Co-application of Humic Acid, Potassium Dihydrogen Phosphate, and Melatonin to Ameliorate the Effects of Drought Stress on Barley (Hordeum vulgare L.)

Drought has an adverse impact on the production and growth of cereals globally. Barley is one of the significant cereals, full of nutrients, and commonly utilized as human feed and forage. Due to drought stress, cereals' cultivation declined day by day, and ultimate yield does not fulfill the required demand. The current research investigated the consequences of drought stress on morpho-physiological, biochemical, and yield characters of barley plants and a comparison of different treatments and their ameliorating capacity towards drought stress. A pot trial was held in a completely randomized design (CRD) in a triplicate manner to investigate the role of humic acid, potassium dihydrogen phosphate, and melatonin foliar application in ameliorating the drought stress. Two barley varieties (Sultan-17 and Jau-17) were selected for this experiment. The treatments applied were as follows: humic acid (HA; 400 mg L-1), potassium dihydrogen phosphate (KH2PO4; 20 mg L-1), and melatonin (MT; 116 mg L-1) with two water levels, i.e., control and drought stress. Under control and drought stress, different growth parameters, i.e., fresh weight of root and shoot, dry weight of root and shoot, leaf area, and physiological and biochemical attributes, i.e., chl a, chl b, antioxidant enzymes, and total soluble proteins, were studied. Moreover, relative water content, phenolics, proline, MDA content, hydrogen peroxide, relative membrane permeability, mineral contents, and yield parameters were also analyzed in this research. Drought severely affects a majority of parameters that were studied. Results indicated that foliar application of all three treatments improved plant growth, antioxidant enzymes, total soluble proteins, total chlorophyll, mineral contents, and productivity parameters, while foliar application of all three treatments alleviated malondialdehyde content, hydrogen peroxide, and relative membrane permeability value studied under drought stress and non-drought stress. The maximum yield was noticed in Jau-17 plants by HA treatment in either control or drought stress. The order of effectiveness of treatments in this study was HA > MT > KH2PO4. All three treatments (HA, KH2PO4, and MT) examined in this study had a potential role in combating against drought stress and all treatments also elevated plant growth and yield under control.