Nitrogen monoxide production and consumption in an organic soil

Factors controlling NO production, consumption, and emission rates were examined in an organic soil. Emission rates were measured in the enclosed headspaces of intact soil cores under three fertilisation treatments (unfertilised or 100 kg N ha(-1) as NH4Cl or as NaNO3), with and without the nitrification inhibitor C2H2 (20-70 mu l l(-1)). Nitrification was always the main source of NO emitted across the soil surface, even when the soil was nearly saturated. Fertilisation of soil with NH4Cl increased NO emission both by stimulating NO production from nitrification, and by decreasing the NO consumption rate constant. Addition of NaNO3 also stimulated the production of NO and N2O during nitrification in aerobic soil slurry experiments. This effect was eliminated by adding C2H2 and was therefore not related to denitrification. In loose soil samples, the increase in NO-N production after NH4Cl addition represented as much as 26% of the added N. However, in intact cores, 95% of the NO produced through nitrification was oxidised within the soil column rather than emitted to the atmosphere. We concluded that nitrification is the primary NO source from this organic soil, that surface NO emissions are much lower than gross NO production rates, and that gaseous N oxide (NO and N2O) losses during nitrification can be affected by both soil NH4+ and NO3-.