| The main source of agricultural N2O is through microbiological production in manure, soils, and groundwater, which is of concern as it contributes to global warming and depletion of stratospheric O3. In order to derive strategies to reduce N2O emissions, determination of the vertical location, timing of major N2O production, and factors affecting N2O production/consumption were investigated on a long-term, manured, and irrigated agricultural field located in Lethbridge, Alberta between June 2003 and May 2004. Groundwater samples were collected and analyzed for dissolved N2O and CO2, DO, anions, cations, DOC, and other parameters affecting production of the gas. Soil depth gas samples and surface flux gas samples were also collected and analyzed for N2O in addition to other gases. Annual average N2O concentrations ranged between 1.4 and 62.9 muL N2O L-1 air in the soil zone and between 2.45 and 13.3 mumol N2O L-1 water in the shallow groundwater. N2O concentrations over 1000x higher than ambient amounts in the atmosphere (over 350 muL N2O L -1 air) were observed in both the soil and shallow groundwater, and N2O emission (average of 6.65 mg N2O-N m-2 d-1) reached up to 260 mg N2O-N m-2 d-1 with the application of irrigation water. Fluctuations in N2O emission rates and soil gas concentrations may have been influenced by unsaturated zone denitrification of manure derived NO3 - and/or degassing of groundwater N2O that was likely produced by denitrification of a geological source of NO3 - deep in the saturated zone. |
