Evaluation of fenugreek under water stress: agronomic traits, seed oil quality and antioxidant capacity

Fenugreek ( Trigonella foenum-graecum L.) is rich in seed bioactive compounds, and its yield depends on irrigation. The effects of deficit irrigation treatments on yield, water-use efficiency, and seed quality traits remain insufficiently characterized. This two-year field study (2021–2022) evaluated five irrigation levels. Fenugreek was sown in late March and harvested in late July. In the fully irrigated treatment (FI100), the soil water depleted from field capacity was fully replenished. The FI75, FI50 and FI25 treatments received 75, 50 and 25% of the water applied to FI100, and FI0 was a rainfed control. The aim was to assess the trade-off between yield and quality under water-limited conditions. Experiments were conducted in randomized complete-block design with three replications under drip irrigation. Crop water consumptions, irrigation and crop water productivity, and both treatment-specific and seasonal yield-response factors (Ky) were determined. Agronomic traits, seed oil and fatty acid composition, phenolic contents and antioxidant activities were measured and analysed by PCA. As the average of two years, the highest seed yield occurred under FI100 (1474 kg ha⁻¹) and the lowest under FI0 (533 kg ha⁻¹), a reduction of about 64%. The seasonal Ky exceeded unity in both years (1.12 and 1.18). At the same time, the treatment-specific Ky increased as the deficit became milder (from ≈ 0.97 under FI0 to ≈ 2.8 under FI75), indicating a non-linear response with greatest sensitivity near full irrigation. Water deficit improved seed quality, total phenolics, flavonoids, hydrolysable tannin, and antioxidant activity peaked under FI0, while saturated fatty acids (SFA) increased and polyunsaturated fatty acids (PFA) decreased. PCA explained 89.1% of the variation and revealed a negative relationship between yield/oil-quality traits and phenolic-based antioxidant traits. Growth and seed yield in fenugreek are highly sensitive to water deficit, whereas seed biochemical quality responds inversely. Irrigation should therefore be planned by objective. Full or near-full irrigation for high yield, and controlled deficit irrigation for phytochemical quality. Where water is the primary limiting resource, FI75 offers a compromise, saving 25% of irrigation water at the cost of about a 41% yield reduction.