MODERN AGRICULTURE FACES A MULTITUDE OF CHALLENGES WITH SEEMINGLY CONTRADICTORY DEMANDS FOR INCREASED CROP PRODUCTIVITY AND REDUCED ENVIRONMENTAL FOOT PRINT FOR LONG-TERM SUSTAINABILITY. NITRIFICATION IS CONSIDERED A PRIMARY CAUSE FOR LOW NITROGEN USE EFFICIENCY OF AGRICULTURAL CROPS. HOWEVER, SUBSTANTIAL NICHE SEPARATION EXISTS AMONG NITRIFIERS AND LARGE KNOWLEDGE GAPS REMAIN IN THE INTERACTIONS BETWEEN CARBON AND NITROGEN MINERALIZATION, CROP NUTRITION, NITRIFICATION, DENITRIFICATION, AND NITROGEN LEACHING IN AGRICULTURAL SYSTEMS. THIS PROJECT INVESTIGATES LINKAGES OF THESE PROCESSES IN FERTILE ORGANIC AND A HIGHLY FERTILIZED SANDY SOILS. THE SPECIFIC OBJECTIVES ARE TO 1) FUNCTIONALLY CHARACTERIZE LINKED CARBON- AND NITROGEN CYCLING ACTIVITY IN ORGANIC AND SANDY AGRICULTURAL SOILS; 2) CHARACTERIZE CARBON- AND NITROGEN CYCLING MICROBIOME FUNCTIONS IN ORGANIC AND SANDY SOILS BY METAGENOMIC AND METATRANSCRIPTOMIC ANALYSIS; AND 3) IDENTIFY EFFECTS OF NITRIFICATION INHIBITORS AND AGRICULTURAL MANAGEMENT ON CARBON- AND NITROGEN CYCLE MICROBIAL INTERACTIONS IN TARGETED MANIPULATION EXPERIMENTS. THE PROJECT ADDRESSES AFRI PROGRAM AREA PRIORITY 1402 AGRICULTURAL MICROBIOMES IN PLANT SYSTEMS AND NATURAL RESOURCES BY FUNCTIONALLY CHARACTERIZING CARBON- AND NITROGEN-CYCLING IN AGRICULTURAL MICROBIOMES AND THEIR LINKAGES TO PLANT NUTRITION, NITRIFICATION, AND NITROGEN LOSS. THE PROJECT WILL PROVIDE A COMPREHENSIVE SEASONAL CARBON- AND NITROGEN CYCLING MODEL FOR BOTH SOIL TYPES. IT WILL GENERATE SIGNIFICANT NOVEL MECHANISTIC INSIGHT INTO CARBON- AND NITROGEN CYCLING IN AGRICULTURAL SOILS WITH A POTENTIAL TO IDENTIFY IMPROVED AGRICULTURAL MANAGEMENT PRACTICES FOR INCREASED NITROGEN USE EFFICIENCY AND IMPROVED CARBON STORAGE. THE PROJECT WILL FURTHER CONTRIBUTE TO TRAINING THE NEXT GENERATION OF SOIL SCIENTISTS AT THE UNDERGRADUATE, GRADUATE, AND POSTGRADUATE LEVELS.