Simultaneous application of nitrification inhibitors and fertilizer N has the potential to delay nitrification processes and reduce atmospheric N loss through N2O emissions. A 2-yr study was conducted to assess the effects of newly available water-soluble nitrapyrin (Instinct) [2-chloro-6-(trichloromethyl) pyridine] on the nitrification kinetics and N2O emissions from urea-NH4NO3 (UAN) band applied to somewhat poorly drained and moderately well-drained silt loam soils in Indiana. The UAN fertilizer, with or without nitrapyrin, was injected post-emergence between corn (Zea mays L.) rows that were 76 cm apart. Soil samples were taken at various increments from the band centers at 1- to 2-wk intervals for up to 14 wk and analyzed for NH4- and NO3-N concentrations. Nitrification rates were determined using appropriate kinetic models. Greenhouse gas samples were collected weekly for 7 to 10 wk and biweekly thereafter for an additional 2 to 4 wk. Our results showed that UAN nitrification followed first-order kinetics, with significantly greater nitrification rate constants without nitrapyrin. On average, UAN half-life was about 15 d without nitrapyrin and 25 d when coapplied with nitrapyrin. Nitrapyrin reduced N2O emissions by up to 44% from sidedress-applied UAN, even though emission quantities varied by location and year due to differences in soil moisture, temperature, and precipitation. These latter variables plus soil NH4-N concentrations, in various combinations, accounted for 40 to 50% of the total variability associated with N2O emissions. These results can help inform UAN management decisions with regard to use of N stabilizers with UAN in the midwestern United States.
