Non-composted grain-based substrates for mushroom production (Agaricus bisporus)

Non-composted grain-based substrates were evaluated for the cultivation of mushrooms (Agaricus bisporus) with the goal of eliminating the need for the lengthy and often malodorous composting process. Millet grain, millet grain mixed with soybean, and commercial rye grain spawn were used as substrates. Treatments included different proportions (100%, 75%, 50%, and 25%) of millet grain, or grain spawn with perlite as an inert bulking material. For the millet and soybean mixtures, the biological matter (millet and soybean) was set at 75% by volume, while the ratios of millet to soybean were varied. To induce fructification, all substrates were overlain with a sterilized mixture of peat and calcium carbonate (casing) containing 25% activated charcoal (v/v), which was shown to be as effective as a commercial non-sterile casing. Among the various treatments, the highest mushroom yield among all three grain treatments was recorded for the 100% millet/0% perlite treatment (8.7 kg/m ²), which was comparable to that of compost (7.7 kg/m ²). In contrast, the millet/soybean mixtures failed to produce any mushrooms when soybean was added to the substrate. The highest recorded mushroom yield for commercial grain spawn was 5.3 kg/m ² for the 100% spawn/0% perlite treatment. This yield was lower when compared to the millet grain and compost substrates. However, biological efficiency (fresh weight of mushroom divided by dry weight of substrates X 100) was 117% for the 25% spawn/75% perlite treatment, while that of compost and the 75% millet/25% perlite treatment were 98% and 55%, respectively. The results suggest that mushrooms can be grown in a non-composted substrate, but further economic analysis will need to be performed to determine economic viability of alternative substrates.