Submitted to: Ecosphere
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/7/2018
Publication Date: 3/1/2018
Citation: Saliendra, N.Z., Liebig, M.A., Kronberg, S.L. 2018. Carbon use and uptake efficiencies of hayed alfalfa and grassland in a semiarid environment. Ecosphere. 9(3):e02147. https://doi.org/10.1002/ecs2.2147.
Interpretive Summary: Pastures occupy a potentially important role in mitigating greenhouse gas emissions from agriculture by acting as sinks for soil organic carbon. Carbon sequestration by pastures can be particularly effective given limited soil disturbance, minimal erosion, and continuous carbon input from above- and below-ground biomass during the growing season. Accordingly, identifying pasture management systems with high potential for further soil carbon sequestration is important. A study was conducted from 2009 to 2013 to determine the daily, seasonal and annual carbon budget of hayed alfalfa and grassland near Mandan, ND USA. Alfalfa was found to be a moderate carbon sink, whereas grassland was a carbon source. Alfalfa was also found to be highly efficient at capturing carbon in both warm/dry and cool/wet growing seasons. Findings from this multi-year study suggest alfalfa can provide efficient carbon accrual across a range of weather conditions in a semiarid region.
Technical Abstract: Land use and management practices are key factors that influence net ecosystem exchange (NEE) for carbon dioxide in semiarid regions. We used alfalfa (Medicago sativa L.) and grassland ecosystems in a multi-year study (2009-2013) to determine the daily, seasonal and annual carbon (C) budget, and partitioned NEE into two components: ecosystem respiration (ER) and gross ecosystem production (GEP). We found consistently higher magnitudes of C fluxes (NEE, ER, GEP) in alfalfa than grassland throughout the study period. Annually, alfalfa was a C sink, whereas grassland was a C source; NEE totals were –245 and 27 g C/m2/yr, respectively. During the dormant season, daily means for ER were 0.97 in alfalfa and 0.66 g C/m2/d in grassland. In the growing season, daily means for GEP were 5.67 and 2.98 g C/m2/d for alfalfa and grassland, respectively. We used a novel method to determine NEE:GEP ratios in alfalfa and grassland ecosystems, where periods of steady CO2 uptake occurred before and after each harvest (haying) during five growing seasons (2009 to 2013). Mean NEE:GEP ratios were –0.44 and –0.27 for alfalfa and grassland, respectively. We also found NEE:GEP and NEE:ER ratios (metrics for C use and uptake efficiency, respectively) were correlated to light use efficiency (LUE) and heat use efficiency (HUE). Lastly, higher C use and uptake efficiencies in alfalfa were evident in both warm/dry and cool/wet growing seasons. Outcomes from this evaluation suggest hayed alfalfa is a more consistent and efficient C sink than hayed grassland under semiarid conditions.