**AWARDS ISSUED PRIOR TO JANUARY 20, 2025, WERE FUNDED UNDER PREVIOUS ADMINISTRATIONS AND MAY NOT REFLECT THE PRIORITIES AND POLICIES OF THE CURRENT ADMINISTRATION.** THE WORLD'S POPULATION IS EXPECTED TO INCREASE BY TWO BILLION OVER THE NEXT 30 YEARS, AND ASIT GROWSSO TOO WILL OUR FOOD REQUIREMENTS.IN ORDER TO MEETPRESENT AND FUTURE FOOD DEMANDS, FARMERS IN THE USA AND AROUND THE WORLD WILL BE CHALLENGED TO PRODUCE MORE FOOD ON THE SAME AMOUNT OF LAND, WITH THE SAME, OR IN SOME CASES LESS RESOURCES, WHILE MITIGATING HARM TO THE ENVIRONMENT. TO MAXIMIZE YIELD, FARMERS OFTEN SUPPLEMENT SYNTHETIC NITROGEN (N) TO THEIR CROPS VIA INORGANIC N-FERTILIZERS, WHICH MAKES UP A SIGNIFICANT PORTION OF THEIR OPERATING COSTS. THE FORM OF NITROGEN FOUND IN N-FERTILIZERS IS HIGHLY MOBILE IN SOIL AND A LARGE PORTION OF THE APPLIED NITROGEN NEVER REACHES ITS INTENDED CROP TARGETS. IN FACT, AGRICULTURE IS RESPONSIBLE FOR ELEVATED LOADS OF NITROGEN IN OUR SURFACE AND GROUNDWATER, CAUSING A SPECTRUM OF PROBLEMS, INCLUDING LOW OXYGEN WATER, OR DEAD ZONES, WHICH POSE SERIOUS THREATS TO HUMAN HEALTH AND TO THE ENVIRONMENT. AS IT STANDS, WE CANNOT ELIMINATE THE USE OF N-FERTILIZERS, BUT WE CAN OPTIMIZE THEIR USE. TO MEET LOCAL AND GLOBAL FOOD CHALLENGES, THE EFFICIENCY BY WHICH WE USE N-FERTILIZERS MUST IMPROVE. ONE SOLUTION IS TO MAXIMIZE NITROGEN USE EFFICIENCY (NUE) - THE AMOUNT OF NITROGEN FOUND IN FOOD VERSUS THE AMOUNT OF NITROGEN APPLIED.INTERESTINGLY, SOYBEAN PLANTS, WHICH ACCOUNT FOR ROUGHLY A THIRD OF ALL US CROPLAND, CAN ACQUIRE MOST OF THEIR NITROGEN REQUIREMENTS WITH THE HELP OF SOIL BACTERIA, KNOWN AS RHIZOBIA. WHEN SOYBEANS AND MOST OTHER LEGUMES (I.E., PEAS, LENTILS, AND CLOVER) FIND THEMSELVES IN N-DEFICIENT SOILS, THEY STRIKE UP A CHEMICAL CONVERSATION WITH RHIZOBIA, INITIATING THE GROWTH OF DOZENS OF ENTIRELY NEW ROOT ORGANS, CALLED NODULES. WITHIN THESE NODULES, THOUSANDS OF RHIZOBIA CONVERT EXISTING NITROGEN GAS (~80% OF OUR ATMOSPHERE IS NITROGEN GAS) INTO A FORM OF NITROGEN THAT PLANTS CAN USE. THIS PROCESS IS CALLED SYMBIOTIC NITROGEN FIXATION (SNF). ALTERNATIVELY, HIGH LEVELS OF SOIL NITROGEN FROM FERTILIZERS TERMINATE SNFIN A PROCESS CALLED NITROGEN-INDUCED NODULE SENESCENCE (NIS), WHICH IS THE FOCUS OF MY RESEARCH. I WANT TO BETTER UNDERSTAND HOW EXCESS NITROGEN FROM SYNTHETIC INORGANIC N-FERTILIZERS ENDS OR INHIBITS THE BENEFICIAL RELATIONSHIP BETWEEN SOYBEANS AND