The Effect of Humic Acid and Zinc Application on Some Vegetative Traits and Anti-oxidant Enzymes of Corn Seedling under Salinity Stress

One of the methods to decrease the oxidative damage caused by salinity is using the nutrition methods and increasing resistance of plants against salinity stress. The aim of this study was to investigate the effect of soil application of humic acid and zinc sulfat on some properties of corn seedlings under salinity stress. For this purpose, an experiment was conducted as split-plot using a randomized complete block design with three replications in the greenhouse. Experimental treatments were included soil salinity (at two levels included non-saline and saline soils with EC of 2.2 and 8 dSm-1, respectively) as the main factor and application of 5 kg ha-1 humic acid [HA], 40 kg ha-1 zinc sulfat  [Zn], 5 kg ha-1 humic acid+40 kg ha-1 zinc sulfate [HA+Zn] and control [Co] as sub-factor. Results showed that the stem height and diameter, wet and dry weight of root and shoot and chlorophyll index decreased significantly with increasing salinity in soil, while proline content, catalase and superoxide-dismutase activities increased. Among the studied treatments, HA+Zn treatment had the greatest effect on improvement of seedling growth parameters, so that the application of treatment increased the amount of stem height, stem diameter, wet and dry weight of shoot and root and chlorophyll index, 18.31, 16.76, 58.27, 59.89, 62.62, 65.25 and 4.85%, respectively compared to control treatment in saline soils. The highest level of catalase and superoxide dismutase activities and proline content were observed under salinity stress along with HA+Zn treatment, and the effect of humic acid was greater than the effect of zinc sulfate. Therefore, the combined use of humic acid and zinc was recommended to improve the growth of corn seedlings in stress salinity conditions.