Nitrous Oxide Fluxes from Cultivated Areas and Rangeland: U.S. High Plains
2007
Weeks, Edwin P. | McMahon, Peter B.
Concentration profiles of N₂O, a greenhouse gas, and the conservative trace gases SF₆ and the chlorofluorocarbons CFC-11, CFC-12, CFC-113, and were measured periodically through thick vadose zones at nine sites in the U.S. High Plains. The CFC and SF₆ measurements were used to calibrate a one-dimensional gas diffusion model, using the parameter identification program UCODE. The calibrated model was used with N₂O measurements to estimate average annual N₂O flux from both the root zone and the deep vadose zone to the atmosphere. Estimates of root-zone N₂O fluxes from three rangeland sites ranged from near 0 to about 0.2 kg N₂O-N ha⁻¹ yr⁻¹, values near the low end of the ranges determined for native grass from other studies. Estimates of root-zone N₂O fluxes from two fields planted to corn (Zea mays L.) of about 2 to 6 kg N₂O-N ha⁻¹ yr⁻¹ are similar to those determined for corn in other studies. Estimates of N₂O flux from Conservation Reserve grassland converted from irrigated corn indicate that production of N₂O is substantially reduced following conversion from cropland. Small N₂O fluxes from the water table or from deep in the vadose zone occurred at three sites, ranging from 0.004 to 0.02 kg N₂O-N ha⁻¹ yr⁻¹ Our estimates of N₂O flux represent space- and time-averaged values that should be useful to more fully evaluate the significance of instantaneous point flux measurements.
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