** AWARDS ISSUED PRIOR TO JANUARY 20, 2025, WERE FUNDED UNDER PREVIOUS ADMINISTRATIONS AND MAY NOT REFLECT THE PRIORITIES AND POLICIES OF THE CURRENT ADMINISTRATION.** SOILS ARE THE LARGEST TERRESTRIAL SINK OF CARBON, AND RESPIRATION BY ROOTS AND HETEROTROPHIC MICROORGANISMS IS THE LARGEST FLUX OF C FROM SOILS. FOR THIS REASON, SOIL RESPIRATION IS A KEY COMPONENT OF THE GLOBAL CARBON (C) CYCLE AND REPRESENTS SOIL'S ECOSYSTEM SERVICES RELATED TO REGULATION OF THE GLOBAL CLIMATE. INDEED, SOIL RESPIRATION IS AN ACCEPTED AND COMMONLY-USED INDICATOR OF BIOLOGICAL SOIL HEALTH. HOWEVER, LAND USE AND CLIMATE CHANGE CAN SHIFT SOIL RESPIRATION RATES SUCH THAT THEY OUTPACE THE RATE OF C INPUTS, DEPLETING SOIL C STOCKS. FURTHER, REACTIONS WITHIN THE SOIL SYSTEM INVOLVING INORGANIC CARBON IN THE SOLID AND AQUEOUS PHASES CAN MODULATE GASEOUS SOIL CO2 EFFLUX, OBSCURING ECOSYSTEM RESPONSE TO GLOBAL CHANGE AND CONFOUNDING EFFORTS TO CHARACTERIZE SOIL HEALTH. THEREFORE, WITH THIS WORK WE WILL UNRAVEL THE ROLES OF CLIMATE AND LAND-MANAGEMENT IN CONTROLLING THE DEVIATION OF SOIL CO2 EFFLUX FROM SOIL RESPIRATION RATES BY TRACKING BOTH ORGANIC AND INORGANIC C IN SOLID, GASEOUS, AND AQUEOUS PHASES IN A GRASSLAND AGROECOSYSTEM OF THE SOUTHERN GREAT PLAINS, UNITED STATES.WE WILL USE BOTH FIELD EXPERIMENTS AND LABORATORY INCUBATIONS TO INVESTIGATE THE ROLES OF DROUGHT, NITROGEN FERTILIZATION, AND HAY HARVEST IN CONTROLLING ORGANIC AND INORGANIC C CYCLING IN SOILS, AND THEREFORE THE DEVIATION OF CO2 EFFLUX FROM SOIL RESPIRATION RATES. TO EXPAND KNOWLEDGE OF KEY CONCEPTS SURROUNDING SOIL HELALTH AND SOIL RESPIRATION, WE WILL ADDITIONALLY DEVELOP LABORATORY ACTIVITIES AND COURSEWORK ABOUT SOIL BIOGEOCHEMISTRY AND SOIL HEALTH DIRECTED TOWARDS INTRODUCTORY LEVEL UNDERGRADUATE COURSES IN THE ENVIRONMENTAL SCIENCES. BECAUSE C FLUX PARTITIONING IS DIRECTLY RELATED TO OUR UNDERSTANDING OF INDICATORS OF SOIL HEALTH, AND SOIL'S ROLE IN REGULATING THE GLOBAL C CYCLE, THIS WORK DIRECTLY ALIGNS WITH THE LISTED PRIORITIES OF SOIL HEALTH AND WILL REPRESENT A SIGNIFICANT ADVANCE IN OUR UNDERSTANDING OF PASTURE AND RANGELAND RESPONSE TO CLIMATE AND LAND USE CHANGES.