Effect of foliar application of different nano-selenium concentrations on quantitative and qualitative traits of barley (Hordeum vulgare L.) under irrigated and rainfed conditions

Introduction
Water scarcity is one of the major constraints limiting crop production, particularly in cereal crops. Drought stress disrupts a wide range of molecular, biochemical, physiological, morphological, and quality-related processes in plants. Supplementary irrigation is an effective strategy to mitigate the adverse effects of drought stress in crops. Early application of supplementary irrigation during dry years or at critical growth stages can enhance yield stability. Among cereal crops, barley is considered the most adaptable species to biotic and abiotic stresses. Although barley shows relatively higher drought tolerance than many other cereals, it is still sensitive to water deficiency during critical growth stages, particularly stem elongation and grain filling. Drought occurring at these stages can cause substantial yield reductions. In recent decades, the adoption of innovative technologies to improve crop performance has increased markedly. Nanotechnology, particularly the application of nanofertilizers, has emerged as a promising strategy for enhancing agricultural productivity. As an efficient alternative to conventional fertilizers, nanotechnology can improve nutrient use efficiency while reducing environmental impacts. Selenium is a non-essential element for most plants but an essential micronutrient for animals and humans. Considering the increasing water scarcity in Iran, the importance of barley production, and the potential of nanotechnology to enhance crop performance, this study aimed to evaluate the effects of different nano-selenium concentrations on selected quantitative and qualitative traits of barley under rainfed and supplementary irrigation conditions.
 
Materials and methods
To evaluate the effects of foliar application of different nano-selenium concentrations on selected morpho-physiological traits and grain yield of barley under rainfed and supplementary irrigation conditions, a split-plot experiment based on a randomized complete block design (RCBD) with three replications was conducted at the research farm of the Faculty of Agriculture, Lorestan University in 2023. The main plot factor was irrigation regime (rainfed and one-time supplementary irrigation at the grain-filling stage), and the subplot factor consisted of four nano-selenium concentrations (0, 10, 20, and 30 mg L⁻¹), applied at two growth stages (4–6 leaves and stem elongation). Leaf soluble sugars and proline content in leaves were determined at 490 nm and 520 nm, respectively, using a spectrophotometer. Grain protein content was measured using a Grain N Analyzer (Perten 7250, Sweden). Data were analyzed using the least significant difference (LSD) test at the 0.05 probability level to evaluate the main effects and interactions.
 
Results and discussion
Drought stress significantly reduced grain yield, carotenoid content, soluble sugars, number of grains per spike, and 100-grain weight, while increasing leaf proline and grain protein content. In contrast, foliar application of nano-selenium improved most of these traits and decreased electrical conductivity. The highest carotenoid (3.87 mg.g⁻¹ FW) and soluble sugar content (86.77 mg.g⁻¹ FW), as well as the highest 100-grain weight (4.8 g), were obtained under supplementary irrigation combined with foliar application of 20 mg L⁻¹ nano-selenium. Additionally, the maximum proline content in leaves (9.66 mg.g⁻¹ FW) and grain protein (13.75%) were recorded under rainfed conditions with 30 and 20 mg L⁻¹ nano-selenium, respectively. The highest grain yield (3357.58 kg.ha⁻¹) was obtained under supplementary irrigation with the application of 20 mg L⁻¹ nano-selenium. Compared with the control, foliar application of 30 mg L⁻¹ nano-selenium under rainfed conditions increased carotenoid content, proline, soluble sugars, grain protein, and grain yield by 51.9%, 9.6%, 27%, 3.8%, and 71.7%, respectively.
 
Conclusion
Overall, supplementary irrigation combined with foliar application of nano-selenium can mitigate the adverse effects of drought stress in barley. Therefore, the application of nano-selenium combined with supplementary irrigation at the grain-filling stage is recommended to enhance barley performance under water-limited conditions.