Winter wheat response to nitrogen rate and management across Kansas environments

Abstract

Nitrogen (N) fertilizer management is one of the primary factors driving winter wheat (Triticum aestivum L.) productivity, profitability, and grain quality in Kansas; however, agroclimatic variability across the state represents a consistent challenge for optimizing fertilizer use. This research evaluated winter wheat response to N fertilization across ten site-years during the 2023-2024 and 2024-2025 growing seasons. The first study evaluated grain yield and grain protein concentration responses to increasing N rates (0 to 202 kg N ha-1) to characterize environmental variability and determine site-specific agronomic optimum N rate (ANOR). The second study evaluated the effectiveness of diverse management strategies, varying in N source, timing, placement, and inhibitor use, applied at a constant N rate of 67 kg N ha-1, using the site-specific expected responses from the first study as a baseline to compare management effects. Results from the first study indicated that grain yield response was highly variable, with AONR ranging from 116 to 185 kg N ha-1 across responsive environments. Environments with limited seasonal precipitation or high initial residual soil N exhibited weak or no grain yield response, whereas grain protein concentration increased consistently across all site-years, often continuing to increase after grain yield had plateaued. In the second study, alternative management strategies did not consistently improve grain yield relative to the expected baseline; instead, environmental conditions were the primary determinants of grain yield at a constant N rate. However, nitrogen management more frequently influenced grain protein concentration and apparent recovery efficiency (ARE). Strategies that delayed or split N application, such as split-applied UAN, often increased grain protein, while fall or early spring applications tended to result in lower protein responses. These findings demonstrate that the effectiveness of both N rate and management practices is defined by site-year conditions, including precipitation patterns and soil N supply. This research highlights the necessity of site-specific management, suggesting that producers must balance N rate and timing decisions based on local environmental conditions, grain yield potential, and specific goals for grain yield versus grain quality.