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Organic Matter and Healthy Soils
by LuAnn Rolling, District Conservationist
According to Fred Magdoff, Emeritus Professor of Soils in the Department of Plant and Soil Science at the University of Vermont, soils breathe as if a single organism, with oxygen diffusing downward and carbon dioxide diffusing back into the atmosphere, completing a cycle. He goes on to say in this April 2021 article in Monthly Review titled, Repairing the Soil Carbon Rift, “when soils are disturbed by digging with a spade or by plowing or harrowing, the soil structure is broken up and particles of organic matter that were not accessible to organisms all of a sudden become available. This causes a burst of biological activity that frees some nutrients for plants to use, but also causes a huge increase in organic matter decomposition, with carbon converted to carbon dioxide and diffusing up into the atmosphere.”
Magdoff has calculated that about three times as much carbon is stored in soils than occurs in the atmosphere as carbon dioxide. A soil that has 1 percent organic matter (or about 0.6 percent carbon) in its surface seven inches would be holding the approximate equivalent of the carbon in the carbon dioxide in the atmosphere above the field. According to Neil Sass, Northeast Iowa Area Soil Scientist for the NRCS, current levels of organic matter in Allamakee county soils is approximately 2.5%. “Studies have shown typical carbon losses of 25-50% in many soils, that would mean this same soil may have originally contained up to 5% Soil Organic Matter, SOM. If soils continue to be tilled and farmed in a continuous corn or corn/bean rotation they will never regain this lost carbon and will actually continue to deteriorate until they are unable to produce crops.” He adds that if a producer is incorporating soil health principles into practices like no-till, cover crops, diverse rotations and the introduction of livestock to replace commercial fertilizer with manure, a good rule of thumb is you can increase SOM by 0.1% per year which is 1% in 10 years.
Magdoff says the changing land use from forests and grasslands to farming, aided by increasingly large tractors and implements able to work immense fields, has contributed substantial quantities of carbon dioxide to the atmosphere, contributing to global warming and climate destabilization. Rattan Lal, a distinguished professor of soil science and director of the Carbon Management and Sequestration Center at The Ohio State University, has estimated that some 110 to 130 billion tons (gigatons) of carbon have been lost from agricultural soils. (This is quite large when compared to the 10 gigaton annual contribution estimated for fossil fuels.)
Magdoff adds that while farming practices contribute to atmospheric greenhouse gases, there is a major additional problem. “As soil organic matter decreases soils hold less water, provide lower levels of nutrients to plants, and have lower biological diversity. As the soil structure deteriorates, plants become more susceptible to disease and insects. As less water infiltrates, more runs off, carrying soil particles and the soil becomes more prone to compaction; and crop yields decrease.”
“The typical answer to soil deterioration has been to view the “problems” that develop as separate issues, each dealt with by its own remedy: applying more fertilizers, using fungicides and insecticides, and employing heavy equipment to try to breakup compact layers,” Magdoff says. “These “remedies,” then create problems of their own, such as insect and weed resistance to pesticides (causing a pesticide treadmill as new pesticides are introduced and higher levels of older ones are used).”
Magdoff says that rather than viewing these negative occurrences as “problems,” they are better understood as symptoms of a deeper underlying problem: unhealthy soils. “Once understood in this way, a whole different approach is needed. Promoting the formation of healthy soils implies a preventive approach. It strives to mimic the strengths of undisturbed natural systems and to create conditions that are optimal for plants. Building soil health is really about enhancing the soil habitat so that plants can grow to their full potential. Building up and maintaining organic matter, while not the only issue, is at the heart of developing healthy soils.”
