Evaluation of N source and timings in no-till winter wheat

Nitrogen fertilizer efficacy is largely dependent upon the application timing and surroundings in which they are placed. Therefore, the variability in Oklahoma’s environmental and meteorological conditions can present a distinctive challenge for the state's agricultural producers looking to apply nitrogen fertilizers in their no-till production systems. This study examines the effects of nitrogen source and application timing on winter wheat grain yield and protein content in no-till systems. Over 11 site-years, four N fertilizers—urea, urea-ammonium nitrate (UAN), SuperU, and UAN + Anvol—were applied at a rate of 66 kg ha⁻¹ across three physiological timings. Due to significant variability between growing seasons, Dunnett’s analysis was used to assess the impact of nitrogen source and timing on grain yield and protein percentage for each growing season. Urea consistently outperformed other N sources in terms of grain yield and protein concentration. Across site years and stages, no significant benefit was observed for the addition of nitrogen stabilizers. Feekes stages correlated with a late February/early March application period maximized grain yield, while later applications resulted in higher protein content. These findings suggest that late February/early March urea applications can optimize yields for Oklahoma winter wheat producers.