Denitrification losses from an Inceptisol field treated with mineral fertilizer or sewage sludge

In order to evaluate the climatic and soil variables which control the denitrification processes in the field, measurements of N2O‐losses using the C2H2 inhibition technique were carried out in an Inceptisol cropped with spring wheat. The silty sand was amended with mineral fertilizer (120 kg N ha−1) or additionally with sewage sludge (620 kg total N ha−1). Soil temperature, moisture, nitrate and available carbon, the release of nitrous oxide (N2O) from the soil surface as well as the N2O concentrations along the soil profile were measured from March until November 1985 The N2O surface fluxes from the inorganically fertilized field were well correlated with those from the sewage sludge amended plots (r = 0.76). Multivariate correlation analyses show that particularly soil moisture and nitrate content had a significant effect on the nitrate respiration. The correlation with the soil water content was more clearly expressed by the N2O surface fluxes than by the N2O concentrations of the soil air. The N2O surface fluxes during 1985 totalled about 3 kg N ha−1 in the minerally fertilized field. Sewage sludge amendments increased the N2O evolution by 5 times. Spatial variability was high and the N2O surface fluxes were not well correlated (r = 0.4) with the N2O concentrations in the soil atmosphere. These experiments provide the background data for a denitrification model and better knowledge about the variables which have to be considered for its validation.