Energy crop production on conservation lands may not boost GHG, new study finds

Growing sustainable energy crops without increasing greenhouse gas emissions, may be possible on seasonally wet, environmentally-sensitive landscapes, according to US-based researchers who conducted a study on Conservation Reserve Program (CRP) land.

Debasish Saha, postdoctoral in plant sciences, Penn State College of Agricultural Sciences and colleagues, measured the amount of nitrous oxide, a potent GHG, emanating from plots of biofuels-producing switchgrass and miscanthus,  growing an experimental area in eastern central Pennsylvania and compared it to emissions from adjacent, undisturbed CRP acres.

The experiment took place in a long-term monitoring site managed by the US Department of Agriculture's Agricultural Research Service.

Nitrous oxide is produced by micro-organisms when soils with excess nitrogen from fertiliser and other sources coincide with a near-saturated soil environment after a storm or snowmelt event. It 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 – when energy crops are established – 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 to September of 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.