A good online resource from Mark Brundrett of Australia for learning more about the science of mycorrhizas (with lots of great photos) is - Mycorrhizal Associations: The Web Resource Comprehensive illustrations and lists of mycorrhizal and nonmycorrhizal plants and fungi. I have it as a book and Mark put it online for free for all.

So, the tricky thing about mycorrhizal fungi is that while people call them "natural biofertilizers", they are living organisms and don't always function in the same way all the time like fertilizers do. The same species of mycorrhizas with the same plant host may function a bit different depending on different soil characteristics- background nutrients, pH, temperature, etc. And different plants may have more or less benefit from mycorrhizas , and there are few  plant families that do not form mycorrhizal associations like- Brassicaeae (broccoli, cauliflower, etc.), Amaranthaceae (pigweed, amaranth grain), Polygonaceae (buckwheat), to name a few important in agriculture. Lastly, there isn't one or few mycorrhizal fungal species that provide the most benefit and in nature plants may be associated with 4-5 mycorrhizal species at one time depending on the various types of benefits and changing environment. So, my long winded goal in telling all of this is that you may not always see an immediate benefit from mycorrhizas in one particular year and like cover crops, its about the long term benefits and impacts on the overall soil health or system.

So there are a lot of mycorrhizal products out there and unfortunately very little if at all regulation on the quality of the products.  And a lot of claims. In working with farmers over the years, I usually ask if mycorrhizal inoculum is needed first. If there has been a lot of fungicide used, any type of biocide/fumigant, or even years of growing non-mycorrhizal hosts then yes, commercial inoculation could be very beneficial. If you don't have these circumstances, and just want to try it I would recommend using very little or a part of the garden/field to figure out if it is useful for you. I don't typically apply mycorrhizal inoculum via drench but there are a few products on the marketplace by Mycorrhizal Applications or I might try Fifth Season Gardening in North Carolina which has a lot of hydroponics and soil inoculants. Because there are more products out there in granular form and they usually have more propagules per unit, if you can I would try those first instead of a drench. In our research, we just add a small amount to the planting hole or grow our transplants with the inoculum added at 10-20% of the soil volume. A little goes a long way.

For more information see Sustainable Practices for Plasticulture Strawberry Production in the Southeast.