Optimizing the Ratio of Water Hyacinth, Cattle Manure, and Sawdust for the Optimum Physicochemical and Biological Properties of Compost

Utilizing water hyacinth (WH) (Eichhornia crassipes L.) offers an opportunity for composting and supports sustainable waste management, despite its invasive nature. Therefore, this study aimed to produce compost using water hyacinth (WH), cattle manure (CM), and Albizia sawdust (AS) as raw materials, and to evaluate its physicochemical and biological properties. Cattle manure and AS were combined in a 1:1 ratio to prepare the initial mixture (M). Then, four compost piles were produced by varying the ratios of WH and M: T0 (1:0), T1 (1:1), T2 (2:1), and T3 (3:1). Colour, odour, moisture content, bulk density, electrical conductivity (EC), organic matter, total nitrogen, total phosphorus, total potassium, total organic carbon, and the C:N ratio were analysed on the 60^th, 90^th, and 120^th days, while sodium, calcium, magnesium, iron, heavy metals, cation exchange capacity (CEC), and germination percentage were evaluated on the 120th day across all treatments. Based on the findings, T0 was rejected due to its high EC (6.01 dS/m), high organic matter content (42.31%), extremely high CEC (90 cmol/kg), all of which reduced its overall quality. T1 had high heavy metal content, and T3 exhibited a high C:N ratio (35.81), and incomplete nitrogen mineralization, making it unsuitable. Among the treatments, T2 was identified as the best compost due to its optimal nutrient composition and superior decomposition indicators, including the lowest C:N ratio (11.46), the highest total nitrogen content (1.395%), and an organic matter content of 27.55%, making it a highly suitable compost based on Sri Lanka Standards (SLS 1635) and United States Environmental Protection Agency (US EPA) standards. There was no significant difference in the germination percentage between T2 and the control. Hence, these findings confirm that T2 (a mixture of water hyacinth at a 2:1 ratio with an equal mixture of cattle manure and Albizia sawdust) is the most nutrient-rich and well-balanced compost among the treatments evaluated in the study.