DROUGHTS AND HEAT WAVES HAVE ALWAYS THREATENED AGRICULTURAL PRODUCTIVITY, AND WILL DO SO EVEN MORE IN THE FUTURE AS DROUGHTS BECOME MORE FREQUENT AND SEVERE. WHILE TACTICS LIKE BREEDING DROUGHT-RESISTANT VARIETIES ARE ESSENTIAL ELEMENTS OF ADDRESSING THIS CHALLENGE, THEY WOULD BE EVEN MORE EFFECTIVE AS PART OF A STRATEGY THAT INCREASES THE RESILIENCE OF THE WHOLE AGROECOSYSTEM. BUILDING BENEFICIAL SOIL MICROBIOTA AND RESTORING SOIL HEALTH MAY FORM THE FOUNDATION OF THIS STRATEGY BY INCREASING THE SOIL-BASED REGULATING AND SUPPORTING ECOSYSTEM SERVICES THAT SUPPORT CROP PRODUCTIVITY IN STRESSFUL CONDITIONS. HERE, WE WILL DETERMINE HOW GREATER CROP ROTATIONAL DIVERSITY, I.E. THE DIVERSITY OF CROPS IN TIME, AFFECTS THE PLANT-SOIL-MICROBE INTERACTIONS THAT COULD BUILD BENEFICIAL MICROBIOTAAND SOIL HEALTH, AND IN TURN LEAD TO GREATER RESILIENCE OF CROP PRODUCTIVITY TO DROUGHTS AND HEAT WAVES. TO DO SO, WE WILL LEVERAGE DECADES OF PRIOR USDA AND UNIVERSITY INVESTMENT IN LONG-TERM EXPERIMENTS THAT COMPARE THE DIVERSITY OF CROPS IN ROTATION. SOIL WILL BE SAMPLED FROMSIMPLE (ONE CROP) AND COMPLEX CROP ROTATIONS AT FIVE LONG-TERM EXPERIMENTS THAT SPAN A GRADIENT OF MEAN ANNUAL PRECIPITATION ACROSS THE CENTRAL U.S. MICROBES IN THE SOIL AND NEAR CORN ROOTS WILL BE CHARACTERIZED USING DNA SEQUENCING TO DETERMINE HOW CROP ROTATIONAL DIVERSITY AFFECTS THE DIVERSITY AND COMMUNITY COMPOSITION OF MICROBES. SOIL FROM THESE SAME ROTATIONS WILL THEN BE USED TO INOCULATE A COMMON SOIL IN A GREENHOUSE EXPERIMENTTO DETERMINE THE EFFECT OF THE WHOLE SOIL BIOTA ON CORN PERFORMANCE UNDER WATER STRESS. WE WILL ALSO MEASURE SOIL ORGANIC MATTER AND MICROBIAL COMMUNITY CHARACTERISTICS THAT DRIVE SOIL CARBON ACCUMULATION TO EVALUATE MECHANISMS UNDERLYING OBSERVED INCREASES IN SOIL ORGANIC MATTER WITH MORE DIVERSE CROP ROTATIONS. FROM THESE FIVE LONG-TERM EXPERIMENTS PLUS AN ADDITIONAL FIVE SIMILAR LONG-TERMEXPERIMENTS, HISTORICAL CROP YIELD AND WEATHER DATA WILL BE ANALYZED TO QUANTIFY THE EXTENTTO WHICH MORE DIVERSE ROTATIONS PERFORM BETTER IN ADVERSE WEATHER CONDITIONS. VARIATION IN THIS ROTATION EFFECT ACROSS SITES WILL BE LINKED TO CHANGES IN SOIL MICROBES AND SOIL ORGANIC MATTER. TOGETHER, THESE APPROACHES WILL PROVIDEFOUNDATIONAL KNOWLEDGE OF HOW CROP ROTATION COMPLEXITY HELPS BUILD A MORE BENEFICIAL RHIZOSPHERE MICROBIOME AND ENHANCES SOIL HEALTH, ULTIMATELY CONTRIBUTING TO GREATER YIELD RESILIENCE TO DROUGHTS AND HEAT WAVES. IN TURN, THIS WILL PROVIDE A STRONG RATIONALEFOR CROPPING SYSTEM DIVERSIFICATION AS A SOUND ADAPTATION STRATEGY TO DEAL WITH INCREASING CLIMATIC VARIABILITY IN THE FUTURE. THE RESULTS WILL BE BROADLY SHARED AND WILL INFORM GROWERS' OPTIONS TO CREATE MORE RESILIENT AGROECOSYSTEMS.