Plants face various stresses, particularly water deficit, which negatively impacts photosynthesis, growth, and development, thereby limiting agricultural production. Utilizing growth regulators, such as amino acids and polyamines, to enhance osmotic stress tolerance is a crucial area of research in sustainable agriculture. This study investigates the impact of arginine and spermine treatments on various growth attributes, enzymatic and non-enzymatic antioxidants, photosynthetic pigments, protein and lipid peroxidation, and yield traits of fenugreek plants under both normal and drought conditions. The results indicate that drought conditions significantly reduce morphological characteristics, leaf pigments, and yield traits. However, the application of arginine and spermine enhances these parameters, with spermine showing a more pronounced effect. Additionally, treatments boost antioxidant enzymes activities and improve the levels of non-enzymatic antioxidants and osmolytes, contributing to better stress tolerance and growth performance. Principal component analysis confirms that drought significantly alters plant physiology, increasing proline and malondialdehyde levels, while arginine and spermine alleviate drought stress by enhancing antioxidant activity and osmolyte accumulation. The current investigation aims to evaluate the effectiveness of spermine and arginine treatments on various growth attributes and stress tolerance of fenugreek plants under normal and drought conditions, focusing on their comparative efficacy.

Despite its value as a culinary, medicinal, and essential oil crop, caraway struggles to grow and develop its biochemical quality in drought-prone sandy soils. To tackle this challenge, we conducted two field trials under drip irrigation, testing four rates of organic manure (0, 5, 10, and 15 ton/hectare (ha) and three foliar biostimulants: vitamin B₁ (50 and 100 mg L⁻¹), vitamin E (50 and 100 mg L⁻¹), and active yeast (100 and 150 mL L⁻¹). We used a randomized split-plot design with three replicates, assigning manure rates to main plots and biostimulants to subplots. We measured plant height, stem diameter, branch number, dry biomass, umbels per plant, 1000-seed weight, seed yield (per plant and per ha), essential oil content, chlorophyll a and b, carotenoids, and leaf N, P, and K. All treatments outperformed the unfertilized control. Applying 15 ton/ha of manure alone increased mean plant height by 185.3 cm, stem diameter by 2.93 mm, branch number by 14.5, and herbal weight by 91.97 g across both seasons—a gain of about 11–15%. Foliar application of vitamin B₁ at 100 mg L⁻¹ (without manure) achieved even larger gains: mean plant height improved by 176.5 cm, stem diameter by 2.6 mm, branches number by 15.1, and herbal biomass by 103.95 g (20–36% growth increases). It also boosted essential oil yield by 1.89 mL per plant (16–50%) and enhanced nutrient uptake. The most pronounced synergy emerged when combining 15 ton/ha of manure with 100 mg L⁻¹ vitamin B₁, raising seed yield to 1698.8 kg/ha (35%), plant height to 184.7 cm (52%), number of branches to 17.4 per plant (56%), umbels to 38.1 per plant (42%), 1000-seed weight to 16.9 g (48%), and essential oil yield to 2.3 mL per plant (115%), compared to the control. Chlorophyll a increased by 50%, chlorophyll b by 33%, carotenoids by 35%, and leaf N, P, and K by 43%, 90%, and 76%, respectively. Manure combined with vitamin E or yeast delivered moderate improvements. These findings demonstrate that integrating organic manure with targeted foliar biostimulants—especially vitamin B₁—under drip irrigation, is a sustainable strategy to maximize caraway yield, oil content, and nutritional quality on marginal sandy soils.