The present study was conducted in 2014 vegetation season in a vineyard of Giresun Hazelnut Research Institute. Isabella (Vitis labrusca L.) grape cultivar were treated with four different boric acid (H3BO3) doses (control, 0.1%, 0.2%, 0.3%) at two different periods (a week before and after full-bloom). The effects of foliar boron treatments on yield, quality and leaf nutrients were investigated. Boric acid treatments positively influenced cluster weight, width and volumes and increasing values were observed with increasing boron doses. Boric acid treatments also influenced berry homogeneity and yielded more homogeneous appearance. Chlorophyll contents increased with increasing boron treatments. The greatest yield, cluster length, cluster volume, cluster size, cluster width, berry width and leaf area were obtained from 0.3% boric acid treatments. In general, leaf nitrogen, phosphorus, calcium, magnesium, zinc and copper concentrations increased, but potassium and iron concentrations decreased with increasing boron doses. As compared to control treatment, all treatments had broader leaf sizes and higher chlorophyll contents. Especially 0.3% boric acid treatments had quite positive influences on quality, size and color homogeneity. Considering the nutrients and pH level of experimental soils, it was concluded that foliar nutrient treatments may support plant growth and development and 0.3% boric acid treatments were recommended for high quality and quantity yields in Isabella grape cultivar.

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