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Soil Biology and Humus Farming
Volume 13 number 5
by Jody Padgham
Š2005 Midwest Organic and Sustainable Education Service

NPK, NPK- how many of us have learned about soil management following the principle developed in the mid 1800's that the availability of inorganic nutrients (such as nitrogen, phosphorus and potassium: NPK) determine if plants thrive? Following the NPK theory, you seek out the limiting nutrients by testing soil for basic chemical composition and increase productivity by making those nutrients available.

In recent years, especially since the interest in organic agriculture has thrived, a new theory on soil fertility has come to the forefront of discussion. Known under various names, current soil biology theory does not focus on only basic minerals in assessing fertility. Instead it highlights the role of soil organisms and the relationship they have with each other, minerals and plants in guiding overall fertility. Several methods for supporting soil life are now being utilized to enhance fertility and overall crop yields.

"Soil biology is fascinating. You can study soil biology your whole life and still barely scratch the surface," Steve Diver of NCAT-ATTRA noted at a recent presentation to organic farmers, titled Soil Biology and Humus Farming. The way Steve presents information on soil biology, it isn't hard to stay fascinated. Steve is passionate about the dynamic world of life found within soil, and the critical role it plays in building plant health. In his presentation he briefly outlined the basics of soil life and a few methods used to enhance the health of plant crops by managing and feeding soil organisms. These include the use of compost, vermi-compost (worm compost), compost tea, Effective Microorganisms (EM) from Japan and IMO from Korea.

Managing soil fertility through biology
Researchers have found that when crop yields are high, the number of microbes found in the soil are also high. Organic farmers are learning that they will be most successful in managing their systems by maximizing soil life. A successful organic farmer will not rely solely on NPK management, but instead learn about the organisms in their soil and how to create conditions in which they thrive.

Soil Biology theory is not new- researchers such as Siegfried Lubke states in his "Vitality Theory of Soil Fertility" that the greater the quantity and variety of soil life growing and feeding in and on the soil, the higher its fertility will be. Lubke's premise is that the complex diversity of soil organisms drives the functions of the soil. These functions include fertility, nutrient availability, soil structure, and disease suppression. Lubke notes that: "A soil isn't fertile because it contains large amounts of humus or minerals or nitrogen, but because of the continuous growth of numerous and varied microbes and soil life, which break down and reconstruct nutrients from organic matter supplied by plants and animals into a plant available form. The populations of soil life benefit us by making minerals plant available, building humus, building slimes and the crumb structure of soil. A soil teaming with varied forms of life is an excellent growth environment for plant roots."

Organisms found in soil
Steve Diver outlined four major categories of organisms found in soil. They include bacteria, fungi, micro fauna (such as protozoa and nematodes, which feed on fungi and bacteria) and mezo fauna (which include arthropods and other insects). Steve jokes that organisms are perhaps more easily categorized as the "stay-putters," the "swimmers," the "crawlers," and the "burrowers." They range in size from invisible (microscopic) to those that can be seen by the naked eye.

When you think sometimes that our world is getting to be a crowded place- just think about these numbers. One TEASPOON of agricultural soil (1 gram dry) has: 100 million to 1 billion bacteria, several yards of fungal strands, several thousand protozoa (amoebas, flagellates and cillates) and 10-25 nematodes, which are mainly feeding on bacteria or fungi with a few predatory individuals wandering through. One square foot of that same soil will also house up to 100 arthropods and 5-30 earthworms.

Dr. Elaine Ingham, President and lead researcher at Soil Foodweb, Inc. has labeled the ways these organisms interact with each other, plants and ultimately, animals "The Soil Food Web." Using a simple diagram, Dr. Ingham captures the complex interactions of soil organisms. An excellent book co-written by Dr. Ingham, Soil Biology Primer explains in detail the roles that different members of the soil food web play. The book begins by pointing out that "Growing and reproducing are the primary activities of all living organisms." Simple organisms derive energy from plants and organic matter, other organisms graze on these primary organisms. Throughout these interactions nutrients are released into the environment. Each soil profile will have its own unique soil food web, which is based on general concepts portrayed in the basic soil food web diagram. For a full understanding of the complexities of the soil food web, read the Soil Biology Primer, which is written in a very accessible format with numerous fascinating pictures and graphs.

From Soil Foodweb, Inc.

Around the U.S. there are now a diversity of biological laboratories, including Soil Foodweb, Inc. run by Dr. Ingham, which will measure different organisms in your soil. By analyzing a properly prepared soil sample from your farm, they will be able to tell you the amount of bacteria and fungi and the percent of those that are actively metabolizing- in essence the "quality" of soil microorganisms found in your soil. Most biological soil labs can test for other types of organisms, and will also test compost, compost teas and leaves and do tests for organic matter content and other parameters of value to organic farmers. (For more information get the publication "Alternative Soil Testing Laboratories" from ATTRA at http://www.attra.org/attra-pub/soil-lab.html or by calling to request a copy, 800-346-9140) These tests take soil analysis to a whole new level. Those seriously interested in managing their soil biology should consider having a soil biology test done.

