U of M study finds that retired cropland has more carbon storage potential
Researchers say the findings could help fight climate change
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Fertilizers help farmers grow healthy plants. According to new research from the University of Minnesota, the chemicals also boost the land’s ability to store carbon.
The findings are the result of a 40-year study by ecology professor Eric Seabloom. His team analyzed the effects of fertilizer on soil plots at the Cedar Creek Ecosystem Science Reserve in East Bethel. The 5,400-acre reserve contains fenced grasslands, savannah, and other habitats.
“The work is really addressing questions that are much more fundamental about ‘how do ecosystems change over time?’” Seabloom said. “How do they respond to increasing supplies of nutrients like nitrogen or phosphorus?”
Plants already naturally store carbon. Through photosynthesis, they absorb and digest atmospheric carbon, transforming it into roots, wood or other biomass lodged in the earth. Once they die, the soil reclaims the plant and its carbon.
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The U of M’s research team applied fertilizer to different plots for 10 years, then stopped fertilizing half the plots for 30 years to see whether reducing fertilizer use would affect their carbon storage capacity. Seabloom says the results surprised him.
“If you just look at these tilled fields, you can see that these fields accumulate carbon for at least 40 years, and that the rate of carbon accumulation is increased in areas that have been fertilized,” he said. “There are more plants, and they're growing by the day. So they're fixing more and more of that CO2 and storing it underground.”
Grasslands in particular, he said, have exciting potential for carbon storage. They can be native to the land, and because of their naturally long roots, carbon can be stored underground even if a wildfire burns the top grass.
“You can burn those grasslands over and over and over again, and that doesn't affect the carbon at all,” Seabloom said. “In fact, it can even speed up the accumulation of carbon, because the plants grow faster after you burn them.”
While Seabloom imagines all the ways his research could be applied in the real world, he lacks the expertise to write policy that could incentivize idling cropland to store carbon. So, he reached out to a colleague in Canada.
The paradox of a healing pollutant
For a number of years now, biology professor Andrew MacDougall of the University of Guelph has been interested in fertilizers such as phosphorus and nitrogen.
“They're critically, critically important, yet ironically, humans have flipped this and now made these two critically important nutrients major global pollutants,” MacDougall said. “That's only something a human can do.”
Since fertilizers often pollute water sources, deliberately applying them to store another pollutant seems paradoxical.
However, MacDougall’s research showed that soil didn’t need continuous applications of fertilizer to store carbon efficiently. It just needed one and the soil would do the rest.
MacDougall initially focused on applications of the research in the natural world. Agriculture didn’t cross his mind until he received emails from local farming organizations, including Alternative Land Use Services (ALUS). The group gave MacDougall and Seabloom access to land owned by its farmer members for further studies.
“It isn't normally a partnership that forms,” MacDougall said. “But my mom was from a farm family, and quite frankly, as soon as this organization reached out, it instantly clicked.”
Bryan Gilvesy, an Ontario cattle farmer, serves as the group’s chief strategy officer. He says the research is exciting because it opens up the possibility that farmers could get paid for maintaining idle land.
“So effectively, the farmer is still growing a crop, but it's an environmental service crop for a different marketplace that hasn't even been conceived before,” Gilvesy said. “We think that's kind of exciting to open up the possibilities to new and different revenue streams.”
MacDougall is still drafting policy ideas he hopes to present at international forums. However, there’s one thing he wants to make clear from the project’s findings. Absorbing carbon, no matter how much, will not stop the problem of exceeding emissions.
“We can't retire our way out of a problem,” MacDougall said. “It's just like when I buy a plane ticket, I'm given the option to pay an extra 100 bucks as a carbon offset. You can do that, but that's not going to eliminate the fact that my flight is actually emitting carbon.”
