The “New” Soil Fertility

A very old Chinese saying goes “Man comes and deserts follow.” So it has been known since early times that human activities, including agriculture, deplete the soil and reduce the capacity of the soil to sustain life. Restoring fertility has, therefore, always been an important goal for human civilization.

The first known renewal technique was slash and burn: when the soil’s productivity went down, early farmers moved on, burned the bushes and trees and planted in the ash and charcoal. This technique improved short-term productivity. But when land became less plentiful, farmers learned to put animal manures on spent soils to gain fertility. Later they learned to let the land stand fallow for a time, and they learned to rotate crops. After growing a heavy-feeder crop like corn, they grew a nitrogen-fixing crop like beans or they would grow corn, then alfalfa, then beans and again corn. Manuring and crop rotation were the main fertility practices, I believe, until the late 1940’s.

After World War II, a “revolution” took place in agriculture. It was named “The Green Revolution” and it rode on the slogan “Better Living Through Chemistry”. War industries that produced explosives and chemical weaponry learned to apply the same chemistry to produce fertilizers instead of bombs, herbicides instead of defoliants and pesticides instead of chemical weapons. The chemical fertilizers, made from petroleum and petroleum bi-products, increased crop yields and the pesticides killed the pests.

The chemical companies gave research grants to land-grant universities to test and demonstrate the effectiveness of their chemicals, and the universities held conferences and invited and promoted the chemical companies as allies. They saw the profits, but not the long-term costs. Manuring and crop rotation fell out of favor and sales for the new fertilizers, herbicides and pesticides skyrocketed.

It took decades for us to see the ill effects of these petroleum products. Wildlife started dying off, fish were floating, and insects developed resistance to pesticides, requiring higher doses and new chemicals. New high-producing hybrid varieties were developed that required more water and fertilizers. Erosion became a bigger problem and the ground got harder requiring “bigger and bigger tractors to pull the plows through the damn dead ground,” as my father described it. He credited this hardening of the soil to the anhydrous ammonia that was applied to the corn fields. I asked a soil scientist if my father was right about this effect. He told me that Dad was absolutely right, because during WWII when the military needed an airplane runway built in a hurry, they had to harden the ground before pouring the cement. And what they used was anhydrous ammonia.

In addition to chemical fertilizers (that burn soil fungi and earthworms), herbicides, fungicides and pesticides (which are all designed to kill life) have further devastated the life of the soil. And because of this reliance on chemicals, farmers nearly stopped returning organic matter to their soils so very little food was available for the fungi and bacteria.

The problems resulting from 60 years of chemical farming are now showing clearly: pollution, health problems and poor nutritional values in foods, to name a few. Now there is a new condition called Peak Soil, which refers to decreasing productivity and the extreme erosion of soils. In addition, a majority of family farms have disappeared. The Green Revolution pushed farmers to buy bigger and bigger farms, bigger tractors and equipment, resulting in ever higher overhead to buy fertilizers, pesticides and hybrid seeds. Fewer people could afford to farm and fewer people wanted to farm that way.

Meanwhile the organics movement got started in the ‘70s, and has gained so much momentum that even agribusinesses are trying to get on the “organics” money wagon. Simultaneously, in the last 5-10 years, interest in microbiology has mushroomed. The value of mycorrhizal fungi for supporting plant life has been recognized, and a new concept in fertilizing called “compost tea” has emerged. We are hearing the term “Soil Food Web” and are seeing products offering to inoculate our gardens with beneficial microorganisms and products that support soil life. So what’s this all about? This is what I am calling The “New” Soil Fertility.

This is the natural alternative to chemicals and poisons. It is natural because these methods are attempting to link up, support and cooperate with natural systems. I call it “New” because it is newly discovered, but it is the oldest system of fertility; it is Nature’s own system of nutrient cycling that has made forests and prairies fertile for centuries.

So how does this work and how do we apply it to growing food and landscapes? We could begin by saying that the old chemical soil fertility method treated soil like dirt, seeing it as an inert matrix (as in hydroponics) to which elements must be added to create fertility, mostly with nitrogen, phosphorus and potassium (NPK). This model was not entirely wrong in assuming that soil fertility does depend on NPK, but as will be shown, this understanding was greatly oversimplified.

In his latest book In Defense of Food, food guru Michael Pollan talks about Fritz Haber, the scientist who invented the method for synthesizing nitrogen fertilizer from fossil fuels: “…Haber completely overlooked the importance of biological activity in the soil: the contribution to plant health of the complex underground ecosystem of soil microbes, earthworms and mycorrhizal fungi. Harsh chemical fertilizers (and pesticides) depress or destroy this biological activity, forcing crops to subsist largely on a simple ration of NPK. Plants can live on this fast-food diet of chemicals, but it leaves them more vulnerable to pests and diseases and appears to diminish their nutritional quality.”

