Teaming with Microbes, The Organic Gardener’s Guide to the Soil Food Web (Revised Edition) by Jeff Lowenfels and Wayne Lewis. Timber Press, 2010.
Unseen, plants are as busy underground as above ground. The authors of this book show that underground, the roots sweat (exudate) as a result of photosynthesis. The rhizophere, the area around the sweating roots, attracts and feeds fungus and bacteria, which in turn are consumed by larger organisms, and on up the food chain. All of these organisms, fungus, bacteria and the critters that eat them and the critters that eat them, excrete wastes. This is what is taken up by the roots as nutrients. All of this activity keeps nutrients from draining from the soil because the nutrients that plants need are bound up in the bodies of the soil life. This is called nutrient immobilization.
An empty, ‘new’ garden becoming populated with plants favors bacteria. As the plants age, more fungus appears. It is interesting to note that the bacteria count in a sample of soil over time remains the same, but the fungus count becomes more abundant.
In order to facilitate and grow healthy soil microbes, which in turn produce healthy plants, the authors have created 19 rules. Rule #1 states that the water soluble fertilizer can suck the life right out of those microbes needed by the plants, but again, the right fertilizer is imperative. So the authors put forth Rule #2 which states most annuals (including vegetables) and grasses prefer nitrogen in the nitrate form and prefer bacteria dominated soil. Conversely, Rule #3 states that most perennials, shrubs and trees prefer nitrogen in ammonium form and grow well in soils heavy in fungus.
The authors describe an interesting procedure by which the soil microbes can be counted, a census if you will, should gardeners want to know exactly what is in their soil. Meanwhile, mulches can support microbe activity. Shredded, wet, green mulches, such as leaves, support bacteria. Dry mulches such as wood chips, support fungus.
What is something that you can do to support microbial activity? Compost tea. This is made by putting compost in water and jiggling it with air bubbles in order to release the microbes attached to the pieces of compost. This is then spread out in the garden. The authors maintain that there is no overdose of compost tea. Compost tea, rich in fungus, squeezes out powdery mildew by out competing it for resources. Fancy that. Compost tea is part of the authors 19 rules on treating soils tenderly in order to maintain an environment conducive to microbes. The rules include things like no rototilling and adding endomycorrhizal fungi to seeds of annuals and veggies.
This book is a must read for gardeners. It will introduce the notions of growing the soil as much as growing the plants. This book is full of explanations, charts, those wonderful photos of microscopic things, chapters on different soil microbes, instructions on making compost tea, and of course, an explanation of the 19 rules of the soil food web.