Reestablishing good populations of beneficial soil organisms after years or decades of synthetic fertilization is no overnight process. Residual overdoses of chemical elements, especially Phosphorus, will have lingering disruptive effects on sensitive fungi and other important microbial life in soil.
Why do growers, both farmers and home gardeners, put damaging amounts of fertilizer in their soil, much of which is not taken up by plants and washes away to end up in streams and underground water supplies? Well, the concept of total surface area (TSA) is one explanation.
Picture an individual asparagus root - long and rope-like. It is relatively large in diameter, but has very few small feeder roots. If you cut up a single cube into four smaller cubes, you greatly increase the TSA. Cut each of those four small cubes into 16 tiny cubes and the TSA is again greatly increased. The one large asparagus root is in actual contact with only a relatively small amount of soil and also has difficulty absorbing nutrients and moisture through its thick skin.
In nature, such thick-rooted plants depend on mycorrhizal fungi attaching to their roots and sending out millions of tiny root threads (hyphae) into the soil, which in effect tremendously increases the root's TSA. Mycorrhizae gives access to soil nutrients that would otherwise be far out of reach of the root itself, as well as adding super efficiency to the nutrient uptake.
When chemical fertilizers disrupt or destroy the soil's mycorrhizal fungi, the plant roots are essentially "on their own" as far as foraging ability is concerned, so relatively huge amounts of NPK must be added to the soil to produce good yields. Growers are then advised that they are dealing with "heavy feeders," a ridiculous notion. In time, most or all of the beneficial organisms in the soil are gone and the grower begins having trouble with salt build ups and soil compaction, as well as increased pressure from diseases and insects that attack plants grown in such soils.
Some time ago, I spoke to a tomato grower near Sacramento who was in the process of converting one of his fields to organic production. He said that it was only in the third growing season that the organic field finally started to show the full benefits of discontinuing chemical fertilization, with excellent yields from extra-healthy plants. He said that a nearby conventional field had substantial disease issues that third year, while the organic field had none.
I guess the point of all this is that decades of killing off valuable bio-life in crop or garden soils, and thereby cutting back on the TSA of roots in those lifeless soils, cannot be reversed in a single season. The disruptive presence of synthetic fertilizer takes time to dissipate, which means the full health of the soil will also take time to recover. But, for growers with the patience and resources to do so, converting their soil back to a natural biologically active low-input operation can have permanent benefits.
A reminder: Fall is a great time to add organic matter and minerals to garden soils.
Cheers, my friends,
President, BioOrganics, Inc.