Different kinds of soils will have different balances of microorganisms. Row crops and grass system soils will be populated with a majority of bacterial microorganisms. Bacteria choose to feed on green, succulent, fresh organic matter. A forest, orchard or vineyard will have soils dominated by fungal species. Fungi prefer woody, starchy food. This simple fact can help you in managing your farm. Have you ever spent long days planting bulk tree seedlings into a grassland, only to have limited survival success? We know that competition for resources, such as moisture and sunlight, will cause the tree problems, but the basic unbalance of microorganisms in the soil creates additional stress. This can be alleviated by surrounding the seedling with wood chip mulch, which will help encourage fungal growth and move the soil organism balance to the fungal dominance in which trees more readily thrive.

The role of soil organisms
The Soil Biology Primer has some good basic information on the different functions of soil organisms, which we won't cover in great detail here. As a broad overview, the various tasks of soil organisms fall into several categories:
" they capture energy through photosynthesis (plants, algae, bacteria),
" they decompose things and break down residue (bacteria, fungi)
" they enhance plant growth through mutual activities such as symbiosis and mycorrhizal relationships (bacteria, fungi),
" some promote disease or are parasites,
" some, such as a few nematodes, eat roots, others eat bacteria or fungi.
" Others break down residue and enhance soil structure through shredding,
" and the higher-level predators perform the role of regulating populations and improving soil structure by passing soil through their guts.

Steve Diver summarizes some of the key organism functions "Think about the bacteria and fungi as the fertilizer bags, and the protozoa and grazers as the fertilizer spreaders."
Diver notes that protozoa will eat over 10,000 bacteria per day, and that this activity is what releases nutrients onto organic farms.

Nematodes in particular have quite a reputation in farming systems, and most of them aren't popular. Diver tells us that nematodes are not inherently bad and that "nematodes are the most important regulator of the nitrogen cycle in Midwest farming systems." Diver says that 3 out of every 4 nematodes are beneficial. When you hear about nematode problems, it is an indicator that there is not enough food for the complexity of the particular soil food web that is present.

Role of other parts of the soil
Let's spend a little time talking about the substrate that these organisms are working on. Organic Matter is made up of about equal parts humus and active organic matter. Active organic matter is what is available for use by soil organisms. This includes all the living biomass, any dead plant or animal material, any decompositional elements, and compounds secreted from roots (such as soluble sugars and amino acids). Humus is made of complex organic compounds that remain after the soil organisms have transformed the base material. Steve Diver states that "humus is to organic matter as flour is to bread."

The fertility of a soil rests upon its clay-humus complex. Soil nutrients and water are retained by a complex of humus and clay particles, and linked by calcium (Ca) and iron (Fe) based compounds. "The most significant aspects of humus in soil is its interaction with clay constituents, which give rise to clay humus." Diver states. He calls clay humus "the seat of soil fertility." He continues "organo-clay complexes have a strong influence on soil availability. Permeability, porosity, water moisture retention, adsorption, cation exchange, nutrient exchange capacity are all tied up in the clay-humus structure." Diver points out that the soil-clay humus crumb in the soil looks "like a head of cauliflower" and that microbes "have lots to do there". "There is a large surface area, which creates a lot of opportunity for microbe activity and nutrient availability."

Diver maintains that if we manage the humus, the soil organisms will then do the work for us of making that humus available for plant growth. Humus provides soil food, housing, and habitat for soil creatures. The creatures organize themselves into a soil food web, with abundance and diversity.

Although minerals such as NPK are important to the functioning of plant life, bio-organisms are the key to making mineral nutrients available to those plants. See the accompanying article to get a introduction on a few ways to stimulate the biological life of the soil.

Managing Soil Biology

Given the importance of soil biology, how can it be increased or managed? Steve Diver presented several ways to affect the complexity and abundance of soil organisms.

Compost
Compost is a term that describes a managed process of organic matter decomposition and recomposition. For those who are certified organic, it is also a very closely regulated process. Those in organic production may only produce and use compost that has been made following the National Organic Program Rule (find details at http://www.ams.usda.gov/nop/indexNet.htm ) Compost is generally made from animal manure and vegetable matter or some other carbon source. To make compost you must manage the carbon to nitrogen ration, monitor the temperature so that pathogen reduction is ensured and mix or aerate so that the decomposition process is aerobic rather than anaerobic. In the composting process raw organic material is attacked by microorganisms and broken down into the building blocks of simple sugars and amino acids, which are more readily available for plants and organisms to use. High quality compost will contain 25-30,000 species of bacteria and 5-8,000 species of fungi. Application of active compost is an excellent way to increase the complexity and diversity of your soil food web.

