Nitrogen fertilizer can boost the growth of crops for biofuel production, but applying too much can cut the climate benefits in half.
Ethanol fuel made from plant cellulose is a promising form of renewable energy. Philip Robertson at Michigan State University in Hickory Corners and his colleagues applied various amounts of nitrogen fertilizer to experimental plots of switchgrass (Panicum virgatum) for three years. They measured emissions of the greenhouse gas nitrous oxide (N2O) and the leaching of nitrate, a water pollutant. The authors found that fertilizer boosted yields in the first year, but that the increase declined with subsequent applications. Levels of both emissions and leaching grew exponentially with increases in fertilizer.
The team suggests that minimizing fertilizer use will be crucial for maintaining the environmental benefits of cellulosic biofuel.