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

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Abstract
Artificial urine containing 20.2 g N per patch of 0.2 m2 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.