Nitrous oxide emissions from artificial urine patches applied to different N-fertilized swards and estimated annual N2O emissions for differently fertilized pastures in an upland location in Germany

Artificial urine containing 20.2 g N per patch of 0.2 m(2) was applied in May and September to permanent grassland swards of a long-term experiment in the western uplands of Germany (location Rengen/Eifel), which were fertilized with 0, 120, 240, 360 kg N ha(-1) yr(-1) given as calcium ammonium nitrate. The effect on N2O fluxes measured regularly during a 357-day period with the closed-chamber technique were as follows. (1) N2O emission varied widely among the fertilized control areas without urine, and when a threshold water-filled pore space >60% was exceeded, the greater the topsoil nitrate content the greater the flux from the individual urine patches on the fertilized swards. (2) After urine application in May, 1.4-4.2% of the applied urine-N was lost as N2O from the fertilized swards; and after urine application in September, 0.3-0.9% of the applied urine-N was lost. The primary influence on N2O flux from urine patches was the date of simulated grazing, N-fertilization rate being a secondary influence. (3) The large differences in N2O emissions between unfertilized and fertilized swards after May-applied urine contrasted with only small differences after urine applied in September, indicating an interaction between time of urine application and N-fertilizer rate. (4) The estimated annual N2O emissions were in the range 0.6-1.6 kg N2O-N per livestock unit, or 1.4, 3.6, 4.1 and 5.1 kg N2O-N ha(-1) from the 0-360 kg ha(-1) of fertilizer-N. The study demonstrated that date of grazing and N-fertilizer application could influence the N2O emission from urine patches to such an extent that both factors should be considered in detailed large-scale estimations of N2O fluxes from grazed grassland.