Abstract: Background, aim, and scope The total amount of spent mushroom substrate (SMS) has been increased continously over the past decades. The current SMS disposals include burning, spreading, burying and landfilling. But all these disposals will cause significant waste of resources as we as envionmental pollution. SMS is also rich in organic matter and nutrient, which can be effectively recycled by composting. Microbial extracellular enzymes play critical roles on the degradation of organic matter and the releasing of nutrients. Therefore, the objectives of this study were to investigate enzyme activities and their underlying mechanisms during SMS composting. These results will provide effective data and theoretical support for the resource utilization of agricultural and forestry residues. Materials and methods SMS composting was carried out at Northwestern Polytechnical University in 2017. In this study, we investigated the effects of different kinds of manure addition on urease activity, invertase activity and cellulase activity along the SMS composting. The experiment treatments are chicken manure (JF), sheep manure (YF) and a combination of JF and YF additions. The pH value and electric conductivity (EC) were also measured along the composting and enzyme measurements. Results Chicken manure addition significantly increased urease activity and invertase activity by 15.74% and 111.49%, respectively. Mixed manure addition (combination of chicken manure and sheep manure addition) significantly increased invertase activity by 111.60%. The three kinds of enzymes activities were significantly correlated with each other after the chicken manure addition. The pH was negatively correlated with the enzyme activities, while EC was positively correlated with the enzyme activities. Discussion As one of the most effective ways to recycle the agricultural and forestry residues, effective composting strategy was one of the research hotspots during the recent years. Extracellular enzymes catalyze the decompostion and depolymerization of organic matter, playing crucial roles in promoting the nutrient cycles. Therefore, it is likely to icrease the composting efficiency by enhancing extracellular enzymes activities. The key findings in the current study showed that manure addition， particularly chicken manure addition, could effectively increase the enzymes activities. Moreover, the enzyme activities were closely correlated with pH and EC, prodiving possible ways to increase composting efficiency by providing favourable conditions for extracellular enzymes. For example, addition of plant ash and frequently dump will be conducive to the composting. Conclusions Our results provide the evidence that chicken manure is more effective than sheep manure in catalyzing the SMS composting, and optimal compost formulation is XG∶JF∶HZ∶YK∶HS∶CM= 6∶2∶1∶1∶1∶1. Recommendations and perspectives Our results highlight the importantce to further study the factors affecting the enzyme activities during the SMS composting, which will contribute to the effective utilization of SMS, such as organic fertilizer production.
Keywords: chicken manure; sheep manure; spent mushroom substrate composting; urease activity; invertase activity; cellulase activity