Effect of Humic Acid on Growth and Yield Indices of Sunflower (Helianthus annuus) in a Saline Soil

This field experiment was carried out in order to investigate the effects of humic acid on the growth and yield of sunflower in a saline soil, using a complete block design with three replications in Kashan, central Iran, in 2014. Treatments consisted of 3 levels of humic acid (1, 3 and 6 liters per ha), no humic acid in soil with sufficient nitrogen, three liters of humic acid per ha in soil without sufficient nitrogen, control of humic acid in soil without sufficient nitrogen. The results showed that the use of humic acid left significant effect on all measured traits. The greatest increase in oil content, 1000 seed weight, head weight, seed yield, head diameter, stem diameter and number of leaves were obtained by use of 3 liters of humic acid in soil with sufficient nitrogen. Maximum increase in plant height and plant weight were obtained‎ by using 6 liters humic acid in soil with sufficient nitrogen and the highest protein content was ‎ achieved‎ by using 1 liter of humic acid per ha in soil with adequate nitrogen. The results of this experiment showed that the application of humic acid in a saline soil improves the growth ‎and yield of sunflower plants.‎