Field experiments were conducted to determine optimal time during the day for N 2O flux determination and to evaluate the effects of wheel traffic and soil parameters on N 2O fluxes following urea ammonium nitrate (UAN) injection and summer UAN fertigations. The experiments were located on silty clay loam soils under no-till irrigated continuous corn of eastern Nebraska. Three approaches were used. First, near-continuous N 2O flux measurements were made in non-wheel-tracked (NWT) interrows in four 24-h periods during the growing season of 2002. Second, point measurements of N 2O flux were made in the wheel-tracked (WT) and NWT interrows at five dates during the growing season of 2002. Third, point measurements of N 2O fluxes and soils (nitrate, ammonium, moisture, and temperature) were made in the NWT interrows from 2001 to 2004. The differences between point vs. continuous flux measurements (<8 g N 2O-N ha -1 d -1) and between the WT vs. the NWT (<3.7 g N 2O-N ha -1 d -1) were not significant. The means of N 2O daily flux within 60 d after injection (period of high soil N) in the first, second, and third year were 26.8, 21.2, and 28.0 g N 2O-N ha -1 d -1, respectively. The means during low soil N were 9.24, 4.05, and 7.50 g N 2O-N ha -1 d -1, respectively. Summer fertigations did not increase N 2O flux. Under the conditions of this study, optimal point measurement for N 2O daily flux can be made any time during the day at the NWT interrows. Among the soil parameters, soil nitrate dynamics in the injection zone correlates best with N 2O fluxes.
