Emission of ammonia (NH3), nitrous oxide (N2O) and methane (CH4) from a dairy hardstanding in the UK
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Emissions of ammonia (NH3), nitrous oxide (N2O) and methane (CH4) from uncovered yard areas (hardstandings) of a UK dairy farm were measured between October 1997 and August 1999. Measurements were concentrated after morning milking when the yard had been scraped, and at positions accounting for differences in slurry coverage and manure type. Over two seasons, the mean NH3 emission from a number of season and position categories on the hardstanding were 0.27 g N m−2 h−1 in winter and spring, 0.45 g N m−2 h−1 in summer when the feeding/loafing area was not included, increasing to 1.51 g N m−2 h−1 when this area was included, and 5.0 g N m−2 h−1 for the feeding/loafing area alone. The feeding/loafing area was close to the slurry lagoon where excreta were continuously deposited and not scraped to the slurry lagoon, as was the rest of the hardstanding. A diurnal study of emissions in the summer showed a marked decrease with time after the yard was scraped following the first milking, with emissions increasing again after evening milking when fresh excreta were deposited. Nitrous oxide emissions were more variable than NH3, with an order of magnitude difference between lowest and highest emissions measured at the same time. Mean N2O emission rates were 3.3 μg N m−2 h−1 in winter and spring, 6.5 μg N m−2 h−1 in summer when the feeding/loafing area was not included, increasing to 7.8 μg N m−2 h−1 when this area was included, and 17.9 μg N m−2 h−1 for the feeding/loafing area alone. Large mean methane emissions were measured, 185 mg C m−2 h−1 in winter and spring, decreasing to 57.3 mg C m−2 h−1 in summer when the feeding/loafing area was not included, increasing to 72.9 mg C m−2 h−1 when this area was included, and 151.2 mg C m−2 h−1 for the feeding/loafing area alone. Therefore in summer, emissions measured directly from a dung pat [0–5 cm] that had not been scraped from the loafing area were much greater than from scraped hardstanding areas, but in winter there were still significant emissions from the remaining slurry post-scraping. The experimental design was not sufficient to elucidate the physico-chemical variables controlling the measured emissions, but the data were put into context by estimating the annual emission of these pollutant gases from this one dairy farm. These were estimated at 0.43 t NH3-N y−1, 0.3 kg N2O-N y−1 and 1.0 kg CH4-C y−1. Therefore, uncovered farmyard areas that regularly have excreta deposited on them are significant but previously unaccounted for sources of NH3 loss, less so for N2O and CH4, and require further study to assess the significance of these emission sources within the UK and worldwide.
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