Hello!

Thank you for contacting Ask Extension.

Here is the response provided by Anne Sawyer, Soil Specialist....

I think it's an emerging area of research with mixed results, but I'm not up-to-date on the research. In many cases, there are plenty of native fungi to do the job, unless the soil is severely degraded, there's been previous use of fungicide, or there has been previous intensive cultivation of crops that don't have fungal associations such as sugar beets or brassicas (cabbage, broccoli, etc). You'll find growers who swear that inoculation has improved their yields and their soils, but the plant/microbe interactions and native microbe/inoculated microbe interactions are so complex and site-specific that it's hard to quantify on a broad scale. In many cases, though, it can't hurt and may even help (see references below - just did a quick search), but you might not make your $$ back for the investment, particularly if your soil is already healthy with an abundance of diverse microbes.

Here's some research from Rodale in partnership with USDA: https://rodaleinstitute.org/science/articles/how-to-innoculate-arbuscular-mycorrhizal-fungi-on-the-farm-part-1/

And another from Wisconsin: https://fyi.extension.wisc.edu/news/2018/06/15/should-you-inoculate-your-soil-with-microbials/

Hope this helps.