The effect of spraying with salicylic acid and humic acid on the physiological and chemical qualities of Acacia cyanophylla seedlings

Given the growing environmental challenges and the imperative for successful afforestation initiatives, there is an increasing demand for enhancing seedling growth and quality through natural treatments. This study was conducted to evaluate the effects of salicylic acid and humic acid on the physiological and biochemical attributes of Acacia cyanophylla seedlings. The experiment was carried out in the nursery of the tourist village of Nineveh forests, where seedlings were sprayed with salicylic acid (0, 200, 400 mg·L⁻¹) and humic acid (0, 1, 2 g per seedling) to assess their effects on selected physiological and chemical traits. The results showed that spraying with salicylic acid at 200 mg·L⁻¹ had a significant impact on carbohydrate content, protein percentage, total chlorophyll content of leaves, and relative moisture content. Similarly, humic acid at 2 g per seedling produced the highest significant increases in these traits. As for the bilateral interaction between salicylic acid and humic acid, the results showed that spraying with salicylic acid at 200 mg·L⁻¹ in combination with humic acid at 2 g per seedling resulted in the highest values for most of the studied traits. This combined application significantly enhanced seedling growth and overall physiological vigor. Foliar application of salicylic acid at 200 mg·L⁻¹ resulted in a marked increase in chlorophyll content, thereby promoting photosynthetic efficiency, while humic acid application markedly improved leaf water retention, substantially augmenting the seedlings’ tolerance to environmental stress. Collectively, these results indicate that the integrated use of salicylic acid and humic acid represents a promising and effective approach for enhancing seedling quality and vigor, particularly in the context of afforestation programs