Interactive effects of nitrogen fertilization and irrigation regimes on seed quality, fatty acid composition, phenolic compounds, and antioxidant capacity of sorghum

Global climate change and the decrease in water resources necessitate effective water and nutrient management for sustainable crop production. The objective of this study was to determine the interactive effects of nitrogen fertilization and different irrigation levels on seed quality traits, fatty acid composition, phenolic compounds, antioxidant capacity, and sugar content in sorghum under subsurface drip irrigation conditions. The field experiment was conducted in 2022 using a split-plot design with five nitrogen rates (0 (unfertilized control), 80, 160, 240, and 320 kg N ha − 1 ) and six irrigation levels (0% (rainfed), 25%, 50%, 75%, 100% (full irrigation control), and 125%). According to the results, the majority of the quality traits examined were significantly influenced by nitrogen rates, irrigation levels, and their interactions. Increasing nitrogen rates enhanced crude protein, total free amino acids, total phenolic compounds, antioxidant capacity, and reducing sugar content, whereas these traits generally increased under deficit irrigation and decreased as irrigation levels increased. It was determined that water use efficiency (WUE) and irrigation water use efficiency (IWUE) values were highest under moderate irrigation conditions. The fatty acid profile was dominated by linoleic, oleic, and palmitic acids, and was only marginally affected by nitrogen and irrigation treatments. Oil content and secondary metabolites increased, particularly under deficit irrigation conditions. PCA, heatmap, and correlation analyses revealed strong relationships among quality parameters. In conclusion, the I50 irrigation treatment combined with 160–240 kg N ha − 1 provided the best balance between seed quality traits and water use efficiency, representing a sustainable management strategy for sorghum production.