Flowering and fruit yield of ‘Aromas’ strawberry as affected by zinc and boron in hydroponic cultivation

As the world's population grows, demand for fruits is increasing day by day. Fruits are an important part of the human diet and their consumption guarantees human health and strawberries are of particular importance. Strawberries are high in fiber, vitamin C, potassium and antioxidants. Due to the high nutritional value of strawberry fruits and the expansion of hydroponic cultivation in the world, and in our country, it is important to pay attention to the plant nutrition. Optimal nutrition of the plant is one of the main strategies to achieve economic productivity. Since nutrient balance is essential for commercial fruit production, improving yield and fruit quality, so foliar application at key stages can have a positive effect on the quantitative and qualitative traits of perennial crops. Among essential minerals that are involved in plant physiology, micronutrients of zinc (Zn) and boron (B), because of their relation with synthetic hormones are particularly important. So according to the importance of micronutrients on horticultural yield improving and environmental protection, this investigation was conducted to evaluate the effect of foliar application of zinc and boron and combination of them on growth and yield of strawberry cultivar ʻAromas’ in hydroponic system.

A 3×3 factorial experiment, arranged in a randomized complete block design (RCBD) with nine replications, was conducted at the research greenhouse of Sari Agricultural Sciences and Natural Resources University in 2016 and 2017. Treatments were zinc sulfate (0, 100 and 200 mg l-1) and boric acid (0, 500 and 1000 mg l-1). Foliar application of the treatments was carried out in three stages. The first stage was carried out a week before the flowering and in the next steps, the treatments were sprayed on plants at intervals of two weeks. In this research, the effect of zinc and boron on the yield, root length, root diameter, chlorophyll index, crown diameter, total chlorophyll, chlorophyll a/b, specific leaf area, specific leaf weight, petiole diameter, leaf width, leaf length, leaf area, flowering time, flowering period, peduncle length, flower diameter, flower number, fruitification time, fruitification period, fruit number, percentage of fruit set, percentage of marketable fruits, percentage of non-marketable fruits, fruit length to diameter ratio (L/D), fruit dry weight, fruit volume and percentage of fruit dry matter were investigated.

Results showed that the application of 200 mg l-1 zinc sulfate plus 500 mg l-1 boric acid significantly increased the crown diameter. Application of zinc and boron sources significantly increased the chlorophyll concentration and index of ‘Aromas’ strawberry compared to the control treatment. The highest increases in specific leaf area (141.52 cm2g-1) were monitored in response to 100 mg l-1 zinc sulfate + 500 mg l-1 boric acid treatment. The application of zinc sulfate and boric acid significantly increased the number of flower, flowering period and number of fruit. However, by increasing the concentration of boric acid (from 500 to 1000 mg l-1) significantly reduced the number of fruit. Generally, application of 200 mg l-1 zinc sulfate plus 500 mg l-1 boric acid to achieve increased fruitification period (91.32 day) and yield (210.4 g) of ‘Aromas’ strawberry fruit is suggested.

In general, it can be concluded that foliar application of zinc and boron and combination of both them in most of the measured reproductive and vegetative factors, improved the parameters studied.Therefore, in order to achieve high yield and improve the growth traits of strawberry cultivar ʻAromas’ in hydroponic system, the results of this research can be applied.