Good Soil Is Full of Life
by Vera Strader
I had not the slightest clue. Over the years I fertilized and tilled, virtuously digging as frequently and deeply as I could. My only concern for life within the soil was the occasional earthworm I faithfully moved aside. But as the years passed, I´ve learned an easier way to garden.
Good soil, it turns out, is literally teeming with invisible life. A mere teaspoon of good garden soil can contain a billion bacteria, several yards of fungal hyphae (filaments), thousands of protozoa, and perhaps a few dozen nematodes. We may cringe at the thought of bacteria and other microorganisms in our soil, however many are good guys, performing in concert with plant roots to create rich, fertile soil.
According to Jeff Lowenfels and Wayne Lewis writing in “Teaming with Microbes, A Gardener´s Guide to the Soil Food Web,” the chores microorganisms carry out are numerous. And just like the insect world above ground, it´s eat and be eaten by your hungry neighbors.
WHO´S WHO IN THE SOIL WEB. Here are the main players in this melodrama:
Bacteria decompose and recycle green materials like grass clippings and kitchen wastes. Bacteria also break down toxins and pollutants and are even used to help clean up oil and gasoline spills. Other bacteria convert nitrogen from the atmosphere to a form beneficial to plants. Some live within the roots “fixing” nitrogen for the plant´s use.
Fungi are the primary decay agents, the heavy workers that attack tougher materials. Sure, there are plenty of bad-guy-fungi including oak root fungus, powdery mildew, and rust. On the other hand, many are good guys, releasing enzymes to break down cellulose in decaying wood and chitin in hard shells of insects and animal bones. Some fungi absorb nutrients like phosphorous, zinc, and iron, and transport them back to plants. On top of that, they trap nematodes and secrete an enzyme to absorb the nutrients from nematodes.
Though some nematodes eat plant roots, others consume bacteria and fungi, helping promote that balance of soil life. Other soil and water organisms include algae and slime molds, protozoa, and amoebae, many having symbiotic relationships that contribute to soil health.
Next are the arthropods, countless insects and spiders living either in or on the soil. Most arthropods living on the soil are shredders, chewing up leaves and other organic material. They expose a greater surface area for bacteria and fungi to further break down organics. Other arthropods live below the soil surface, contributing their own waste products, mixing and aerating as they go.
Earthworms are master shredders and eating machines, feasting largely on bacteria. Add to their menu fungi, nematodes, protozoa, and other miscellaneous organics. When devoured by their “enemies,” these microorganisms release water and nutrients to nourish other microorganisms and the plants that depend upon them.
Earthworms´ waste, or vermicastings, makes a nourishing soil amendment. According to Lowenfels and Lewis, worms can annually deposit a whopping 10 to 15 tons of castings per acre on the soil´s surface. Furthermore, they burrow through the soil, sometimes several feet deep, increasing its porosity and water-holding abilities.
WHY SHOULD GARDENERS CARE? Nurturing the soil web helps create:
Superior nutrient retention (as opposed to that provided by chemical fertilizers). Microorganisms leave nutrients behind in a plant-available form right where plants need them.
Better soil structure. Burrows formed by soil life create tunnels of all sizes. Soils have improved drainage with greater root access to water and oxygen.
Enhanced defense against diseases and overpopulation of “troublemaker” organisms.
Improved pH balance (acid-base ratio) and breakdown of pollutants including garden and lawn pesticides and fertilizers.
BECOME A “DO-NOTHING” GARDENER. How do we go about acquiring this healthy soil food web? Lee Reich, a noted soil scientist writing in “Fine Gardening” observes that he has not tilled the soil in his vegetable and flower beds for two decades.
Since most of a plant´s feeder roots lie near the surface where biological activity and aeration are greatest, he believes tilling serves little purpose. All that soil churningƒ??whether from spade, tiller, or worse, bulldozerƒ??can severely disrupt helpful organisms and crush their tunnels. Dr. Reich designates walkways and adds stepping stones through planting beds to direct foot traffic, preventing further damage.
Tilling also brings weed seeds, which have lain dormant for lack of light and water, to the surface where they then enthusiastically germinate. It is best to lay compost and mulch on top of the soil the way Mother Nature does. Remove weeds from mulched soil by pulling or chopping with a sharp hoe.
If you are working with heavy clay soil or in a compacted construction site, Dr. Reich notes that a one-time mixing of generous quantities of organic material into the soil is called for. For those who really prefer tilling as a soil management method, he recommends adding abundant organic materials and tilling no more than necessary. Till at varying depths to avoid creating a hardened layer called “plowpan.”
Letting Mother Nature do much of the hard garden labor seems like a wise and easier way to go. Anyone in the market for a well-used spade?
Master Gardener Vera Strader spends her time not tilling the soil in her Sonora garden.