Comparison of six spent mushroom composts as growing media for transplant production of lettuce

We investigated the physical and chemical properties of six spent mushroom composts (SMCs) and addressed the possibility of reusing SMCs as growing media for transplant production by comparing the seed germination and growth characteristics of lettuce transplants grown in the SMC-based media. The tested SMCs were collected from factory-like mushroom production systems that produced major mushrooms, such as Agaricus bisporus, Flammulina velutipes, Pleurotus eryngii, Hipsizigus marmoreus, Grifola frondosa and Pholiota nameko. We used SMCs discharged from factory-like mushroom production systems because of their year-round uniformity in composition. SMC uniformity is critical for plant growing media used in transplant production that requires highly sophisticated control of edaphic environments. The six tested SMCs had a higher nutrient content than the commercial medium and the bunasimezi SMC had the highest bulk density. The pH and EC of the white button mushroom SMC were higher than those of other SMCs. Lettuce transplants grown in the white button mushroom SMC had a high seed germination and early growth, similar to results obtained with commercial medium. The use of bunasimezi SMC resulted in the smallest percentage of germination and retarded early growth.