Evaluation on maturity and stability of organic fertilisers in semi-arid Ethiopian Rift Valley

Case studies that have comprehensively examined local organic fertilisers (OFs) for their maturity and stability are rare in sub-Saharan Africa. Farmers in the semi-arid Ethiopian Rift Valley use indigenous compost (kosi) and household wastes for OFs. With the entry of fast compost that was introduced by the administration, maturity and stability of these OFs were assessed. Their maturity was assessed by: monitoring pile temperature and volume, pH, organic matter and total nitrogen contents, and carbon to nitrogen ratio; determination of NO(3)(–) to NH(4)(+) ratio; and respirometric measurement of CO(2) evolution. Their stability was assessed by weed seed germination tests and phytotoxicity bioassays. Weed seeds that were originally contained in the feedstock of the kosi and fast compost samples became inactive during the composting process. The CO(2) evolution tests and phytotoxicity bioassays indicated a probable presence of some phytotoxic compounds in the kosi. Mature kosi and immature kosi in a kosi pile should be mixed before the field application. Some samples (15%) of the household wastes contained weed seeds. The combination of several assessment methods used in this study and determination methods for nitrogen components using RQ-flex is considered to be effective for on-site quality assessment of OFs in sub-Saharan Africa.