For some years now, biochar has been studied extensively as an alternative to phosphate fertilizer. Biochar is a recyclate produced by biomass pyrolysis, i.e., organic feedstocks are incinerated without oxygen at temperatures ranging from 400°C to 700°C. The biochar bases may differ considerably. Waste wood, chicken manure, or leaves can be processed to fertilizers.

TL;DR: New research shows that biochar made from phosphate-poor feedstock encourages much more symbiosis with mycorrhizal fungi, compared to biochar made from phosphate-rich feedstock, which encourages very little mycorrhizal symbiosis.