The effect of organic amendments and irrigation management in the field were studied with respect to Eh, NO3-, and soluble organic C concentrations in the soil solution, and gaseous concentrations of N2O, CO2, and the ratio N2 to O2. Duplicate plots were treated with fresh bovine manure as follows: control 45t·ha-1, 180 t·ha-1 with a standard irrigation cycle (SI), and 180 t·ha-1 with a double irrigation (DI). Samples to 230cm were obtained at several depths in each profile during the 84-day study. The general order for treatment effects upon CO2 concentrations and soluble C was the same: SI > DI > 45 t·ha-1 > control. The order for N2/O2 was 180 t·ha-1 (SI and DI) > 45 t·ha-1 and control. The order for both N2O and NO-1 was the same: 45 t.ha-1 and DI > SI and control. The most important factor affecting N2O concentrations was the NO3- concentration; soil solution concentrations greater than 16 μN·ml-1 had much higher frequencies of high N2O concentrations. The sequential reduction of NO-13→ N2O → N2 was noted in all treatments by the following observations: (i) the concentrations of both NO-3 and N2O were highest at the beginning of the experiment; (ii) the concentrations of CO2 and N2/O2 were higher near the end: (iii) sub-ambient concentrations of N2O were more frequent near the end of the study. Use of N2O as an indicator of denitrification is cautioned since one of the highest manured treatments (SI) had N2O concentrations no different than the control, but had much higher CO2 and N2/O2 concentrations and more reduced (Eh) conditions. We conclude that use of a single irrigation method is far superior to the double irrigation method with respect to reducing losses of NO3- and N2O and for conserving organic N arid water. © 1979.
