Yield decline in mechanically harvested clonal tea (Camellia sinensis (L) O. Kuntze) as influenced by changes in source/sink and radiation interception dynamics in the canopy

Abstract

High labour costs and shortages and the cost of production has resulted in tea (Camellia sinensis (L)O. Kuntze) industries in central and southern Africa becoming unprofitable. This has led to the fullmechanization of shoot harvesting, however, a reduction in yield has been observed with mechani-cal harvesting. It was hypothesized that the decline in yield as a result of mechanical harvesting is aresult of the indiscriminate harvesting of shoots which leads to a change in sink/source and radiationinterception dynamics within the canopy. As a result whole plant photosynthesis is impacted; whichultimately impacts tea bush productivity. Studies conducted at Tingamira estate, Chipinge, Zimbabweshowed significant yield differences between hand plucking and machine harvesting treatments, withhigher yields under hand plucking across all seasons (43 945 kg green leaf ha−1) as compared to hand-held(35 114 kg green leaf ha−1) and ride-on machines (36 268 kg green leaf ha−1) (p < 0.05). This reduction inyield was associated with a decrease in both the number and mass of desirable shoots over each season.The cause of this change was largely attributed to the indiscriminate removal of foliage by the machineswhich resulted in the proliferation of immature shoots, with an associated increase in sink strengthand competition for available photo-assimilates. In addition, the depletion of the maintenance layer inmechanically harvested bushes, as indicated by reduced fractional interception of photosyntheticallyactive radiation in the top 10 cm in these bushes and reduced photosynthetic rates in these bushes, sug-gests that these bushes were also source limited, as compared to hand plucked bushes. Therefore thechanges in tea bush architecture, as a result of mechanical harvesting, resulted in changes in sink/sourcedynamics which led to a proliferation of immature shoots which competed for limited photo-assimilates.