Chemical and microbiological determination of flower residue composting in Ethiopia

Abstract

The rapidly expanding floriculture sector in Ethiopia generates substantial quantities of organic waste, posing significant environmental challenges. To address this issue, windrow composting was evaluated using three treatments of floral residues: residues mixed with cow dung (Pile 1; C/N ratio = 30), residues amended with effective microorganisms (EM) and molasses (Pile 2), and residues alone as a control (Pile 3). Over a 90-day composting period, samples were collected at eight intervals and analyzed for key physicochemical and microbiological properties. Significant variations in temperature, moisture content, and pH (p = 0.001) were observed, all of which strongly influenced compost transformation processes. Ammonium nitrogen (NH₄⁺-N) showed a positive correlation with temperature, moisture, pH, and organic carbon, whereas nitrate nitrogen (NO₃⁻-N) exhibited negative correlations with most parameters except pH. Pile 1 demonstrated clear compost maturity after 90 days, characterized by a germination index exceeding 80%, reduced NH₄⁺-N concentration (140 mg/kg), a low NH₄⁺/NO₃⁻ ratio (0.12), and a decreased C/N ratio (14). In contrast, Piles 2 and 3 required a longer period to reach comparable maturity levels. Microbial succession patterns were evident across treatments: bacteria dominated the early stages in Pile 1, while actinobacteria (Pile 2) and fungi (Pile 3) became more prominent during later stages. All compost treatments contained sufficient macro-nutrients (P and K) and micro-nutrients (Mn, Zn, Fe, and Cu), highlighting their potential suitability as soil amendments for horticultural applications.