Modulation of Maize Yield Response to Vapor Pressure Deficit by Nitrogen Nutrition and Phenological Stress Windows

This study explored how nitrogen fertilization modulates the grain yield response of maize to atmospheric stress across distinct phenological windows. Field trials were conducted from 2023 to 2025 under three nitrogen regimes (N0, N69, and NFull) with 237 maize testcrosses. Atmospheric stress was quantified as the cumulative number of hours with a vapor pressure deficit (VPD) exceeding 3.0 kPa. Data were analyzed using linear mixed-effects models. The 15-day pre-silking window was identified as the most sensitive among the three evaluated phenological windows, exhibiting a strong negative scaled effect of −0.390. The interaction between nitrogen treatment and pre-silking stress was highly significant. Elevated VPD did not operate as an independent determinant of final yield, as the highest mean grain yield was achieved during the hydrothermally intense 2025 season (8.319 t ha−1). NFull effectively mitigated the physiological impact of stress, securing the shallowest yield decline slope (−0.038 t ha−1 per hour). Conversely, the intermediate N69 treatment exhibited the highest statistical sensitivity (−0.109 t ha−1 per hour), reflecting phenotypic plasticity. Random-effects analysis revealed substantial genetic variability for pre-silking VPD sensitivity. The lack of correlation between absolute yield potential and stress sensitivity enables simultaneous selection for both high yield and phenotypic stability within this germplasm.