CO2 evolution tests, but inhibited germination. Agricultural residue composts on the other hand were found to be mature when subjected to all three maturity tests. This is indicative that composts may pass certain maturity parameters, yet fail germination test. It is therefore concluded that the germination test index is able to discriminate better between mature and non-mature composts. © 2009 Elsevier B.V. All rights reserved.