Biochar and deactivated yeast as seed coatings for restoration: performance on alternative substrates

Seedling establishment is often a critical bottleneck to revegetation of mine tailings and similar substrates with a low capacity to retain water and plant nutrients. Biochar and deactivated yeast are potential sustainable, low-cost materials with high nutrient- and water-holding capacity that could be used in this context as seed coatings to aid in seedling establishment on challenging substrates. We conducted a greenhouse study to assess the effectiveness of biochar and deactivated yeast, applied alone in a factorial combination, as seed coatings, on the germination, establishment, and early growth of white clover (Trifolium repens) and purple prairie clover (Dalea purpurea). Coated seeds were applied to a mine tailing, a coarse granitic sand, and potting soil mix substates; seedling establishment and growth were monitored over 75 days. Results indicate strong interactive effects of seed coating type with effects of species and substrate. Biochar coatings enhanced germination of Trifolium, while yeast coatings did so for Dalea. In some cases, these effects persisted throughout the experiment. Biochar coatings resulted in a ~5-fold increase in Trifolium biomass at harvest for plants in the potting soil mix but had neutral effects on sand and tailings. Yeast seed coatings enhanced biomass at harvest on tailings for Dalea. Our results indicate that biochar- and yeast-based seed coatings can have lasting effects on plant growth well beyond germination, but also emphasize highly species-specific responses that highlight the need for further study of broader patterns and mechanisms.