Impacts of Water Table Management on N2O and N2 from a Sandy Loam Soil in Southwestern Quebec, Canada

Abstract

Nitrous oxide (N2O) is primarily produced as intermediate in denitrification and, to a lesser extent, through nitrification processes. Nitrous oxide emission and, consequently, its atmospheric impacts depend on the extent to which N2O is reduced to dinitrogen gas (N2) by denitrifiers. Field experiments were conducted from 1998 through 2000 growing seasons at St. Emmanuel, Quebec, Canada, to investigate the combined impact of water table management (WTM) and N fertilization rate on the soil denitrification (N2O + N2) rate, rate of N2O production, and the N2O:N2O + N2 ratio. Water table treatments included subirrigation (SI) with a target water table depth of 0.6 m and free drainage (FD) with open drains. The tile drains (75 mm diameter) were laid at a 1.0 m depth from the soil surface. Nitrogen fertilizer was applied at two rates:120 and 200 kg N ha−1 as ammonium nitrate (34-0-0). The N2O + N2 evolution rates were greater in SI (12.9 kg N ha−1) than in FD (5.8 kg N ha−1) plots. The percentages of N2O relative to overall N2O + N2 evolution were 35 and 11% for 1998, 29 and 8% for 1999, and 37 and 20% for 2000, under FD and SI, respectively. The reduced N2O production under SI was due to a greater reduction of N2O to N2. Results indicate that greater N2O + N2 evolution under shallow water tables are not necessarily accompanied by higher N2O emissions.