EFFECTIVE POLICIES TO MANAGE/REDUCE NUTRIENT RUNOFF IN U.S. AGRICULTURE MUST HAVE AT THEIR CORE AN ACCURATE 'MODEL' OF THE DECISION PROCESSES USED BY FARMERS WHEN THEY MAKE NUTRIENT MANAGEMENT CHOICES. RESEARCHERS HAVE RELIED ON REVEALED PREFERENCE APPROACHES TO INVESTIGATE DECISIONS UNDER UNCERTAINTY, OR HAVE SIMPLY ASSUMED THAT RATIONAL DECISION MAKING PREVAILS. OUR RESEARCH USES RECENTLY-IMPROVED METHODS FOR MEASURING SUBJECTIVE BELIEFS TO IDENTIFY FARMERS' ACTUAL SUBJECTIVE BELIEFS ABOUT CROP YIELD DISTRIBUTIONS, AND THE ROLE OF NITROGEN -- QUANTITY, TIMING, METHOD OF APPLICATION -- ON THE PERCEIVED SHAPE OF YIELD DISTRIBUTIONS.A 2014 PILOT STUDY CONDUCTED BY OUR RESEARCH TEAM DEMONSTRATES THAT MEASURING FARMERS' SUBJECTIVE DECISION PROCESSES DIRECTLY IS VIABLE AND ILLUMINATING. PRELIMINARY RESULTS REVEAL KEY PATHWAYS FOR NUTRIENT REDUCTION POLICY DESIGN. FOR EXAMPLE, PILOT STUDY RESULTS SHOW THAT FAMERS' SIGNIFICANTLY OVERESTIMATE THE GROWTH ENHANCEMENT EFFECTS OF APPLIED NITROGEN. FURTHER RESULTS REVEAL THE SOURCE OF THESE BIASED BELIEFS. OUR PROPOSED RESEARCH BUILDS ON OUR PILOT STUDY METHODS AND FINDINGS.OUR RESEARCH WILL PROVIDE THE FIRST ASSESSMENT OF MIDWEST U.S. FARMERS' SUBJECTIVE BELIEFS ABOUT CROP YIELD DISTRIBUTIONS AND THE ROLE OF NUTRIENTS (NITROGEN AND PHOSPHOROUS) ON THE MEAN AND VARIANCE (RISK) OF YIELDS, AND THUS FARM PRODUCTIVITY AND PROFITABILITY. WE BELIEVE THIS WORK WILL SET A NEW DIRECTION FOR DESIGNING NUTRIENT RUNOFF REDUCTION POLICIES FOR U.S. AGRICULTURE.