Teaming with Microbes, a Gardener’s Guide to the Soil Food Web, is a fairly popular book in the gardening community and I thought it was time to do a review. This book is written by Jeff Lowenfels, a garden writer and attorney, and Wyne Lewis a lifelong gardener. Both gardeners clearly follow the teachings of Dr. Ingham and her soil food web. They have adopted her methodologies and present the ideas in this book.
Teaming with Microbes – Overview
The book is divided into two parts. The first part is a primer about soil and soil organisms. The second part takes the information in part one and turns it into practicable action items that a gardener can follow.
Part one 0f Teaming with Microbes gives a very good introduction to the various life forms in the garden including bacteria, fungi, nematodes, protozoa and dew worms, to name the main players. The material is will organized and easy to read by the average gardener. From a biology point of view the material is factually correct and interesting without being too heavy on the science.
The authors also discuss some of the chemistry going on in the soil. For example they discuss the importance of pH, and the conversion of different forms of nitrogen. Unfortunately, some of the chemical descriptions are misleading or incorrect.
The second section discusses action items using 19 simple rules for the gardener to follow. In summary the rules use the application of compost, mulch and compost tea to improve the soil food web. All three methods are very well explained in the book. Compost and mulch are accepted scientific methods for improving soil and plant health. Compost tea is not.
For the most part Teaming with Microbes supports the teachings of Dr. Ingham and the soil food web. One exception is the section on using a microscope to identify microbes, where the authors say “when it comes to the microorganisms, we will be the first to admit that you will not be able to determine precisely what is in your soil, even with a powerful microscope.“ (ref 1). The book clearly downplays the importance of counting different kinds of microbes. This is the same conclusion I reached in Soil Bacteria – The Myth of Identification and Management, and goes against Dr. Ingham’s strong promotion of using the microscope to evaluate your soil.
Teaming with Microbes has played an important role in educating gardeners about soil, and the importance of microbes. The authors deserve a lot of credit for this accomplishment. It does a good job of explaining the high level concepts of the soil food web even if some of the details are not completely correct.
I think the book is quite good as an introduction to the food soil web and microorganisms. The inclusion of compost tea is unfortunate, and the emphasis on the importance of adding microbes to the soil limits the value of the book, in my opinion.
I recommend that gardeners read the book with an understanding that some of the claims are not supported by science and that some of the facts are incorrect.
Teaming with Microbes follows most of the key concepts of Dr. Ingham’s soil food web program. The rest of this post will briefly discuss these concepts and provide an overview of the issues.
This post will be followed up by two additional posts that will look more closely at some details in the book.
Synthetic Fertilizers and Pesticides Kill All Microbes
This is repeated throughout the book and forms one of the key reasons why you need to follow the 12 steps to start building your soil food web from scratch. As proof they say “what gardener has not seen what table salt does to a slug”.
Pouring high concentrations of salt onto a slug is nothing like putting fertilizer on the soil. The pesticides and fertilizers will dissolve in water and flow through the soil as a diluted liquid – not a solid.
In the scientific community it is accepted that synthetic fertilizers and pesticides, when used in appropriate amounts do not kill all the soil microbes. I am not saying that some chemicals might have a temporary negative effect on some microbes, but the idea that all or even most are killed by adding fertilizer or pesticides is completely without merit.
Adding Microbes Increases Diversity
This is not supported by science for most most home gardens. Science does not understand the diversity in soil since the majority of organisms have not even been identified. If you don’t know what is there or what is being added – how can you say that diversity is being increased or that there was a lack of diversity before you added the microbes? We don’t know enough about soil organisms to make such claims.
The method proposed in the book for increasing diversity is to take plant material from your garden, compost it, and then return it back to the same garden. So you are taking the microbes that already exist in your garden and returning them back to your garden. How does that increase diversity? If you really wanted to try to increase diversity you would at least get your plant material from another location.
The authors seem to miss the fact that their actions, adding compost and mulching, are really feeding the existing local populations of microbes and as a result plants do better. It is the feeding of existing microbes that is important, not the addition of more.
Different Plants Need Different Amounts of Fungi in the Soil
The advice given is as follows. Perennials, trees and shrubs prefer fungal dominated soil. The fungus makes soil acidic and produces a high ammonium to nitrate ratio. Annuals, vegetables and grasses prefer bacterial dominated soil. Bacteria make the soil alkaline and create a low ammonium to nitrate ratio. Bacteria convert the ammonium to nitrate which is what this group of plants wants. Interestingly, what Dr. Ingham says in one of her YouTube videos (ref 2) is that weeds require a bacterial dominated soil, vegetables need some fungus, with potatoes for example, needing a balance of both. Grasses also need a balance of both, and perennials and trees prefer a fungal environment. Dr. Ingham clearly does not agree with the book.
