Instead, the thinking people of the industrial world gather together in their virtual cathedrals to discuss saner options than pumping ever-more of a precious and vanishing resource to water crops growing in declining soils (that is, soils with, among other problems, compromised water-holding capacity). The last two posts here at Small Batch are my little contribution to that discussion, and, put into practice, are slowly and steadily improving soil quality, and therefore our soil's ability to retain moisture, around the ol' homestead. This post, in sequence, is about learning to manage organic plant growth to our benefit. The "then green" part. It's a very brief discussion of the soil food web, and how to work with it.
There are of course more comprehensive treatments of the subject, and I highly encourage everyone interested in the garden (or in life for that matter!) to read Lowenfels and Lewis's book "Teaming With Microbes," for a more thorough discussion of the topic. I just reread it a couple of weeks ago and it was well worth revisiting. In a tiny little nutshell:
Plants are in charge of the soil food web, but they depend on the activities of various soil microbes for their nourishment. Thousands of species of bacteria and fungi permeate every crevice of healthy soils, billions of them in one teaspoon, and live in conjunction with plant roots in the rhizosphere. Plants have the ability to attract the bacteria and fungi they want with the production of specific root exudates - carbohydrates mostly - that they trade with the microbes for minerals and water. I'll give you some yummy sugar if you bring me the phosphorus and potassium I need to build flowers and fruit. And this has been an effective partnership for eons! Just look at the nearest forest. It didn't require one drop of fertilizer or pesticide to attain its current stature, just the ceaseless exchange of water and nutrients with its soil-dwelling symbionts. It's an economy of complex exhange beyond human imagination.
Bacteria and fungi alone can't make the system work, though. When a bacterium or fungal strand consumes the nutrients needed by plants, the nutrients are "immobilized." That is, they are not available to the plant partner. The opposite of immobilized is "mineralized," and it's what happens when the bacteria and fungi in question die or are consumed by larger organisms - namely protozoa and nematodes. Remember those amoeba and paramecium from high school biology? These also live in the rhizosphere and make their living feasting on bacteria and fungi. Their waste products, in turn, release, or mineralize, the nutrients the plants need. And they release them right around the roots, in the thin rhizosphere, right where the plants want them.
Commercial fertilizers, by contrast, soak the soil with water-soluble minerals that occasionally find their intended target, the root, via sheer volume. The rest enters the water cycle where it does plenty of unintended damage. Another problem with inorganic fertilizers is that they are salts. Ever poured salt on a slug? Salts make the soil environment a lot less inviting to the myriad nutrient cyclers, from earthworms and beetles (and slugs!) all the way down to the tiny bacteria. Without worms, beetles, nematodes, and protozoa around to cycle nutrients, the gardener has to take on the massive amount of work they do himself, and the fitness of the system enters a terminal decline. All nitrogen is not the same.
And the kind of nitrogen plants want is the next part of the story. As soils mature from bare beach to interior old growth, the soil becomes increasingly dominated by fungi. The overall number of bacteria remains relatively constant, from pioneer weed lot to redwood forest, but the volume and organization of fungi becomes ever more dominant along the successional road. Naturally, certain plants prefer one microbial dominance over the other.
|This is the first little flush of blue oyster mushrooms on that oak we inoculated back in May with the wedge technique.|
So we want soils dominated by bacteria in the annual garden, and soils dominated by fungi in the orchard. How do we get that? Here's the next rule: in order to promote bacterial dominance we feed the soil food web things that bacteria are best adapted to eat. Bacteria are miniscule, and accordingly, they want their food to be easy to get into. Feed the bacteria with composts, mulches, and teas that are green, wet, and fine. Give them grass clippings, and compost made from "green" materials like kitchen scraps, even cereal straws are considered "green," but the finer the material is chopped the more accessible it is to bacteria. By contrast, fungi thrive on organic material that is coarse, dry, and brown. Feed fungi brown leaves, sticks, wood chips, etc, make them coarse, and lay them on the surface of the soil. Bacteria have a harder time accessing coarse material on the surface. Therefore, another way to promote bacterial dominance is to lightly chop the organic matter you're feeding them into the top couple of inches of soil. In this way the same mulch material can be used to create bacterial or fungal dominance, with only the form and delivery of the material altered.
Do not, however, confuse this recommendation with tillage. Tilling the soil, while it does shred fungal networks and encourage the bacterial dominance preferred by vegetables, shreds everything else too - soil structure, earthworms, nematodes, protozoa, on and on. In other words, tillage damages soil. Stop tilling. Don't buy that roto-tiller you want for Christmas. Put that money back in your pocket or do something constructive with it. Tilling isn't constructive, it's destructive. And we'll talk more about cultivation and how to apply more of the soil food web strategies in the next post.
First blue, then green. Next is black, and black is what we're really after in the garden.