The impact of foliar application of boron nano-chelated fertilizer and boric acid on fruit yield, oil content, and quality attributes in olive (Olea europaea L.)

A wide range of Boron-containing compounds is available in the world market, with different formulations and efficiencies. Among these compounds, nano-chelated products are becoming popular, although there is only limited information on their efficiency. Thus, this study considers the effects of boron nano-chelated fertilizer and boric acid foliar sprays on fruit and oil yield in olive cv. 'Zard'. Their quality attributes were studied during the growing seasons of 2017 and 2018. Fertilizers were used at the concentration of 105 (B-1) and 158.8 (B-2) mg boric acid, 200 (nano-B-1) and 300 (nano-B-2) mg nano-chelated boron, corresponding to 180 mg (B-1 and nano-B-1) and 270 mg (B-2 and nano-B-2) pure boron per liter. Spraying with water was considered as the control (B-0). Fruit characteristics were affected mainly by nano treatments and fruit yield efficiency increased by the use of nano-B-2. In spite of the heavy fruit weight and yield, the nano-B-2 caused a lower amount of oil accumulation in fruits. A high oil percentage was achieved by the treatment of boron (B-2) which resulted in a low crop load. Traits such as oil yield, free fatty acids, antioxidant activity and total phenol content were improved by the application of nano-B-2 fertilizer. Fatty acid composition was affected by B-1 foliar application. Generally, the data obtained from this study showed that nano-B-2 could provide beneficial effects on the growth, fruit and oil yield rather than on oil percentage. The main fatty acid composition was influenced more by boric acid treatments.