Vermicompost stimulates mycorrhizal colonization of roots of Sorghum bicolor at the expense of plant growth

Summary Two greenhouse experiments were conducted on the biological and nutritional effects of vermicompost on Sorghum bicolor growth and root infection by arbuscular mycorrhizal fungi (AMF). Two rates of sterile and non-sterile vermicompost (5% and 20%) were added to two media (peat and mineral). In experiment 1, all treatments received AMF inoculant but in experiment 2 uninoculated treatments were included. The addition of vermicompost to substrates increased N, P and K levels. Vermicompost stimulated mycorrhizal colonization of roots in both experiments, particularly in the peat medium. Shoot and root dry weights were increased by vermicompost in the absence of AMF. Inoculation with AMF reduced dry weights particularly at the higher rate (20%) of vermicompost. Steam sterilization of vermicompost had no consistent effect on mycorrhizal colonization but generally enhanced dry weights relative to the non-sterile treatment.