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Crop production increases nitrous oxide emissions

A new ecosystem modeling study led by Iowa State University has found that, during the last century, crop production in the United States has led to a significant increase in the emissions of nitrous oxide, a potent and dangerous greenhouse gas contributing to climate change and ecological destruction. The results suggest that nitrous oxide emissions from U.S. soils have more than tripled since 1900, with nearly three-quarters of that rise in emissions originating from agricultural soils with corn and soybean production.

The scientists drew on massive amounts of data on weather patterns, soil conditions, land use, agricultural management practices, and other variables to design a mathematical model that could accurately mimic ecological processes.

“The model we are using is a process-based ecosystem model,” said study lead author Chaoqun Lu, an associate professor of Ecology, Evolution, and Organismic Biology. “It’s similar to mimicking the patterns and processes of an ecosystem in our computer. We divide land into thousands of pixels at a uniform size and run algorithms that simulate how ecological processes respond to changes in climate, air composition, and human activities.”

“Behind the scenes, there are thousands of lines of algorithms to guide the computer model to make predictions. It takes decades of efforts, and more to come, to reduce modeling uncertainties and incorporate better ecological process understanding resulting from the hard work of field scientists.”

By analyzing this vast amount of data, the scientists found that nitrous oxide emissions have more than tripled during the 20th century in the United States. This rise in emissions corresponded to an expansion of cropland in the U.S. and was most probably caused by the widespread application of nitrogen fertilizers to agricultural land and legume crop production. Although the added nitrogen is partly used by crops, a significant remainder remains in the soils and is consumed by microorganisms that give off nitrous oxide as a byproduct. 

Since more nitrogen fertilizer is applied in corn production than in any other crops, soils where corn is grown tend to emit more nitrous oxide per unit of fertilizer used. Better understanding which crops lead to the greatest emissions can lead to better climate mitigation policies.

“Our study suggests a large nitrous oxide mitigation potential in cropland and the importance of exploring crop-specific mitigation strategies and prioritizing management alternatives for targeted crop types,” the authors concluded.

The study is published in the journal Global Change Biology.

By Andrei Ionescu, Staff Writer

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