Soil Biology Basics

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Garden, Live

Soil Biology Basics

As I write this article, I am sitting under a 300-ft.-tall canopy of old growth redwoods just off the coast of California. With more biomass per acre than anywhere else in the world, this environment is flush with fertility and almost overwhelming in its scale. How is it that this forest, and old growth systems the world over, are able to grow such massive plants, consistently, for thousands of years, without a single drop of fertilizer?

Contrast this with any conventional farm on the globe where, should you cut off the fertilizer input, what would happen? The yield would diminish by at least half the first year, half again the second year, and by the third year the farmer would be unable to produce anything of note…except weeds. (When I say “weeds,” I’m referring to the quickly growing pioneer plants with a short life cycle. Often a weed is defined simply as any plant growing where you don’t want it.)

Now, let’s look at those weeds, the bane of almost every gardener’s existence. Many of us simply throw in the towel once a garden is overrun with bindweed, climbing and strangling the joy out of our experience. Something I’ve noticed for years is that invasive thistles, goat heads, kosha, cheatgrass and other nasties only grow where humans have disturbed the soil. Why is it that these weeds grow along every roadside, but 20 ft. from the road you find hardly any?

The answer can be found by taking a look at how healthy soil functions. Fertility, soil structure and the types of plants a particular soil will support directly correspond to the health of the microorganisms within it.

A tablespoon of healthy garden soil has more microscopic citizens than Salt Lake City has people, a lot more. Bac­teria, protozoa, fungi, nematodes, micro arthropods, and earthworms form the “soil food web,” the network that produces and cycles fertility in the soil, as well as builds soil structure. Disrupt the balance of this community and you destroy your soil. You are left with dirt. Unfortunately, the vast majority of the world’s farmland is now exactly that, dirt.

Thanks to almost 30 years of university level research by Dr. Elaine Ingham (see “It’s Alive! A conversation with Dr. Elaine Ingham, renown3ed soil microbiologist,” June 2015 CATALYST) and her team, we now have a solid understanding of how this system actually functions. I’ll do my best to break it down, but bear in mind that the following is a grossly oversimplified representation of advanced soil microbiology.

Soil fertility

First, let’s wrap our heads around soil fertility. Every soil on the planet contains almost every single nutrient needed to support plant growth. These are tied up in the mineral compounds that make up inorganic particles of the soil: the silts, sands, clays and rock. Specialized bacteria excrete acids that dissolve and break up these compounds, utilizing and consuming them, thus forming the foundation of fertility. The other two major building blocks, nitrogen and carbon, make up the bulk of the atmosphere. Plants pull carbon from the air, in the form of CO2 and, utilizing the power of the sun, convert it to sugars. They send most of this sugar down to their roots, where they excrete them in the form of exudates. These exudates attract and feed hordes of bacteria and beneficial fungi, who are themselves consumed by protozoa, beneficial nematodes and micro arthropods (translation: teeny tiny bugs). Every time one of these microorganisms is eaten by another member of the web, nutrients are released in a form available to the plants.

Finally, specialized bacteria are able to convert atmospheric nitrogen into a form plants can utilize. The soil is literally buzzing with commerce, guided by the plants. These nutrients cycle endlessly and, driven by the power of the sun, grow massive forests and endless meadows fueled by microscopic life, rock and sunshine.

Contrast this with the standard approach of fertilizing with inorganic petroleum-based nutrients. It’s long been the conventional wisdom of industrial agriculture that plant nutrients need to be applied in a water-soluble form, as otherwise the plant cannot “absorb” them. (To their credit, without a healthy soil biology most nutrients aren’t available.) To make matters worse, when these fertilizers are applied, only a small fraction of the nutrients are absorbed by the plants they were intended for, and the majority are washed away into the surrounding ecosystem, polluting aquifers and watersheds.

Agricultural chemicals are one of the leading pollutants in waterways worldwide. With every application of these inorganic fertilizers the health of the microorganisms in the soil are set back, decreasing the ability of the life in the soil to cycle nutrients and make them available to the plants. In essence, what is being marketed to farmers and gardeners worldwide are products that provide minimal fertility while disrupting the soil’s ability to cycle the nutrients that were already present, creating a dependency on the purchased product while at the same time generating massive amounts of pollution. Do you sense a hustle? I do.

Making sense of weeds

What if I were to tell you that most home gardeners, and in fact almost every single commercial farmer, has been hustled on their path to weed-free, fertile soil? Now, I don’t like my people getting hustled, and I have your back. It’s time to arm you with some information.

Ecosystems are constantly evolving, and generally moving forward in a predictable succession of plant complexity. Bare, disturbed soils give way to our first wave of pioneer plants, or weeds. These soils are dominated by bacteria, and have little diversity. The purpose of these pioneer weeds is to quickly cover these disturbed soils, preventing erosion and UV damage while beginning the process of building up organic matter. Next, more complex annuals move in, with deeper taproots and longer, more complex life cycles. They pull up subsoil nutrients and then contribute additional organic matter to the soils as they decay. After a sufficient level of organic matter builds up in the soil, the microbiology becomes more diverse and more beneficial fungi begin to populate the soil.

The most complex annuals begin to appear, followed by perennial plants. The biology of the soil is beginning to mature. The pioneer weedy species no longer serve any purpose, and disappear from the scene.

The next phase sees a balance of fungi to bacteria, and favors perennial grasses. As the balance moves more and more to fungal dominance, we move into more woody perennials, brambles and shrubs and then trees, climaxing in multi-story old-growth forests. With each increase in the volume of life in the soil, the soil has better structure, more fertility, more resilience to pests and disease, and an increased ability to hold onto moisture.

This is why we don’t see weeds in untouched native environments. The soils have already progressed in their succession beyond the need for them. As soon as the landscape is razed or disrupted, the succession is knocked back as the biology in the soil is ravaged.

Stop the hustle!

Every time you take the tiller to your garden, or the farmer plows the field, the succession is knocked back. Every time you use an inorganic fertilizer, herbicide or fungicide, you harm the microorganisms and knock back this progression. Do any of these things enough times, and you’re perpetually growing in an environment that caters to the pioneer species of weeds. Don’t play that game, stop the hustle, and quit working so hard!

The first step to cultivating a robust soil biology is to avoid the poor gardening practices that harm it in the first place. Stop tilling, walking on your soil, or otherwise compacting your soil layers. Nature abhors bare soil, so make sure to keep soils covered with mulches or cover crops at all times, except in early spring when we allow the sun in to warm the soil for planting. Avoid overwatering, which creates anaerobic condi­tions harmful to the good-guy microbes. And finally, put an end to the use of inorganic fertilizers, herbicides, fungicides and pesticides. These offer only a short term gain and guarantee long term harm.

We are happy to be welcoming James Loomis back to Utah!

 
 
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