Teaming With Microbes - A Gardener’s Guide to the Soil Food Web

Lowenfels, Jeff and Wayne Lewis

Teaming with Microbes introduces readers to the vast abundance of living creatures in the soil. Through complex inter-relations between microorganisms, a soil food web is formed. While chemicals and many farming techniques disrupt this balance, the authors explain ways to help the soil life flourish, which in turn provides a suitable environment for plants to thrive.

The following book review and detailed summary was written by Kip from Victoria Farm, and was originally printed in Growing Green International, a magazine published by the Vegan Organic Network.

Teaming With Microbes: A Gardener’s Guide to the Soil Food Web has been available since late 2006. It is an entertaining, easy to read yet comprehensive introduction to the biological workings of the soil and how to influence the same for your own particular horticultural interests. The book contains strong support of organic methods, on-farm fertility and avoidance of the use of animal manures. I will try to pass along some of the concepts presented by the authors in this review.

Author Jeff Lowenfels has written a gardening column for the Anchorage Daily News for the past 30 years. Co-author Wayne Lewis is a lifelong gardener. Both subscribed to the chemical approach to horticulture. One day by happenstance they saw an electron microscope picture of a root-eating nematode trapped by a fungal strand and another picture of a nematode, untouched by fungal strands entering a tomato root. This sparked a great curiosity and their ensuing research lead them to soil microbiologist Dr. Elaine Ingham, who became their mentor. Lowenfels and Lewis went on to apply biological growing techniques to their own soils and were amazed by the results. They then wrote this book to share what they had learned.

In the book, the authors focus on the diverse microbiology of the soil as metaphorical ‘actors’ on a ‘stage’ set of classic soil science parameters such as pH, texture, porosity, organic matter content and cation exchange capacity among others. It is organized as follows:

Part 1. The Basic Science

Foreword by Dr. Elaine Ingham Ph.D.
Preface

  1. What Is the Soil Food Web and Why Should Gardeners Care?
  2. Classic Soil Science
  3. Bacteria
  4. Fungi
  5. Algae and Slime Molds
  6. Protozoa
  7. Nematodes
  8. Arthropods
  9. Earthworms
  10. Gastropods
  11. Reptiles, Mammals, and Birds

Part 2. Applying Soil Food Web Science to Yard and Garden Care

  1. How the Soil Food Web Applies to Gardening
  2. What Do Your Soil Food Webs Look Like?
  3. Tools for Restoration and Maintenance
  4. Compost
  5. Mulch
  6. Compost Teas
  7. The Lawn
  8. Maintaining Trees, Shrubs and Perennials
  9. Growing Annuals and Vegetables
  10. A Simple Soil Food Web Garden Calendar
  11. No One Ever Fertilized an Old Growth Forest

Appendix: The Soil Food Web Gardening Rules
Resources
Index

Did you know that one teaspoon of good garden soil (about as much as can be balanced on your pinky finger) contains one billion bacteria of between 20,000 and 30,000 species, several yards of fungal hyphae, several thousand protozoa and a few dozen nematodes? If this is news to you as it was to me, you will never look at soil the same way again. All these soil organisms are quite active and need to eat something containing carbon for the energy to power their metabolisms. This carbon may come from organic plant material or the waste or bodies of other organisms. Most soil organisms eat other organisms, and many different ones at that. When this food chain is drawn, it forms more of a food web.

Interestingly, this chaotic feeding frenzy is controlled by plants in the area, for the benefit of themselves. Much of the energy produced by plants through photosynthesis is used to make chemicals that are exuded from their roots in the forms of carbohydrates and proteins. The exudates attract specific bacteria and fungi, which consume them. These bacteria and fungi attract and are eaten by larger microorganisms, specifically protozoa and nematodes. The wastes of these larger microbes are then absorbed by plant roots as nutrients.

