Net fluxes of CO2, but not N2O or CH4, are affected following agronomic-scale additions of urea to prairie and arable soils

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 °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.