Are we underestimating nitrous oxide emissions from corn fields?

Nitrous oxide (N2O) is a dangerous greenhouse gas and one of the biggest threats to our ozone layer. Most of this gas comes from fertilizer, and so national measurements are done during the growing season, but a lot of the N2O from agriculture is emitted outside of the growing season as well.

A recent study from Agricultural & Environmental Letters estimated that 31% of all U.S. N2O emissions from corn agriculture come from outside the growing season. This is a huge challenge because if we’re missing a big chunk of the emissions out there, we might make the wrong policy decisions going forward. Management is possible, but the entire system needs to be considered to craft best practices.

Nitrous oxide is the third most important greenhouse gas in the world. Emissions have been rising for decades with the highest rates appearing in the 2020s. Managing N2O emissions is tough because they tend to appear in high concentrations at very specific moments in time. 
Some studies found that 89% of normal N2O emission measurements only take place during the growing season. Many other studies have reported huge emissions outside of the growing season, incentivizing scientists to broaden their scope.

How much N2O is emitted outside the growing season?

During the fallow period, the time when farmers don’t seed their land so that the soil can recover and retain moisture, N2O can still be emitted from thawing freezes, wet soil, and other factors. Different studies have made various estimates for how much N2O is emitted at these times with variance ranging from 7–93% and typical estimates suggesting 30–50%.

The study took data from corn plantings across the country before calculating nitrogen applications at the county level. Ultimately, it estimated that the total N2O emissions that happen outside the growing season are equal to anywhere from 10,000 to 15,000 gigagrams (about 22 to 33 trillion pounds) of CO2 every year. 

This is the first holistic assessment of how much growing-season-focused methods may underestimate N2O emissions from corn fields, and hopefully, it can push the industry to discuss new solutions and innovations for combatting climate change.

Thankfully, policies can still be put in place to reduce these emissions without sacrificing yields—focusing on reducing surplus nitrogen fertilizer can lower N2O emissions without penalizing farmers that apply nitrogen amounts well matched to crop growth needs. With more global measurements and awareness given through reports like these, we can push policymakers to set new regulations and make sure that our atmosphere and planet don’t have to suffer.