Does the advice in the book make sense? Similar plants in the same genus can be either perennial or annual – I doubt their biochemisty is so different that they prefer completely different microbes and pH levels in their soil. Our local soil is alkaline, which according to the book, means that trees will not grow well here. But we have lots of forests? We either have unusual trees or the information in the book is not correct.
Most plants can use both nitrate and ammonium, although they might prefer one over the other and some plants don’t do well at the extremes of only nitrate or only ammonium. The term ‘prefer’, in the book, is never explained or quantified. But if the levels are wrong, whatever that means, you need to add the right kind of microbes to fix the problem! How can you fix the problem if it is not defined?
Most gardens have a mixture of both groups of plants growing just fine. I grow grasses, perennials and shrubs in the same garden, with their roots close together – they are all doing well. It seems that most plants grow in a balanced environment – some bacteria and some fungi – some nitrate and some ammonium.
Is this a case of taking some scientific facts and turning them into a complex gardening practice?
All Plant Nutrients are Tied Up in the Microbes
The authors seem to use the term nutrients to mean both the traditional plant nutrients – K, Mg, Ca etc, as well as all of the complex organic molecules found in living organisms. Most of the contents of microbes are not nutrients that plants can use, even if the microbe dies. The microbe consists of large molecules like DNA, proteins, and carbohydrates which first need to be broken up into smaller and smaller molecules until the free nutrients are released.
The book also ignores the plant nutrients found in soil, and the role soil plays in holding nutrients. The majority of nutrients plants use come from soil and pieces of organic matter. Both of these hold the nutrients until they are released into the water surrounding the roots.
In her lectures, Dr. Ingham makes it very clear that the mineral components of soil contain all the nutrients plants need. She goes on to say that soil contains enough nutrients to grow plants forever! In Teaming with Microbes the role of soil as the main nutrient source seems to be ignored.
The Chicken and Egg Conundrum
Much of Teaming with Microbes, as well as the soil food web theory is based on the idea that if you add the right microbes to soil, they will condition the soil environment around the roots to make it suitable for plant growth. Add more bacteria and they will make the soil alkaline. Add fungi and they make it acidic. The microbes are controlling the whole thing. Is this really true?
An alternative view is that the plant roots create an environment around themselves which in turn provides an environment for the right microbes to inhabit. The plants create their own desired environment. They even control when and if fungi connect with their roots. This is the more accepted position – plants are controlling the environment around roots. The microbes are invited guests into the environment.
Numerous recent studies show how plants change their exudates to cultivate the right kinds of microbes at their root surfaces. At the same time, the scientific evidence shows that adding microbes to soil using things like compost tea, have very little impact on growing plants in the field. This strongly suggests that microbes are not making the soil suitable for plants. Instead, plants are making the rhizosphere suitable for themselves.
Adding Bacteria to Soil
Both the soil food web and the idea of using compost tea base their theories on the concept that adding bacteria back to soil is beneficial. How many bacteria are they adding back to soil?
Teaming with Microbes provides some numbers that we can use to answer this question. They suggest that a 5 gal pail of ACCT (aerated compost tea) is sufficient for 1 acre, and that ACCT has 4e6 bacteria per teaspoon. They are adding 4e5 (400,000) bacteria to every sq ft of soil.
That sounds like a lot, but consider this. A gram (weight of a paper clip) of half decent garden soil contains 100,000 bacteria. A sq ft of soil, 6” deep, contains 2e9 bacteria. That is 2,000,000,000 bacteria. Will adding 400,000 more make much of a difference?
This idea of adding small amounts of bacteria to soil does not seem logical, and so far science has failed to show any consistent benefits in field trials. Adding microbes seems to have little effect on plants except in some special cases.
A Closer Look at Teaming with Microbes
For a more detailed look at specifics in Teaming with Microbes have a loot at these followup posts.
- Teaming with Microbes – A Gardener’s Guide to the Soil Food Web, by Jeff Lowenfels and Wayne Lewis, Timber Press Inc, 2006.
- The Roots Of Your Profits by Dr. Elaine Ingham https://www.youtube.com/watch?v=x2H60ritjag