The effect of early season nutrition of calcium and zinc on yield, sugar content and enzymatic and non-enzymatic antioxidant capacity of grape

Foliar spray of nutritional elements is one of the methods for increasing the yield and quality of horticultural products. For this purpose, at the end of winter of 2016, a factorial experiment was conducted under a randomized complete block design at a 15 years old commercial vineyard of ' Bidaneh Sefid' grape cultivar. Plants were sprayed with calcium sulfate (0, 1 and 2%) and Zinc sulfate (0, 0.5 and 1%) during two stages in late March. Cluster weight and yield of vines treated with 1% Ca + 1% Zn was the highest and showed 26.11% increase compared to the control vines. TSS content was highest in 1% Zn treatment in solely. The pH, TA and anthocyanin content reached to peak in response to medium levels of both fertilizers. The phenol content in vines treated with 2% Ca + 0.5% Zn increased up to 31% compared to the control plants. Moreover, the highest flavonoid content was found in vine treated with three levels of both fertilizers. The highest resveratrol was recorded for vines treated with 1% Ca + 1% Zn. In the case of viniferin, the highest amount was found in fruit of vines treated with 1% Zn in solely. The lowest amount of viniferin was related to control vines. The highest content of sucrose was seen in vines treated with 1% Ca in combination with 1% Zn. The content of glucose in vines treated with 2% Ca + 1% Zn was higher than other treatments. On the other hand, the highest content of fructose was related to fruit of vines treated with 1% Zn in solely. The highest levels of activity of catalase and guaiacol peroxidase enzymes were associated with 1% Ca- treated vines in combination with 1% Zn. Also, the most activity of ascorbate peroxidase was observed in the vines treated with the third level of Zn in solely. Antioxidant capacity in 1% Zn- treated vines was higher than other treatments. Totally, combined application of moderate levels of CaSO4 and ZnSO4 at early season through nutritional status improvement resulted in yield increasing and qualitative and antioxidant indices of grape.