The effect of combined application of nitrogen, zinc and manganese on yield and fruit qualitative characteristics of grape

Foliar application is one of the fast and effective methods for providing of plants with nutrition requirements, especially in the critical stages of growth. The aim of this study was to investigate the effect of foliar application of nitrogen, zinc and manganese on leaf element content, yield and quality indices of Bidaneh-Sefid grapevines during one stage before and two stages after bloom. The experiment was factorially (three factors of urea, zinc nano-chelate, and manganese nano-chelate, each at two levels of Zero and 0.08%) based on a randomized complete block design with eight treatments and three replications. According to the results, the highest cluster weight and yield were related to the combined treatment of the second level (0.08%) of urea, zinc nano-chelate, and manganese nano-chelate. Also, the content of soluble solids of the vines treated with the 0.08% urea and 0.08% zinc nano-chelate was higher than in other treatments. The antioxidant capacity of vines treated with all three fertilizers at 0.08% was found to be higher compared to other treatments. The highest flavonoid contents were obtained with 0.08% urea and 0.08% zinc nano-chelate and the highest total phenol contents were related to 0.8% urea in combined with 0.08% manganese nano-chelate. Vines treated with the second level of zinc and manganese fertilizers had higher peroxidase activity. While the highest activity of catalase and ascorbate peroxidase was observed with all three fertilizers at 0.08% foliar application of urea, zinc nano-chelate, and manganese nano-chelate increased the content of nitrogen, zinc and manganese in leaves and fruits. The leaf potassium content of 0.08% manganese nano-chelate sprayed vines was higher alone compared to other treatments. In general, the combined application of these fertilizers (at 0.08%) while improving the leaf elements contents, led to improved berry weight, cluster weight, and yield and also increased quality indicators and enzymatic and non-enzymatic antioxidant capacity of the fruits..