RELATIONSHIPS BETWEEN FIELD-MEASURED DENITRIFICATION LOSSES, CO2 FORMATION AND DIFFUSIONAL CONSTRAINTS

Approaches to quantify denitrification losses from arable land and other ecosystems are frequently hampered by the methods available. Extensive measurements of denitrification losses with the acetylene inhibition technique (AIT) over 3 years in various soils and crops (N2O surface fluxes and soil air concentrations), when compared with simultaneously CO2-production determinations, revealed that NO3-respiration in well-aerated soils depends primarily on carbon and nitrate availability. N2O concentrations in soil air exhibited significant correlations with soil depth, whereas the correlations between the N2O soil air concentrations at 10 cm depth and the N2O soil surface fluxes were not significant. Increasing soil water contents reduced N2O diffusion through the silty sand soil columns considerably, especially in the carbon-enriched upper 10 cm. Denitrification losses ha-1, calculated from the N2O concentrations in soil air and an assumed mean annual air-filled pore volume of about 20%, were higher than losses at the soil surface, suggesting that other soil variables besides carbon, nitrate and water availability are influencing N2O + N2 surface fluxes measured by the AIT. Soil processes controlling N2O formation in the presence of C2H2 as well as the N2O fluxes from the place of production to the soil surface are ranked and discussed.