Corn Yield and N Responses in Recent North Carolina Field Tests Vs Published Nitrogen Rate Recommendations.

Nitrogen (N) application rates that meet the USDA NRCS 590 Nutrient Management Standard are established through a table consisting of realistic yield expectations (3 of the best 5 years of yields; RYE), N factor (lb N per unit yield), and N application rate (RYE * N factor).   Corn data from the RYE table were compared with results from 72 recent corn N rate experiments at field sites across North Carolina. Some response to N fertilization was measured at all but 4 locations, and a maximum yield was documented for 57 of the sites. Averaged across all sites, maximum grain yield was approximately 20% higher than the published RYE values. Since optimum N fertilizer rates from these trials were almost identical to table rates but yields were higher, actual corn N efficiency (N factor) was improved; less N was required per unit grain in the field experiments than in the standard N-rate table. Additional trends noted in N efficiency: irrigated corn required more N per unit grain than did non-irrigated corn, and corn following corn required more N per unit grain than if corn followed soybean. Even with recent increases in grain yield potential, recommended N rates should not be increased for non-irrigated corn, because N efficiency has also improved. Data for the nitrogen rate table were collected approximately twenty years ago; based on the results from this study, periodic updates to yield potential and N efficiency values will be needed.