Estimating the greenhouse gas balance of cellulosic biofuel: Understanding the importance of nitrous oxide from soils
The transportation sector contributes around 27 percent of total greenhouse gas emissions in the U.S. The substitution of fossil fuels with biofuel has been proposed as one strategy to reduce greenhouse gas emissions in this sector. Accurately estimating the greenhouse gas balance of biofuel is critical to understanding biofuel’s ability to reduce emissions. Producing accurate greenhouse gas balances is difficult because of uncertainty surrounding emissions of gases like nitrous oxide from agricultural land used to grow biofuel feedstocks. Nitrous oxide has a global warming potential 298 times greater than carbon dioxide, meaning that small quantities released during feedstock production can have major impacts on the greenhouse gas balance of biofuel.
This study measures emissions of nitrous oxide from soils of prospective cellulosic biofuel crops in Kansas. We compared the measured emissions to emission factors commonly used to estimate nitrous oxide emissions in biofuel greenhouse gas balances. The measured emissions and crop yield data were used as inputs into a life cycle analysis model which estimates the greenhouse gas balance of cellulosic biofuels. This study found that nitrous oxide emissions from soils can represent a major greenhouse gas source in cellulosic ethanol production and that current estimates of nitrous oxide used in life cycle analyses may not sufficiently account for nitrous oxide emissions. Future research will evaluate agroecosystem models for estimating nitrous oxide emissions in cellulosic biofuel cropping systems and use these models to estimate emissions at the landscape scale.