** AWARDS ISSUED PRIOR TO JANUARY 20, 2025, WERE FUNDED UNDER PREVIOUS ADMINISTRATIONS AND MAY NOT REFLECT THE PRIORITIES AND POLICIES OF THE CURRENT ADMINISTRATION.** GROUNDWATER NITRATE CONTAMINATION UNDER AGRICULTURAL LANDSCAPES POSES A PERVASIVE AND MULTIFACETED CHALLENGE WITH SERIOUS IMPLICATIONS FOR HUMAN HEALTH AND THE ENVIRONMENT. IN NEBRASKA, NEARLY ONE IN FIVE DRINKING-WATER WELLS STATEWIDE CONTAIN NITRATE CONCENTRATIONS ABOVE DRINKING WATER STANDARD (10 MG/L). HOWEVER, GROUNDWATER CONTAMINATION IS NOT UNIFORM ACROSS SPACE NOR IS IT CONSISTENT WITH CROPLAND MANAGEMENT PRACTICES. THE UNDERGROUND PROCESSES THAT ALLOW NITRATE TO DEGRADE TO LESS HARMFUL FORMS REMAIN UNCLEAR, AND THEVARIABILITY OF THESE PROCESSES FROM PLACE-TO-PLACE IS INADEQUATELY CHARACTERIZED. THESE KNOWLEDGE GAPS HINDER EFFECTIVE PRECISION-BASED AGRICULTURAL PRACTICES TO MEET AGRONOMIC AND HUMAN HEALTH NEEDS. TO ADDRESS THESE CHALLENGES, THE GOAL OF THIS INTEGRATED RESEARCH AND EXTENSION PROJECT IS TO ADVANCE UNDERSTANDING OF GROUNDWATER NITRATE PROCESSES, THEREBY INFORMING EVIDENCE-BASED LAND MANAGEMENT, POLICY, AND GROUNDWATER MONITORING. OBJECTIVES WILL: (1) CO-DEVELOP A FIELD INVESTIGATION PROGRAM WITH STAKEHOLDERS USING RUST STAINING ON CENTER-PIVOT IRRIGATION SYSTEMS AS A GUIDE TO SUBSURFACE PHYSICAL, CHEMICAL, AND BIOLOGICAL CONDITIONS; (2) BUILD 3DMODELS OF SUBSURFACE GEOLOGY AT SELECT SITES AND INTERPRET THE ENVIRONMENTS UNDER WHICH THESE GEOLOGICAL MATERIALS FORMED; (3) QUANTIFY NITRATE CHEMICAL REACTIONS IN THE SUBSURFACE THAT ARE ASSOCIATED WITH VARIOUS GEOLOGICAL DEPOSITS AND MATERIALS, AND PREDICT THE MOVEMENT OF NITRATE USING NUMERICAL MODELS; AND (4) CO-DEVELOP A ROADMAP WITH STAKEHOLDERS THAT WILL ENABLE IRRIGATION MANAGERS AND PRODUCERS TO IMPLEMENT TARGETED NITRATE MANAGEMENT OUTSIDE THE STUDY AREA. ULTIMATELY, THIS WORK WILL PROTECT WATER QUALITY IN GROUNDWATER SYSTEMS THROUGH IMPROVED NUTRIENT MANAGEMENT AND UNDERSTANDING OF NITRATE PROCESSES.