Modulatory effects of biochar, hydrochar and vermicompost on the growth of horticultural plants and phytopathogenic fungi

Carbon-rich materials are increasingly produced and added to soil for the need to sequester carbon and improve soil fertility. In this study, we compared biological effects of two biochars (BC) obtained from red spruce wood (BCrs) and grapevine pruning residues (BCgv), two hydrochars (HC) from urban pruning residues (HCup) and the organic fraction of municipal solid wastes (HCuw), and two vermicomposts (VC) prepared vermicomposting digestates from buffalo manure (VCbm) and a mixture of manure and olive mill wastewater (VCmf). In plant assays, the six materials were tested at doses of 0.1, 0.5, and 1% (w/v) on the germination and early growth of tomato and lettuce. Results showed that all materials generally stimulated the early growth of seedlings of both species enhancing root and shoot elongation and dry biomass. Furthermore, the impact of BC and VC samples at concentrations of 0.2 and 1% (w/v) was assessed in vitro on mycelial growth and sclerotia production of the phytopathogenic fungus Sclerotinia sclerotiorum. In all treatments and the control, the radial mycelial growth fitted well a linear model with breakpoint. Based on the radial growth rate, μ, and the lag time, λ, it was evident that all materials tested caused marked suppressive effects on the fungus that showed hyphal growth reduction and early and more abundant production of sclerotia, compared to the control, according to the trend BCgv > BCrs > Vbm > Vmf. The overall results obtained in this work suggest that when these materials are adequately chosen for type and dose and used for soil amendment or for preparing growing media, they could contribute to stimulate plant growth and, at the same time, protect plants from fungal pathogens.