Vermi-compost
Worm compost, or vermi-compost is very high in fungal components. A vermi-compost system is made up of worms that are fed some form of waste- kitchen scraps or vegetable waste etc. The worms don't eat the waste- they in their own way "farm" it, in that they encourage fungi and fuzzy things to grow on the waste, and then eat the fungi and micro organisms that are growing. The "farmed" microbes actually eat the waste, not the worms. Vermi-compost can be used to make compost tea or used as a direct compost, and brings thousands of beneficial bacterial and fungal components into the soil food web.

Compost tea
Compost tea is an on-farm method of preparing microbial cultures. Local biomass sources (such as compost, vermi-compost or peat-humus material) are used to prepare the tea, which can be used to enhance fertility, for pest control and to enhance a farms ecosystem health. Compost teas are a very "hot" topic, and worthy of their own article (if not several books.) A great resource for more information is the ATTRA publication by Steve Diver "Notes on Compost Teas" which can be downloaded at http://www.attra.org/attra-pub/compost-tea-notes.html (or a hard copy can be obtained by calling ATTRA at 1-800-346-9140). Compost teas can be made with or without aeration, and with or without additives (such as molasses or kelp) and are made during a specific extraction period.

Compost teas have been found to be a very good source of soluble nutrients (acting as an organic liquid fertilizer), as a source of bio-active substances, some of which are growth promoting, some are plant protective. Compost teas are also a good source of beneficial microorganisms, and some actually provide a microbially enhanced nutrient delivery. They can be applied to the soil, or directly to plant leaves and have been proven to have significant effects on plant health, with positive effects of suppression of specific diseases. For more information on compost teas, see the Soil Foodweb, Inc. website at www.soilfoodweb.com.

Because they can be made from compost, which is generally made from manure, compost teas have created a furor with organic certification. A "compost tea" sub committee composed of farmers and researchers has made recommendations to the National Organic Standards Board and expects a final ruling soon on how the NOP recommend using compost teas.

Effective Microorganisms
Farmers in Japan have been "growing" and harvesting the benefits of microorganisms for many years. Under the umbrella of the "Nature Farming" movement, which parallels the organic farming movement in western countries, EM is a very well established mechanism for promoting plant growth and developing microbial activity. Early developers experimented with a diversity of microbial cultures, but have narrowed in on a basic "mother" containing 3 elements: 1. Lactic acid bacteria. 2. Various photosynthetic bacteria and 3. yeast. The "mother" is added to plant material to culture, and it has been found that other organisms will "join" the original culture to eventually form a very complex microbial stew, which can then be used for many purposes. The process of culturing is often anaerobic, and much like a pickling process. The resultant stew can be used in creating compost, vermi-compost, as a livestock probiotic, in food waste treatment, waste water treatment and to control flies and livestock odors and many other uses. There are hundreds of EM recipes, and hundreds of research papers documenting EM effects. It is used in many countries around the world for a multitude of purposes. Proper use of EM utilizes a low-dose, multiple application, slow and accumulative effect. There are only a few sources of EM mother culture in the U.S. at this time. An internet search on "Effective Microorganisms" will bring up several sources of mother cultures in the U.S. and research on EM use for hundreds of applications.

EM is widely used in India, where one popular culture is made with Neem leaves, 14 other plants and sugar cane. It is said that this ferment is excellent for pest control, and will control 54 insect and disease problems on farms.

IMO
IMO is similar to EM in Japan, but is a Korean tradition that has just been gaining acclaim in the English speaking world in the last few years. Unfortunately, there are very few written resources on IMO written in English. IMO is not based on any purchased product. A mother culture is created that is unique to a particular farm or area by putting a patty of boiled rice out into the forest and covering it with forest duff. The patty is protected from rodents and disturbance, and left for a week. Local fungi and bacteria will invade and feed on the rice. After the first week, the rice is brought in and 1/3 volume of molasses is added. The culture is moved to a crock pot, where it is left to sit for another week. Then molasses is again added, at a 1:1 ratio. This becomes the IMO stock solution. Diluted with 20 parts of water this becomes a microbial inoculant for compost, soil or plants.

This is only one recipe for IMO- there are hundreds of others, using fermented fruit juice, fish, plant juice, amino acids, brown rice syrup etc. as the base. In Japan and Korea there are large neighborhood fermentation vats, which people can bring their cooking and yard wastes to, to go into the ferment. The ferment reduces problematic smells and pests, allowing kitchen waste to accumulate until it is convenient to move it to a composting facility.

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