**AWARDS ISSUED PRIOR TO JANUARY 20, 2025, WERE FUNDED UNDER PREVIOUS ADMINISTRATIONS AND MAY NOT REFLECT THE PRIORITIES AND POLICIES OF THE CURRENT ADMINISTRATION.** IN MANY PARTS OF THE COUNTRY, GROUNDWATER WITHDRAWALS EXCEED RECHARGE RATES AND HAVE CAUSED GROUNDWATER-LEVEL DECLINES, REDUCTIONS TO THE VOLUME OF GROUNDWATER IN STORAGE, LOWER STREAMFLOW AND LAKE LEVELS, OR LAND SUBSIDENCE. IT IS EXPECTED THAT THE DEMAND FOR GROUNDWATER WILL CONTINUE TO INCREASE BECAUSE OF POPULATION GROWTH AND CLIMATE CHANGE, ESPECIALLY IN THE SEMI-ARID AND ARID REGIONS. THE DEVELOPMENT OF BRACKISH GROUNDWATER AS AN ALTERNATIVE WATER SOURCE CAN HELP ADDRESS CONCERNS ABOUT THE FUTURE AVAILABILITY OF WATER AND CONTRIBUTE TO THE WATER SECURITY OF THE NATION. THUS, INFORMATION ON USING BRACKISH GROUNDWATER AS A NONTRADITIONAL IRRIGATION SOURCE IMPACTS ON CROP PRODUCTION, SOIL HEALTH, WATER QUANTITY AND QUALITY AT THE FIELD AND WATERSHED SCALES IS NEEDED TO UNDERSTAND THE POTENTIAL EXPANSION OF USING THE BRACKISH GROUNDWATER RESOURCE AND TO PROVIDE A SCIENTIFIC BASIS FOR MAKING POLICY DECISIONS. HOWEVER, IN SITU MEASUREMENTS OF THE COMPONENTS OF THE SALTS, NUTRIENTS, AND WATER CYCLES IN SOIL PROFILES FROM AGRICULTURAL IRRIGATION SYSTEMS IN THE SEMI-ARID AND ARID REGIONS ARE SCARCE. IN ADDITION, WHILE THERE HAVE BEEN A CONSIDERABLE NUMBER OF FIELD PLOT STUDIES INVOLVING IRRIGATION WATER USE, VERY FEW STUDIES HAVE LOOKED AT THE INTERACTIONS BETWEEN THE BRACKISH IRRIGATION WATER, SALTS, NUTRIENTS, AND WATER CYCLES AT THE WATERSHED LEVEL. ADDITIONAL INFORMATION IS ALSO REQUIRED REGARDING THE ANTICIPATED LAND USE CHANGE AND CLIMATE CHANGE AT THE REGIONAL SCALE. IN PARTICULAR, INFORMATION IS NEEDED ON THE COMBINED, SCALED-UP EFFECTS ON REGIONAL CONDITIONS OF MULTIPLE HYDROLOGICAL AND BIOGEOCHEMICAL PROCESSES ACTING AT THE FIELD SCALE. THE RATIONALE FOR THIS PROPOSED RESEARCH IS THAT A BETTER UNDERSTANDING OF THE HYDROLOGICAL AND BIOGEOCHEMICAL PROCESSES REGULATING SALTS, NUTRIENTS, AND WATER EXCHANGES BETWEEN THE SOIL, PLANT, AND GROUNDWATER WILL HELP US TO DEVELOP MORE ACCURATE PREDICTIONS ON THE IMPACTS OF USING BRACKISH GROUNDWATER AT THE REGIONAL AND GLOBAL SCALES, AND UNDERSTAND HOW THESE EXCHANGES WILL RESPOND TO LAND USE CONVERSION AND CLIMATE CHANGE.THE OGALLALA AQUIFER (OA) HAS BEEN USED EXTENSIVELY FOR AGRICULTURAL IRRIGATION IN THE SEMI-ARID TEXAS HIGH PLAINS (THP), WHICH RESULTED IN A SIGNIFICANT DECLINE OF GROUNDWATER LEVELS AND REDUCED FRESHWATER AVAILABILITY. SUPPLEMENTING IRRIGATION