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A paradox of agriculture and greenhouse gases

Written by Paul Brewer, SoGES 2013-2014 Sustainability Leadership Fellow, and PhD Candidate in the Department of Biology and Graduate Degree Program in Ecology

I never thought I would be doing research on soil - though I was wildly curious in high school and college it did not even cross my mind to read about it, soil science sounded like the dullest discipline imaginable. But after learning about biotic soil crusts during a spring in the Mojave desert I realized soils are not just inert matter we walk around on but are alive, and I started to get curious. I wanted to work on solutions to major environmental problems and the more I read the more I saw that soils and the living organisms within them have immense impacts on the world around us. One of these impacts is the role soils play in carbon cycling – carbon resides in soils in a vast array of forms and is slowly eaten and turned into CO2 by microorganisms and bugs. Because of how slowly soil carbon can decompose, soils are an excellent place to store carbon to reduce the severity of climate change. We often think of planting a tree to reduce CO2 concentrations, but, surprisingly, the amount of carbon currently in soils is four times greater than the carbon in all the trees and plants put together and three times greater than all the CO2 in the atmosphere (Ontl & Schulte, 2012).

(Caption for the above photo: Slow decomposition in soil: Plant material in the center of this soil core still looked like fresh wheat straw even though the surrounding material has decomposed and darkened in the 14 week study.)

Soils each have a different capacity for the amount of carbon they can hold and most cropland soils can store much more. These soils are also very accessible to us – already farmers make massive alterations to cropland soils every year through specific plowing, cultivation, and harvest techniques. In the United States alone this affects over 430 million tons of soil (or 300 million acres). There is enormous opportunity for changes in farming techniques to cause rapid, large increases in carbon stored in these agricultural soils. Ending the plowing of a field, that is moving to no-tillage techniques, is the most common approach used to store more carbon. When a field is no longer plowed dead roots and other pieces of the plant are left in the soil, slowly decomposing and storing that year’s plant carbon in the meantime.

Caption for this image: 100-year global warming potential of the three primary greenhouse gases, bars not to scale (IPCC 2013).

However, even though the dead plant material helps prevent that carbon from becoming CO2 quickly it also allows stronger greenhouse gases, methane (CH4) and nitrous oxide (N2O), to be produced (Johnson et al.,  2007). This paradoxical effect, that avoiding CO2 emissions can lead to greater emission of other greenhouse gases, could mean that farmers and governments won’t try to increase soil carbon if there is not a good understanding of how or why this can happen. Over the past two years I have found that buried plant material can create significant quantities of CH4 and N2O, but that the amount of those strong greenhouse gases produced depends on soil moisture, available nutrients, and the size of plant pieces. This means that when farmers stop plowing and plant material is left in the ground production of the strong greenhouse gases could be avoided by choosing a particular timing of fertilizer application and irrigation. The specific situations that create greenhouse gases vary by soil and crop type, so continued studies will give us the knowledge necessary to minimize climate change by nudging cropping practices one way or another. This topic is a good example of how more abstract ecological research can be combined with applied agricultural work to help solve a global problem.


Ontl, T. A. & Schulte, L. A. 2012. Soil Carbon Storage. Nature Education Knowledge 3(10):35

Johnson, J. M.-F., A. J. Franzluebbers, S. L. Weyers, and D. C. Reicosky. 2007. Agricultural opportunities to mitigate greenhouse gas emissions. Environmental Pollution 150:107–124


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