1. Do not till. Tillage breaks up the myriad of hyphae/mycellium, most of which can never reconnect. Once broken, they must start all over, says Wendy Taheri, an expert on arbuscular mycorrhizal fungi. Dramatically shorter mycellium equals dramatically reduced plant food for your crops or forages. One source says it is not uncommon to have 20 meters of fungal root in one cubic centimeter of soil. Calculate that out to just the top inch of soil in an acre and you get a length that would stretch about 80% of the way to the moon; roughly 195,000 miles of food collectors per acre, all interconnected, all sharing stuff.
2. Do not provide much phosphorus. Taheri says too much phosphorus fertility in the soil, especially with crops and farm ground, can be almost as damaging as tillage. The plants latch onto the inorganic phosphorus source when young and never develop much of a trading relationship with the AMF. Remember that phosphorus is so necessary to plant life and so generally unavailable in a natural setting, that plants are programmed to make most of the trade deals with AMF based first on the need for phosphorus. You want the plants to be a bit hungry for phosphorus, Taheri says. For example, 200 ppm of phosphorus in a soil test is usually considered adequate for crop growth. If you want AMF to successfully colonize and trade with your plants, 50-100 ppm is a more AMF-encouraging range for phosphorus fertility.
3. Avoid pesticides as much as possible. Although AMF have a lot of resistance to even such compounds as fungicides, Taheri says most pesticides can be hard on AMF. The more you put on and the more frequently and the more you rotate pesticides, the more you will damage your AMF.