Plant-soil feedback (PSF) can both positively and negatively affect plant populations. Diverse communities should dilute pathogens and mitigate negative PSF, whereas plant dominance should have the opposite effect. It is unclear, however, whether increased species and genetic diversity can have additive effects on pathogen dilution. Using soils from Medicago sativa production systems varying in dominance and diversity, we inoculated multiple species and cultivars to assess effects on PSF. We linked dominance and diversity to intra- and interspecific variation in PSF via changes in microbiome composition. Intraspecific PSF was more negative and variable as Medicago dominance increased driven by multiple microbiome components. The mean and variance in interspecific PSF responded to different microbiome components but was unlinked to plant composition. Only oomycete pathogens had similar effects within and among species. Independent variation in PSF within and among species suggests additive benefits of genetic and species diversity for pathogen dilution.