**AWARDS ISSUED PRIOR TO JANUARY 20, 2025, WERE FUNDED UNDER PREVIOUS ADMINISTRATIONS AND MAY NOT REFLECT THE PRIORITIES AND POLICIES OF THE CURRENT ADMINISTRATION.** HEALTHY SOILS ARE THE FOUNDATION OF RESILIENT, PRODUCTIVE, SUSTAINABLE AGROECOSYSTEMS BECAUSE THEY PERFORM ESSENTIAL FUNCTIONS SUCH AS NUTRIENT CYCLING, CARBON STORAGE, WATER RETENTION, AND CATION EXCHANGE. THIS IS A BROADLY ACCEPTED CONCEPT, BUT WHEN IT COMES TO DEFINING AND QUANTIFYING SOIL HEALTH, FUNDAMENTAL QUESTIONS REMAIN UNANSWERED. FOR EXAMPLE, WHAT ARE THE BEST INDICATORS OF SOIL FUNCTIONING THAT WE CAN USE TO QUANTIFY SOIL HEALTH AND PREDICT AGRONOMIC SUSTAINABILITY, PRODUCTIVITY, AND RESILIENCE? THIS QUESTION IS ESPECIALLY RELEVANT FOR SOIL ORGANIC MATTER, WHICH IS ONE OF THE MOST COMMONLY MEASURED SOIL HEALTH PROPERTIES BUT DOES NOT CONSISTENTLY CORRELATE WITH AGRONOMIC PERFORMANCE. SOLVING THIS DILEMMA REQUIRES THE DEVELOPMENT OF QUANTITATIVE SOIL HEALTH INDICES FOR SOIL ORGANIC MATTER THAT ARE MECHANISTICALLY LINKED TO SOIL FUNCTIONING AND THEREFORE TO AGRONOMIC OUTCOMES SUCH AS INCREASED YIELD, YIELD STABILITY, AND REDUCED INPUTS. TOTAL SOIL ORGANIC MATTER IS USED ACROSS VIRTUALLY ALL SOIL HEALTH STUDIES AND COMMON SOIL HEALTH TEST PROTOCOLS BECAUSE IT IS WIDELY ACCEPTED THAT IT UNDERLIES MULTIPLE SOIL FUNCTIONS, INCLUDING WATER PURIFICATION, NUTRIENT CYCLING, AND HABITAT PROVISION FOR SOIL ORGANISMS. YET, SOIL ORGANIC MATTER IS NOT CONSISTENTLY RELATED TO AGRONOMIC PERFORMANCE, AND THE MECHANISMS BEHIND THIS PARADOX REMAIN UNEXPLORED. WE PROPOSE TO RESOLVE THIS PROBLEM BY SEPARATING SOIL ORGANIC MATTER INTO TWO FUNCTIONAL POOLS, PARTICULATE (POM) AND MINERAL-ASSOCIATED ORGANIC MATTER (MAOM), AND EXPLORING THEIR USE AS NEW SOIL HEALTH INDICATORS. OUR GOALS ARE TO ADVANCE UNDERSTANDING OF THE ROLES OF POM AND MAOM IN SOIL FUNCTIONING AND AGRONOMIC PERFORMANCE AND FACILITATE THEIR WIDESPREAD USE AND MEASUREMENT. OUR OBJECTIVES AND RELATED ACTIVITIES ARE: 1) COMPARE EFFECTS OF POM AND MAOM ON SOIL FUNCTIONING AND PLANT PERFORMANCE THROUGH A CONTROLLED GREENHOUSE STUDY; 2) EVALUATE POM AND MAOM AS NEW SOIL HEALTH INDICATORS USING OVER 300 SOIL SAMPLES AND RELATED DATA FROM A VARIETY OF AGROECOSYSTEMS UNDER VARIED MANAGEMENT; AND 3) DETERMINE BEST PROTOCOLS FOR POM AND MAOM QUANTIFICATION THROUGH RIGOROUS METHODS TESTING. FURTHER, OUR ACTIVITIES WILL ALLOW US TO QUANTITATIVELY ASSESS SOIL ORGANIC MATTER REGENERATION AND SOIL CARBON SEQUESTRATION POTENTIAL ACROSS US AGRICULTURAL SOILS IN RESPONSE TO COMMON MANAGEMENT PRACTICES. THE PROPOSED WORK WILL ENHANCE UNDERSTANDING OF BIOGEOCHEMICAL PROCESSES INVOLVED IN SOIL HEALTH AND DEVELOP SOIL HEALTH INDICATORS TO ENHANCE MEASUREMENT AND MANAGEMENT OF SOIL ORGANIC MATTER POOLS TO IMPROVE SOIL HEALTH AND AGRICULTURAL SUSTAINABILITY. LINKING THE NEW, EMERGING UNDERSTANDING OF MEASURABLE, FUNCTIONAL SOIL ORGANIC MATTER POOLS TO INDICATORS AND DRIVERS OF SOIL HEALTH WILL ALLOW FOR INCREASED ADOPTION AND EFFICACY OF AGRICULTURAL PRACTICES THAT INCREASE SOIL ORGANIC MATTER STOCKS, WHICH CAN ULTIMATELY INCREASE THE PERFORMANCE AND RESILIENCE OF US CROPPING SYSTEMS.