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This week's Book of the Week feature is Farming in the Presence of Nature, by Athena Tainio.
From Chapter 3: Living Soil
Carbon, Nitrogen and Nematodes
Soil organic matter consists of two general groups: non-decomposed plant and animal material and humus. Bruce often commented on carbon as being too often overlooked as a plant nutrient, even though it is the key component in all life on Earth.
Carbohydrates (sugars) provide the necessary energy for beneficial bacterial populations to thrive. These plant growth enhancers (PGEs) are most abundant in soils where the carbon to nitrogen ratio (C:N) is 30:1, which means for every 30 units of carbon, there is one unit of nitrogen. The C:N ratio within the bodies of soil microbes is about 8:1, which is important for energy and cellular metabolism. During respiration, the microbes burn about one third of the carbon they consume, releasing it into the atmosphere as carbon dioxide, which is used by plants for photosynthesis. In order to support microbes in maintaining a healthy C:N ratio, their feedstock (compost/organic matter) ideally should have a C:N ratio of between 20:1 and 30:1.
“The list of things we do to soil that can destroy its natural balance is long, from fumigation and overuse of herbicides, to overuse of nitrogen.”
— Bruce Tainio
When nitrogen is overused, the soil’s C:N ratio narrows, which means less carbon is available for bacteria and fungi, and populations dwindle and become dormant or die. A suppressed microbe population leads to poor digestion of organic matter, poor soil quality, limited mineral availability, and leaves plants vulnerable to nematodes and other pathogens.
In the soil there are two basic types of nematodes: free-living (beneficial) nematodes and parasitic nematodes. Most soil nematodes are of the beneficial type, and are important for decomposition of organic matter and recycling of nutrients.
But parasitic nematodes have their place in the ecosystem too, and only cause problems when something has gone wrong to deplete the soil of its armies of beneficial microbes, which are responsible for keeping the pathogenic nematodes in check. Low microbe populations in the rhizosphere usually go hand in hand with a C:N imbalance; but nematodes can be brought under control by restoring balance to the soil’s C:N ratio, which will replenish beneficial microbe populations.
Bruce Tainio’s Recipe for Nematode Control
First, with a soil analysis, determine how much carbon is needed by establishing a baseline C:N ratio. One can almost always expect the C:N ratio to be below 20:1 when pathogenic nematodes are present. It would be a good idea at this time to also get a baseline nematode count and an aerobic/anaerobic microbial plate count for later comparison. A plate count will give you a rough indication of the microbial activity in your soil.
Apply a carbon source, such as humic acid, to restore the carbon to nitrogen ratio to at least 20:1, but not more than 30:1. A ratio of over 30:1 could set up a situation of competition for nitrogen between microbes and plants, causing a shortage of N for the plants. This is not a good idea when plants are already stressed.
Along with the application of carbon, apply a soil inoculant containing a broad spectrum of beneficial bacteria and fungi, and for best results, an enzyme product to quickly jumpstart the inoculants as well as stimulate the starving indigenous microbes.
By implementing these three steps, beneficial microbes should quickly multiply, increasing to population densities large enough and diverse enough to bring harmful nematodes under control in a natural, sustainable way.
In a biological soil management program, fertilizers are regarded as food for soil microorganisms, which in turn provide mineral availability and disease control for plants. For this reason, the forms of fertilizers we use matters a great deal.
Organic fertilizers are made mostly of insoluble materials, which are not available to plants until decomposed and transformed by soil microbes into forms the plants can use, a process called mineralization. In this process, a measure of minerals, held safely in place within the bodies of microbes, are continuously released as the microbes die or get eaten and excreted by other soil dwellers, spoon-feeding the plants in manageable increments.
Synthetic fertilizers, on the other hand, are made of highly soluble inorganic materials, which, although readily taken up by plants, can actually inhibit and even kill microbes and other soil dwelling organisms. Because soil microbes can’t utilize much of these synthetic nutrients, anything not immediately captured by the plants can easily be leached away into the groundwater or volatilize into the atmosphere.
The rate of leaching of soluble fertilizers depends on the amount of available soil moisture and the holding capacity of the soil. In dry soil there is little danger of leaching; but with irrigation or a significant rain, they quickly dissolve and move down through the soil, out of reach of plant roots and into the groundwater table, polluting wells and waterways.
In warm, dry weather, especially under alkaline soil conditions, ammonia from inorganic fertilizers can volatilize into the atmosphere, which eventually comes back to earth as acid rain, causing over-nitrification of water bodies and overgrowth of algae. Acid rain has also been linked to deforestation due to over-nitrification of trees.
Organic nitrogen can become temporarily tied up in the bodies of microbes. This sometimes occurs in the first year of transition from conventional to organic farming. Soils that have been exhausted from synthetic fertilizer and chemical overuse typically have little biological activity.
Sometimes, when organic fertilizers and organic materials are first introduced, microbial life can explode in a flurry of activity, breaking down organic matter, mineralizing organic nutrients and creating humus. During this initial phase of transition, as microbes work hard to repair and rebuild the soil, they use up much of the nitrogen for their own energy and protein-building needs, potentially causing a shortage for plants. Eventually the soil’s structure and fertility is restored to a point where the flurry of microbial activity slows to a normal pace, and adequate amounts of nutrients become available for plants (see figure 3.1). This is a normal and necessary phase in the restoration of lifeless dirt to living, productive soil; but there is no reason for plants and their growers to suffer through these transitional periods!
Anticipating and supporting the needs of the soil’s biology by striving for a carbon to nitrogen ratio of at least 20:1 (but no more than 30:1) by paying attention to the C:N ratio of inputs and cover crops, will give plants needed protection from soilborne pathogens, and help speed up the transitional process.
Fine-tuning and supporting the plant’s nutritional needs through tissue testing and correcting/maintaining with appropriate routine foliar nutrition will help to ensure good quality and yield.
With each subsequent season under a balanced biological program, soil structure and nutrient availability continues to get better, plants become healthier, and yields bigger.
About the Author:
Athena "Teena" Tainio is the president and CEO of Spokane-based Tainio Biologicals, a company that specializes in natural soil enhancing additives. She assumed leadership when her husband, company founder Bruce Tainio, died in 2009. Today, Tainio products are used throughout the United States, Canada, Central America, Australia and New Zealand. Athena continues to help Tainio lead the way in the soil health and agriculture industries.
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