WATER NEEDS FROM BRACKISH GROUNDWATER RESOURCES HAS THE POSITIVE BENEFIT OF REDUCING THE FRESHWATER WITHDRAWALS AND HELP PROLONG FRESHWATER USEFUL LIFE, AND ENHANCE THE ECONOMIC VITALITY FOR THE THP. USING BRACKISH GROUNDWATER RESOURCES REQUIRES A HOLISTIC FOOD, SOIL, AND WATER ASSESSMENT TO HELP UNDERSTAND IMPACTS ON FOOD PRODUCTION, SOIL HEALTH, AND WATER QUALITY AT THE WATERSHED/REGIONAL SCALE. THE GOAL OF THE PROPOSED RESEARCH IS TO DEVELOP A MODELING FRAMEWORK TO EVALUATE THE IMPACTS OF USING BRACKISH GROUNDWATER AS A NONTRADITIONAL IRRIGATION SOURCE ON FOOD PRODUCTION, SOIL HEALTH, AND WATER QUANTITY AND QUALITY IN THE THP. BASED ON THE,WIDELY USED SOIL AND WATER ASSESSMENT TOOL (SWAT) MODEL, WE PROPOSE TO FURTHER DEVELOP NEW FUNCTIONS REGARDING IRRIGATION WATER QUALITY AND SCHEDULING, SOIL WATER MOVEMENT, SALT FATE AND TRANSPORT, AND CROP RESPONSES TO SALINITY. FIELD EXPERIMENTS ARE PROPOSED TO MEASURE SOIL SALINITY AND SOIL WATER QUANTITY AND QUALITY AT SELECTED SITES IN THE THP CONSIDERING DIFFERENT IRRIGATION TREATMENTS IN ATTEMPTING TO CALIBRATE AND VALIDATE THE PROPOSED NEW MODEL FUNCTIONS. TWO REPRESENTATIVE WATERSHEDS FROM THE NORTHERN AND SOUTHERN HIGH PLAINS (NHP AND SHP) WILL BE USED AS TESTBEDS TO EVALUATE AND CONSTRAIN THE PROPOSED MODELING FRAMEWORK AND TO EVALUATE TRADEOFFS BETWEEN FOOD, SOIL, AND WATER AT DIFFERENT IRRIGATION AND LANDSCAPE CONFIGURATIONS IN THE THP. RESULTS OF THE STUDY WILL BE USED TO ASSESS THE SUSTAINABILITY OF AGRICULTURE IN THE THP VIA THE EVALUATION OF AN ALTERNATIVE IRRIGATION SOURCE (BRACKISH GROUNDWATER) WHICH COULD BE A VIABLE ALTERNATIVE TO FRESH GROUNDWATER RESOURCES WHICH HAVE BEEN EXTENSIVELY EXPLOITED DURING THE PAST FEW DECADES AND PROJECTED TO BE CONTINUOUSLY DEPLETED IN THE NEAR FUTURE. MEASUREMENTS AND MODELING CONDUCTED IN THIS STUDY WILL BE USED TO DETERMINE THE POTENTIAL ROLE OF THE BRACKISH GROUNDWATER IN THE THP AGRICULTURAL PRODUCTION AND WILL PROVIDE THE BASIS FOR ASSESSING THE POTENTIAL FOR IMPROVING SOIL HEALTH, CONSERVING WATER RESOURCES, AND REDUCING NUTRIENT LOADS TO GROUNDWATER AND RIVER SYSTEMS. THE RESULTING DATASETS AND MODELING FRAMEWORK SHOULD BE OF USE IN ASSESSING SUSTAINABILITY AND IMPACTS ON AGROECOSYSTEM SERVICES FOR SIMILAR REGIONS IN THE U.S. THE MODEL WILL ALSO HELP IN ASSESSING THE IMPACT OF USING BRACKISH GROUNDWATER ON THE REGIONAL SALTS, NUTRIENTS, AND WATER CYCLES THAT ARE SIGNIFICANT TO SUSTAINING AGRICULTURAL PRODUCTION, IMPROVING THE ENVIRONMENT, AND ADAPTING TO CLIMATE CHANGE.