RHIZOBIA. I WANT TO KNOW HOW MUCH APPLIED NITROGEN IS REQUIRED FOR NIS, AND WHICH SOYBEAN GENES ARE RESPONSIBLE FOR RESPONDING TO EXCESS NITROGEN AND TERMINATING SNF. I ALSO WANT TO INVESTIGATE WHETHER DIFFERENT SOYBEAN VARIETIES HAVE A HIGHER THRESHOLD OR TOLERANCE TO THE PRESENCE OF EXCESS NITROGEN, ALLOWING SNF TO PERSIST WITH HIGHER SOIL NITROGEN LEVELS, WHILE SUSTAINING CURRENT YIELDS.SNF IS AVAILABLE TO SOYBEAN FARMERS AT LITTLE TO NO COST AND IT IS ADVANTAGEOUS TO LEVERAGE MAXIMUM SNF COMBINED WITH MINIMAL APPLIED NITROGEN. THE VARIETY-SPECIFIC DATA OBTAINED WILL ENABLE FARMERS SEEKING HIGH YIELDS, GREATER THAN 60 BUSHELS/ACRE (ONE BUSHEL OF SOYBEAN IS 60 POUNDS), TO MORE PRECISELY DETERMINE THE AMOUNT AND TIME OF N-FERTILIZER APPLICATION, HELPING TO MAXIMIZE THEIR YIELD WITHOUT TERMINATING SNF. THE POTENTIAL IMPACT OF THIS RESEARCH WILL RESULT IN IMPROVED SOYBEAN N-MANAGEMENT PRACTICES AND INCREASE SOYBEAN'S NUE BY PROVIDING NEW NUE BREEDING MARKERS.TO OPTIMIZE SOYBEAN NUE AND N-MANAGEMENT PRACTICES, I WILL USE CUTTING-EDGE IMAGING (USING X-RAY COMPUTED TOMOGRAPHY SYSTEM (XRT) COUPLED WITH MACHINE LEARNING ALGORITHMS), COMBINED WITH INNOVATIVE TRANSCRIPTOMIC APPROACHES (HIGH RESOLUTION, NEAR SINGLE-CELL RNA SEQUENCING, KNOWN AS SPATIAL TRANSCRIPTOMICS). TRANSCRIPTOMICS TELLS US WHICH GENES ARE ON OR OFF AT A SPECIFIC TIME, AND AT WHAT LEVELS THEY ARE EXPRESSED. SPATIAL TRANSCRIPTOMICS TELLS US NOT ONLY WHICH GENES AND THEIR EXPRESSION LEVELS, BUT ALSO INCORPORATES IMAGING TECHNOLOGY TO OBSERVE WHERE THEY ARE BEING EXPRESSED AT NEAR SINGLE-CELL RESOLUTION. XRT WILL ALLOW ME TO VISUALIZE SOYBEAN ROOTS AND THEIR NODULES DIRECTLY IN THE SOIL, WITHOUT DISTURBING THEM, DURING DIFFERENT NITROGEN TREATMENTS. USING THE ABOVE TECHNOLOGIES, I WILL EVALUATE SEVERAL VARIABLES KNOWN TO INFLUENCE NIS INCLUDING NITROGEN CONCENTRATION, TIME OF APPLICATION, AND PERCENTAGE OF ROOTS SENSING APPLIED NITROGEN, IN FIVE ELITE SOYBEAN VARIETIES, AS WELL AS THREE ACCESSIONS OF AN UNDOMESTICATED WILD-TYPE RELATIVE OF SOYBEAN. STUDIES LIKE THIS, WILL NOT ONLY PROVIDE DATA THAT IS DIRECTLY APPLICABLE TO OPTIMIZE FARMING N-MANAGEMENT PRACTICES, SAVING FARMERS MONEY AND DECREASING THE PRESENCE OF LOST NITROGEN TO OUR WATERWAYS, IT WILL ALSO HIGHLIGHT NEW RESEARCH TECHNOLOGIES, ARMING RESEARCHERS WITH MORE TOOLS TO ADVANCE AGRICULTURAL RESEARCH AND SUSTAINABLE FARMING IN THE 21ST CENTURY.