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Soil Biology and Humus Farming
This article was first printed in the September - October 2005 issue of the Organic Broadcaster, published by the 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
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
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.
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
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
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
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.
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.
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.
Jody Padgham has been with MOSES since 2002. She is the organization's Financial Manager, the editor of the Organic Broadcaster newspaper and co-coordinator of the Organic University. Jody raises poultry and sheep organically on a 60-acre farm in west-central Wisconsin.Return to TOP