Nitrogen Management and Nitrification Inhibitor Effects on Nitrogen‐15 Urea: I. Yield and Fertilizer Use Efficiency

Nitrification inhibitors (NI) are sometimes recommended for use with ammoniacal fertilizers in corn ( Zea mays L.) production to improve fertilizer N use efficiency (FUE). The objectives of this experiment were to evaluate the effects of the NI nitrapyrin [2‐chloro‐6‐(trichloromethyl) pyridine] application on yield and FUE of irrigated corn, and to monitor the fate of a single application of 15 N‐enriched urea during a multiyear period in both soil and plant. Treatments included a factorial combination of two N rates (90 or 180 kg urea‐N ha −1 yr −1 ) applied during a 3‐yr period, with or without a NI and with or without incorporation, plus a zero‐N control. Twenty‐seven nonweighing lysimeters were used to quantify leaching load. Treatment effects on yield and FUE differed each year due to interactions of climate and N‐management variables. Nonincorporated urea + NI reduced grain yield when leaching load was low and increased yield at the 90 kg ha −1 N rate when leaching load was high. Maximum FUE occurred at the 90 kg ha −1 N rate when leaching load was low. The NI increased FUE only at the 90 kg ha −1 N rate when leaching load was high. Incorporation of urea + NI reduced plant recovery of fertilizer‐derived N (FDN) in the year of application, but resulted in increased uptake of residual FDN in subsequent years. Incorporation of NI with moderate N rates coupled with conservative irrigation management should reduce the risk of yield loss and minimize NO 3 movement to groundwater.