THE PROPOSED RESEARCH WILL ADDRESS TWO OVERLAPPING THEMES INCLUDING: (1) NUTRIENT CYCLES AND MANAGEMENT AND (2) CHEMICALS OF ENVIRONMENTAL CONCERN. AGRICULTURAL SYSTEMS ARE HAVING A PROFOUND INFLUENCE ON THE GLOBAL N CYCLE AND THE FLUX OF REACTIVE NITROGEN (NR) INTO THE ATMOSPHERE. NITROUS OXIDE (N2O) IS A POWERFUL GREENHOUSE GAS (300 TIMES THE GLOBAL WARMING POTENTIAL OF CARBON DIOXIDE ON A 100 YEAR TIME HORIZON), BUT MORE IMPORTANTLY, HAS BECOME THE PREDOMINANT STRATOSPHERIC OZONE-DEPLETING SUBSTANCE EMITTED INTO THE ENVIRONMENT. AMMONIA (NH3) IS ALSO A CHEMICAL OF ENVIRONMENTAL CONCERN BECAUSE OF ITS ROLE IN AEROSOL FORMATION AND ITS ACUTE IMPACT ON HUMAN HEALTH. WE PROPOSE TO: 1) CONSTRAIN REGIONAL EMISSIONS OF N2O AND NH3 BASED ON TALL TOWER AND AIRCRAFT OBSERVATIONS AND INVERSE MODELING; 2) IDENTIFY N2O AND NH3 EMISSION HOTSPOTS AND HOT MOMENTS WITHIN THE REGION RELATED TO CROP AND ANIMAL PRODUCTION; 3) EXAMINE THE SENSITIVITY OF N2O AND NH3 EMISSIONS TO CLIMATE VARIABILITY; 4) ASSESS IF ALTERNATIVE (ASPIRATIONAL) CROPPING SYSTEMS (I.E. RECOUPLING OF GRAIN AND ANIMAL PRODUCTION) CAN SIGNIFICANTLY REDUCE N2O AND NH3 EMISSIONS; AND 5) WORK CLOSELY WITH TWO MAJOR COMMODITY GROUPS (MINNESOTA CORN GROWERS ASSOCIATION AND MINNESOTA MILK) TO HELP ACHIEVE MITIGATION OF NR IN THE ENVIRONMENT. BY PLACING BETTER CONSTRAINTS ON N2O AND NH3 EMISSIONS, WE BELIEVE THAT NEW MANAGEMENT PRACTICES COULD BE DEVELOPED TO HELP MITIGATE EMISSIONS WHILE MAINTAINING HIGH PRODUCTIVITY AND PROMOTING SUSTAINABILITY WITHIN THE US CORN BELT.