Anaerobically digested food waste in compost for Agaricus bisporus and Agaricus subrufescens and its effect on mushroom productivity.

BACKGROUND: Source-separated food waste is increasingly being treated by means of hygienisation followed by anaerobic digestion. The fibrous digester residue (digestate) is a potential mushroom substrate, while heat from the biogas can provide steam for the cultivation process. Using bag experiments the present study explored digestate as a full substitute for chicken manure conventionally used in mushroom composts. RESULTS: After mixing, a rapid temperature development in the compost was stimulated by a small amount of chicken manure, as aerobic microbial seeding. Mechanical elimination of lumps was essential for full mycelial colonisation. Three straw digestate composts had Agaricus bisporus mushroom yields above 370 g kg⁻¹ substrate. The optimal compost water content was 600 g kg⁻¹ at inoculation, and high digestate content (up to 500 g kg⁻¹ by dry weight) did not affect yield for this species. High yields of A. subrufescens (200 g kg⁻¹) were related to drier composts of lower digestate content (more straw) and lower pH values at inoculation. CONCLUSION: Digestate successfully substituted chicken manure in straw composts without affecting mushroom yields for both species. There were no clear differences between straw digestate and control composts in terms of mushroom dry matter, size, nitrogen or ash content.

Manganese and other micronutrient additions to improve yield of Agaricus bisporus.

Previous experiments have demonstrated that significant increases in yield of Agaricus bisporus mushrooms were achieved by adding a micronutrient rich fertilizer, Micromax, to the compost. This study was performed to determine the mineral(s) that are responsible for this yield improvement. An initial experiment determined that manganese was the mineral of primary importance; addition of 184 mg kg-1 Mn increased yield by 10.8%, compared to the control. Subsequent experiments demonstrated that the addition of manganese to the compost has a stimulatory effect on mushroom yields. Significant yield increases, ranging from 9.6% to 11.8% (compared to the control), were observed as a result of manganese additions varying between 50 and 300 mg kg-1. Also, data from the last set of experiments indicated that Micromax additions always resulted in greater yields indicating that micronutrients in Micromax, in addition to manganese, may be responsible for increasing yields.