Alfalfa, a significant carbon sink due to high productivity and nitrogen fixation, may also be a large nitrous oxide (N₂O) source, offsetting its climate change mitigation potential. This study used long-term automated instrumentation and satellite imagery to quantify greenhouse gas fluxes in a continuous alfalfa agroecosystem in California. Results show the system was a large N₂O source (624 ± 28 mg N₂O m⁻² y⁻¹), offsetting the ecosystem carbon sink by up to 14% annually. Short-term N₂O emission events (hot moments) accounted for a small percentage of measurements but a large portion of annual emissions, primarily driven by rainfall and irrigation. Plant activity also influenced background N₂O emissions. Annual N₂O emissions significantly lower the carbon-sink potential of continuous alfalfa agriculture.

Tyler L. Anthony, Daphne J. Szutu, Joseph G. Verfaillie, Dennis D. Baldocchi, Whendee L. Silver