Spent mushroom compost as an alternative to peat-based soilless media for greenhouse potted basil production

Peat moss is the most popular growing medium used for horticultural productions. However, with the continued expansion of the greenhouse industry and the slow regeneration rate of peat bogs, the cost of peat is increasing along with concerns about the sustainability of peat-based soilless media. In Pennsylvania the Agaricus bisporus (Agaricus) mushroom industry generates over 1.1 M t of spent mushroom compost (SMC) annually. While considered a waste, often used as a soil amendment, SMC has a relatively high content of minerals and could potentially be recycled to substitute at least in part peat moss as a growing medium, contributing to improve the sustainability of both the mushroom and greenhouse industry. To this purpose, a study was conducted to evaluate the potential of SMC as an alternative to peat as a soilless substrate. Peat moss was mixed with SMC and perlite in different ratio to obtain five growing media mixture: T1 (50% peat, 50% perlite), T2 (12.5% SMC, 37.5% peat, 50% perlite), T3 (25% SMC, 25% peat, 50% perlite), T4 (37.5% SMC, 12.5% peat, 50% perlite), T5 (50% SMC, 50% perlite). A commercial peat and perlite mix (T6, Premier Tech Growers, PRO-MIX BX) was used as a control. The alternative substrate mixes were compared for their physicochemical characteristics and their effects on yield and quality of potted Italian Genovese basil (Ocimum basilicum L.). Significant differences were observed in the mineral composition, pH and soluble salt content of the substrate mixes tested. Substituting 50% (T3) or 75% (T4) of the peat with SMC provided a yield comparable to the commercial control (T6), while lower yield levels were observed with T1 and T5 mixes. Substrate mixes also influenced basil quality and mineral profile. In conclusion, SMC with its residual fertility could be used to partially substitute peat without reducing basil yield and quality.