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While experimental addition of nitrogen (N) tends to enhance soil fluxes of carbon dioxide (CO2), methane (CH4), and nitrous oxide (N2O), it is not known if lower and agronomic-scale additions of urea-N applied also enhance trace gas fluxes, particularly for semi-arid agricultural lands in the northern plains. We aimed to test if this were true at agronomic rates [low (11 kg N ha(-1)), moderate (56 kg N ha(-1)), and high (112 kg N ha(-1))] for central North Dakota arable and prairie soils using intact soil cores to minimize disturbance and simulate field conditions. Additions of urea to cores incubated at 21 degrees C and 57% water-filled pore space enhanced fluxes Of CO2 but not CH4 and N2O. At low. moderate, and high urea-N, CO2 fluxes were significantly greater than control but not fluxes of CH4 and N2O. The increases in CO2 emission with rate of urea-N application indicate that agronomic-scale N inputs may stimulate microbial carbon cycling in these soils, and that the contribution Of CO2 to net greenhouse gas source strength following fertilization of semi-arid agroecosystems may at times be greater than contributions by N2O and CH4. Published by Elsevier Ltd