Enhanced Wheat Yield: Fulvic Acid Application's Impact on Yield Factors under Heat Stress

Terminal thermal stress, occurring under various climatic conditions, significantly reduces wheat yield by disrupting fertilization and grain filling processes. Biostimulants offer a potential solution to mitigate the impact of terminal heat stress on wheat crops. This research aims to alleviate the effect of heat stress on wheat through the application of fulvic acid. The wheat crop was subjected to elevated temperature stress during the booting and grain initiation stages under field conditions, with heat stress at staggered intervals in the main plot. Fulvic acid was applied at different concentrations (water spray, 1.25 mg L-1, 2.50 mg L-1, and 3.75 mg L-1) in field and heat stress conditions upon booting (H1) and grain initiation (H2) stage. Results revealed that heat stress H1 and H2 stages significantly decreased the spike length (22.59% & 21.45%), spikelets per spike (14.35% & 6.66%), grains per spike (27.9% & 20.23%), grain weight per spike (40.24% & 32.54%), test weight (17.84% and 15.69%), biological (41.19% & 32.61%) and straw yield (31.20% & 19.16%), and harvest index (9.8% & 8.31%) as compared to control (H0). The impact was more pronounced during the booting stage compared to the grain filling stage. Application of fulvic acid at concentrations of 3.75 mg L-1 during heat stress at the booting stage and 2.50 mg L-1 upon heat stress at grain initiating stages substantially enhanced the recorded parameters compared to the foliar application of water and 1.25 mg L-1 fulvic acid. These findings revealed that foliar application of fulvic acid promotes thermotolerance in wheat, positively influencing yield and yield-contributing factors during heat stress.