Plant response to biochar, compost, and mycorrhizal fungal amendments in post-mine sandpits: Synergism among soil amendments

Extreme growing conditions inhibit restoration in sandpit mines. Co-amendment of soil conditioners such as biochar, compost, and arbuscular mycorrhizal fungi (AMF) may alleviate these stresses and lead to a more successful restoration. We conducted a multiyear restoration experiment in a sandpit in Southern Ontario, Canada, following industrial-scale grassland restoration protocols. The sandpit substrate was sand with low carbon (C) and nutrients. We tested the effect of biochar, compost, and AMF inoculum in two experiments (plant plugs vs. seed application). In the plant plug trial, we investigated the treatment effects on the growth of eight grassland plant species and colonization of plant roots by AMF over two growing seasons. We found that co-amending soils with compost plus biochar (20T/ha+ 10T/ha) was more beneficial than other amendment combinations. Amendments including AMF were not more beneficial to plant growth than those without AMF. In the seed application trial, direct inoculation of AMF in the field combined with high compost addition (20T/ha or 40T/ha) resulted in the highest plant cover compared to other treatment combinations. Our results indicate that co-amending sandpit substrates with biochar, compost, and AMF are practical restoration tools that enhance grassland restoration.