Cropping systems can affect greenhouse gas (GHG) emissions due to variations in farm operations, root respiration, and soil organic matter mineralization that need further exploration. We examined the effect of tillage (conventional till [CT] and no-till [NT]) and crop phases (sugarbeet [Beta vulgaris L.] and corn [Zea mays L.]) on CO2, N2O, and CH4 fluxes and GHG balance (GHGB or sum of CO2 equivalents of all GHGs) in an irrigated barley (Hordeum vulgare L.)-sugarbeet-corn-soybean (Glycine max L.) rotation from 2016 to 2020 in the US northern Great Plains. A static chamber method was used to measure GHG fluxes at 3-30 d intervals, depending on crop performance and soil environment, throughout the year. While CO2 peak fluxes occurred mostly during the crop growing season, N2O peak fluxes occurred throughout the year. The CH4 flux was minimal, except for some peaks in October 2017 and January and April 2019. Cumulative CO2 flux from May to April and GHGB were 26-44 % greater for CT with sugarbeet than NT with sugarbeet or corn in 2016-2017 and 24-41 % greater for NT with sugarbeet than CT with corn in 2018-2019 and 2019-2020. Cumulative N2O flux was 70-244 % greater for CT with sugarbeet than NT with sugarbeet in 2016-2017 and 2019-2020 and 38-73 % greater for NT with sugarbeet than other treatments in 2018-2019. Cumulative CH4 flux did not vary among treatments in any year. The GHG emissions can be reduced by using CT with corn and NT with corn and sugarbeet compared with CT with sugarbeet during the dry year and using CT with corn compared with other treatments during the wet year in the barley-sugarbeet-corn-soybean rotation under sandy loam soils of the US northern Great Plains, indicating that treatments effect on reducing GHG emissions varied with climatic conditions.
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