|Rotz, Clarence - Al|
Submitted to: Journal of Environmental Quality
Publication Type: Peer reviewed journal
Publication Acceptance Date: 8/23/2013
Publication Date: 6/20/2014
Citation: Rotz, C.A., Montes, F., Hafner, S.D., Heber, A.J., Grant, R.H. 2014. Ammonia emission model for whole farm evaluation of dairy production systems. Journal of Environmental Quality. DOI:10.2134/jeq2013.04.0121. Interpretive Summary: Gaseous emissions from animal agriculture have become an important issue in the United Sates and many other developed countries. Two compounds of particular interest are ammonia and hydrogen sulfide due to their regulation by the U.S. Environmental Protection Agency under the Clean Air Act. This regulation requires the reporting of the emission of either of these compounds that exceeds 45 kg within any 24-hour period. Daily emissions from large animal feeding operations can exceed this level, particularly for ammonia. Accurate measurement and monitoring of animal feeding operations is very difficult and costly due to the many emission sources on farms, the large areas of exposure, and the relatively low concentrations of these compounds. Another approach is to estimate emissions using a model that simulates the important farm and emission processes. A tool for whole farm quantification of ammonia and hydrogen sulfide emissions was created by incorporating relationships for simulating the formation, dissociation, aqueous-gas partitioning, and mass transport processes of these compounds in a farm simulation model called the Integrated Farm System Model. Management effects on the emission of these compounds are predicted along with their effects on nitrate leaching, greenhouse gas emissions, nutrient runoff, and farm profit. This revised farm model provides a useful tool for evaluating and comparing management effects and mitigation strategies on ammonia and hydrogen sulfide emissions along with other environmental impacts and farm profitability.
Technical Abstract: Emissions of ammonia (NH3) and hydrogen sulfide (H2S) vary considerably among farms as influenced by climate and animal and manure management. Because the measurement of these emissions is difficult and expensive, the use of process based models provides another option for estimating whole farm emissions. Models for simulating the processes of NH3 and H2S formation, dissociation, aqueous-gas partitioning, and mass transport were developed and incorporated in a whole farm simulation model (Integrated Farm System Model or IFSM). Emissions are predicted considering the influence of farm processes on the simulation of emission processes in dairy and beef production. The major farm sources include manure on the floor of the housing facility, manure in storage if one is used, field applied manure, and deposits on pasture if grazing is used. Daily weather and manure characteristics are used to predict emissions from each source using an hourly time step. Excretion amounts and nutrient contents predicted by IFSM are used to establish the initial characteristics of the manure, and losses and transformations in each source are used to predict the manure characteristics at the succeeding source. Farm and emission processes are simulated for the conditions of each day, and daily emissions from all sources are summed to give annual emissions. The model has been evaluated by comparing predicted emissions to measured values from several published studies (Rotz et al., in review). This evaluation has verified that predicted emissions respond appropriately to the effects of temperature, protein in animal diets, and manure handling practices. The farm model provides a useful tool for evaluating and comparing management effects and mitigation.