Predicting Management Effects on Ammonia Emissions From Dairy and Beef Farms

Relationships were developed to predict ammonia (NH3) nitrogen losses from cattle manure in animal housing,during manure storage, following field application, and during grazing. Ammonia loss in each phase was predicted using amechanistic model for NH3 volatilized from the surface of an aqueous solution of ammonium where the NH3 is transportedto the free atmosphere through a pathway with finite resistance. Ammonia emission rate was a function of the ammoniacalN content in the manure, ambient temperature, manure pH, manure moisture content, and the exposed manure surface area.Model relationships were calibrated by selecting values for the resistance to NH3 transport for the various loss pathways,which predicted daily and annual emissions similar to those reported in published studies. In further evaluation, thesecalibrated relationships predicted average annual losses similar to those documented in previous work over a range in climatelocations. These relationships were integrated into a whole-farm simulation model to provide a tool for evaluating andcomparing long-term nitrogen losses along with other performance, environmental, and economic aspects of farm production.Whole-farm simulations illustrated that the use of a free stall barn, bottom-loaded slurry storage, and direct injection ofmanure into the soil reduced NH3 emissions by 33% to 50% compared to other commonly used dairy housing and manurehandling systems in the northeastern U.S. The improvement in nitrogen utilization more than offset the increased cost inmanure handling, providing a small increase in farm profit. The farm model provides a research and teaching tool forevaluating and comparing the economic and environmental sustainability of dairy and beef production systems.