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In this study, we quantify the effect of plant age and environmental (rainfall, pH, and soil organic carbon) and management (NPK fertilizers and pruning) factors that influence tea (Camellia sinensis) yields. The motivation for the study is that, recently, tea yield has stagnated in Northeastern India. We applied a statistical analysis on the agronomical factors influencing yield at the estate level as well as the within estate section level, using the datasets collected at seven tea estates between 1998 and 2007. The rationale was to identify the genotype, environmental, and management variables that have a significant influence on tea yield at the two spatial scales. Mean tea yields range between 1500 and 2500 kg ha−1 Tea yield is correlated with rainfall (R2 = 0.665 at one estate, R2 = 0.249 on an average) and it has a weak but significant correlation with organic carbon (R2 = 0.1 on average) on estates where organic carbon contents <2%. Plant age had a negative (R2 = 0.28 on average) and N fertilizer application a positive effect (R2 = 0.30 on average) on tea yield. Combined analysis of the effect of age and fertilizer application gave higher regression coefficients than separate analysis (R2 values ranging between 0.146–0.637). A pruning analysis was inconclusive due to the recovery time needed for freshly pruned plants. At the section level, we could include spatial dependence using spatial autoregression at one estate with sufficient data. Spatial dependence was shown most clearly in a reduced linear mixed model that only includes N fertilizer as an independent variable. We conclude that at the estate level, major differences in tea yield occurred due to variation in management practices and uncontrolled environmental factors. Tea yield at the section level is mostly affected by age and N application.

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Tea (Camellia sinensis L.) leaf contains a large amount of catechins (a group of very active flavonoids) which contribute to major quality attributes of black tea. Based on morphological characters tea plants were classified as Assam, China, and Cambod varieties. The present study is an attempt for biochemical fingerprinting of the tea varieties based on catechin composition in green leaf of cultivars grown in Northeast India. Assam variety cultivars contained the highest level of catechins followed by Cambod and China. The average catechin contents were 231 ± 7 mg g−1, 202 ± 5 mg g−1, and 157 ± 4 mg g−1 of dry weight of green leaf for Assam, Cambod, and China cultivars, respectively. Among the individual catechins the variations in epigallocatechin gallate (EGCG) and epigallocatechin (EGC) were the most prominent among the varieties. High EGC content was found to be a characteristic of Assam variety which was further corroborated through multivariate analysis.

The formation of thearubigin pigments in prevalent commercial manufacturing systems such as orthodox roll, roll followed by curling, tearing, crushing (CTC), rotorvane combined with CTC and CTC alone was studied in the six Tocklai released clones TV-1, TV-2, TV-8, TV-9, TV-17 and TV-18. The contribution of the pigment composition, especially thearubigins of high, intermediate and low molecular weights as separated by a Sephadex LH 20 column, was examined on the basis of the types of leaves, degree of wither and roll, conditions of fermentation and the temperature and type of drying. It was apparent that the biochemical pathway in the black tea processing could be conveniently followed from the thearubigin formation. Further, the amount of high molecular weight thearubigin could determine the quantity of cream formed in a black tea brew. The thearubigin and concomitant pigments such as theaflavin have distinct organoleptic properties and their variation was reflected in the overall quality of the finished product.