Purpose: Water scarcity poses a serious threat to agricultural cropping systems of arid and semi-arid regions, affecting many aspects of plant metabolism and performance. Bentonite is a natural and nontoxic soil amendment that can effectively ameliorate water utilization in crop production. The target of the present study was to monitor morphological, physiological, and biochemical responses of fenugreek (Trigonella foenum-graecum L.) to bentonite application under water deficit. Methods: This study was arranged as factorial based on a completely randomized design with three replications. Treatments were three levels of bentonite application (0, 50, and 100 g kg-1 soil) and different irrigation regimes (90, 60, and 30% Field capacity (FC)). The traits were measured at the flowering stage. Results: Based on the results, compared to the corresponding control, in the presence of bentonite, drought-stressed fenugreek showed higher leaf area, length, and width and lower root length, volume, and diameter, dry and fresh weight. In addition, bentonite application enhanced relative water content (RWC) and photosynthetic pigments (chlorophyll a, b, and total) and minimized drought stress indexes such as electrolyte leakage (EL), osmolytes (soluble carbohydrates and proline), protein content, hydrogen peroxide (H2O2), malondialdehyde (MDA), antioxidant enzymes, catalase (CAT) and polyphenol oxidase (PPO), total phenol and antioxidant activity under severe drought stress. Conclusion: This study demonstrated the high efficacy of bentonite for increasing drought tolerance in fenugreek. However, the intensity of the positive response of plants to the use of bentonite is related to the severity of drought stress.

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