ESTIMATES OF AMMONIA EMISSION FROM DAIRY-COW COLLECTING YARDS

Two approaches were used to estimate ammonia (NH3) emission from dairy cow collecting yards. In the first, a system of small wind tunnels wa s used to estimate emission from urine spread on small concreted areas dirtied with faeces and to identify some of the factors controlling t he extent of the loss. In the second, a hood was used to measure emiss ion per unit area from a collecting yard on a commercial dairy farm. M ean emission from urine applied to concrete in the wind tunnel experim ents was 49% of the applied urea-N. Cleaning concreted areas reduced e mission, with mean emission of applied urea-N of 25 and 36% if concret e areas were scraped at 2 or 6 h, respectively. Hosing the concrete wa s more effective at reducing emission, but considered to be less typic al of practice on UK dairy farms. Mean emissions from the collecting y ard on the commercial dairy farm accounted for 93 and 40% of urea-N in put to the yard for summer and winter, respectively, the lower winter emissions possibly being due to a combination of lower urea-N input to the yard and lower temperature. An average emission factor estimated from the hood measurements was 8.3 g N/cow d. Inclusion of this emissi on factor in a recent inventory of NH3 emission from UK agriculture, i ncreased the estimate of annual emission per dairy cow by 11%, showing it to be a significant source which may not have previously been acco unted. (C) 1998 Silsoe Research Institute.