Nitrous oxide is a potent greenhouse gas that impacts the Earth’s protective ozone layer, and recent research suggests that standard measuring methods tend to underestimate the emissions of nitrous oxide, or N2O, as it relates to agricultural production systems. A new study published this month describes how a system developed by a Colorado State University researcher and federal colleagues gives the most accurate estimate of nitrous oxide emissions in agriculture at the farm, regional and global scales.
"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," said William Parton, senior research scientist at CSU’s Natural Resource Ecology Laboratory and co-author of the study published in American Geophysical Union’s weekly newsletter.
The study by scientists at CSU, 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 – individual farms, for example – 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," said Stephen Del Grosso, USDA scientist and CSU Natural Resource Ecology Laboratory researcher. "However, to reliably estimate emissions at the farm scale, recent study has shown that more sophisticated bottom-up methods are required."
To that end, the DAYCENT ecosystem model, developed at CSU’s Natural Resource Ecology Lab with help from USDA-ARS scientists, has been broadly applied to evaluate the environmental impacts of cropping and other land-use practices.
DAYCENT is now being used as part of an EPA-funded project to determine the environmental impact of different biofuel cropping systems across the United States.