Impact of Humic Acid Application on Some Growth Properties and Grain Yield of Three Bread Wheat Cultivars

A field experiment was conducted during the 2024–2025 growing season in the Al-Rumitha district, Al-Muthanna Governorate, Iraq. The objective was to evaluate the response of three bread wheat cultivars (Wafiya, Ibaa 99, Babil) to three levels of humic acid applied to the soil (0, 6, 12 kg ha⁻¹). The experiment followed a randomized complete block design (RCBD) in a split-plot arrangement with three replications, the varieties put in the main plots, while the humic in sub plots are placed. The results indicated that, the application of 12 kg ha-1 of humic acid significantly improved flag leaf area (50.84 cm2), spike length (11.28 cm), number of spikes m-2 (358.90 m-2), 1000-grain weight (38.52 g), grain yield (4.795 t ha-1), and harvest index (32.60%) compared to the control. Significant differences were observed among cultivars, where 'Wafiya' exhibited the highest chlorophyll content (47.53 SPAD), flag leaf area (74.69 cm2), length of the spike is (13.98 cm), number of grains per spike (61.60 grain spike-1), 1000-grain weight (44.11 g), and grain yield (5.223 t ha-1). The interaction between 12 kg ha-1 humic acid and 'Wafiya' cultivar significantly achieved the maximum spike length (14.90 cm) and grain yield (5.437 t ha-1) which did not differ significantly in grain yield from the combination at the comparison level with Wafia variety, which gave an average of (5.493 t ha⁻¹). It is concluded that, the interaction of the Wafiya cultivar with high humic acid levels of 12 kg ha-1 optimizes wheat productivity under local environmental conditions.