Coarsely ground bamboo and rapeseed oilcake produce a lower-cost vermicompost with damping-off suppressiveness

Bamboo-based vermicompost has potential as a disease-suppressive nursery medium. We previously developed a vermicompost from finely ground bamboo and kudzu (VFBK) that suppressed damping-off caused by several pathogens, but its practical use is limited by high production costs and low nitrogen content. Here, we produced vermicompost using coarsely ground bamboo and nitrogen-rich rapeseed oilcake (VCBR) to reduce grinding costs and improve nitrogen availability and compared it with vermicompost produced from finely ground bamboo and rapeseed oilcake (VFBR) and VFBK in terms of costs, water-soluble nutrients, damping-off suppressiveness, relative chlorophyll content in seedlings and microbial properties. Cost estimates for practical production for VCBR were markedly lower than for VFBK and VFBR. All three vermicomposts reduced damping-off incidence relative to the non-vermicompost control medium in at least some experimental runs, but VCBR showed the most consistent suppressive effect across the two pathosystems. However, all three vermicomposts reduced SPAD values in seedlings. These results indicate that VCBR is a lower-cost alternative with damping-off suppressiveness, although the reduced SPAD value observed in seedlings should be considered for its practical use.