Effects of Foliar Spray Application of Selected Micronutrients on the Quality of Bush Tea

Abstract

Bush tea (Athrixia phylicoides DC.) is a herbal beverage and medicinal plant indigenous to South Africa. The aim of the study was to provide the baseline for foliar spray application of micronutrients to enhance the quality of bush tea. A trial was conducted to determine the effect of micronutrients on the quality of bush tea. Four separate trials for boron (B), iron (Fe), zinc (Zn), and copper (Cu) were laid out in a completely randomized block design. Treatments consisted of an unsprayed control and single foliar sprays of B, Fe, Zn, and Cu, with 10 replicates. The levels of each element were unsprayed control, 50 mL·L−1, 100 mL·L−1, and 150 mL·L−1. Parameters recorded were leaf tissue B, Fe, Zn, and Cu, and total polyphenol, total antioxidant, total flavonoids, and total tannin contents. Results from this study demonstrated that foliar application of B did not induce significant response in terms of total polyphenol content after B application. There was a quadratic response for total flavonoids (167 mg·g−1), with most of the total flavonoids reaching maximum at 100 mL·L−1. Foliar application of Fe exhibited a quadratic response, with most of the total polyphenols (45.1 mg·g−1) reaching maximum at 100 mL·L−1. All treatments showed a linear response for total antioxidant, total flavonoids, and total tannin contents. Treatments elicited a quadratic response for total polyphenols (70.6 mg·g−1), total antioxidants (78.3 mg·g−1), total flavonoids (148.9 mg·g−1), and total tannin contents (78.3 mg·g−1) after foliar Zn application, reaching maximum at 100 mL·L−1. Foliar application of essential elements in bush tea led to a significant increase in the Zn, Fe, Cu, and B content; application at 100 mL·L−1 is recommended for improved chemical composition of bush tea. A further trial with treatment combinations is required to determine chemical responses of bush tea.