Managing Livestock to Mitigate Nitrogen Losses and Adapt to Climate Change.

Animal production systems in the US vary widely by animal species, type of product, and the economic, geographic and cultural characteristics of the production region. The manure produced by farm animals is considered the major source of gaseous NH₃ emission in the US, and manure is a significant contributor to N₂O and NO_x fluxes both during handling and following soil application. To reduce nitrogen’s effect on the environment, the N use efficiency in animal production must be improved. This begins by feeding animals to more precisely meet their protein or amino acid requirements. Feeding less protein N reduces N excretion in feces and particularly urine, and thus reduces potential losses throughout manure handling and following application to cropland. Volatile losses in the form of NH₃ can be reduced up to 50% through more efficient manure removal from the housing facility, the use of covered manure storages, and subsurface injection during application in the field. Improved management can also reduce N loss from grazing animals, but the benefit of these changes may be small and implementation may be impractical. For efficient use in feed production, manure N must be applied to farmland at the appropriate amount and time to meet crop requirements. Excess N applied will be lost through NO₃ leaching to ground water or N₂O and N₂ emission from nitrification and denitrification processes in the soil. Interactions occur among the various farm processes, so a comprehensive approach must be taken to assure that N loss reductions in one part of the system do not lead to greater losses of a different form or in a different part of the production system offsetting the perceived benefit. Adaptation to climate change will require changes such as better insulation of housing facilities and greater use of shading and evaporative cooling systems. Genetic changes in animals to develop greater tolerance to heat may also help in this adaptation. If animals cannot be fully adapted to future climate changes, decreases in production efficiency will increase N losses per unit of production. Livestock’s interaction with nitrogen and climate is very complex requiring integrated assessment and management of all processes making up their production systems.