LOSS OF SOIL BIODIVERSITY, DEPLETION OF SOIL ORGANIC MATTER (SOM) AND POLLUTION OF GROUNDWATER BY NITRATE LEACHING ARE SOME OF THE MANY WIDESPREAD CONSEQUENCES OF INTENSIVE, HIGHLY-SIMPLIFIED AGRICULTURAL SYSTEMS, WHICH UNDERMINE THE NATURAL RESOURCE BASE ON WHICH AGRICULTURE DEPENDS AND THREATEN THE HEALTH OF RURAL COMMUNITIES ACROSS THE UNITED STATES. RESTORATION OF SOIL HEALTH, AN INTEGRATIVE CONCEPT DESCRIBING THE DYNAMIC PROPERTIES OF SOIL,ESPECIALLY SOIL MICROBES AND SOIL ORGANIC MATTER,THAT UNDERPIN KEY SOIL FUNCTIONS IS INCREASINGLY RECOGNIZED AS A CRUCIAL STEP TOWARD CREATING MORE SUSTAINABLE AGROECOSYSTEMS BY ENHANCING SOIL-BASED ECOSYSTEM SERVICES. BIOLOGICALLY DIVERSIFIED FARMING SYSTEMS USE MANAGEMENT PRACTICES AT MULTIPLE TEMPORAL AND SPATIAL SCALES THAT PROMOTE BENEFICIAL ORGANISMS IN THE FARM AND THE SURROUNDING LANDSCAPE, THEREBY SUPPLYING CRITICAL ECOSYSTEM SERVICES THAT CAN RESULT IN PRODUCTION IMPROVEMENTS WITH FEWER INPUTS.YET KNOWLEDGE OF HOW SUCHPRACTICES (FOR INSTANCE, COVER CROPS, ORGANIC MATTER AMENDMENTS, AND CROP ROTATION) AFFECT SOIL MICROBES AND SOM AND THE ECOSYSTEM SERVICES THEY TOGETHER UNDERPIN REMAINS LIMITEDON WORKING FARMS, ESPECIALLY IN HIGH-INTENSITY VEGETABLE SYSTEMS. FURTHER,SUCH TECHNIQUES ARE OFTEN NOT ADOPTED BY FARMERS BECAUSE OF MULTIPLE, REINFORCING MARKET, KNOWLEDGE, AGRONOMIC, ENVIRONMENTAL, AND POLICY BARRIERS.IN THIS PROJECT, WE WILLASSESS HOW DIVERSIFIED FARMING SYSTEMS AFFECT SOIL HEALTH AND SOIL-BASED ECOSYSTEM SERVICES, AND THE KEY BARRIERS, MOTIVATIONS, AND CONDITIONS FOR ADVANCING BENEFICIAL SOIL HEALTH OUTCOMES IN AN INTENSIVE AGRICULTURAL LANDSCAPE, USING A SET OF LETTUCE FARMS IN CALIFORNIA'S CENTRAL COAST REGION AS OUR RESEARCH SITE.THE CENTRAL COAST, ALSO KNOWN AS AMERICA'S SALAD BOWL, EXHIBITS STRONG TRADEOFFS BETWEEN AGRICULTURAL PRODUCTION AND ENVIRONMENTAL OUTCOMES (E.G. HIGH VALUE CROPS BUT SEVERELY IMPAIRED WATER QUALITY), AS WELL AS FACTORS LIKE HIGH LAND VALUES AND FOOD SAFETY CONCERNSTHAT COULD MAKE USING SOIL HEALTH BUILDING PRACTICES MORE CHALLENGING COMPARED TO OTHER REGIONS.WE WILL DETERMINEHOW GOVERNMENT POLICIES (INCLUDING REGULATIONS AND INCENTIVES) AND SUPPLY CHAIN REQUIREMENTS INFLUENCE FARMERS' DECISIONS TO ADOPT OR NOT TO ADOPT DIVERSIFIED FARMING PRACTICES USING SEMI-STRUCTURED INTERVIEWS WITH UP TO 30 FARMERS AND OTHER AGRICULTURAL PROFESSIONALS, AS WELL AS A QUANTITATIVE SOCIO-ECONOMIC SURVEY. BASED ON THESE INTERVIEWS, WE WILL THEN IDENTIFY A GRADIENT OF DIVERSIFICATION PRACTICES ACROSSTHE SAME SET OF FARMS, FROM HIGHLY SPECIALIZED FARMS USING FEW OR NONE OF THESE PRACTICES TO HIGHLY-DIVERSIFIED FARMS USING SEVERAL. ALONG THIS GRADIENTWE WILL MEASURE SOIL MICROBIAL COMMUNITY COMPOSITION AND DIVERSITYANDINDICATORS OF KEY SOIL-BASED ECOSYSTEM SERVICES, INCLUDING POTENTIAL FOR SOIL CARBON SEQUESTRATION, NITROGEN RETENTION, WATER CONSERVATION, AS WELL AS LETTUCE YIELDS. TO FACILITATE KNOWLEDGE EXCHANGE AMONG FARMERS, WE WILL HOST TWO ON-FARMFIELD DAYS AND FACILITATE FARMER-TO-FARMER KNOWLEDGE EXCHANGE ALONG WITH DISCUSSION OF QUANTITATIVE RESULTS ON ECOLOGICAL OUTCOMES AND ECONOMIC TRADEOFFS AND BENEFITS OF DIVERSIFICATION PRACTICES IN THE CENTRAL COAST REGION. THROUGH THIS RESEARCH, WE ANTICIPATEDOCUMENTING THE EXTENT TO WHICH ON-FARM INNOVATIONS LEAD TO BENEFICIAL SOIL HEALTH OUTCOMES ANDINCREASE THE ADOPTION OF SOIL HEALTH PRACTICES THROUGH DESIGN OF BETTER POLICY INCENTIVES (BASED IN PART ON THIS SCIENTIFIC DATA) AND INCREASING FARMERS' AWARENESS OF BOTH OPPORTUNITIES AND CHALLENGES.