Emissions From Dairy Production Systems in a Semi-Arid Climate.

Concentrated dairy operations emit trace gases such as ammonia (NH₃), methane (CH₄), and nitrous oxide (N₂O) to the atmosphere. The implementation of air quality regulations in livestock-producing states increases the need for accurate on-farm determination of emission rates. Our objective is to compare the emission rates of NH₃, CH₄, and N₂O from three commercial dairies in southern Idaho that vary in size, animal housing, and manure handling systems. The three dairies consisted of a small open lot dairy (700 cows), large open lot dairy (10,000 cows) and a large open-freestall dairy (10,000 cows) with an anaerobic digester.  Both housing and manure management systems were monitored in order to determine “whole farm emissions” and determine the effects of manure handling practices on emissions from the different farm sectors.   Gas concentrations and wind statistics were measured and used with an inverse dispersion model to calculate emission rates. Average emissions from the housing area per cow per day for the three farms ranged from 0.10 – 0.14 kg NH_3, 0.33-0.49 kg CH₄ and 0.01 - 0.02 kg N₂O.  Average emissions from the wastewater ponds (g cow^-1 d^-1) were 10 - 129 NH₃, 27 – 1,028 CH₄ and 3.7 – 4.9 N₂O. Data from this study can be used to develop trace gas emissions factors from dairies in southern Idaho and other production systems in similar climatic regions.