Energy crop production on CRP lands could improve water quality without greenhouse gas increases

Growing sustainable energy crops without increasing greenhouse gas (GHG) emissions may be possible on seasonally wet, environmentally sensitive landscapes, according to researchers at Penn State College of Agricultural Sciences, Pennsylvania (PA), who have conducted a study on Conservation Reserve Program (CRP) land.

CRP is a US land conservation program whereby farmers, in exchange for an annual rental payment, agree to remove environmentally sensitive land from agricultural production and plant species that will improve environmental health and quality.

Expanding energy crops could help reduce the carbon footprint of the US economy with a domestic source of a renewable fuel but could also displace other existing land uses. Therefore the several million acres of CRP lands in the US, which have been set aside for conservation, seem to be particularly suitable for this expansion.

Solution or problem?

An increase of nitrous oxide (N2O) emissions from CRP land planted with energy crops would though undermine the logic of using CRP lands for energy crops production. N2O, a potent GHG, 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.

N2O is mostly emitted from agricultural activities and contributes about 6 percent of the total warming influence on the planet.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 N2O emissions in the bottom of a watershed that is a realistic example of CRP lands in a seasonally wet landscape. An existing tract of CRP land in a long-term experimental site in eastern central Pennsylvania managed by the US Department of Agriculture’s Agricultural Research Service was partially converted to switchgrass (Panicum virgatum L), a native perennial grass, and miscanthus (Miscanthus x giganteus), a non-native grass species.

The researchers measured N2O emissions from May to September of 2013 with gas-sampling devices and compared it to emissions from adjacent, undisturbed CRP acreages. They found that although N2O emissions did rise above the baseline provided by CRP lands, the increase only happened in a small portion of the landscape suggesting that CRP and other marginal, streamside lands set aside for conservation are good candidates for biomass production. The results have been published in the journal Global Change Biology – Bioenergy.

– Nitrous oxide emissions were only higher in the slopes nearest the stream that are wet and retain subsoil moisture for the longest period of time after a storm or snowmelt event. So, are energy crops a problem or a solution in this regard? Clearly, a large portion of the landscape planted with switchgrass and miscanthus did not emit more nitrous oxide than the rest of the CRP land, and it is expected that once established, large emissions from the footslope can be suppressed, said Debasish Saha, a postdoctoral scholar in plant sciences and one of the authors.

– Grass energy crops in these landscape locations can provide additional water-quality benefits. Due to the high biomass production potential, these crops can use up nutrients that otherwise would go to the stream and end up in the Chesapeake Bay. Thus, when these perennial energy crops are added to heavily agricultural landscapes, the results can be a win-win — low-carbon energy and cleaner water, Armen Kemanian, Associate Professor of Production Systems and Modeling, Penn State University.