Net Fluxes of CO2, but Not N2o, and CH4, Are Affected Following Agronomic Additions of Urea for Prairie and Arable Soil Cores.

While experimental addition of nitrogen (N) tends to enhance soil fluxes of carbon dioxide (CO₂), methane (CH₄), and nitrous oxide (N₂O), it is not know if lower and agronomic 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 (11, 56, and 112 kg N ha^-1) for central North Dakota arable and prairie soils using intact soil cores to minimize disturbance and mimic 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 emissions with rate of urea-N application indicate that agronomic-scale N inputs may stimulate microbial carbon cycling in these soils, and the contribution of CO₂ to net greenhouse gas source strength following fertilization of semi-arid agroecosystems may be greater than contributions by N₂O and CH₄.