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Title: Landscape control of nitrous oxide emissions during the transition from conservation reserve program to perennial grasses for bioenergy

item DEBASISH, SAHA - Pennsylvania State University
item RAU, BENJAMIN - Savannah River National Laboratory
item KAYE, JASON - Pennsylvania State University
item MONTES, FELIPE - Pennsylvania State University
item Adler, Paul
item ARMEN, KEMANIAN - Pennsylvania State University

Submitted to: Global Change Biology Bioenergy
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/7/2016
Publication Date: 7/27/2016
Citation: Debasish, S., Rau, B., Kaye, J., Montes, F., Adler, P.R., Armen, K. 2016. Landscape control of nitrous oxide emissions during the transition from conservation reserve program to perennial grasses for bioenergy. Global Change Biology Bioenergy. doi:10.1111/gcbb.12395.

Interpretive Summary: Nitrous oxide emissions are the largest source of greenhouse gas emissions from crop production; highly variable soil moisture can be found in marginal lands targeted for biomass production for bioenergy, leading to areas of potentially high nitrous oxide emissions. We measured nitrous oxide emissions across a small watershed with variable soil moisture. We found that nitrous oxide emissions varied over the watershed, but were highest in the wet areas in the lower portion of slopes. Knowing where in the landscape higher nitrous oxide emissions are occurring may reduce costs of implementing a plan to target and reduce these emissions.

Technical Abstract: Future liquid fuel demand from renewable sources may, in part, be met by converting the seasonally wet portions of the landscape currently managed for soil and water conservation to perennial energy crops. However, this shift may increase nitrous oxide (N2O) emissions, thus limiting the carbon benefits of energy crops. Particularly high emissions may occur during the transition period when the soil is disturbed, plants are establishing, and nitrate and water accumulation may favor emissions. We measured N2O emissions and associated environmental drivers during the transition of perennial grassland in a conservation reserve program (CRP) to switchgrass (Panicum virgatum L.) and Miscanthus x giganteus in the bottom 3-ha of a watershed in the Ridge and Valley ecoregion of the northeastern United States. Replicated treatments of CRP (unconverted), unfertilized switchgrass (switchgrass), nitrogen fertilized switchgrass (switchgrass-N), and Miscanthus were randomized in four blocks. Each plot was divided into shoulder, backslope, and footslope positions based on the slope and moisture gradient. Soil N2O flux, soil moisture, and soil mineral nitrogen availability were monitored during the growing season of 2013, the year after the land conversion. Growing season N2O flux showed a significant vegetation-by-landscape position interaction (P<0.009). Switchgrass-N and Miscanthus treatments had 3 and 6-times higher cumulative flux respectively than the CRP in the footslope, but at other landscape positions fluxes were similar among land uses. A peak N2O emission event, contributing 26% of the cumulative flux, occurred after a 108-mm of rain during early June. Prolonged subsoil saturation coinciding with high mineral N concentration fueled N2O emission hot spots in the footslopes under energy crops. Our results suggest that transitioning CRP to energy crops only caused significant increase in N2O emissions from footslopes within the watershed. Thus, managing the landscape during its transition to energy crops may mitigate increase N2O emissions.