COVER CROPS, OR NON-HARVESTED CROPS, ARE ESSENTIAL COMPONENTS OF ORGANIC CROP ROTATIONS. ORGANIC FARMERS PLANT COVER CROPS IN THE LEGUME FAMILY TO SUPPLY NITROGEN TO FIELDS, AND ARE INCREASINGLY EXPERIMENTING WITH COVER CROP MIXTURES TO PROVIDE MULTIPLE ECOSYSTEM SERVICES AT ONCE. KEY SERVICES OF INTEREST TO FARMERS INCLUDE RETAINING SOIL NITROGEN AND PHOSPHORUS, BUILDING SOIL ORGANIC MATTER, AND CONTROLLING WEEDS. THERE IS A CRITICAL NEED TO DETERMINE HOW THE DIVERSITY OF PLANT TRAITS IN MULTI-SPECIES COVER CROP MIXTURES, AND RESULTING ECOSYSTEM SERVICES, VARY ACROSS ENVIRONMENTAL GRADIENTS. OUR MULTI-INSTITUTION RESEARCH AND EXTENSION PROJECT WILL USE NOVEL APPROACHES, INCLUDING A PARTICIPATORY EXPERIMENT ON 15 WORKING FARMS, TO ADDRESS SEVERAL KNOWLEDGE GAPS FOR OPTIMAL MIXTURE PERFORMANCE. FIRST, WE WILL DETERMINE MIXTURE PERFORMANCE ALONG A SOIL HEALTH GRADIENT RESULTING FROM DIFFERENCES IN FARM MANAGEMENT HISTORY AND SOIL TYPE. SECOND, WE WILL IDENTIFY RELATIONSHIPS BETWEEN PLANT FUNCTIONAL TRAIT DIVERSITY IN COVER CROP MIXTURES AND ECOSYSTEM SERVICES. THIRD, WE WILL QUANTIFY LEGUME NITROGEN FIXATION, PHOSPHORUS CYCLING, ROOT BIOMASS, AND WEED SUPPRESSION ON FARMS TO SUPPORT THE SUCCESS OF DIVERSIFIED, ORGANIC CROPPING SYSTEMS. FINALLY, WE WILL GENERATE PRACTICAL MANAGEMENT RECOMMENDATIONS FOR ORGANIC AND TRANSITIONING FARMERS, INCLUDING AN ECONOMIC ASSESSMENT OF MIXTURES, WHICH WILL SUPPORT BROADER IMPLEMENTATION OF COVER CROP MIXTURES IN MICHIGAN AND BEYOND. KNOWLEDGE OF COVER CROP MIXTURES THAT IMPROVE ECOLOGICAL NUTRIENT MANAGEMENT ON FARMS COULD BE EXTENDED TO ADDRESS BROADER CONSERVATION GOALS FOR WATER QUALITY. RESULTS WILL ALSO INFORM IMPROVEMENTS TO AN ONLINE COVER CROP DECISION TOOL, AND WILL BE SHARED WIDELY THROUGH OUTREACH ACTIVITIES INCLUDING EXTENSION BULLETINS, PRESENTATIONS AT FARMER MEETINGS, FIELD DAYS, WORKSHOPS, AND ENGAGEMENT WITH POLICY COMMUNITIES.