ENHANCING SOIL ORGANIC MATTER (SOM) LEVEL IS ESSENTIAL TO RESTORING DEGRADED SOILS, PROMOTING HIGHER AGRONOMIC PRODUCTIVITY, AND MITIGATING CLIMATE CHANGE. RECENT CONCEPTUAL AND ANALYTICAL ADVANCEMENT INDICATE THAT THE MICROBIAL PATHWAY OF SOM FORMATION AND STABILIZATION MIGHT BE THE PRIMARY MECHANISM FOR C ACCUMULATION. HOWEVER, OUR ABILITY TO ADOPT MANAGEMENT PRACTICES TO IMPROVE SOM IS STILL HINDERED BY THE LACK OF EVIDENCE OF HOW MICROBIAL SOM DYNAMICS RESPOND TO AGRICULTURAL MANAGEMENT AT LARGE SCALE. THIS PROJECT AIMS TO ADDRESS THIS KNOWLEDGE GAP AND STUDY THE IMPACT OF CROP MANAGEMENT STRATEGIES ON THE MICROBIALLY-REGULATED SOM DYNAMICS ACROSS A RANGE OF AGROECOSYSTEMS IN THE UNITED STATES. WE HYPOTHESIZE THAT INCLUDING LEGUMES IN THE ROTATION AS CASH OR COVER CROPS WILL INCREASE THE QUALITY OF PLANT-C INPUT (LOWER C:N RATIO) THEREFORE LEAD TO GREATER MICROBIAL C USE EFFICIENCY AND GREATER MICROBIAL NECROMASS ACCUMULATION, HENCE INCREASE THE SOM CONTENT. BY EMPLOYING A COMBINATION OF LABORATORY AND FIELD-BASED ANALYSES AT THREE LONG-TERM TRIALS IN WISCONSIN, IOWA, AND PENNSYLVANIA, WE AIM TO EVALUATE HOW LONG-TERM CROP MANAGEMENT STRATEGIES INFLUENCE THE STRUCTURAL AND FUNCTIONAL POTENTIAL OF SOIL MICROBIAL COMMUNITIES, SOM QUALITY AND STABILITY, AND THE ABILITY OF SOM TO SUPPLY NUTRIENTS. IMPROVED KNOWLEDGE ON SOIL C ACCUMULATION GENERATED BY THIS RESEARCH DIRECTLY ADDRESSES THE GOAL OF INVESTIGATING THE EFFECTS OF MANAGEMENT PRACTICES ON SOIL MICROBIAL COMMUNITY'S FUNCTION AND THEIR CONTRIBUTION TO HEALTHY SOILS AND SUSTAINABLE AGROECOSYSTEMS UNDER PROGRAM AREA PRIORITY A1401-SOIL HEALTH. THE FINDINGS CAN ALSO FACILITATE THE ADOPTION OF BEST MANAGEMENT STRATEGIES TO MAXIMIZE PRODUCTIVITY AND PROFITABILITY, AND SUSTAINABILITY OF AGROECOSYSTEMS.