the effect of urea foliar spray on parameters of tomson navel orange

nitrogen foliar spray is one of the most important components in fertilizing programs for citrus in iran, as it can reduce nitrate leaching. the goal of this research was to determine the most effective concentration of foliar urea application on “thamson navel’’ orange trees, for achieving the highest yield. foliar sprays were carried out, in two stages with total concentrations of 0.4, 0.8 and 1.2%. the first stage applied in april with concentrations of (0.25, 0.5 and 0.75%) and second stage in the end of july with concentrations of (0.15, 0.35 and 0.45%). results of statistical analysis showed that urea treatment at concentration of 1.2% had significant effect on increasing the mean fruit weight. also significant increase in mean fruit diameter and total soluble solids to acidity ratio in urea treatment at 0.4% concentration were observed. the results indicated that, there is no significant effect on vitamin c and ratio of fruit length to fruit diameter in urea treatment at concentration of 1.2%. all spray treatments increased fruit set. finally, urea treatment at concentration of 1.2% had the best effects on more of studied traits.