Carbon dioxide fluxes in corn-soybean rotation in the midwestern U.S.: Inter- and intra-annual variations, and biophysical controls

► We monitored CO2 fluxes using eddy-covariance and soil chambers in two adjacent production fields within four years. ► Available light and/or air temperature explained up to 81% of variations in CO2 fluxes during fallow and growing seasons. ► Daytime CO2 exchanges over crops depicted hysteresis with available light with greater uptake in mornings than afternoons. ► Corn exhibited 1.7-fold greater peak rates of diurnal CO2 uptake and 18% longer duration of CO2 sink periods than soybean. ► While corn showed annual net CO2 uptake and neutral system C balance, soybean showed neutral CO2 exchange and C depletion.