Effects of spent mushroom compost (SMC) as an ingredient in phase I compost on production of Agaricus bisporus

Experiments were performed to determine the effect of using 20% spent mushroom compost (SMC) as an ingredient in phase I compost on mushroom yield. Yields from compost prepared with two 20% SMC formulations (80Ctl, 80LC) were compared to a standard control (Ctl) containing no SMC. The 80LC compost was formulated with a higher level of lignocellulose raw materials, including corn stover, corncobs, cottonseed hulls, and wheat straw. The 80Ctl compost contained 20% SMC plus the same raw materials used to prepare Ctl compost. Yields of 80LC matched or exceeded yields of the Ctl compost in all three crops while yields of 80Ctl were significantly lower. As an additional factor, lignocellulose supplements were added at spawning and were a significant factor in increasing mushroom yields, although not superior to a standard commercial supplement applied at 3.7% (dry compost weight). Compost bulk density was significantly higher (19-20%) in compost formulations containing 20% SMC compared to the non-SMC Ctl. Populations of four prominent phyla of bacteria (Firmicutes, Actinobacteria, Proteobacteria, and Chloroflexi), as determined by pyrosequence analysis, were similar in both compost types and did not appear to influence mushroom yield.