SUMMARYLosses of N by denitrification from an imperfectly drained grassland soil were measured by the acetylene‐inhibition technique over a 1‐yr period, during which applications of up to 200 kg ha−1of N as cattle slurry or calcium nitrate were made. The quantities of N lost from nitrate‐treated soil were much greater than from slurry‐treated areas, and ranged up to 21% of the N applied. The losses occurred predominantly over brief periods following fertilizer application in the spring. Ratios of N released as N2to that released as N2O increased as denitrification rates increased. The highest ratio recorded, 24, may have been a conservative estimate because inhibition of N2O reduction may not have been complete on all occasions. Increased respiration was observed in the soil profile as a result of adding C2H2. This effect should be taken into account in interpreting experiments using the C2H2‐inhibitio