MAINTAINING OR INCREASING AGRICULTURAL SOIL ORGANIC CARBON (SOC) IS KEY FOR BOTH FOOD SECURITY AND CLIMATE CHANGE MITIGATION. REGENERATIVE AGRICULTURAL PRACTICES, WHICH ARE DESIGNED TO INCREASE SOC, FACE A BARRIER TO ADOPTION BECAUSE THE MAGNITUDE OF SOC GAIN IS HIGHLY VARIABLE ACROSS SOILS. THE MAJORITY OF SOC IN AGRICULTURAL SOILS IS COMPRISED OF MINERAL-ASSOCIATED ORGANIC CARBON (MAOC), A SLOW-TURNOVER CARBON POOL THAT IS A PROMISING TARGET FOR CLIMATE CHANGE MITIGATION. LEADING HYPOTHESES ABOUT CONTROLS ON MAOC FORMATION CENTER ON SOIL MICROBIAL ECOPHYSIOLOGY, SOIL MINERALOGY, LEGACY MANAGEMENT-INDUCED MAOC STOCKS, AND PH. THIS PROJECT SEEKS TO TEST AND INTEGRATE THESE HYPOTHESES.THIS PROJECT WILL LEVERAGE SOILS FROM LONG-TERM AGRICULTURAL RESEARCH SITES TO CAPTURE NATURAL VARIABILITY IN MINERALOGY, MICROBIAL ECOPHYSIOLOGY, AND PH ACROSS A SOIL WEATHERING GRADIENT; DIFFERENT CROPPING REGIMES WITHIN SITES WILL CAPTURE CONTRASTING MANAGEMENT-INDUCED MAOC STOCKS. USING SOIL MINERALOGICAL AND MICROBIAL CHARACTERIZATIONS, STABLE ISOTOPE TRACING, AND COMPUTER MODELLING, THIS PROJECT WILL 1) CHARACTERIZE TOTAL MAOC AND ITS RESPONSE TO SOIL REGENERATIVE PRACTICES; 2) DETERMINE THE PREDICTIVE STRENGTH OF SOIL MINERALOGY, MICROBIAL ECOPHYSIOLOGY, AND PH IN CONTROLLING THE FORMATION OF NEW MAOC FROM LABILE PLANT ROOT INPUTS, A PRIMARY SOURCE FOR MAOC; AND 3) ASSESS THE ABILITY FOR INCORPORATING SOIL MINERALOGY AND MICROBIAL ECOPHYSIOLOGY INTO A NEW GENERATION SOC MODEL TO IMPROVE PREDICTIONS OF TOTAL AND MANAGEMENT-INDUCED INCREASES IN MAOC. BY DESCRIBING CONTROLS ON AND POTENTIAL FOR THE FORMATION OF MAOC IN AGRICULTURAL SOILS, THIS PROJECT WILL ALLOW FOR BETTER SPATIAL TARGETING OF RESOURCES FOR REGENERATIVE PRACTICES AND FOR IMPROVED FORECASTING OF ENSUING SOC RESPONSES.