Maturity Evaluation of Spent Mushroom Compost

Maturity of compost is an important practical factor in agricultural and horticulture production. This study was conducted to perform maturity assessment for spent mushroom compost (SMC). Compost maturity were evaluated using standard chemical analyses (pH, EC, CEC, total C and N content, C/N ratio, NH₄⁺-N, NO₃^--N). Subsequently, potential phytotoxicity from SMC was assessed by germination bioassay using Lepidium sativum L. (cress). SMC samples were collected periodically during a 28-d rapid composting period from a single windrow. Following composting time, the pH and EC values had a tendency to increase, and in the end, the two values maintained constant. The increasing continuously CEC did not appear to be a more sensitive indicator. Although total C content (TC) and total N content (TN) were of limited value in assessing compost maturity, C/N ratio decreased significantly. NH₄⁺-N declined within the first 14 days of composting, while NO₃^--N did not increase until 14+ days. According to seed germination index (GI), when composting time was prolonged, the toxicity of SMC had a tendency to decrease. Results from the experiments indicate that 21 days after rapid composting, SMC is considered to be mature. It is therefore concluded that pH, EC and GI have potential as useful indicators for SMC maturity evaluation.