Mitigating water deficit stress in wheat ( Triticum aestivum L.) through foliar application of humic acid, fulvic acid, and amino acids during critical growth stages

Wheat ( Triticum aestivum L.) is one of the most important cereal crops and a staple food worldwide. This study evaluated the effects of foliar applications of humic acid, fulvic acid, and amino acids under well‐watered and water‐deficit conditions at three key growth stages on grain yield of the Taktaz wheat cultivar over two consecutive growing seasons. Field experiments were conducted under well‐watered and drought stress conditions. A split‐factorial arrangement within a randomized complete block design with three replications was employed. The main factor consisted of growth stages (tillering, stem elongation, and flowering), while the subplot factor included foliar application treatments with humic acid, fulvic acid, and amino acids. Analysis of variance revealed significant differences ( p < 0.05 or p < 0.01) among treatments for the tolerance index (TOL), relative drought index, and mean relative performance indices across all growth stages. Yield comparisons between well‐watered and stress conditions showed that treatment T24 (fulvic acid 6L/ha, amino acid 1.5 L/ha, and humic acid 8L/ha) comprising high concentrations of humic and fulvic acids combined with a moderate concentration of amino acids was the most effective in mitigating drought effects. Moreover, drought TOL analysis identified treatment T6 (amino acid 1.5 L/ha, and humic acid 12 L/ha), characterized by a high concentration of humic acid, as the most efficient across all indices. Graphical and cluster analyses further confirmed the superior performance of treatments T6 (amino acid 1.5 L/ha, and humic acid 12 L/ha) and T24 (fulvic acid 6L/ha, amino acid 1.5 L/ha, and humic acid 8L/ha) at all growth stages. Overall, the results demonstrate that treatments containing high concentrations of humic acid, particularly when combined with moderate levels of amino acids, exhibited superior performance in enhancing wheat tolerance to water deficit, while moderate concentrations of fulvic acid and amino acids contribute positively to grain yield stability under drought conditions.