Some factors involved in Phase II of mushroom compost preparation

Temperature, initial ammonia levels and aeration were found to be major factors determining the time required to complete the Phase II stage of mushroom compost preparation. Ammonia disappeared most rapidly in the region of 40–45°C, though disappearance was still relatively fast over the range 35–50°C. As temperatures rose above 50°C, the rate of disappearance of ammonia slowed down considerably, and above 55°C a different pattern of change in ammonia levels with time was revealed, with a rapid initial fall being followed by a long slow decline. At these higher temperatures, and also at 40°C or below, the final composts were not selective and supported the growth of competitor fungi as well as the mushroom. Selective composts were produced over the range 45–55°C, though much more time was required to complete Phase II towards the top of this range. The initial levels of ammonia in the compost also affected the time required to complete Phase II, with the higher initial levels requiring more time. Aeration was also an important factor. A reduction of average oxygen levels from 19 to 14%, accompanied by a corresponding increase in carbon dioxide levels, almost doubled the time required to complete Phase II. The results indicated an active involvement in the Phase II process of the thermophilic microflora in the compost.