RESUMO
The tea plant is widely cultivated in southwest Ethiopia. But the impact of seasonal variation on monthly yield, leaf quality, and the long-term yield response potential of clones has not been studied. The objective of the study is to determine the impact of seasonal change and climate variables on the yield and leaf quality of tea plants in southwest Ethiopia. The experiment consisted of five clones and four seasons under a split-plot design and was replicated three times. The results indicated that the yield and leaf quality showed significant variation in the different seasons at P < 0.05. The highest peak yields of 12.68, 12.59, and 11.3 kg plot-1 were recorded in May, June, and April, respectively, and the yield suddenly dropped by 5.1% in July. Then the soft banjhi increased by 5-10% in July. The yield response potential of clones is highly affected by monthly climate variation at P < 0.05. Clone BB-35 recorded the highest (18.8 kg plot-1) yield in June, followed by clones 11/4 (18.3) in May, 11/56 (14.7) in November, 6/8 (11.7) in December, and 12/38 (5.78 kg plot-1) in June. The lowest mean green leaf and a longer shoot replacement cycle were created due to a decrease in rainfall to 760 mm/month and rising temperatures above 26.35 °C in winter. The leaf phenological response of tea clones is strongly governed by the monthly temperature and suitable precipitation pattern of a season. The highlands have two harvesting seasons, i.e., a dry and a wet harvesting season. The dry harvesting season, which exists between the middle of December and March, accounts for 18.3-24.3% of the total annual yield. The wet harvesting season is subdivided further into two peak harvesting seasons. The first harvest is characterized by a short plucking round, and the highest peak yield occurs in April, May, and June, accounting for 40.22-42.2% of the total annual yield. The second wet harvesting season begins in September and ends in the middle of December, contributing to 35.5-40% of the annual yield. Seasonal variation has a direct impact on leaf quality and clone yielding potential. Clones show higher yield and shorter plucking rounds at maximum temperatures above 23.03 °C and below 26.35 °C, but temperatures above 28.34 °C and below 10.38 °C have a negative effect on leaf quality and yield. Over the last two decades, rainfall, maximum, and mean temperatures all increased by 16.09 mm y-1, 0.127 °C, and 0.0566 °C y-1, respectively, and the tea plant showed a strong correlation with maximum temperature (76%), whereas mean temperature (44.6%) and annual rainfall (32.8%) correlated weakly. Green leaf production is well explained by around 85.4% of the observed climate variance, with an increase of 1287.18 tonnes y-1, and highland tea production will exhibit a positive net benefit from expected climate change in the future.
RESUMO
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.