Ammonia Losses from an Open Lot Southern High Plains Dairy during Summer.

Animal agriculture is a significant source of ammonia (NH₃). Cattle excrete most ingested nitrogen (N); most urinary N is converted to NH₃, volatilized and lost to the atmosphere. Open lot dairies on the southern High Plains are a growing industry and face environmental challenges that include reporting requirements for NH₃ emissions. We quantified NH₃ emissions from the open lot and wastewater lagoons of a commercial New Mexico dairy during a two week summer campaign in 2009. The 3500-cow dairy consisted of open lot, manure-surfaced corrals (22.5 ha). Milking cows comprised 73% of the herd. A flush system using recycled water intermittently removed manure from the feed alley to four lagoons (1.8 ha). Most manure was retained on the corral surface. Open path lasers measured atmospheric NH₃ concentration, sonic anemometers characterized turbulence, and inverse dispersion analysis was used to quantify emissions. Mean N intake was 612 and 701 g cow^-1 d^-1 for all cows and milking cows, respectively. Nitrogen in milk averaged 145 g cow^-1 d^-1. Open lot NH₃ fluxes (15-min) ranged from 8 to 221 µg m^-2 s^-1 and averaged 55 µg m^-2 s^-1, with maxima in the afternoon and minima during early morning. Lagoon NH₃ fluxes followed a similar pattern; fluxes ranged from 8 to 108 µg m^-2 s^-1 and averaged 56 µg m^-2 s^-1. Per capita emission rate (PCER) of NH₃-N averaged 252 g cow^-1 d^-1 from the open lot (41% of N intake) and 21 g cow^-1 d^-1 from lagoons (3% of N intake). Open lot PCER was near the upper range reported in the literature. However, our study was conducted during late summer when temperature-dependent NH₃ emissions are expected to be greatest. Because only the production herd was present, the per capita N intake, excretion and NH₃ emissions were greater compared with dairies that include calves.