Most of the articles and research about soil biology focus on plant nutrition - how mycorrhizal fungi greatly boost the ability of plants to uptake nutrients. Indeed, an efficient mycorrhizal plant requires far less fertilizer. A light application of dry organic low-analysis fertilizer at planting time is typically enough feeding for a full season of annual plants.
Of perhaps equal or even greater importance is the ability of biologically-active soils to hold moisture. The millions of tiny root threads of beneficial fungi extend out from their host plant roots and either separate clay platelets or bind together sand particles, depending on the soil type. This results in soil that does not become soggy in the case of clay, or clumps together a moisture-retaining bio-mass in the case of loose sand. For either type of soil, the end result is ideal for keeping a plant alive during drought conditions - a survival tactic that the plants/fungi developed over many millions of years in order to survive low-rainfall years.
We humans can use this to our advantage. As irrigation water becomes scarcer (and in some areas it may become very scarce in the foreseeable future) and more expensive, pressure will build to conserve water. For every growing situation, from golf courses to gardens to field crops and especially lawns, it will become important to cut back on watering.
A chemically-fed plant that lacks soil-conditioning mycorrhizal fungi also lacks drought resistance. A few days without water makes the plant's leaves go into wilting status in a desperate attempt to retain water within its system. If water is not provided in large regular amounts by the human caretaker, the plant dies.
Of course, watering all the time also washes away chemical fertilizers (which then contaminate underground drinking water). This heavy watering routine creates the need for frequent doses of "plant food". Unless you happen to be in the employ of a chemical fertilizer company or have a lawn-feeding business, this is not a good thing.
In my own garden, I hold off watering until I begin to see mid-day wilting. If some of the plants wilt slightly in the late afternoon, that's OK and normal. For me, this is part of obtaining maximum yields - forcing the mycorrhizal fungi to go into a higher gear in order to sustain the plants during what they feel is a drought situation. It's a little trick I play on them, and an effective one!
This is working with nature, not fighting it.
Cheers, my friends. Good growing.
President, BioOrganics, Inc.