It is very simple for home gardeners to use biological methods to grow super-healthy vegetables and flowers, and not too difficult for landscapers, small farms and market growers - but what about large corn and other grain farms that have been following a chemical fertilization routine for decades?
In most situations, heavily-fertilized farms have eliminated the beneficial bio-life in their soils - as evidenced by lack of earthworms and compaction problems. These vast acreages across the grain belt of the country are now dependent on continued applications of synthetic fertilizer, and one can't really argue that it isn't an effective way to force good yields.
The question is whether chemically-pushed soils are sustainable. Is there a point at which minor and trace elements, plus humic matter, become depleted? Can NPK fertilizers continue to produce yields from lifeless soils forever?
This is the gist of sustainability arguments. My opinion, for what it's worth, is that there will probably come a threshold point at which some "unimportant" soil factors are used up and yields will then suddenly drop off the end of the table, no matter what amount of NPK is applied. Contributing to this sudden drop-off will be the build-up of salts, which is already a serious problem for more marginal soils. Rich volcanic and deep glacial soils will be the last to fail, as farmers with those type soils can plow deeper and deeper as a delaying strategy.
There are many different soils, crops, and farmers. For those who see problems developing and want to get off the chemical treadmill, a program of reducing amounts of fertilizer, using slow-release types, replenishing organic matter, and reintroducing beneficial microorganisms can create productive soils that will last indefinitely.
Seeds can be used as the carrier for mycorrhizal spores to be scattered evenly throughout a field, and the plant-assisting fungi will then spread from one plant to its neighbors. In a matter of weeks, if not harmed by excess fertilizer, the entire field will be colonized. After that, the field will require less fertilizer and become more drought-tolerant - a financial as well as an ecological benefit.
The first step for conversion is to have both a full chemical analysis and a bioassay done on the soil. This can accomplish two goals - to serve as a benchmark measure to compare future readings; and to help develop a strategy for reducing the fertilizing. Note that some amount of fertilization may always be required, but there are types that are less harmful to the bio-life, allowing them to multiply their populations.
During the growing season, another bioassay should be done on samples of plant roots to see what degree of mycorrhizal colonization is present. If taken at the same growing stage each year this will be a valuable measure of year-to-year success in restoring full soil health.
Or maybe the first step is seeing any need to change from "conventional" use of heavily promoted "complete" petro-fertilizers, and I'm doubtful that this will happen as long as yields hold up. It is a good thing that so many gardeners and smaller growers are now following a biological-organic program with their soils. They will be the models for the big farms to copy some day down the road.
Cheers, and good growing,