WEED MANAGEMENT IS ONE OF, IF NOT THE, GREATEST CHALLENGE FOR ORGANIC CROP PRODUCTION. ORGANIC FARMERS RELY ON TILLAGE FOR WEED CONTROL; HOWEVER, TILLAGE IS OFTEN LESS EFFECTIVE THAN CONVENTIONAL FORMS OF WEED MANAGEMENT (E.G. HERBICIDES) AND THEREFORE WEEDS CAN REDUCE YIELDS IN ORGANIC SYSTEMS. ADDITIONALLY, INTEREST IN ECOLOGICALLY PRODUCED FOOD IS INCREASING AMONG THE PUBLIC. SOIL MICROBES CAN INFECT AND KILL WEED SEEDS, THEREBY REDUCING POPULATIONS OF PROBLEMATIC WEED SPECIES. DETERMINING WHAT CROP MANAGEMENT APPROACHES CAN INCREASE MICROBIALLY-MEDIATED MORTALITY OF WEED SEEDS IN THE SOIL COULD GREATLY IMPROVE THE ABILITY OR ORGANIC FARMERS TO CONTROL WEEDS. HOWEVER, RESEARCH HAS BEEN LIMITED ON WHICH MICROBIAL TAXA CAN INCREASE WEED SEED MORTALITY, AND WHAT MANAGEMENT FACTORS PROMOTE THOSE MICROBIAL POPULATIONS.TO ADDRESS THIS KNOWLEDGE GAP, WE WILL CONDUCT COMPLEMENTARY FIELD EXPERIMENTS. FIRST (OBJ. 1), WE WILL CONDUCT TWO COMPLEMENTARY EXPERIMENTS (ONE IN FIELD CROPS AND ONE IN VEGETABLES) EXAMINING HOW ORGANIC SOIL AMENDMENTS INFLUENCE BOTH WEED SEED MORTALITY AND MICROBIOME, AS WELL AS THE SOIL MICROBIOME. TO DO THIS, WE WILL COMPARE ORGANIC SOIL FERTILITY AMENDMENTS THAT VARY IN CHEMICAL AND NUTRIENT QUANTITIES. SECOND (OBJ. 2), WE WILL LEVERAGE A LONG-TERM ORGANIC EXPERIMENT AT PSU TO EVALUATE HOW DISTINCT PERENNIAL FORAGE CROPS (COMPARED TO A STANDARD ORGANIC ANNUAL CROP ROTATION) INFLUENCE WEED SEED MORTALITY AND MICROBIOMES, AS WELL AS THE SOIL MICROBIOME. FOR BOTH EXPERIMENTS, WE WILL USE AMPLICON SEQUENCING TO CHARACTERIZE THE BACTERIAL AND FUNAL COMMUNITIES WITHIN WEED SEEDS, AND TETRAZOLIUM TESTS TO ASSESS SEED VIABILITY. ADDITIONALLY (ONJ. 3), USING A SERIES OF ON-FARM TRIALS AS WELL AS OUR ON-STATION TRIALS, WE WILL DETERMINE THE DRIVERS (E.G. SOIL ABIOTIC FACTORS AND SOIL MICROBIOME) OF WEED SEED MORTALITY AND MICROBIOMES. FINALLY IN COLLABORATION WITH ORGANIC FARMERS, (OBJ. 4) WE WILL USE OUR FARMER ADVISORY PANEL, ON-FARM TRIALS, AND OTHER EXTENSION EVENTS TO DEVELOP A MUTUAL UNDERSTANDING OF HOW SOIL FERTILITY AND CROP ROTATIONS CAN BE LEVERAGED WITHIN ORGANIC SYSTEMS TO ENHANCE WEED SEED MORTALITY IN THE SOIL SEEDBANK.WE EXPECT THE PROPOSED RESEARCH TO IDENTIFY SPECIFIC MICROBIAL TAXA THAT ARE ASSOCIATED WITH GREATER MORTALITY OF WEED SEEDS. THE INTEGRATED RESEARCH AND EXTENSION PUBLICATIONS AND EVENTS (SUCH AS FIELD DAYS AT ON-FARM SITES, STUDY CIRCLES, AND PRESENTATIONS AT GROWER MEETINGS) WILL PROVIDE VALUABLE INFORMATION TO ORGANIC FARMERS IN HOW TO MANAGE THE SOIL IN WAYS THAT PROMOTE MICROBIALLY MEDIATED WEED SEED MORTALITY. ULTIMATELY, OUR PROPOSED RESEARCH WILL RESULT IN A GREATER UNDERSTANDING OF HOW TO USE ECOLOGICAL APPROACHES TO MANAGE WEEDS IN ORGANIC SYSTEMS. THIS PROPOSED PROJECT ALIGNS WITH THE PRIORITIES IN THE ORGANIC TRANSITIONS PROGRAM BY FOCUSING ON UNDERSTANDING THE EFFECTS OF ORGANIC MANAGEMENT ON POPULATIONS OF PROBLEMATIC WEEDS.