Entrapment and displacement of nitrous oxide in a drained pasture soil

The objective of this work was to investigate a possible reason for the 'unaccounted for N-15' fraction, of N-15 mass balances, being so large in pasture systems, namely: the displacement and physical release of entrapped N2O gas from within a soil profile. A soil core was placed inside a purpose built perspex glovebox and the internal N2O concentration was continuously monitored. KNO3 was applied followed by periodic applications of distilled water. After 256 h the soil core was physically broken open in an attempt to release any N2O which may have been entrapped in the soil core. Instantaneous increases in glovebox N2O concentrations occurred when surface applied water displaced N2O from the base of the soil core and when the soil core was broken open (equal to 9.5% of N applied). The relative contribution these two mechanisms make will depend on the concentration of denitrification products present, the frequency and volume of irrigation/rainfall and the duration of the experiment.