Response of Total Polyphenol Content to Nitrogen, Phosphorus, and Potassium Nutrition of Bush Tea (Athrixia phylicoides)

Bush tea ( Athrixia phylicoides ) belongs to the Asteraceae family. It is a popular beverage, commonly used as an herbal tea and for medicinal purposes. In some parts of South Africa, people consume or drink it as an aphrodisiac. Bush tea was grown under varying nitrogen (N), phosphorus (P) and potassium (K) levels in the four seasons to determine the seasonal nutrient requirements for improved quality. Treatment consisted of 0, 100, 200, 300, 400, or 500 kg·ha –1 N, P, or K in a randomized complete-block design under 50% shade nets. Three N, P, and K parallel trials were conducted per season (autumn, winter, spring, and summer). Total polyphenols were extracted using Folin-Ciaocalteau reagents and analyzed in a spectrophotometer. Results for the N trial suggested that total polyphenols increased quadratically in response to N nutrition during summer, winter, and spring, but not in autumn. The optimum N level was 300 kg·ha –1 . The highest total polyphenol was 51.1 mg·g –1 in winter. For the P trial, total polyphenols also increased quadratically in response to P nutrition regardless of season. Again winter had the highest total polyphenols (46.8 mg·g –1 ). The optimum P level was 300 kg·ha –1 . In the K trial, regardless of season, total polyphenols plateaued at 200 kg·ha –1 and the highest polyphenols were in winter (43.3 mg·g –1 ). Therefore, for improved total polyphenol content, 300 kg·ha –1 N and P and 200 kg·ha –1 K are recommended regardless of season.