FIELD MEASUREMENT OF DENITRIFICATION IN IRRIGATED SOILS

Abstract

The objectives of this study were to compare two methods of introducing C2H2 to the soil atmosphere for denitrification measurement by the C2H2 inhibition technique and observe the effects of nitrogen fertilizer source and cropping on denitrification losses. During June and July 1981, C2H2 was dissolved in the water used to irrigate fallow plots left unfertilized or fertilized with (NH4)2SO4 or KNO3 at the rate of 200 kg N ha-1. Total denitrification losses of 10.1, 19.7, and 18.7 kg N ha-1 were measured from unfertilized plots, and plots fertilized with (NH4)2SO4 and KNO3, respectively. Approximately 3.70 kg N2O-N ha-1 were emitted from fertilized plots that received no C2H2. In the summer of 1982, denitrification losses from cropped soils irrigated with C2H2-treated water were compared to those from soils that received C2H2 through dispersion tubes inserted into the soil. The denitrification loss from plots cropped to spring wheat (Triticum aestivum L.) were 0.22 kg N ha-1 during the 4-wk study when C2H2 was supplied through dispersion tubes. During the same period, 0.30 kg N ha-1 was lost from cropped plots irrigated with C2H2-treated water. Acetylene should be supplied to the soil atmosphere, both through dispersion tubes and through the irrigation water, to provide adequate C2H2 partial pressures for inhibition of N2O reduction throughout the irrigation cycle.