Nitrogen-water management regimes modulate fatty acid profile, antioxidant defense system, and oxidative status in sorghum (Sorghum bicolor L.) silage.

Optimizing nitrogen and water management in sustainable silage production is critical for both improving biochemical quality and maintaining plant oxidative balance. This study examined the effects of different nitrogen doses and irrigation levels on the oil content and fatty acid composition, total phenolic content, antioxidant capacity (DPPH and CUPRAC), and antioxidant enzyme activities such as superoxide dismutase (SOD), catalase (CAT) and peroxidase (POD) and oxidative stress activities as malondialdehyde (MDA) and hydrogen peroxide (H2O2) in sorghum (Sorghum bicolor L.) silage. The experiment was conducted in a split-plot design with five nitrogen doses (0, 80, 160, 240, and 320 kg N ha- 1) and six irrigation levels (0, 25, 50, 75, 100, and 125% of ET₀). Deficit irrigation applications resulted in increases of 9.42-23.82% in total phenolic content and 1.61-32.26% in antioxidant capacity for DPPH and 4.16-33.33% for CUPRAC compared to full irrigation applications. Medium nitrogen applications (160-240 kg ha- 1) strengthened the antioxidant defense system, especially under moderate water stress conditions, showing significant increases in SOD and POD activities. Oil content and unsaturated fatty acid ratio were significantly affected by nitrogen-water interactions. Severe water deficit increased MDA content by 81.81% and H2O2 accumulation by 32.74%, while the application of appropriate nitrogen doses limited this increase. Multivariate analyses (heat map, PCA, and Pearson correlation) revealed strong positive relationships between total phenolic content and antioxidant capacity, while different correlation interactions were observed between antioxidant enzyme activities and oxidative stress indicators. In conclusion, nitrogen and irrigation management were found to be strategic tools for optimizing biochemical quality and oxidative stability by reshaping the coordination between lipid metabolism and the antioxidant defense system in sorghum silage.