1. Evaluating the Existing Calibration Curve for Sensor-Based N Management in Grain Sorghum

Nitrogen (N) response in grain sorghum is spatially and temporally variable, complicating estimation of optimum N rates and limiting the effectiveness of uniform fertilizer recommendations. This study evaluated within-field and year-to-year variability in N response using block-level response modeling and soil variability analysis. Field experiments were conducted in Stillwater, Oklahoma, during the 2024 and 2025 growing seasons using six N fertilizer rates (0,39, 79, 118, 157, and 196 kg N ha⁻¹).... D. Pokharel