Impacts of Early‐ and Late‐Terminated Cover Crops on Gas Fluxes

Cover crops (CCs) could alter soil processes, but the effects of early versus late termination of CCs on gas fluxes are not well known. We evaluated temporal changes in fluxes of CO₂, N₂O, and CH₄ and related soil properties in no‐till corn (Zea mays L.) with and without winter rye (Secale cereale L.) CCs that were terminated early (30 d before planting) or late (at planting) in a rainfed silty clay loam and an irrigated silt loam in Nebraska from April 2016 to June 2017. Gas fluxes, soil temperature, and soil water content were measured biweekly to monthly, and wet aggregate stability and particulate organic matter concentrations were measured seasonally. We also compared our results with a global literature review. Late‐terminated CCs did not affect CH₄ fluxes but increased daily CO₂ fluxes by 59% compared with no CC at both sites and N₂O fluxes by 92% at the rainfed site only. Early termination did not affect gas fluxes. Termination date did not affect cumulative fluxes and had minimal effects on soil properties. The literature review supports our study results, which indicate that CC effects on (i) CO₂ fluxes are driven by plant respiration during the CC growing period, and (ii) N₂O and CH₄ fluxes are minimal under grass CCs. Overall, under no‐till, CC termination date has small effects on N₂O and CH₄ fluxes, but late CC termination can increase CO₂ fluxes in spring due to greater biomass yield compared with early termination. CORE IDEAS: Early‐terminated cover crops had limited effects on CO₂ fluxes in this study. Late‐terminated cover crops increased CO₂ flux mainly in spring due to higher cover crop biomass yield. Cover crop termination effects on N₂O and CH₄ fluxes were generally nonsignificant. Our literature review showed cover crops affected CO₂ mostly during their growing period. Our literature results also showed grass cover crops had limited effects on N₂O.