Sources and Levels of Zinc Fertilization on Soil Zinc Availability and Zinc Uptake by Small Onion (Allium cepa L. var. aggregatum)

Onion, the King of vegetable is one among the oldest cultivated vegetables. The quality and yield of crops are affected by micronutrient deficiencies in soil. Micronutrients which enhance the efficiency of macronutrients are equally important for the growth of a crop. Indian soils are deficient in zinc by an average deficiency of about 50 % at present. It is revealed that the presence of zinc has direct effect on yield and growth parameters of aggregatum onion. To study the Zn uptake and Zn availability to onion, different levels and sources of Zinc was evaluated in a pot culture experiment with onion var. CO(On) 5 in a soil with andy clay loam in texture, non-calcareous and deficient in soil available Zn with 16 treatments comprising different sources of Zn (ZnSO4, Zn-EDTA and Zn citrate) and levels of Zn (1,2.5,5.0, 7.5 and 10.0 kg Zn ha-1 for ZnSO4 and 0.1,0.25, 0.5, 0.75 and 1.0 kg Zn ha-1 for Zn-EDTA and Zn citrate)­. Significantly highest plant Zn at bulb initiation and harvest stages was observed with ZnSO4 application 10 kg Zn ha-1 followed by Zn-EDTA @ 1 kg Zn ha-1and both were comparable. Uptake of Zn by onion was significantly higher with Zn-EDTA @ 1 kg Zn ha-1 and it was comparable with ZnSO4 @ 10 kg Zn ha-1and Zn-EDTA @ 0.75 kg Zn ha-1. Regarding the Zn content and uptake by onion at the same level of 1 kg Zn ha-1, it was observed that Zn-EDTA performed better than Zn citrate and ZnSO4. The soil available Zn at bulb initiation and harvest stages was the highest with the application of ZnSO4 @ 10 kg Zn ha-1 followed by ZnSO4 @ 7.5 kg Zn ha-1and ZnSO4 @ 5 kg Zn ha-1. With the application of same level of Zn at 1 kg Zn ha-1, Zn-EDTA showed significantly higher soil available Zn which was on par with Zn citrate. From the results obtained, it can be inferred that Zn fertilization had a significant influence on Zn content, Zn uptake and soil available Zn by onion. The performance of 1 kg Zn ha-1 as Zn-EDTA and 10 kg Zn ha-1 as ZnSO4 in improving the Zn uptake of onion was comparable. Hence, it can be concluded that application of either Zn-EDTA @ 1 kg Zn ha-1 or ZnSO4 @ 10 kg Zn ha-1 can be recommended for obtaining higher growth and Zn uptake of onion.