The Impact of a Kura Clover Living Mulch on the Nitrous Oxide Balance of a Minnesota Corn/Soybean System.

Nitrous oxide (N₂O) is an important greenhouse gas and the dominant ozone depleting substance.  Produced primarily in agricultural soils, efforts to reduce the strength of this source are underway, but successful results have been inconsistent.  Living mulches provide numerous environmental benefits including reduced nitrate leaching and soil erosion, increased soil organic matter, and greater pest resilience.  The leguminous perennial kura clover (Trifolium ambiguum M. Bieb.) successfully grows side-by-side cash crops in rotational corn-soybean systems.  Through biological nitrogen fixation, kura clover provides land managers an opportunity to reduce external fertilizer inputs that may reduce problematic N₂O losses.  However, the N₂O balance of leguminous cover crops, and kura clover in particular, are uncertain because of few field studies.  To investigate the effectiveness of kura clover in reducing N₂O emission, automated soil chambers (n=8) coupled to a N₂O analyzer were used to measure hourly fluxes from March through November in a corn-soybean rotation.  Annual (n=2) N₂O emissions from the kura clover plot were greater than the control (no kura clover) plot (mean = 54.3 mg N₂O-N m^-2 yr^-1), although emissions were only significantly greater (p<0.001) during the soybean phase.  We observed greater cumulative N₂O emission from the kura clover plot despite 55% less nitrogen applied during the corn phase.  Fluxes were greater (p=0.5) from the control plot in the early season, likely because of a greater nitrogen application rate.  N₂O fluxes from the kura clover plot were significantly greater (p<0.001) during senescence indicating the mineralization of biologically fixed nitrogen.  These findings cast doubt on the efficacy of using kura clover as an N₂O mitigation management option in corn-soybean systems.  However, because emissions were not significantly different during the corn years, we acknowledge that future work spent optimizing nitrogen inputs and testing kura clover in different climates could lead to N₂O benefits elsewhere.