Recent trends in livestock concentration in major corn producing states suggest that increasing risk of water pollution from manure applications may be offsetting declines in risk of water pollution from chemical fertilizer. Analysis of data from ARMS surveys found that potential excess nitrogen and phosphorous per corn acre increases sharply between 1996 and 2001 when manure nutrient credits are included. Cohort analysis of farms found that the level of technical efficiency appears to be positively associated with potential nutrient pollution from both sources. Operations with high ratios of manure applied to manure produced and excess phosphorous tend to be more technically efficient than operations with low ratios of manure applied to manure produced and low levels of excess phosphorous. Factors influencing or associated with performance differ by states. In general, the results suggest that adjusting the performance measures to include excess nutrients as a Abad output@ would tend to narrow the gap between high and low performance compared to measures that ignore pollution.