Prior to termination, the rye cover crop increased the soil methane sink

Even though the impact of cover crops on soil moisture has been well documented, little work has investigated the resulting impact on methane emissions. Therefore, the objective was to determine the influence of a dormant seeded rye (Secale cereale) cover crop on soil temperatures, soil moisture, inorganic N, and total CH₄-C emission in a well-drained frigid soil from the start of growth in April/May through corn's (Zea mays) V4 growth stage. In this study, soil moisture, temperature, CH₄-C, and N₂O-N fluxes were measured near-continuously. The rye cover crop: (1) reduced the water-filled porosity in the surface 5 cm in 2018 and 2020; (2) did not influence soil temperature prior to corn's V2 growth stage, increased the soil temperature between the V2 and V4 growth stages in 2019, and reduced the soil temperature in 2020; and (3) reduced (p < 0.01) the CH₄ flux prior to corn seed emergence (VE) in 2018, 2019, and 2020. Over the 3 years, rye reduced (p = 0.04) CH₄ flux (increased soil methane sink) by 6.4 g (ha × day)⁻¹ prior to VE and reduced (p = 0.02) carbon dioxide equivalence (CO₂e) from −1.9 to −11.9 kg CO₂e ha⁻¹. These decreases accounted for 22.3% of the CO₂e derived from N₂O (53.4 kg CO₂e-N₂O) and suggest that the rye cover crop induced reductions in CH₄ emissions need to be considered in carbon intensity calculations.