** AWARDS ISSUED PRIOR TO JANUARY 20, 2025, WERE FUNDED UNDER PREVIOUS ADMINISTRATIONS AND MAY NOT REFLECT THE PRIORITIES AND POLICIES OF THE CURRENT ADMINISTRATION.** COVER CROPS PROVIDE NUMEROUS ECOSYSTEM SERVICES; HOWEVER, THERE IS POTENTIAL FOR THEM TO REDUCE CASH CROP YIELD (I.E., 'YIELD DRAG'). REDUCED SOIL NITROGEN (N) AVAILABILITY (DUE TO MICROBIAL IMMOBILIZATION) AND/OR INCREASING SEEDLING DISEASE (BECAUSE OF INOCULUM PERPETUATION BY COVER CROP ROOTS) ARE POSTULATED REASONS FOR REDUCED CORN YIELD. OUR GOALS ARE: (1) TO IDENTIFY THE CAUSE OF 'YIELD DRAG' BY EVALUATING CEREAL RYE (CR) COVER CROP ROOT AND SHOOT BIOMASS EFFECTS ON CORN GROWTH AND DEVELOPMENT, SOIL N DYNAMICS, CORN SEEDLING DISEASE, POPULATION DYNAMICS OF PYTHIUM (THE PATHOGEN THAT CAUSES SEEDLING DISEASE), AND SOIL PHYSICAL PROPERTIES; AND (2) ESTABLISH THE FIRST AGRICULTURAL DETRITUS INPUT AND REMOVAL TREATMENTS (AG-DIRT) EXPERIMENT TO EXAMINE CORN AND CR BIOMASS CONTRIBUTION TO SOIL CARBON (C) ACCRUAL. OUR OBJECTIVES ARE: (1) ESTABLISH THE RELATIVE CONTRIBUTION OF SOIL MICROCLIMATE, N DYNAMICS, AND SEEDLING DISEASE TO CORN YIELD DRAG ASSOCIATED WITH CR ROOT AND SHOOT BIOMASS (GOAL 1); (2) CHARACTERIZE PYTHIUM POPULATION DYNAMICS DUE TO CR ROOT AND SHOOT BIOMASS (GOAL 1); (3) EVALUATE HOW CR ROOT AND SHOOT BIOMASS AFFECT CORN AGRONOMIC OPTIMUM N RATE AND YIELD (GOAL 1); AND (4) DETECT SOIL C CHANGES DUE TO THE INTERACTION BETWEEN CR ROOT AND SHOOT BIOMASS AND N FERTILIZER INPUTS (GOALS 1, 2). TO ACCOMPLISH OUR GOALS, WE WILL MANIPULATE CR ROOT AND SHOOT BIOMASS AND N FERTILIZER INPUTS IN SMALL PLOT FIELD TRIALS AT TWO LOCATIONS IN IOWA.