COMPETING HYPOTHESES THAT EMPHASIZE THE CHEMICAL RECALCITRANCE VS. MICROBIAL-MINERAL STABILIZATION OF SOIL ORGANIC MATTER (SOM) GENERATE ALTERNATIVE REPRESENTATIONS IN BIOGEOCHEMICAL MODELS. SYNTHESIS OF MULTI-SITE DATA PRESENTS OPPORTUNITIES TO EVALUATE AND REFINE THE THEORIES, ASSUMPTIONS, AND PARAMETERS ASSOCIATED WITH THESE ALTERNATIVE MODEL STRUCTURES AND, ULTIMATELY ADVANCE SOIL AND ECOSYSTEM SCIENCE. TWO RECENT SYNTHESIS ACTIVITIES PULLED TOGETHER DATA FROM DISPARATE SOURCES INTO THE INTERNATIONAL SOIL RADIOCARBON DATABASE (ISRAD) AND SOILS DATA HARMONIZATION FROM RESEARCH NETWORKS (SODAH-REN), BUT NEITHER OF THESE EFFORTS HAD ADEQUATE SUPPORT TO EXTEND THEIR FINDINGS INTO THE DEVELOPMENT AND EVALUATION OF MODELS THAT ARE INTENDED TO PROJECT SOM DYNAMICS UNDER ENVIRONMENTAL CHANGE. THUS, WE PROPOSE A TWO-SESSION SERIES OF CONFERENCES TO IMPLEMENT FINDINGS FROM ISRAD AND SODAH-REN INTO AN ENSEMBLE OF SOIL BIOGEOCHEMICAL MODELS. OUR OBJECTIVES WILL BE TO: (1) DEVELOP AND PARAMETERIZE FUNCTIONS THAT USE 'SMARTER' PROXIES FOR PHYSICOCHEMICAL STABILIZATION INTO MODELS; (2) VALIDATE STEADY-STATE SOM POOLS SIMULATED ACROSS SITES FROM MULTIPLE RESEARCH NETWORKS; AND (3) EVALUATE MODEL RESPONSES TO EXPERIMENTAL MANIPULATIONS.GIVEN THE CONTINENTAL-SCALE ECO-CLIMATOLOGICAL AND EDAPHIC GRADIENTS THESE OBSERVATIONS COVER, THE SYNTHESES ARE IS UNIQUELY SUITED TO FURTHER OUR UNDERSTANDING OF SPATIAL AND TEMPORAL VARIABILITY IN SOM AND TO INVESTIGATE DRIVERS OF SOM CHANGE. USING SYNTHESIS AND MODELING, THIS PROPOSAL AIMS TO CLOSE KNOWLEDGE GAPS THAT CURRENTLY THWART MODEL DEVELOPMENT BY INCLUDING SOM RESPONSES TO MULTIPLE EXPERIMENTAL MANIPULATIONS. THE WORKSHOPS AIM TO PROVIDE FOUNDATIONAL RESEARCH TO ADVANCE SCIENTIFIC UNDERSTANDING OF SOIL PHYSICAL AND BIOGEOCHEMICAL PROCESSES AND INTERACTIONS; AND FACILITATE THE ASSESSMENT, DEVELOPMENT AND ADOPTION OF MODELS, DECISION SUPPORT TOOLS AND NEW MANAGEMENT/CONSERVATION PRACTICES THAT WILL LEAD TO IMPROVING OR MAINTAINING SOIL HEALTH AND PRODUCTIVITY WHILE MAINTAINING OR IMPROVING ENVIRONMENTAL HEALTH AND SUSTAINABILITY OF OUR NATURAL RESOURCE BASE.