Use of Spent Mushroom Substrates in Radish (Raphanus ssp.) Microgreens Cultivation

This study evaluated the effects of incorporating spent mushroom substrates (SMS) derived from Agaricus bisporus, Pleurotus ostreatus, and Lentinula edodes into peat-based growing media on the morphological traits, photosynthetic parameters, and mineral composition of radish and black radish microgreens. Six substrate mixtures were tested, with 2.5–30% SMS and two composting durations (97 and 153 days). The results showed that a low proportion of A. bisporus SMS (2.5–5%) significantly enhanced biomass production, plant length, and leaf area, particularly in radish. In contrast, higher proportions (20–30%) of P. ostreatus and L. edodes SMS, especially when short-time composted, inhibited plant growth and photosynthetic performance (Fv/Fm, PIabs), likely due to phytotoxic compounds, high salt content, or nutrient imbalances. Mineral analysis revealed substantial increases in K, Fe, and Zn accumulation in microgreens grown on selected SMS media, particularly Agaricus 5% and Lentinula 30, while also highlighting the risk of excessive Na or heavy metal content in some treatments. Differences between the species were observed: black radish produced higher dry mass and accumulated more minerals, suggesting greater adaptability to suboptimal substrates. These findings support the potential use of well-composted SMS as a sustainable growing media component for microgreens, provided proper substrate selection, composting, and dosage control are applied.