** AWARDS ISSUED PRIOR TO JANUARY 20, 2025, WERE FUNDED UNDER PREVIOUS ADMINISTRATIONS AND MAY NOT REFLECT THE PRIORITIES AND POLICIES OF THE CURRENT ADMINISTRATION.** NUTRIENT RUNOFF FROM AGRICULTURAL PRODUCTION LEADS TO EUTROPHICATION IN THE GULF OF MEXICO AND OTHER LOCATIONS WITH SIGNIFICANT DETRIMENTAL CONSEQUENCES FOR AQUATIC ECOSYSTEMS. COST-EFFECTIVE MANAGEMENT OF NUTRIENT RUNOFF FROM CROPLAND REQUIRES A THOROUGH UNDERSTANDING AND QUANTITATIVE MODELING OF THE EFFECTS OF FERTILIZER USE, IRRIGATION AND BEST MANAGEMENT PRACTICES (BMPS) ON CROP PRODUCTION AND NUTRIENT RUNOFF IN THE RESPECTIVE WATERSHEDS. SINCE CROP PRODUCTION AND FERTILIZER USE ARE PRIMARILY DRIVEN BY ECONOMIC INCENTIVES, INCLUDING INPUT AND OUTPUT PRICES, IT IS ESSENTIAL THAT THE QUANTITATIVE ASSESSMENT INCLUDES BOTH ECONOMIC AND BIOPHYSICAL DETERMINANTS OF NUTRIENT RUNOFF. IN THIS PROJECT, WE WILL DEVELOP A LARGE-SCALE SPATIALLY EXPLICIT INTEGRATED ASSESSMENT MODEL (IAM) TO EXAMINE THE INTERDEPENDENCIES BETWEEN CROP PRODUCTION AND WATER QUALITY AND QUANTITY. THE INTEGRATED HYDRO-ECONOMIC AGRICULTURAL LAND USE (IHEAL) MODEL COMBINES A US SCALE MULTI COMMODITY (CORN, WHEAT, SORGHUM, SOY) PARTIAL EQUILIBRIUM MARKET FORMULATION WITH A PROCESS-BASED SOIL AND WATER ASSESSMENT TOOL (SWAT). THE SYSTEM INCLUDES SPATIALLY EXPLICIT COUNTY SCALE PRODUCTION DECISIONS FOR PLANTING, NITROGEN (N) FERTILIZER USE, AND IRRIGATION. THIS PROJECT WILL EXPAND THE CURRENT IHEAL MODEL TO INCLUDE ADDITIONAL FOUR CROPS, EXPLICIT CONSIDERATION OF BEST MANAGEMENT PRACTICES (BMPS), AND PHOSPHORUS (P) USE VIA HYDROLOGIA AND WARE QUALITY SYSTEM (HAWQS). THE MODEL WILL BE USED TO STUDY INTERDEPENDENCIES BETWEEN WATER QUALITY OUTCOMES ACROSS WATERSHEDS WITH SIGNIFICANT NUTRIENT RUNOFF. WE WILL ALSO EXAMINE THE IMPLICATIONS OF NUTRIENT RUNOFF ABATEMENT POLICIES FOR REGIONAL PRODUCTION, COMMODITY PRICES, REGIONAL WATER QUALITY, AND DEMAND FOR IRRIGATION WATER IN AREAS WITH LIMITED WATER SUPPLIES.