The most frequent articles about mycorrhizal fungi deal with their ability to improve the nutrient and moisture uptake for host plants, which are obviously important benefits. However, we can't overlook the powerful physical effects that the fungi have on the surrounding soil after they colonize a plant's root system.
After the fungi send their many millions of microscopic root-threads (hyphae) out into the soil, acting like foraging hair roots, the effect on clay soil is to separate "stacked" clay platelets. This allows air to penetrate deep into the root zone and permits water to drain through without causing soggy anaerobic conditions.
Some years back, when we moved into a new home, I planted some extra potato seeds in extremely heavy clay - had to work to wedge a shovel in. I was surprised at how well the plants grew with no fertilizer, and even more surprised when I went to dig some new potatoes for dinner one day. I could push my hand down several inches into the soil around the plants with no effort. It was like reaching into a bag of loose potting soil. About 18 inches out from each plant, the soil was still rock-hard. The mycorrhizal fungi had, in effect, created ideal growing conditions for their host plants out of what would otherwise be a suffocating soil situation.
I also found it interesting that about a month after the final harvest, the spots where the potato plants were located went back to being just as hard-packed as before. These fungi are obligate organisms, dependent on host plants, and could not continue living after the plant was dead. This is part of a normal cycle for annuals, and there would be fungus spores left behind in the soil for next year's crop. I still put a small pinch of new inoculant on my transplants each spring, but it is probably not necessary as long as the soil has not been drenched with liquid fertilizer or fungicides.
Rototilling will fluff up soil for a short time, but having the right type of mycorrhizae on plant roots will keep it fluffed for the season. Both commercial growers and home gardeners can use this technique to their advantage - putting nature to work for you.
Soil chemistry still dominates our cultural practices, but microbiology is gaining ground (or soil?) each year because of advantages in cost, performance, and sustainability. Good healthy soil produces good healthy plants.
Cheers, and have a great growing season this year,
President, BioOrganics, Inc.