Impact of Nitrification Inhibitor Centuro^TM on Field-Scale N Balances in Maize

Nitrification inhibitors have been shown to increase maize (Zea mays L.) yield and tissue N, but their environmental co-benefits are less studied. Our objective was to determine the impact of a novel nitrification inhibitor (Centuro^TM) on grain yield, N concentrations of grain and stover, losses of N to surface waters as NO₃-N, and losses to the atmosphere as the potent greenhouse gas, N₂O. This study was conducted from January 2021 to December 2023 using 10 x 30-m tile-drained lysimeters at Purdue’s Water Quality Field Station (WQFS). Centuro^TM was applied to the maize component of a conventional maize-soybean (Glycine max L. Merr.) rotation receiving 157 kg N ha^-1 as urea-ammonium nitrate (UAN) as a pre-plant application. Two ongoing WQFS treatments were selected as controls. Continuous maize receiving 180 kg N ha^-1 applied pre-plant has a history of similar yields and nitrate load losses when compared to rotational maize receiving 157 kg N ha^‑1 without a nitrification inhibitor. A maize-soy rotation that included a rye (Secale cereale L.) cover crop, harvested at anthesis, that received 135 kg N ha^-1 as a side-dress application served as an N stewardship control. Grain and stover yields were obtained at maturity, tissues were dried, and N concentration of milled tissues were analyzed. Water flow rates and water samples were obtained daily (when tiles lines flowed), NO₃-N concentrations of samples were measured, and annual NO₃-N load losses determined as the product of NO₃-N concentration and flow. The static chamber method was used to measure N₂O levels at weekly intervals from April to December. The experimental design was a randomized complete-block design with 4 replicates. Mixed effects models’ analysis was used to partition variation into treatment, year, and replication effects and corresponding interactions. Where F-tests were significant (p < 0.10), an LSD was calculated. Grain yield of maize receiving Centuro^TM with 157 kg N ha^-1 was numerically higher (avg. 1.1 Mg ha^-1) but statistically similar to continuous maize receiving 180 kg N ha^-1, and both were higher than the maize-soybean + rye receiving 135 kg N ha^-1. Maize grain N concentrations were similar for the Centuro^TM treatment and the continuous maize receiving 180 kg N ha^-1. Annual tile flow volume was highly variable between plots and did not differ among treatments. Flow weighted NO₃-N concentrations of the Centuro^TM plots with maize were lower in 2 of 3 plot series when compared to continuous maize receiving 180 kg N ha^-1, while N₂O emissions were consistently lower in the Centuro^TM treated plots. Inclusion of this nitrification inhibitor often improved environmental performance of maize in a maize-soy rotation receiving 157 kg N ha^-1, while maintaining high grain yields when compared to continuous maize receiving 180 kg N ha^-1.