Bench-Scale Preparation of Mushroom Substrates In Controlled Environments

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Conventional composting for mushroom cultivation involves a largely uncontrolled phase in which there are wide variations in temperature and oxygen level, resulting in the production of odor pollutants. The experiments reported in this paper investigated environmental conditions for compost preparation in an attempt to minimize odor production. Substrates for mushroom culture were prepared in flasks under controlled temperature and aeration. The temperature (48 to 72°C), O2 concentration (0.6 to 8.7 percent v/v) and duration (6 or 20 h) of an initial pasteurization phase were varied before all the substrates were given a standard aerated conditioning period at 47°C. Compost decomposition, initial mineralization rates of 14C labelled glutamic acid (a measure of microbial activity) and actinomycete and fungal populations all decreased as the pasteurization temperature increased from 48°C to 72°C. The duration and O2 concentration of the pasteurization treatment did not affect the overall decomposition of the substrate, mineralization of 14C labelled glutamic acid and subsequent mushroom mycelial extension rate and yield from the substrate. Under the controlled temperature conditions, the optimum pasteurization temperature for mushroom mycelial extension rate and sporophore yield was 60°C but possible benefits of higher temperature zones in a large stack situation were identified: 1) a higher concentration of ammonia which may assist substrate degradation over a prolonged period; 2) the development of high populations of intercellular bacteria following pasteurization at 72°C, 0.6 percent O2; 3) the recovery of low rates of mineralization of 14C labelled glutamic acid following the pasteurization of substrate at 72°C to rates above those of the 48°C and 60°C pasteurization treatments.