Soil bacteria and fungi store nutrients in their bodies, in the plant root zone or rhizosphere. Protozoa and nematodes make these nutrients available to plants when they consume the bacteria and fungi. These nutrients stay in the soil, unlike synthetic or chemical nutrients, which if not immediately taken in by plant roots, leach into ground water. Protozoa and nematodes are in turn eaten by arthropods; i.e. insects and spiders. Arthropods also eat each other and are eaten by moles, snakes, birds and other animals.

Chemical fertilizers decimate large portions of the soil food web. This is due to the salts contained within them. Water in the cells of soil microbes flows to the higher concentration of salts outside the organisms, literally bursting through the cell walls in what is referred to as osmotic shock. As little as 100 pounds of nitrogen per acre can destroy a soil food web.

Bacteria play a key role in cycling nutrients, especially nitrogen, which is inert in the atmosphere and must be fixed by bacteria such as Azotobacter, Azospirillum, Clostridium or Rhizobium or combined with oxygen or hydrogen to produce ammonium (NH4+), nitrite (NO2) or nitrate (NO3-). When protozoa and nematodes consume bacteria and fungi they excrete wastes of ammonium. Then Nitrosomonas bacteria convert the ammonium into nitrites, which are then converted by Nitrobacter spp. Bacteria into nitrates.

Nitrifying bacteria start to diminish in the soil when ph drops below 7. When this happens, more and more ammonium remains unconverted in the soil. As fungal populations grow, the acidic enzymes they produce lower soil pH. As soils become dominated by fungi, the nitrogen available is increasingly ammonium.

Some plants, like brassicas and other vegetables, prefer their nitrogen in the form of nitrates and do better in bacterially dominated soils. Others, such as perennials, shrubs and trees prefer their nitrogen in ammonium form and do better in fungally dominated soils. Fungi to bacterial ratios have been observed for different plant groups. Vegetables such as lettuce, broccoli and carrots like 0.3:1 to 0.8:1 while tomatoes, corn and wheat prefer 0.8:1 to 1:1. Orchard trees on the other hand do well with 10:1 to 50:1 and hardwoods from 10:1 to 100:1.

Good compost has per teaspoon 1 billion bacteria, 400 to 900 feet of fungal hyphae, 10,000 to 50,000 protozoa and 30 to 300 nematodes. Compost can inoculate, maintain or alter a soil food web in a given area. Careful selection of compost ingredients can produce a bacterial, fungal or balanced pile.

Mulch ingredient selection can support bacterial or fungal webs also. Even the same mulch material applied in different ways can influence a specific soil food web. Mulch placed on the surface supports fungi while mulch worked into the soil will support bacteria. Coarse, dry material benefits fungi and finely chopped, moist material benefits bacteria. If too much carbon exists in the mulch, nitrogen can be used from the soil, causing nutrient locking. This usually only occurs at the thin soil/mulch interface and not in the rhizosphere according to the authors. This locking can be minimized by ensuring that woody materials are kept at 3/8 inch or larger to prevent most bacterial colonization.

Compost and mulch take time to work down into the root zone. Their use can also involve lots of work in larger holdings. Also neither compost nor mulch will stick to leaf surfaces (plants create exudates from their leaves also). Actively Aerated Compost Teas or AACTs are an exciting tool for the grower which began to appear in commercial agriculture about 10 years ago. AACTs work faster because the microbiology is not bound up in the hummus of the compost. They are easy to apply and inexpensive, too. AACTs are not extracts, leachates or manure teas but rather ‘brewed’ aerobic mixtures highly concentrated with beneficial microbes. A teaspoon of AACT can have up to 4 billion bacteria compared to 1 billion bacteria in a teaspoon of compost alone. In a nutshell, AACT is made by adding compost plus a little microbe food to dechlorinated water and bubbling air through the mixture for one to two days. The finished tea is then applied as a soil drench or foliar spray. The authors describe how you can make your own brewer with common locally found materials.

