Research Accomplishment Reports 2007

Nitrogen Cycling, Loading, and Use Efficiency in Forage-Based Livestock Production Systems

E.S. Vanzant
Department of Animal and Food Sciences

 

Project Description

In 1918, Fritz Haber received the Nobel Prize in Chemistry for his work in developing the Haber-Bosch process for producing ammonia from atmospheric nitrogen and hydrogen. Since that time, global food production has become so dependent upon this process that some estimates suggest that a third of the human population on the planet survives on protein that is derived from atmospheric N via the Haber-Bosch process.

This enormous shift in the global N cycle comes at a cost. For example, late in 2007, the National Geological Survey found that states with watersheds draining into the Ohio River (including Kentucky) were major contributors to the 'dead zone' in the Gulf of Mexico. This vast zone is essentially devoid of fish life primarily as a consequence of high levels of N (and phosphorus) flowing into the Gulf from the Mississippi River. Although N fertilizers used in crop production are a major contributor, temperate-region grassland agriculture is also highly dependant on N fertilization. In order to convert the cellulose from grasslands into usable product, we are dependant upon ruminant animals, and, in the United States, particularly dependant on cattle. Although cattle are well suited to the conversion of cellulose into food (and other products) that are usable by humans, there are considerable inefficiencies in the utilization of N in forage-based cattle production systems.

This project is designed to gain a better understanding of what those efficiencies are, and to help identify factors that limit the efficiency of converting N into usable product, while simultaneously decreasing waste N that enters the environment. Because we have little information on the total quantities of N that enter the atmosphere and ground water in such pastoral systems, we collaborated in the submission of a multi-state grant to the USDA NRI Managed Ecosystems program. If funded, this grant will support research at 8 research stations throughout the US that will provide much-needed quantitative data on the movements of N through grassland ecosystems in the U.S.

Additionally, we have continued work on projects designed to better understand the efficiencies of N use by ruminant animals in order that we may minimize opportunities for N to adversely affect the environment in forage-based cattle production systems. Specifically, we have conducted research to understand how combinations of dietary nutrients (i.e. how dietary starch interacts with dietary forage) affect N recycling and excretion by cattle consuming moderate- to high protein forage. Results of this research indicate that consumption of moderate levels of starch will have little impact on total N excretion. However, these results also indicate that we can use the diet to manipulate the route of N excretion. This can be beneficial because deposition of excreted N in the feces, as opposed to urinary excretion, may minimize volatilization of N compounds to the atmosphere, as well as minimize runoff and leaching into groundwater.

Impact

Results from this study will allow us to quantitatively determine the influence of increasing ruminal or abomasal carbohydrate supply on critical elements of the nitrogen efficiency complex in forage-fed ruminants. This information is critical to enhance existing predictive models of nutrient utilization and excretion in livestock and ultimately will allow us to better manage resources to simultaneously optimize animal performance and nutrient return to the environment.