Carbon induced subsoil denitrification of N-15-labelled nitrate in 1 m deep soil columns

Nitrate in soils is potentially a contaminant of groundwater and can also b e denitrified to form nitrous oxide (N2O), a global warming gas that is als o involved with stratospheric ozone depletion. The objective of this work w as to examine the fate of N-15-labelled NO3- when it was injected into the subsoil (80 cm) in the presence of carbon. Gas fluxes from the soil surface and gas concentrations in the soil profile were monitored for 38 d. On ave rage, after this time only 13% of the N-15-labelled N was present as NO3- w ith immobilisation (54%), entrapment in soil pore space (7%), dissolution o f N in soil water (2%), gas fluxes from the soil column surface (N2O < 1%, N-2 1.8%) and unaccounted for N-15 (20%) making up the remainder of the N-1 5 balance. As N-15-labelled N gases diffused from the zone of denitrificati on towards the soil surface the ratio of N2O-N:(N2O-N + Na) decreased (rang e of 0.90 to 0.17). (C) 1998 Elsevier Science Ltd. All rights reserved.