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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.