Growing Good Plants In Bad Soils

One of the benefits of mycorrhizae - the symbiotic linking of a plant root system with microscopic fungi - is the ability of the fungi to selectively regulate the uptake of elements from the surrounding soil. This is quite common knowledge among experienced soil restoration people, who routinely see transplants all die in “toxic” soils (mine tailings, etc.) unless mycorrhizal fungi are on the plant roots. In simple terms, the fungi seek out what is needed by the plant and block out what would be harmful.

I’ve witnessed this first-hand at a Central Valley California farm where a market vegetable grower had a few acres in a low swale where the soil was so extremely alkaline it had a white crust. He had tried several times to grow plants there, but none had survived. As an experiment, he dusted pepper plants with our mycorrhizal inoculant and transplanted them into the field.

Later, the grower invited me to see the results. I noted that the healthy plants were typical of those grown with mycorrhizae - short and stocky with very thick stems and nearly every blossom had set a pepper. It’s normal to see similar effects with tomato vines, where even beefsteak types form crowded clusters of fruit - a fully-nourished plant apparently senses that it is able to support a heavy fruitset.

Why is there such a great difference in ability to tolerate bad soil between a mycorrhizal plant and one that has only its own root system to uptake nutrients? I asked that question of a USDA scientist who had studied these beneficial organisms for more than twenty years, and he told me that the fungi, in effect, disable the plant’s own uptake system and take complete control of that function.

Mycorrhizal fungi not only seek out nutrients in required amounts, (working in cooperation with nutrient-producing bacteria) but they also prevent the plant from taking in harmful elements from the soil. This is nature’s survival design for both organisms. As the fungi’s only food source is root exudates, it is imperative that their host plants be kept alive; consequently, the fungi evolved the ability to completely regulate uptake.

What does this all mean to growers? Well, for one thing, it means that soil tests can be one of the worst things a grower can do. The measuring of a few macro elements and pH level is a chemistry-based way of thinking and can lead one down the wrong path as far as healthy soil is concerned.

Think about it: When a “scientific test” indicates that a crop soil is “deficient” in some element or the pH level is “too high/low”, the typical grower will rush to add N or P or K or pH-adjustment products to “correct the problem”, right? This has become so routine that it is rarely questioned. Why would it not be a good idea to change the soil so it is better suited for plants?

Unfortunately, such corrective chemistry processes often damage the very bio-life in the soil which might have made those additives unnecessary. If the plant-tending fungi are destroyed by chemicals, then plants have only their own roots for nutrient uptake and seem to lack the ability to regulate that uptake. After all, smart foraging is the fungi’s evolved responsibility, not the plant’s.

Without the regulating fungi, plants are hyper-sensitive to any soil problems. With sensitive and vulnerable plants to tend, growers perform more chemistry tests, make more “corrections” in their soil preparation/fertilization, and further mess up their soil biology. It is both difficult and expensive for humans to replicate what mycorrrhizal fungi do instinctively correct day and night all season long.

In the long run, I think better use of natural plant-fungi partnerships will let us produce good crops in marginal or poor soils with minimal inputs. To me, this makes more sense than continuously “testing and fixing”.

Cheers, my friends,

Don Chapman
President, BioOrganics, Inc.
www.bio-organics.com
Feb. 2003