Submitted to: Review Article
Publication Type: Literature Review
Publication Acceptance Date: 8/11/2014
Publication Date: N/A
Technical Abstract: Greater public awareness of the potential effects of food production on the environment calls for livestock management systems that are sustainable with regard to the environment, society, and the economy. The concept of sustainable agriculture challenges producers to better understand the dynamics of agricultural systems and consider the long-term implications of management practices, particularly from an ecological perspective, and to balance production efficiency and profitability with community and consumer needs. Issues that impact beef feedyards and other concentrated animal feeding operations include global warming, air quality, ground and surface water availability and quality, and wildlife. The possibility of a more highly regulated cattle industry always looms as public concerns grow. Environmental issues frequently arise when livestock are raised in high densities typical of beef cattle feedyards. Most issues revolve around the large quantity of manure (a mixture of urine and feces) produced in a relatively small area. Less than 20% of the nutrients consumed by livestock are converted into animal product (meat and milk). The rest are excreted, accumulate, and constitute an active system of physical, chemical and biological processes and transformations. A key element in this system is nitrogen (N), an element vital for all life. Reactive N compounds, such as ammonia, nitrous oxide, and nitrate, are needed for for the myriad biochemical reactions that occur in biotic systems. Reactive N is the limiting factor in the function of many ecosystems; however, in highly managed systems like feedyards, it is abundantly present. The benefits of reactive N can be realized when it is kept in place; however, environmental costs accrue when it escapes or leaks from feedyard systems, with potential impacts on climate change, air, water, and biodiversity. Cattle producers are challenged to manage N to realize its benefits and to minimize its costs. The concept of N balance is key when considering the role of N in feedyards. An N balance is constructed by accounting for all the types of N in the feedyard system. Nitrogen inputs, predominantly as feed, are balanced against N outputs. Nitrogen outputs include N retained in cattle and excreted manure, losses of gases like ammonia and nitrous oxide, and soluble forms of N like nitrate that can move in water or through soil. Efforts to improve the sustainability of feedyard operations revolve around managing the components of the N balance so that N is used efficiently and losses are minimized. In response to a call from the Beef Checkoff, we examined the critical components of the feedyard N balance. Following this analysis, we produced a comprehensive analysis of the state-of-the-science of each N balance component, and identified ways to minimize the negative impacts of nitrogen that detract from sustainability. The critical components addressed are cattle diet and metabolism, ammonia and nitrous oxide emissions, and nitrogen leaching and runoff. We highlight processes, potential mitigation measures, and identified knowledge gaps and areas for further research.