PASTUREAND FORAGE-BASED PRODUCTION SYSTEMS USING RUMINANT ANIMALS DOMINATE PRODUCTION OF MEAT, MILK, AND FIBER WORLD-WIDE. RUMINANT ANIMALS CONVERT HUMAN-INDIGESTIBLE PLANT MATTER INTO HIGH-QUALITY PROTEIN-BASED FOODS. UNFORTUNATELY,FORAGE-BASED PRODUCTION SYSTEMS ARE AMONG THE MOST INEFFICIENT IN TERMS OF FEED CONVERSION AND NITROGEN (N)-USE EFFICIENCY WHEN COMPARED WITH OTHER MEAT-PRODUCING PRODUCTION SYSTEMS SUCH AS POULTRY. AGRICULTURE IS ONE OF LARGEST SOURCES OF N POLLUTION IN THE US, RELEASING GASEOUS POLLUTANTS (NITROUS OXIDE,A POTENT GREENHOUSE GAS,ANDAMMONIA)AND NITRATE WHICH CAN MOVE INTOAND CONTAMINATE GROUNDWATER. NUTRIENT CYCLING EFFICIENCY IN FORAGE-BASED ANIMAL PRODUCTION SYSTEMS NEEDS TO BE IMPROVED FOR ENVIRONMENTAL AND ECONOMIC SUSTAINABILITY.OUR OVERALL, LONG-TERM GOAL IS TO IMPROVE N-USE EFFICIENCY WHICH IN TURN IMPROVES ANIMAL PRODUCTION AND REDUCES NEGATIVE ENVIRONMENTAL IMPACTS IN THE ENVIRONMENT.WE PROPOSE A SERIES OF ANIMAL DIGESTION AND N-BALANCE EXPERIMENTSBASED ON SILAGE FEEDING WITH ADJUSTED PROPORTIONS OF ALFALFA AND TANNIN- OR OTHER TOTAL POLYPHENOL-CONTAINING FORAGES. URINE AND MANURE (URINE + FECES) FROM OUR N-BALANCE STUDIES WILL BE APPLIED TO SOIL GROWING TALL FESCUE IN CONTROLLED EXPERIMENTSIN ORDER TO EVALUATEN LOSSES, INCLUDING NH3 AND GREENHOUSE GAS EMISSIONS AND NO3- LEACHING, AND CHANGES IN SOIL PROPERTIES AND THE SOIL MICROBIAL COMMUNITY. THIS INFORMATION WILL BE INTEGRATED TO PROVIDE ESTIMATES OF COMPARATIVE NET N-USE EFFICIENCY AND LONG-TERM BENEFITS OF DIETARY MODIFICATIONS ON THE FORAGE ECOSYSTEM.OUR PROJECT OBJECTIVE IS TO OPTIMIZE SOIL N RETENTION AND PLANT N UPTAKE AND REDUCE N EMISSIONS BY MANIPULATING THE DIET OF ANIMALS BY INCORPORATINGTANNIN- OR OTHER TOTAL POLYPHENOL-CONTAINING FORAGES. THE INFORMATION FROM THESE EXPERIMENTS WILL PROVIDE RUMINANT PRODUCERS WITH OPTIONS TO IMPROVE AGROECOSYSTEM EFFICIENCY, CAPTURE GREATER QUANTITIES OF N IN THE ANIMAL, SOIL, AND PLANT, AND SIMULTANEOUSLY REDUCE THE N LOSSES ASSOCIATED WITH RUMINANT ANIMALS. THESE BENEFITS IN TURN SHOULD IMPROVE FARM PROFITABILITY AND SUSTAINABILITY THROUGH REDUCTION IN PURCHASE OF OFF-FARM COMMODITIES SINCE N FERTILIZER AND CRUDE PROTEIN IN FEED ARE BOTH EXPENSIVE.?