** AWARDS ISSUED PRIOR TO JANUARY 20, 2025, WERE FUNDED UNDER PREVIOUS ADMINISTRATIONS AND MAY NOT REFLECT THE PRIORITIES AND POLICIES OF THE CURRENT ADMINISTRATION.** CALIFORNIA'S AGRICULTURAL COMMUNITIES FACE THE DUAL CHALLENGES OF INCREASINGLY VARIABLE AND LIMITED IRRIGATION WATER SUPPLIES, ALONGSIDE PERSISTENT GROUNDWATER QUALITY DEGRADATION FROM NITRATE LEACHING THAT HAS IMPERILED DRINKING WATER FOR NEARLY ONE MILLION RESIDENTS OF RURAL COMMUNITIES IN THE STATE. THESE CHALLENGES COME TOGETHER MOST ACUTELY IN CALIFORNIA'S CENTRAL COAST REGION, THE SALAD BOWL OF THE U.S., WHERE INTENSIVE, HIGH-VALUE VEGETABLE AND BERRY PRODUCTION DOMINATES. THE ECOSYSTEM SERVICES PROVIDED BY ADDING WINTER COVER CROPS TO THESE ANNUAL CROPPING SYSTEMS ARE CONSIDERED ESSENTIAL TO IMPROVING GROUNDWATER QUALITY, BUT PERCEPTIONS AMONG FARMERS AND POLICYMAKERS THAT COVER CROPS CONSUME TOO MUCH WATER MAKE A FORMIDABLE BARRIER TO ADOPTION IN THIS MEDITERRANEAN CLIMATE. HERE, WE PROPOSE TO ADDRESS THE QUESTION OF HOW FARMERS IN MEDITERRANEAN, SEMI-ARID CLIMATIC REGIONS CAN IMPLEMENT COVER CROPPING IN A WATER SCARCE ENVIRONMENT WHILE MEETING WATER QUALITY REGULATORY GOALS. THROUGH BOTH CONTROLLED TRIALS AND ON-FARM, PARTICIPATORY RESEARCH, WE AIM TO DETERMINE HOW DIFFERENT COVER CROP MANAGEMENT PRACTICES AFFECT THE BALANCE BETWEEN WATER REGULATION AND PROVISIONING AND WATER QUALITY PROTECTION, AS WELL AS THE SUPPLY OF NITROGEN (N) FOR CASH CROPS. WE WILL FORM A COMMUNITY OF PRACTICE, INCLUDING FARMERS, TECHNICAL ASSISTANT PROVIDERS, RESEARCHERS, AND COMMUNITIES LACKING ACCESS TO CLEAN DRINKING WATER TO TEST THESE QUESTIONS AND FACILITATE CO-LEARNING THAT IS EMBEDDED IN THE RESEARCH PROCESS.