Influence of clone and nitrogen application level on quality of green tea in some selected tea (Camellia sinensis (L.)O. Kuntze) in Southwest Ethiopia

The biochemical constituents and organoleptic characteristics of Camellia sinensis (L.) O. Kuntze clones are not studied well in Ethiopia. The study aims to evaluate the polyphenols, caffeine, antioxidant content, and cup quality of clones at different nitrogen application rates and identify suitable clones and processes for daily consumable antioxidant-rich green tea. The experiment consisted of five clones (6/8, BB-35, 11/56, 11/4, and 12/38) and five nitrogen application rates (i.e., 0, 75, 150, 225, and 300 kg ha⁻¹) under a split-plot design and was replicated three times. The biochemical constituents and overall quality of green tea were examined using HPLC, chemical analysis, and a cup taster. The results indicate that the polyphenol content increased slightly (P < 0.018) as the nitrogen application rate increased, with a weak correlation (r = 0.387). The caffeine content varies from 1.82 to 3.06%. Clone BB-35 scored the highest (3.06%), and clone 6/8 scored the lowest caffeine content in all nitrogen treatments. The total nitrogen content varied between 2.27 and 4.01 mg g⁻¹ and slightly increased as the nitrogen application rate increased (r² = 0.798). The antioxidant activity showed a significant variation (P < 0.001) among clones, and the tested clones had a high antioxidant inhibition percent ranging from 51.9 to 66.5%. The cup quality, aroma, liquor color, and dry leaf appearances of green tea were positively correlated (r = 0.68, r = 0.70, r = 0.48, and r = 0.30), and the overall quality of green tea improved as the nitrogen application rate increased. Clones 6/8 and 11/4 recorded the highest overall quality above the total mean value, whereas clones BB-35, 12/38, and 11/56 scored below the total mean value (77.68%). Clone 6/8 produced an excellent full aroma, balanced bitterness, and a slightly sweeter cup in all nitrogen treatments than other clones. Moreover, this clone contains less caffeine and high polyphenol content in high nitrogen treatment. The second-best, clone 11/4, has a good marketable green liquor, aroma, and dry-made tea appearance, but it is slightly bitterer than clone 6/8. The research concluded that clone 6/8 can produce a more acceptable and high-quality green tea at 300 kg N ha⁻¹.