Recent research suggests that standard measuring methods tend to underestimate the emissions of nitrous oxide, or N2O, as it relates to agricultural production systems, according to a study by Colorado State University.

Nitrous oxide is a potent greenhouse gas that affects the Earth's protective ozone layer, "Agriculture is responsible for the majority of human-generated N2O emissions, and without accurate estimates, we are unable to rigorously assess the environmental impacts of biofuel and other cropping systems," says William Parton, senior research scientist at CSU's Natural Resource Ecology Laboratory and co-author of the study.

The study by scientists at CSU in Fort Collins, U.S. Department of Agriculture Agriculture Research Service and the Environmental Protection Agency shows that two broadly distinct methods used to calculate emissions give substantially different estimates on small scales, such as individual farms.

But at national and global scales, the methods yield remarkably similar estimates. Emissions of gases such as nitrous oxide are commonly estimated using a simple bottom-up method that assumes that emissions are proportional to soil nitrogen additions through fertilizer and other sources.

More complex bottom-up methods account for nitrogen additions but include other factors that influence emissions, such as crop type, weather and soil properties.

In contrast, the top-down approach infers surface emissions based on changes in the atmospheric concentration of N2O and information on how long it resides in the atmosphere.

"Agreement between these methods at large spatial scales is not surprising," says Stephen Del Grosso, USDA scientist and CSU researcher. "However, to reliably estimate emissions at the farm scale, recent study has shown that more sophisticated bottom-up methods are required."

That method, which uses the DAYCENT ecosystem model, was developed by the CSU and ARS scientists. It has been broadly applied to evaluate the environmental impacts of cropping and other land-use practices.

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