Effects of nitrogen, phosphorus and potassium nutrition on seasonal tannin content of bush tea (Athrixia phyliciodes DC.)

Abstract

Three trials were conducted over four seasons (summer, autumn, winter and spring) to determine the nutritional requirements of bush tea regarding nitrogen (N), phosphorus (P) and potassium (K) and the influence of these nutrients on tannin content of cultivated bush tea leaves. Treatments consisted of 0, 100, 200, 300, 400 and 500 kg ha⁻¹ N, P or K in a randomized complete block design with four replications. At the end of each season, tannin contents were extracted using 90% acetone. BuOH-HCl_Fe^III reagent was used to analyze condensed tannins while hydrolysable tannins were analysed using potassium iodate. Extracts were analysed with a spectrophotometer. Results demonstrated that condensed and hydrolysable tannins increased in a quadratic fashion in response to N nutrition, reaching a maximum at 300 kg ha⁻¹ N. Maximum condensed tannins (4.5%) occurred in autumn and winter and hydrolysable tannins (0.1%) in spring and summer. In the P trial, both hydrolysable and condensed tannins increased, reaching a maximum at 300 kg ha⁻¹ P, regardless of season. The highest concentrations of condensed tannin (5.0%) were obtained during summer, whereas the hydrolysable tannin contents were best during spring (0.018%) and summer (0.020%). In the K trial, both hydrolysable and condensed tannin contents peaked at 200 kg ha⁻¹ K, regardless of season, with maximum condensed tannins (5.0%) occurring in winter, and hydrolysable tannins (0.021%) in summer. Therefore, for improved condensed and hydrolysable tannins, 300 kg ha⁻¹ N or P and 200 kg ha⁻¹ K are recommended, regardless of season.