Ammonia emissions from grazing

The ammonia-N emissions from artificially prepared urine patches on grassland on a sandy soil were measured with a wind tunnel method. Artificial urine with a N-content of 6-12 g/litre was applied at a rate of 5 litre/m2. At a urine application rate of 600 kg N/ha the ammonia-N emission varied between 6% and 19% (mean 13%) of the urine-N. It was argued that the emission rate is proportional to the urine-N concentration. The ammonia emission rate is 10% at an average urine-N concentration of 9 g/litre. The results of the emission measurements were confirmed by N-budget analyses of the urine patch system. The total ammonia emissions from grazed pastures at various levels of N-supply were calculated using known data on grass production, intake and digestion. The calculated ammonia-N emissions varied from 16 kg/ha at a N supply of 100 kg/ha to 38 kg/ha at a N-supply of 500 kg/ha. The calculated ammonia emissions were similar to the results of measurements in grazed fields with the micrometeorological mass balance method. At low levels of N-supply the mass balance data were disproportionally low, probably as a result of lower urine-N concentration during grazing and an underestimation of the emission by the mass balance method due to a relatively high background interference.