Effects of Genotype, Environment and Management on Yields and Quality of Black Tea

Abstract

The tea beverages processed from the young tender shoots of Camellia sinensis (L.) O. Kuntze, are claimed to be the most widely consumed fluids after water. The tea plant originates from the point of confluence of Northeast India, North Burma, Southwest China and Tibet. Its production has spread and economic production has been reported in between 49 ∘ N in Outer Carpathians to 33 ∘ S in Natal, South Africa, at altitudes ranging from sea level to 2,700 m above mean sea level. The adaptability of the plant to areas with large variations in geographical, climatic and environmental factors can cause changes in growth patterns in different genotypes leading to variations in yields and black tea quality. Tea producers usually import genotypes, management and production techniques suitable for optimal production in one region in the hope that beneficial attributes observed at source shall be maintained in the new areas. But the tea plant responses in new environments have not always yielded the desired results. Here we review the effects of genotypes, environment and management on the yields and quality of black tea. Previous investigations demonstrated that black tea yields and quality changes are due to environmental factors like soil type, altitude, seasons, weather factors, geographical areas of production, agronomic inputs, processing technologies and management. Black tea quality and yields of similar genotypes grown on different soils vary. The extent and patterns of the variations change with varieties. High altitude grown teas are more aromatic than low altitude grown black teas, implying that the low grown teas are plain in character. Thus producers at high altitudes should aim at producing aromatic black teas, although yields will be lower than same genotypes at lower altitudes. Producers growing teas at low altitudes should focus on high output and ensure optimal conditions for production of plain black teas. There are seasonal black tea quality and yield variations. Cold seasons lead to slow growth resulting in low yields, but high black tea quality. Provided soil moisture and temperatures are adequate, warm temperatures lead to fast growth, leading in turn to high yields, but low black tea quality. It is therefore not possible to have uniform production or to produce the same black tea quality throughout the year. The situation is adverse further away from the equator with no production in winter as the labour management can be critical during the long cold seasons, necessitating long labour layoffs. Many genotypes have been developed, some with very high yields and quality. As a result, producers continuously try to access the good varieties into new geographical areas in the hope the genotypes would retain their economic advantages. While some genotypes are stable to locational changes, most show wide variations due to planting in the new areas. Management policies induce yield and black tea quality differences. Imported management policies should be domesticated and modified to suit the new environments. Harvesting, by hand plucking, the young tender shoots is done when they are of the right size. Delayed harvesting leads to shoot overgrowth and crop loss. Whereas plucking two leaves and a bud is a compromise between yields and black tea quality, some growers practice coarser plucking standards. Black tea quality declines with coarse plucking standards. Short plucking rounds lead to high production and high quality black teas. When a plucking standard is preset, growers in a location need to establish the shortest harvesting interval for realization of good yields and quality. Fertilizers are essential for establishment and growth. Varying results have been recorded on yield and quality responses to NPK application. For potassium and phosphorus, evaluations are necessary in different regions because where there is no beneficial effects their application can be reduced to decrease costs. High rates of nitrogen reduce black tea quality and do not increase yields. Nitrogen fertilizers need to be applied at rates that are a compromise between yields and black tea quality. Such rates vary with regions and genotypes. To reach high production and quality, region- and genotype-specific fertilizer rates are needed. In regions producing relatively inferior black teas producers try to import processing technologies from other areas. These efforts may not improve quality due to variations of environmental conditions. Indeed, for the same genotype grown in different regions and processed under identical conditions, differences in quality and chemical composition have been reported. This was due to variations in the leaf biochemical constituents composition caused by the environment in which the plant was grown. Different regions must therefore optimize their processing conditions to realize high quality.