We all know tractors burn fuel and release CO2 into the atmosphere. It is rather obvious, then, that plowing with tractors increases the concentration of greenhouse gases in the atmosphere.
But did you also know that simply opening the soil to air during plowing also releases greenhouse gases? When the organic matter in soil (such as roots, plant debris, and dead organisms) is exposed to oxygen, the processes of decomposition speed up. That means some of the carbon and nitrogen molecules that had been trapped in plant and animal tissues underground gets converted into CO2 and N2O. Those gas molecules then become part of the atmosphere, increasing its concentration of heat-trapping gases.
Scientists estimate that between 1900 and 1950, when American farmers initially converted the Great Plains from native grasslands to croplands,[1] 50% of the soil’s natural carbon stores were released into the atmosphere.[2]
Another estimate figures that “[b]y 1980, roughly a third of the carbon humanity had already added to the atmosphere since the Industrial Revolution came from plowing up the world’s soils, primarily in the Great Plains, Eastern Europe, and China.”[3] We usually only think of factories, vehicles, and fires as adding CO2 to the air. But digging into the earth and uncovering carbon-rich, fertile soil also significantly alters the chemistry of our earth’s atmosphere.
(Image of ice core samples at the Byrd Polar and Climate Research Center; photo by Presian Burroughs)
Not only does plowing cause CO2 to disperse into the air, it also decreases the soil’s fertility. Without sufficient carbon in the soil, microbes and macrobes (think, bacteria and worms) don’t have enough to eat and therefore die. Without the microbes and macrobes living there, minerals in the soil and nitrogen from the atmosphere cannot be converted into the nutrients plants need to absorb. Over the years, the process of plowing actually decreases the fertility of the soil and the earth’s ability to make new topsoil.
In addition to decreasing the amount of carbon in the soil, plowing speeds up the process of mineralization—the process by which nitrogen that once made up the proteins and amino acids of decaying plants and animals is broken down and converted into molecules plants can absorb.[4] Although this feeds plants in the short-term, after a few years, once the initial nitrogen is used up, the soil no longer has the ability to replenish the nitrogen unless nitrogen-fixing legumes are grown there.
Meanwhile, some of the soil’s nitrogen ends up as N2O and dissipates into the atmosphere. Consequently, from 1900 to 1950 when the native grasslands of the Great Plains were being plowed up and made into crop fields, the earth experienced “an increase in soil N2O emissions, translating into a substantial net release of [greenhouse gases]”.[5]
Plowing, then, not only diminishes soil fertility but also increases greenhouse gas concentrations.
(Image of water vapor and other gases rising from plowed field is from https://pixabay.com/photos/fog-mood-landscape-fog-bank-66270/.)
Decreasing soil fertility is a perennial problem farmers face, and scientists have been eager to find solutions. By the early 1900s soil scientists recognized the fundamental importance of nitrogen (in addition to potassium and phosphorus) for plant health and agricultural yield. Simultaneously, the bomb-making war efforts of WWI and WWII gave scientists new technologies that could take unreactive N2O from the atmosphere and convert it into ammonia through an energy-intensive reaction called the Haber-Bosch process. This process provided the means for chemists to create liquid chemical fertilizers that the now degraded soil in America’s heartland needed more than ever. But these fertilizers come at a high energy and ecological cost: making nitrogen fertilizers “consumes more energy than any other aspect of the agricultural process. It takes the energy from burning 2,200 pounds of coal to produce 5.5 pounds of usable nitrogen.”[6] In other words, in our fossil fuel based economy, manufacturing synthetic nitrogen fertilizers necessarily releases large amounts of CO2 into the atmosphere.
But that’s not all. Some of the nitrogen-based fertilizer sprayed on fields ends up as N2O in the atmosphere. Scientists estimate that about 1% of nitrogen fertilizer dissipates into the atmosphere.[7]
While this may not sound like much, the collective global effect of spraying fields with nitrogen fertilizer and spreading organic sources of nitrogen, such as manure, is staggering. Globally, the agricultural sector emits over 7,000,000 tons of N2O each year.[8]
(Image of increasing global N2O concentrations is from https://www.esrl.noaa.gov/gmd/hats/combined/N2O.html.)
A significant problem attending this situation is that nitrous oxide “is about three hundred times more powerful than carbon dioxide in creating climate warming.”[9] Nitrous oxide is a much more effective blanket than CO2.
