Site of nitrous oxide production in field soils

Abstract

Nitrous oxide (N2O) fluxes at the soil surface and concentrations at 0.1, 0.2, and 0.3 m were determined in a 40-year-old planted tallgrass (XXX) prairie, a 40-year-old white pine (Pinus strobus) plantation, and field plots treated annually for 18 years either with 33 metric tons of manure ha−1 (330 kg N ha−1) and NH4NO3 (80 kg N ha−1) or with only NH4NO3 (control). Nitrous oxide fluxes from the prairie, forest, manure-amended, and control sites from 13 May to 10 November 1980 ranged from 0.2 to 1.3, 3.5 to 19.5, 3.7 to 79.0, and 1.7 to 24.8 ng N2O-N m−2s−1, respectively. We observed periods when there was no apparent relationship between the N2O flux from the surface and N2O concentrations in the soil profile. This was generally the case in the prairie and in the field sites following the application of N fertilizer. The N2O concentrations in the soil profile increased markedly and coincided with increased soil water content following periods of heavy rainfall for all sites except the prairie. Nitrous oxide concentration gradients indicate that following heavy rainfalls the site of N2O production was moved from the surface deeper into the soil profile. We suggest that the source of N2O production near the surface is nitrification and that N2O is produced by denitrification of NO3 leached into the soil following heavy rainfall.