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 CO, NO, and CH and related soil properties in no-till corn ( L.) with and without winter rye ( 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 CH fluxes but increased daily CO fluxes by 59% compared with no CC at both sites and NO 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) CO fluxes are driven by plant respiration during the CC growing period, and (ii) NO and CH fluxes are minimal under grass CCs. Overall, under no-till, CC termination date has small effects on NO and CH fluxes, but late CC termination can increase CO fluxes in spring due to greater biomass yield compared with early termination.