Evaluation of denitrification losses by the acetylene inhibition technique in a permanent ryegrass field (Lolium perenne L.) fertilized with animal slurry or ammonium nitrate

In a field experiment, the effect of animal slurry, (with and without the nitrification inhibitor dicyandiamide on total denitrification losses estimated by the C₂H₂ inhibition technique was measured over 2 years (1989–1990). During this period, four different plots (each with four replicates) were fertilized six times with 150 kg N ha^-1 in the form of cattle-pig slurry or NH₄NO₃. Soil samples (0–20 cm) were analysed at regular intervals for NH _inf4 ^sup+ and NO _inf3 ^sup– concentrations. The soil water content was determined gravimetrically. During the first year (1989) total denitrification losses from unfertilized, mineral-fertilized, and animal slurry-amended plots (with or without dicyandiamide) were estimated as 0.2, 3.1, 0.7, and 0.6 kg N ha^-1, respectively. During the second year (1990) the denitrification losses were 0.4, 1.3, 0.7, and 0.7 kg N ha^-1, respectively. There was a clear relationship between the NO _inf3 ^sup– concentration or soil water content and the denitrification rate. The results are siteund experiment-specific and cannot be generalized so far.