THIS PROJECT SEEKS TO IMPROVE PHOSPHORUS (P) MANAGEMENT IN ACTIVELY MANAGED AGROECOSYSTEMS WHERE SUBSURFACE/LATERAL FLOWS DRIVE P TRANSPORT. THE RESEARCH SITES ARE LOCATED IN MAJOR POULTRY AND DAIRY MANURE PRODUCING REGIONS OF ALABAMA AND WISCONSIN, RESPECTIVELY. THE MAJOR GOAL OF PROPOSED RESEARCH IS TO IMPROVE OUR KNOWLEDGE OF COLLOIDAL-FACILITATED P TRANSPORT PROCESSES IN THE SUBSURFACE ENVIRONMENT AND REFINE HYDRUS-1D MODEL TO ACCURATELY PREDICT COLLOIDAL P LOSSES. WE PROPOSE TO QUANTIFY THE EFFECT OF SOIL PHYSICAL AND CHEMICAL CHARACTERISTICS ON WATER DISPERSIBLE COLLOIDS, COLLOIDAL P AND TOTAL P LOSSES USING FIELD DATA COLLECTION, LABORATORY EXPERIMENTS AND MODELING. SPECIFICALLY, WE WILL: (1) USE X-RAY COMPUTED TOMOGRAPHY TO QUANTIFY THE SOIL MACROPORE CHARACTERISTICS/PARAMETERS (E.G., CONNECTIVITY, MACROPOROSITY) AT FIELD SCALES; (2) CHARACTERIZE THE EFFECT OF SOIL PHYSICO-CHEMICAL PROPERTIES ALONG WITH THOSE OF THE INFILTRATING WATER ON SUBSURFACE MIGRATION OF WATER DISPERSIBLE COLLOIDS AND P IN DIFFERENT FORMS (COLLOIDAL, DISSOLVED, PARTICULATE); AND (3) DEVELOP A NEW AND IMPROVED VERSION OF HYDRUS-1D MODEL TO SIMULATE COLLOIDAL-FACILITATED P AND TOTAL P TRANSPORT IN STRUCTURED SOILS. THE LONG-TERM GOALS OF THIS PROJECT ARE TO ADVANCE OUR KNOWLEDGE ON FUNDAMENTAL P TRANSPORT PROCESSES, PROVIDE A VALUABLE DATASETS TO SUPPORT DECISION SUPPORT TOOLS, DEVELOP/REFINE MODELS THAT LACK THE CAPABILITY TO QUANTIFY SUBSURFACE P LOSSES, AND CONTRIBUTE TO THE SUSTAINABILITY OF U.S. AGRICULTURE WHILE MAXIMIZING WATER QUALITY BENEFITS.