According to a study on Conservation Reserve Program (CRP) land, growing sustainable energy crops won’t increase greenhouse emissions if used on seasonally wet, environmentally sensitive landscapes.
Debasish Saha, postdoctoral scholar in plant sciences, and Penn State College of Agricultural Sciences, measured the amount of nitrous oxide, a potent greenhouse gas, emanating from plots of biofuels-producing switchgrass and miscanthus growing in an experimental area in eastern central Pennsylvania and compared it to emissions from adjacent, undisturbed CRP acres.
Nitrous oxide is produced by micro-organisms when soils with excess nitrogen from fertilizer and other sources coincide with a near-saturated soil environment after a storm or snowmelt event. It is mostly emitted from agricultural activities and contributes about 6% of the total warming influence on the planet. An increase of nitrous oxide emissions from CRP land planted with energy crops would undermine the logic of using CRP lands for energy crops production. The transition phase is one of the most sensitive periods because the plants are small and are just establishing their root system.
The researchers measured nitrous oxide emissions in the bottom of a watershed that is a realistic example of CRP lands in a seasonally wet landscape. An existing CRP tract was partially converted to switchgrass and miscanthus and the researchers measured nitrous oxide emissions from May September 2013 with gas-sampling devices.
The sampling frequency varied from weekly to biweekly, and increased after fertilization and precipitation events. The researchers also continuously monitored soil water content to understand soil water dynamics in the landscape, a critical trigger for nitrous oxide emissions. They installed soil moisture sensors at three soil depths in each of 48 monitoring points and connected each to data loggers through a network of buried cables.
Saha and colleagues published their findings in Global Change Biology: Bioenergy, suggesting that CRP and other marginal, streamside lands set aside for conservation are good candidates for biomass production. They found that although nitrous oxide emissions did rise above the baseline provided by CRP lands, the increase only happened in a small portion of the landscape.