As with compost, AACT can be tailor made to be bacterially or fungally dominated or balanced between the two. Five gallons of tea can treat up to an acre and it is impossible to over apply good tea. Foliar use of AACT has prevented and suppressed pathogens and diseases through its microbes occupying potential infection sites and outcompeting pathogens by consuming plant leaf exudates before the detrimental microbes can get to them. Author Jeff Lowenfels strongly cautions against using any animal manure in compost or AACT due to the pathogens and synthetic materials found therein.

Throughout the book, the authors emphasize the impact that rototilling and other deep soil disturbances have on the soil food web. They tell the story of Jethro Tull’s experiments in agriculture and how he noticed that broken up soils produced better vegetables. He thought it was because plant roots actually ate soil particles and the broken soil contained smaller, more bite-sized particles for them. In reality, the vegetables did better because when Jethro Tull pulled his horse drawn hoe through the soil he was destroying years of fungal hyphae growth. The soil then became more bacterially dominated, which vegetables preferred. The addition of manures to broken up soil fed bacterial populations well, adding to the effect. Unfortunately, including the loss of fungi, deeply tilled soil loses worm tunnels and pores between soil particles are broken apart. Weed seeds are also exposed. When water contacts tilled soil, it starts the compacting process, which continues at each occurrence. Even bacterially dominated soils need fungal presence for structure and microbial diversity.

Instead of tilling, the authors recommend feeding the soil food web by putting down 1 to 2 inches of tailored compost before planting. Plant using a dibble, trowel or the corner of a hoe drawn lightly across the surface and backfilled with compost. Then apply bacterial, fungal or balanced AACT as the situation requires to the soil followed by the appropriate mulch. Weeds are prevented by loss of light due to the mulch cover and also by the locking of nitrogen, phosphate and sulfur needed by weeds to germinate at the thin surface soil/mulch interface. The mulch acts as a physical barrier as well.

As a critique, I found the book written in an informative yet entertaining manner. It was well illustrated with many color images of the microbes involved. A copy of a microbiology test from a Soil Foodweb, Inc. lab was included at the end of chapter 13. While the authors are not veganic growers themselves, there are only a couple non-vegan techniques, which can easily be modified to suit the vegan ethic. For instance, the authors suggest using ground up fish in chapter 17 as one of several optional ingredients to shift compost tea to a more fungal dominance. Soluble kelp meal or oatmeal can be used instead. The book is currently available in hardback from online booksellers, from the publisher Timber Press (www.timberpress.com) and from some of the larger retail book stores. I found my copy on the shelf of the gardening section at just such a place completely by accident!

If the message presented in this book could be condensed down to one sentence, it would seem to be: take care of the ‘little things’ and the ‘big things’ will take care of themselves.

If you would like to read further about the soil food web, the organization founded by Dr. Ingham, Soil Foodweb Inc., has a good website that offers a wealth of information. Check out the soil foodweb approach and the different pictures of soil microbes. If you are interested in a very accurate assessment of the microbiology of your own soil, compost or compost tea, you can have them tested at a Soil Foodweb laboratory. Currently, there are labs in the US, Canada, Australia, New Zealand, South Africa and soon in Japan and Mexico. The lab for the Central and South America and the US is:

Soil Foodweb, Inc.
1750 SW 3rd St Suite K, Corvallis, OR 97333-1796
phone: (541) 752-5066 fax: (541) 752-5142
www.soilfoodweb.com

The lab for Canada is:

Soil Foodweb Canada Ltd
Box 915 Bay 1, 285 Service Road Vulcan
Alberta T0L 2B0 CANADA
Phone: (403) 485-6981
Fax: (403)485-6982
Website: www.soilfoodweb.ca

Also, author Jeff Lowenfels moderates a compost tea group at yahoo for further discussion on the subject. He and Dr. Ingham both participate regularly.

LOWENFELS, Jeff and Wayne Lewis. Teaming with Microbes – A Gardener’s Guide to the Soil Food Web. Timber Press, 2006, 197 p.


14 May 2008
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