Effect of increased fertilization on the phytochemical constituents and antioxidant activity of Jatropha zeyheri tea under greenhouse conditions

Abstract

Tea fertilization is one of the key factors influencing tea’s physiological, physical and chemical qualities. However, the influence of NPK fertilizer on phytochemical constituents and antioxidant activity of Jatropha zeyheri indigenous tea has not been documented. Therefore, this study aimed at assessing whether different fertilizer application rates would affect the phytochemical constituents and antioxidant activity of J. zeyheri tea leaves under greenhouse conditions. Six treatments constituting NPK fertilizer rates (0, 2, 4, 8, 16 and 32 g) were arranged in a randomized complete block design, with five replications. After 130 days, leaves were harvested and oven-dried for 72 h at a temperature of 60°C. The dried leaves were ground through a 1 mm sieve using a grinder before analysis. After laboratory preparations, phytochemicals and antioxidant activity were analyzed using the UV-visible spectrophotometer. Data were subjected to ANOVA using the Statistix 10.0 software. Treatments had a highly significant effect (P ≤ 0.01) on antioxidant activity and total flavonoid content contributing 46 and 73% in total treatment variation (TTV), respectively. In contrast, NPK fertilizer had a significant effect (P ≤ 0.05) on total phenols and tannins, contributing 71 and 59% in TTV, respectively. Jatropha zeyheri tea leaves antioxidants and phytoconstituents exhibited positive quadratic relations with increasing fertilizer levels. Fertilizer requirements for phytoconstituents and antioxidant activity were optimized at 3.97 g fertilizer/plant. In conclusion, antioxidant activity, total phenol, total tannin and flavonoid contents were affected by increasing NPK fertilizer rates.