Management to reduce nitrogen losses in animal production

ABSTRACT Reduction of nitrogen loss in animal production requires whole-farm management. Reduced loss from one farm component is easily negated in another if all components are not equally well managed. Animal excretion of manure N can be decrerased by improving the balance of protein or amino acids fed to that required by individual animals or animal groups or by improving production efficiency. Management to increase milk, meat, or egg production normally improves efficiency by reducing the maintenance protein required per unit of production. Large losses of manure nitrogen occur through the ammonia and nitrous oxide that are emitted into the atmosphere and the nitrate leached into groundwater. Up to half of the excreted nitrogen is lost from the housing facility, but this loss can be decreased through frequent manure removal and by avoiding deep litter systems and feedlots. Techniques such as acid treatment of manure, scrubbing of ventilation air, and floor designs for separating feces and urine substantially reduce ammonia emissions, but these practices are often impractical or uneconomical for general use. Manure storage units improve nutrient utilization by allowing better timing of nutrient application with crop needs. At least 70% of the nitrogen entering anaerobic lagoons is typically lost, but a less than 10% loss can be maintained using slurry storage with a natural crust or other cover, or by drying poultry manure to at least 50% dry matter. Irrigation and surface spreading of manure without soil incorporation often ensures the loss of all remaining nonorganic nitrogen (typically, 20 to 40% of remaining nitrogen). Rapid incorporation and shallow injection methods decrease this loss by at least 50%, and deep injection into the soil essentially eliminates this loss. For grazing animals, excessive loss can be avoided by not overstocking pastures and avoiding late fall and winter grazing. Reducing emissions between the animal and the soil can lead to greater leaching and denitrification losses from the soil if this additional nitrogen is not used properly. The use of a crop rotation that efficiently absorbs these nutrients and applying nitrogen near the time it is needed by crops reduce the potential for further loss. Maintaining the proper number of animals per unit of land available for manure application is always crucial for efficient recycling of nitrogen. Our understanding of nitrogen loss processes is improved through modeling, and computer models assist in the development of integrated systems for efficient and economical nitrogen use in animal production.

Key Words: Ammonia, Denitrification, Farm Production, Leaching, Management, Nitrogen Loss

© 2004, by the American Society of Animal Science. All rights reserved.

J. Anim. Sci. 2004. 82(E. Suppl.):E119-E137

Implications

Whole-farm management is necessary to decrease nitrogen losses in animal production. If steps are taken to reduce loss in one component of the farm, the nitrogen saved will likely be lost elsewhere if all components are not equally well managed. Management must focus on improving the nitrogen use efficiency of the animals to reduce nitrogen excretion, retaining that nitrogen in the manure until it is incorporated into the soil, and applying the appropriate amount of manure in a timely manner to enhance crop uptake. Management of all the factors involved in the nitrogen cycle of the farm is complex. Whole-farm research on nitrogen management is needed, but such research is difficult and expensive. Computer simulation and other farm models provide research tools that integrate farm components to assess and compare long-term effects of production systems. These models can provide help with strategic farm planning and tactical operations to reduce adverse environmental effects, while maintaining or improving farm profit.