It helps to understand that there is a food chain that occurs under the ground equivalent to the food chain that exists above the ground. This may be more technical than interests most gardeners but it is important to know what happens in the soil to make it a healthy soil community. Since I am not a biology major, I will quote from a book that does a good job of explaining the soil food web in simple terms. The book is "Teaming with Microbes" by Jeff Lowenfels and Wayne Lewis.
"The typical gardener knows very little about soil and why it matters." (That is about to change if you bear with me.) "After all, an acre of good garden soil teems with life, containing several pounds of small mammals, 133 pounds of protozoa, 900 pounds each of earthworms, arthropods, and algae; 2000 pounds of bacteria; and 2400 pounds of fungi." (And I thought it was just dirt.)
"Most gardeners think of plants as only taking up nutrients through root systems and feeding the leaves. Few realize that a great deal of the energy that results from photosynthesis in the leaves is actually used by plants to produce chemicals they secrete through their roots. These secretions are known as exudates. A good analogy is perspiration, a human's exudate.
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 the exudates and the cellular material sloughed off as the plant's root tips grow. All this secretion of exudates and sloughing -off of cells takes place in the rhizosphere, a zone immediately around the roots, extending out about a tenth of an inch. The rhizosphere contains a constantly changing mix of soil organisms, including bacteria, fungi, nematodes, protozoa, and even larger organisms.
Plants control the food web for their own benefit, an amazing fact that is too little understood and surely not appreciated by gardeners who are constantly interfering with Nature's system. Studies indicate that individual plants can control the numbers and the different kinds of fungi and bacteria attracted to the rhizosphere by the exudates they produce. 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.
Soil bacteria and fungi are like small bags of fertilizer, retaining in their bodies nitrogen and other nutrients they gain from root exudates and other organic matter. Carrying on the analogy, soil protozoa and nematodes act as "fertilizer spreaders" by releasing the nutrients locked up in the bacteria and fungi "fertilizer bags." The nematodes and protozoa in the soil come along and eat the bacteria and fungi in the rhizophere. They digest what they need to survive and excrete excess carbon and other nutrients as waste.
Left to their own devices, then, plants produce exudates that attract fungi and bacteria; their survival depends on the interplay between these microbes. Soil life provides the nutrients needed for plant life, and plants initiate and fuel the cycle by producing exudates."
Why does this matter? I think that it is important to know how the soil food web works to understand what happens when we destroy parts of the web. That is why we have bins of worms and piles of leaves, manure and coffee grounds. Our goal is to help people create healthy soil not only for our benefit but most of all, for the benefit of our children and grandchildren and their children and grandchildren.
