**AWARDS ISSUED PRIOR TO JANUARY 20, 2025, WERE FUNDED UNDER PREVIOUS ADMINISTRATIONS AND MAY NOT REFLECT THE PRIORITIES AND POLICIES OF THE CURRENT ADMINISTRATION.** NITROGEN FERTILIZATION IS OFTEN NECESSARY TO REACH THE PRODUCTIVITY POTENTIAL OF CEREAL CROPS, BUT SURPLUS N FERTILIZER CAN LEAD TO ENVIRONMENTAL HARM AND ECONOMIC LOSSES. IN CROP FIELDS THAT VARY IN TOPOGRAPHY AND SOIL TYPE, UNIFORM N FERTILIZER APPLICATIONS OFTEN RESULT IN ZONES OF N DEFICIENCY AND SURPLUS, WHICH CAN CHANGE DEPENDING ON THE WEATHER. MEETING CROP DEMANDS FOR N WHILE MINIMIZING LOSSES WITHIN HETEROGENEOUS FIELDS WILL REQUIRE IMPROVED SYNCHRONY OF N SUPPLY AND CROP DEMAND OVER SPACE AND TIME. COMPLEMENTING THE ONGOING DEVELOPMENT OF PRECISION AGRICULTURE TECHNOLOGIES, THIS PROPOSAL WILL EVALUATE A NOVEL AGROECOLOGICAL APPROACH - GRASS/LEGUME COVER CROP MIXTURES - TO ADVANCE PRECISION N MANAGEMENT BY REDUCING VARIATION IN N FERTILIZER NEEDS WHILE IMPROVING SOIL HEALTH. OUR OBJECTIVES ARE TO: 1) DETERMINE HOW N INPUTS FROM GRASS/LEGUME COVER CROP MIXTURES RESPOND TO VARIATION IN SOIL N SUPPLY, 2) DEVELOP A MIXED COVER CROP MODEL CAPABLE OF SIMULATING INTERSPECIFIC COMPETITION, AND 3) DETERMINE THE EFFECT OF GRASS/LEGUME COVER CROP MIXTURES ON SPATIAL AND TEMPORAL VARIABILITY IN N FERTILIZER NEEDS OF CORN. OUR PROJECT WILL COMBINE FIELD TRIALS WITH CROP MODEL SIMULATIONS TO INVESTIGATE HOW GRASS/LEGUME COVER CROP MIXTURES IMPACT N SUPPLY, CROP N DEMAND, N LOSSES, AND THE ECONOMIC OPTIMUM N RATE IN DIFFERENT LANDSCAPE POSITIONS AND WEATHER CONDITIONS AS COMPARED TO WINTER FALLOW AND A MONOCULTURE GRASS COVER CROP. OUR PROJECT WILL INCREASE CROPPING SYSTEM PRODUCTIVITY, PROFITABILITY, RESILIENCE, AND SOIL HEALTH, ALIGNING WITH GOALS OF THE USDA A1102 PROGRAM AREA.