Dry Matter Accumulation Pattern and Growth Rate of Onion as Affected by Foliar Application of Various Zn Fertilizer Sources

The pattern of dry matter accumulation and crop growth rate are important characteristics affecting optimal crop production. Plant nutrition has a significant impact on plant growth pattern. In this research, the effect of foliar application of Zn in the form of ZnSO4 and synthetic complexes of methionine-Zn (Zn-Met) and lysine-Zn (Zn-Lys) on pattern of dry matter accumulation, crop growth rate, and other growth indicators of onion (Allium cepa L. cv. Primavera) was evaluated. Foliar Zn application at a concentration of 0.5 % was performed at two stages: once at the early rapid vegetative growth stage (at stage of leaf blade growth), and the other at the early bulbing. The results indicated that, at all fertilizer treatments, the slow growth period lasted 128 days after seed germination followed by the rapid growth period. The maximum leaf area index (LAI) (3.44), bulb growth rate (31.30 g m-2 day-1), crop growth rate (40.70 g m-2 day-1), relative growth rate (0.0966 g g-1 day-1) and total biomass was obtained at the Zn-Lys treatment. For this reason, the highest total biomass (14.87 kg m-2) belonged to this treatment. Foliar application of Zn treatments was ineffective on the bulbing time. Among different treatments, the pattern of dry matter accumulation showed that Zn-Lys complex resulted in significant increase of plant dry mass (33% over the control treatment), and this trend continued until the end of the growing season. According to the results, foliar spray of Zn-Lys complex affected the growth pattern of onion and thereby resulted in significant improvement of dry matter accumulation, LAI, bulb growth rate, and crop growth rate. The highest total biomass was also produced in the Zn-Lys treatment. Also, Zn-Met complex significantly increased total biomass and blub quality but zinc sulfate only significantly increased zinc concentration in onion bulb. According to the results of this research, foliar spray of Zn-Lys complex is recommended for improving onion yield and quality in zinc deficient calcareous soils.