Along with increasing the earth’s concentration of N2O, nitrogen fertilizers also harm aquatic ecosystems. Scientists figure about half of the nitrogen fertilizer farmers spray on crops isn’t even absorbed by the plants![10] Where does so much of the nitrogen-based chemical go? A bit of it floats into the atmosphere, as indicated above, but a lot of it ends up in our waterways, causing algal blooms and dead zones (I’ll discuss this in a future post). Overall, relying so heavily on chemical nitrogen fertilizers is simply not efficient or sustainable.
Although we might assume plowing is a benign and essential part of growing food, the facts of the matter indicate that plowing isn’t exactly healthy for our ecosystems. Plowing results in:
- A decrease in the soil’s carbon stores (which leads to degraded soil fertility and structure)
- An increase in atmospheric CO2 concentrations (from tractor power, soil exposure, and the manufacture of nitrogen fertilizers)
- A decrease in the soil’s nitrogen stores
- An increase in atmospheric N2O concentrations (from soil exposure and dissipation of nitrogen-based fertilizers)
- An increase of nitrogen in waterways and a decline in aquatic biodiversity and vitality
- A decline in the soil’s biome (the microbes and macrobes that make fertile soil possible)
With all these drawbacks (in addition to another big one: soil erosion), it becomes clear why scientists and farmers work hard to find alternatives to conventional, industrial agricultural methods.
And when I consider these ecological factors in conversation with the Christian scriptures, I find theological reasons for supporting ecologically healthier forms of agriculture. For example, since Genesis 1 indicates that God created the world to be fertile and filled with a diversity of living beings (see my “The Creative Roles of Water & Land in Genesis 1:1-25”), I am led to question the ways in which industrial forms of agriculture undermine fertility and biodiversity. And since Genesis 1:29-30 explicitly teaches humans to share the plants of the earth with the rest of God’s creatures (see my “A Call to Share Plants & Soil: Genesis 1:29-30”), the destructive effects of plowing on the soil’s biome and global climate stability lead me to think long and hard about how we grow and eat our food.
Whether motivated by theological principles or not, people are beginning to recognize that plowing actually works at cross-purposes with our efforts to grow abundant and healthy food. Consequently, some farmers have turned to no-till and low-till methods of planting crops not only to avoid the problems outlined here but also soil erosion. These methods, however, often (but not always) rely on the use of herbicides and GMO crops. Since these are complex topics in and of themselves, we’ll consider them soon. Stay tuned!
[1] This transition from grassland to crops of course took place after the US unjustly and violently confiscated the lands and livelihoods of the Native Americans who once made their homes in the Great Plains. The foundation upon which American agriculture has been built is bloodstained and a shameful part of US history.
[2] Melannie D. Hartman et al., “Impact of Historical Land-Use Changes on Greenhouse Gas Exchange in the U.S. Great Plains, 1883-2003,” Ecological Applications 21, no. 4 (2011): 1117, http://dx.doi.org/10.2307/23022983.
[3] David R. Montgomery, Growing a Revolution: Bringing Our Soil Back to Life (New York: W. W. Norton & Company, 2017), 57.
[4] David Crohn, “Nitrogen Mineralization and Its Importance in Organic Waste Recycling,” accessed January 4, 2020. https://alfalfa.ucdavis.edu/+symposium/proceedings/2004/04-277.pdf.
[5] Hartman et al., 1117.
[6] Jason McKenney, “Artificial Fertility: The Environmental Costs of Industrial Fertilizers,” in The Fatal Harvest Reader: The Tragedy of Industrial Agriculture, ed. Andrew Kimbrell (Washington: Island Press, 2002), 127.
[7] Hartman et al., 1117.
[8] Debra A. Miller, Farming and the Food Supply, Confronting Global Warming (Detroit: Greenhaven Press, 2011), 80-81.
[9] Ibid.
[10] The Intergovernmental Panel on Climate Change calculates that “approximately 50% of the N applied to agricultural land [is] not taken up by the crop” [Gensuo Jia and Elena Shevliakova, “Chapter 2: Land-Climate Interactions,” in Climate Change and Land: An Ipcc Special Report on Climate Change, Desertification, Land Degradation, Sustainable Land Management, Food Security, and Greenhouse Gas Fluxes in Terrestrial Ecosystems (27/04/2019), 5.].
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