Teaming with Microbes: A Gardener's Guide to the Soil Food Web

“Chemical fertilizers, pesticides, insecticides, and fungicides affect the soil food web, toxic to some members, warding off others, and changing the environment. Important fungal and bacterial relationships don’t form when a plant can get free nutrients. When chemically fed, plants bypass the microbial-assisted method of obtaining nutrients, and microbial populations adjust accordingly. Trouble is, you have to keep adding chemical fertilizers and using “-icides,” because the right mix and diversity—the very foundation of the soil food web—has been altered. It makes sense that once the bacteria, fungi, nematodes, and protozoa are gone, other members of the food web disappear as well. Earthworms, for example, lacking food and irritated by the synthetic nitrates in soluble nitrogen fertilizers, move out. Since they are major shredders of organic material, their absence is a great loss. Without the activity and diversity of a healthy food web, you not only impact the nutrient system but all the other things a healthy soil food web brings. Soil structure deteriorates, watering can become problematic, pathogens and pests establish themselves and, worst of all, gardening becomes a lot more work than it needs to be.”

“Water freezes in rock cracks and crevices and expands, increasing its volume by 9% (and exerting a force of about 2000 pounds per square inch) as it turns to ice. Hot weather causes the surfaces of rock to expand, while the inner rock, just a millimeter away, remains cool and stable. As the outer layer pulls away, cracks form, and the surface peels off into smaller particles.”

“Visualize any wooded area you remember visiting. It is beautiful, majestic - and no one ever fertilized any of the plants there. Not one single time.”

“Who wants what? The answer to what any given plant prefers is found in the next two soil food web gardening rules. Rule #2 holds that most vegetables, annuals, and grasses prefer their nitrogen in nitrate form and do best in bacterially dominated soils. Rule #3 points out that most trees, shrubs, and perennials prefer their nitrogen in ammonium form and do best in fungally dominated soils.”

“Without this [Soil Food Web system of bacteria, fungi etc], most important nutrients would drain from soil. Instead, they are retained in the bodies of soil life. Here is the gardener's truth: when you apply a chemical fertilizer, a tiny bit hits the rhizosphere, where it is absorbed, but most of it continues to drain through soil until it hits the water table. Not so with the nutrients locked up inside soil organisms, a state known as immobilization; these nutrients are eventually released as wastes, or mineralized.”

“Besides silicon, they contain water and often aluminum, magnesium, and iron as well.”

“Sample your soils Good garden soil contains 30 to 50% sand, 30 to 50% silt, and 20 to 30% clay, with 5 to 10% organic matter. You can find out how close your soils come to this ideal, loam. All it takes is a quart jar, two cups of water, and a tablespoon of a water softener, such as Calgon liquid. You will also need soil from the top 12 inches (30 centimeters) of the areas you want tested, be it your vegetable garden, flower bed, or lawn. Mix each soil sample with two cups of water and a tablespoon of water softener. Put it in the jar, close the jar, and shake it vigorously, so that all the particles become suspended in the water. Then put the jar down and let things settle. After a couple of minutes, any sand particles in your soil will have settled out. It takes a few hours for the smallest silt particles to settle on top of this sand. Much of the smallest clay-sized particles will actually stay in suspension for up to a day. Organics in the soil will float to the top and remain there for an even longer period. Wait 24 hours and then measure the thickness of each of the layers with a ruler. To determine the percentages of each, divide the depth or thickness of each layer by the total depth of all three layers and then multiply the answer by 100. Once you know what percentages of each material are in your soil, you can begin to physically change it if need be. How to do this is discussed in the second half of the book.”

“If you really want to be a good gardener, you need to understand what is going on in your soil.”

“nematode trapped by a single looped fungal strand, or hypha.”

“Few realize that a great deal of the energy that results from photosyntheisis in the leaves is actually used by plants to produce chemicals they secrete through their roots. These secretions are known as exudates. [...]Root exudates are in the form of carbohydrates (including sugars) and proteins. Amazingly, their presence wakes up, attracts and grows specific beneficial bacteria and fungi living in the soil that subsist on these exudates and the cellular material sloughed off as the plant's root tips grow. [...]During different times of the growing season, populations of rhizosphere bacteria and fungi wax and wane, depending on the nutrient needs of the plant and the exudates it produces. [...]Plants produce exudates that attract fungi and bacteria (and, ultimately, nematodes and protozoa); their survival depends on the interplay between these microbes. It is a completely natural system, the very same one that has fueled plants since they evolved. Soil life produces the nutrients needed for plant life, and plants initiate and fuel the cycle by producing exudates.”

“Bacteria are so small they need to stick to things or they will wash away; to attach themselves, they produce a slime, the secondary result of which is that individual soil particles are bound together. [...]Fungal hyphae, too, travel through soil, sticking to them and binding them together, thread-like, into aggregates. [...]The soil food web, then, in addition to providing nutrients to roots in the rhizosphere, also helps create soil structure: the activities of its members bind soil particles together even as they provide for the passage of air and water through the soil. [...]The nets or webs fungi form around roots act as physical barriers to invasion and protect plants from pathogenic fungi and bacteria. Bacteria coat surfaces so thoroughly, there is no room for others to attach themselves. If something impacts these fungi or bacteria and their numbers drop or they disappear, the plant can easily be attacked.”