The “New” Soil Fertility paradigm sees the soil as alive. A teaspoon of soil can have 10,000-100,000 species, not individuals, but kinds of individuals, most of which have never been identified or studied. We now see soil as a complex ecosystem that exists on several levels: mineral, biological and electrical (ionic), all relating through the media of water and air. The Soil Food Web is defined in the excellent book Teaming with Microbes  by Jeff Lowenfels and Wayne Lewis  as “…the complex interactions, relationships and chemical and physical processes involving the nutrition of many kinds of soil organisms including plants.” These plants and microbes interact to perform such functions as bringing water and releasing acids, hormones, antibiotics, enzymes and nutritional juices. At the same time, the physical movements and growth and death of beings in the soil affect the structure of the soil. Bacteria, fungi and worms all produce sticky substances that bind small particles of soil together forming aggregates. These clusters create porosity and tilth in soil, allowing water and air to enter and be stored more easily, creating storage areas for soluble nutrients, and making it much easier for the gardener to dig.

Bacteria and fungi are the primary decomposers. They are the main agents responsible for making compost and humus. They break down plant and animal wastes by eating them, holding the nutrients in their bodies, and in the process sequestering carbon (keeping it from being released as carbon dioxide into the atmosphere). Some are attracted to plant roots that “leak” carbohydrates to their benefit. Nematodes and protozoa then eat the bacteria and fungi and their excrement contains nutrients for the plants. Some bacteria fix nitrogen from the air for plant use, some stabilize phosphorus, some make iron available, and all are a main food source for other soil organisms. Soils dominated by bacteria support annuals, grasses and vegetables.

Soils that are dominated by fungi, are preferred by trees, shrubs, grapes and perennials. Fungi have been the focus of groundbreaking mycologist Paul Stamets for over 30 years. He has explored the many roles of fungi as food, as medicine, as pesticides and as healers of the earth. In his latest book Mycelium Running, Stamets explains: “…from dead plants, fungi recycle carbon, hydrogen, phosphorus and minerals into nutrients for living plants, insects, and other organisms sharing that habitat.” Some fungi are soil builders while other mycorrhizal fungi partner with the roots of plants, bringing water and other nutrients through their vast network of mycelia, expanding a plant’s contact with the soil up to 700 times more than the root system alone. In addition, fungal mycelia create a web that prevents erosion and aerates soils.

So how can gardeners harness these hordes of tiny beings to improve our gardens’ fertility?

In the next issue we will explore this question as well as discuss compost tea and the value of earthworms.

In the last issue we discussed soil fertility, how chemicals became a part of agriculture and the “new” approach to fertility that is based on Soil Life.

We have been taught to be afraid of bacteria and fungi and insects. We were told that they are the causes of diseases, illnesses and allergies and that they kill our plants. Well, now the truth comes out that the vast majority of these creatures are beneficial, and in fact, strong and diverse populations of these beneficials not only out-compete the bad guys, but reduce the need for pest-management in our gardens and farms.
How can gardeners harness these hordes of tiny beings to improve their gardens’ fertility? I suppose the best explanation is: Be nice to them. They know their jobs, they have millennia of experience in creating nutritional systems and they live by a principle that humans lack faith in, which is that: cooperation is more successful than domination so everybody does better when everybody does better. Stamets says there is scientific evidence that fungal mycelium distribute nutrients in forest habitats so that all the trees, even young trees in the shade of big trees, prosper. These microbes need the same things people need: food, water, air and a non-toxic environment.

Here  is a list of dos and don’ts to support the “New” Soil Fertility

  1. don’t kill the microorganisms with chemical fertilizers, fungicides, herbicides and pesticides
  2. do feed the microorganisms with various kinds of organic matter in both composted and partially composted forms
  3. do control pests with non-toxic sprays if needed, but mostly, prevent pest problems by growing strong plants in a vital soil
  4. don’t use chemical fertilizers as they are water-soluble, wash away quickly through the soil, pollute rivers and oceans, and leave the soil life hungry
  5. do use organic fertilizers which break down slowly and feed the microorganisms and plants over a 6 month period.
  6. don’t plow or rototill a garden except the first year when you are incorporating a lot of organic matter, because plowing and tilling breaks up the mycelium webs and the destroys the porosity. Let the worms and other soil life till the soil.
  7. do use animal manures, especially if they are low in salt, are aged or composted and are free of weed seeds. Manures support bacteria more than fungi.
  8. do apply mulch to keep soils moist and cooler, and to add organic matter
  9. do add small amounts of a variety of additional nutrients for a richer soil and a more diverse population of microorganisms: kelp meal, worm castings, humate, rock dust, greensand, soybean meal, fish meal, blood meal, feather meal
  10. do add mycorrhizae to the root zones, and well-aerated compost tea which can be sprayed onto the foliage or added to the soil with a sprinkling can.

