Determining the nitrous oxide transfer velocity and emission factor of an agricultural drain

Abstract

There have been few studies examining indirect nitrous oxide (N₂O) emissions (E N₂O ) associated with nitrogen (N) leaching from agricultural soils. For agricultural drainage water, N₂O equals the water’s E N₂O concentration in excess of the atmospheric value multiplied by the N₂O transfer velocity (V N₂O ). Using this equation, tracers and chamber methods, E N₂O and V N₂O were measured from an agricultural drain. Estimates of V N₂O were made by measuring water speed and depth using the relationship developed by O’Connor and Dobbins [1958. Mechanisms of reaeration in natural streams. Transactions of the American Society of Civil Engineers. 123:641–684]. The measurements and estimates were not significantly different and V N₂O averaged 5 m d⁻¹ . Alternatively, for the method developed by the Intergovernmental Panel on Climate Change, E N₂O equals the mass of N flowing in the water multiplied by an emission factor (EF). By additional measurements of the drain’s width, the water’s flow rate and nitrate (NO₃⁻) concentration, the estimated EF was 1.2 × 10⁻⁴ kg N₂O kg⁻¹ NO₃⁻ − N.