Simultaneous measurements of ammonia volatilisation and deposition at a beef feedlot

The nitrogen (N) excreted at intensive livestock operations is vulnerable to volatilisation, and, subsequently, may form a source of indirect nitrous oxide (N2O) emissions. The present study simultaneously investigated volatilisation and deposition of N at a beef feedlot, semi-continuously over a 129-day period. These data were examined relative to pen manure parameters, management statistics and emission-inventory calculation protocols. Volatilisation measurements were conducted using a single, heated air-sampling inlet, centrally located in a feedlot pen area, with real time concentration analysis via cavity ring-down spectroscopy and backward Lagrangian stochastic (bLS) modelling. Net deposited mineral-N was determined via two transects of soil-deposition traps, with samples collected and re-deployed every 2 weeks. Total volatilised ammonia amounted to 210 tonnes of NH3-N (127 g/animal.day), suggesting that the inventory volatilisation factor probably underestimated volatilisation in this case (inventory, 30% of excreted N; 65 g N volatilised/animal. day; a value of similar to 60% of excreted N is indicated). Temperature contrast between the manure and air was observed to play a significant role in the rate of emission (R-2 = 0.38; 0.46 Kendall's tau; P < 0.05). Net deposition within 600 m of the pen boundary represented only 1.7% to 3% of volatilised NH4+-N, between 3.6 and 6.7 tonnes N. Beyond this distance, deposition approached background rates (similar to 0.4 kg N/ha. year).