Effect of Different Levels of Humic Acid and Zinc Sulfate on Morphological and Phytochemical Traits of (Salvia officinalis L.)

Introduction  Humic acid as an organic matter, made during chemical processes in the soil leads to improved root growth and aerial part of the plant. It increases the penetration of elements in the plant and improves water permeability. Zinc is involved in the maintenance of root cell membranes, the activation of antioxidant enzymes, and the production of RNA and DNA. This study aimed to investigate the effect of applying humic acid and zinc sulfate on some morphological and phytochemical traits of Salvia officinalis L.   Materials and Methods  In this regard, this experiment was conducted as a factorial based in a completely randomized design with two factors (concentrations of 0, 1.5, 3 and 4.5 g/l humic acids and concentrations of 0, 3, 6 and 9 g/l zinc sulfate) in five replications in 2021. The studied traits included plant height, stem diameter, fresh weight, and dry weight, number of sub-branches, chlorophyll, carotenoids, phenols, flavonoids and essential oils. Seedlings of the same size and age as sage were grown under equal. The properties of the soil used in the laboratory were examined. Treatments were sprayed with humic acid 6% and zinc sulfate 34% in five steps, every two weeks.   Results and Discussion Result showed that application of humic acid and zinc sulfate had no significant effect on plant height and only their simultaneous use had a significant effect on this trait and the highest plant height was observed for treatment of 1.5 g/l humic acid and 9 g/l zinc sulfate (66.50 cm). In stem diameter analysis, the use of humic acid (p≤0.01) and the application of zinc sulfate (p≤0.05) and the interaction of these two treatments(p≤0.05) affected the stem diameter. According to the results, the highest stem diameter was 8.69 mm, which occurred in the treatment of 4.5 g/l humic acid and 3 g/l zinc sulfate. Application of humic acid significantly (p ≤ 0.01) affected the fresh weight of the plant. Application of zinc sulfate also had a significant effect (p ≤ 0.05) on fresh weight. The effect of simultaneous use of humic acid and zinc sulfate on the fresh weight of this plant was significant at the level of 1% probability and the highest fresh weight was 87.26 g.plant-1, which achieved at a concentration of 4.5 g/l humic acid and 6 g/l zinc sulfate. Compared to the control plant, it has increased by 12.56 grams. The effect of humic acid on dry weight was significant at the level of 5% probability, while the effect of zinc sulfate application on this trait was not significant. The combined use of humic acid and zinc sulfate was significant at the 1% probability level. The maximum dry weight reached 29.73 grams per plant, achieved with a concentration of 4.5 grams per liter of humic acids and 3 grams per liter of zinc sulfate. Both humic acid and zinc sulfate exhibited a significant effect (at the one percent level) on the number of branches. Furthermore, the combined application of humic acid and zinc sulfate proved to be highly effective (p<0.01). The greatest number of sub-branches was observed at the 1.5 grams per liter level of humic acid. Humic acid had a substantial impact on chlorophyll a, b, total chlorophyll, and carotenoids (p≤ 0.01). Similarly, the application of zinc sulfate showed significant effects on chlorophyll a, b, and carotenoids (p≤ 0.01), as well as on total chlorophyll (p≤ 0.05). In the end, the simultaneous application of humic acid and zinc sulfate significantly influenced chlorophyll a, b, total chlorophyll, and carotenoids (p<0.01). The most significant effects on photosynthetic pigments (carotenoids, chlorophyll a, and total chlorophyll) were observed with concentrations of 4.5 grams/liter of humic acid and 6 grams/liter of zinc sulfate. The highest chlorophyll b content was obtained with the treatment of 3 grams/liter of humic acid and 6 grams/liter of zinc sulfate. The effect of humic acid and zinc sulfate application as well as their simultaneous use on the amount of phenols and flavonoids was significant at the level of 1% probability. The highest amount of phenol was 0.372 (mg gallic acid per gram of fresh tissue) which was obtained at a concentration of zero zinc sulfate and 3 g/l humic acid. The highest flavonoid content was 0.527 (mg quercin per gram of fresh tissue) which was observed in the treatment of 4.5 g/l humic acids. The use of humic acid had significant effect on the amount of essential oil. The percentage of essential oil reached the highest levels at the concentrations of 1.5 and 3 g/l humic acids.   Conclusion  Based on the results, the use of humic acid alone and in combination with zinc sulfate, had the greatest effect on most of the studied traits.