** AWARDS ISSUED PRIOR TO JANUARY 20, 2025, WERE FUNDED UNDER PREVIOUS ADMINISTRATIONS AND MAY NOT REFLECT THE PRIORITIES AND POLICIES OF THE CURRENT ADMINISTRATION.** BIOLOGICAL NITROGEN FIXATION IN ROOT NODULES OF SOYBEAN HELPS REDUCE THE NEED FOR EXPENSIVE, ENERGY-INTENSIVE, AND ENVIRONMENTALLY DAMAGING SYNTHETIC NITROGEN FERTILIZERS. NODULE NITROGEN SUPPLY PEAKS DURING EARLY REPRODUCTIVE STAGES (R1-R3) AND DECLINES THEREAFTER, WHEREAS GRAIN NITROGEN DEMAND INCREASES IN THE LATER REPRODUCTIVE STAGES (R5-R7). THEREFORE, HIGH-YIELDING SOYBEAN VARIETIES TAKE UP NITROGEN FROM THE SOIL, DEPLETING SOIL NITROGEN RESERVES THAT WOULD OTHERWISE BE AVAILABLE FOR THE FUTURE CROPS NECESSITATING RESEARCH TO INCREASE NODULE NITROGEN SUPPLY IN LATER REPRODUCTIVE STAGES. WE HYPOTHESIZE THAT SOYBEAN GENOTYPES WITH A HIGHER NUMBER OF NODULES WITH DELAYED MATURATION CAN CONTINUE TO FIX NITROGEN AT THESE REPRODUCTIVE STAGES AND HELP MEET NITROGEN NEEDS IN A SUSTAINABLE MANNER. PRIOR RESULTS AND PRELIMINARY DATA FROM THE PD'S LABORATORY AS WELL AS THOSE FROM OTHER RESEARCH SUGGEST THAT ALTERING THE BALANCE BETWEEN TWO PLANT HORMONES AUXIN AND CYTOKININ CAN LEAD TO HIGHER NODULE NUMBERS WITH DELAYED MATURITY. THIS RESEARCH PROJECT WILL (1) EVALUATE GENOME SEQUENCES OF 1,110 ACCESSIONS FROM THE USDA SOYBEAN GERMPLASM COLLECTION TO IDENTIFY NATURAL GENETIC VARIANTS IN GENES ASSOCIATED WITH AUXIN AND CYTOKININ BIOSYNTHESIS, (2) VALIDATE THEIR ROLES THOROUGH GENOME EDITING AND LABORATORY ANALYSIS, AND (3) CHARACTERIZE SOYBEAN GERMPLASM WITH SPECIFIC GENETIC MODIFICATION FOR OPTIMAL NITROGEN FIXATION. THE ACCESSIONS OR DERIVATIVES INCLUDING KNOWLEDGE WOULD HELP DEVELOP SOYBEAN VARIETIES WITH OPTIMAL NITROGEN FIXATION THAT DO NOT DEPLETE SOIL NITROGEN OR REQUIRED ADDITIONAL NITROGEN FERTILIZER APPLICATION.