EFFECT OF MECHANICAL HARVESTING ON YIELD AND QUALITY OF TEA IN TANZANIA

摘要

Hand plucking of tea is labour intensive, and with rising labour costs mechanical harvesting (MH) is of increasing interest. However, effects of MH on yield and quality of tea remain unclear. We harvested two tea clones for eight years with a small, wheeled machine, to investigate effects of different cutting heights on yield and quality. The harvest interval for machine plots was 40% longer than for hand plucking in the first three years and 100% longer thereafter. The yield response, relative to hand plucking, depended on cutting height. Provided that increase in bush height (table rise) was 6 cm per year or less, yields were 15–21% higher than with hand plucking and increased yield was still being maintained after eight years. The increase in yield appeared to be mainly attributable to the longer harvest interval for machine plots, so that larger shoots were harvested. There was no increase in the number of shoots harvested per year, despite more intensive plucking with the machine. In less intensively harvested plots, where table rise was 11–14 cm per year, yield was reduced compared to hand plucking, and shoot number was nearly 30% lower. Dry matter production was greatest under the least intensive harvesting, but greater intensity gave higher harvest index and yield. In plots with no table rise, but not in other plots, a large amount of die-back of plucked points was observed. This may indicate source limitation of shoot numbers. We conclude that, with an extended harvest interval and careful management of cutting height, the yield of tea can be maintained under MH. There was a reduction in green leaf quality, with coarser shoots and increased mature leaf, but a limited number of taster evaluations of quality of the black tea showed significant differences for only one clone.