What is compost tea and what is it for? According to Dr. Elaine Ingham at, compost tea is an aerated liquid made by steeping compost and other nutrients for 12-24 hours in a brewer with continual aeration. This process extracts bacteria, fungi, protozoa and beneficial nematodes and increases their populations. Compost tea is used to inoculate microbes into the soil and onto the leaves of plants and to add soluble nutrients to the soil. It’s use results in improved plant growth, prevention of diseases, reduced water use and improved soil structure. An article in Tree Care Industry magazine stated compost tea “…has proved to be highly beneficial for relieving stress when transplanting or pruning trees. It’s also helpful when applied directly to roots that have been cut during construction….”

The value of compost tea is related to the exact ingredients used, the type of brewer and the length of time in brewing. It can be made to propagate more bacteria or more fungi. It is essential that the brew remains highly aerobic (oxygenated) because low oxygen conditions favor disease-causing organisms. To get the most benefit, use within 6 hours of brewing (aeration), although some people say the tea is still effective up to10 hours.

In addition to microorganisms, earthworms are a part of soil life that support soil fertility. Earthworms have long been known to play an important role in soil, but recently their role has been recognized not only as aerators and turners of soil, but as significant contributors to plant growth and health. Numerous studies have shown the value of worm castings which are called “worm poop” but which are really the enriched soil that has passed through the worm. These castings can reduce fungal diseases like damping-off and powdery mildew, when used either as a compost tea or as a soil amendment at 5%-20% by volume of soil. The Soil Biology Laboratory at Ohio State University researched this thoroughly and found that even small amounts added to potting mixes “…resulted in dramatic improvements in plant growth,” and changes in the defensive chemistry of plants resulting in improved plant health. (in particular, fewer aphids)

Even though the NPK of earthworm castings is low, their nutrients are powerful because they are so readily available to plants, and because the castings are so rich in microorganisms. In addition, researchers at Purdue University have discovered that when earthworms eat organic matter on the surface, they take it down into the soil and mix it in, thus reducing the normal oxidation which sequesters the carbon so it is not released into the atmosphere as carbon dioxide.

The “New” Soil Fertility model is coming forward just in time to meet the demands for sustainability. Obviously the chemical model was not at all sustainable. Now if we cooperate with the natural biology of soil life by feeding it, not poisoning it and not disrupting it, the soil will improve mostly on its own. All we need to do is feed the soil with our organic wastes, make some special additions for the production of food, maybe sprinkle some compost tea once in awhile to build up microbial populations, add water and…Presto: Sustainablility. It sounds too good to be true.

Obviously we need to learn how to operate in this new system. We know more about the dark side of the moon than we do about the workings of our soils. We are going to have to learn a lot more about the unnamed, unstudied microorganisms; we will have to experiment with different approaches; and we will have to start thinking of ourselves as cultivators of the soil, as well as the plants. We have been brought up to see plants as living and soil as dead. Even though there is an ancient adage, “Feed the soil, not the plants,” we think of the soil and the plants as separate.

Things are different now. It is widely known: the soil is alive-alive-o. Soils high in organic matter sequester twice as much carbon as the vegetation and atmosphere above it; (could soil building become an answer to global warming?) We meet the rest of the planet at the soil level, sharing water and using resources, and adding or not adding to the poisons in our environment. We are running out of petroleum anyway, so sooner or later, we will have to change our methods. If we fight Nature, we are going to lose. The “New” Soil Fertility model depends on a greater vision of giving up a Domination model in exchange for a Partnership model. Paul Stamets sees it the way his mushrooms see it: “The interconnectedness of life is an obvious truth that we ignore at our peril.”

Article by Mikl Brawner, 2009


Teaming with Microbes by Jeff Lownfels & Wayne Lewis
Soul of the Soil by Grace Gershuny and Joseph Smillie
The Earth Moved by Amy Stewart
Mycelium Running by Paul Stamets
In Defence of Food by Michael Stamets
Growing Green by Jenny Hall and Iain Tolhurst
Weedless Gardening by Lee Reich
Life in the Soil by James B. Nardi
“Dig It! The Secrets of Soil”-Smithsonian exhibit through Jan 3, 2010