Staff publications - Cranfield University at Silsoe

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Browsing Staff publications - Cranfield University at Silsoe by Publisher "Cambridge University Press"

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    Evaluation of simple hand-held Mechanical systems for harvesting tea (Camellia Sinensis)
    (Cambridge University Press, 2006-04-01T00:00:00Z) Burgess, Paul J.; Carr, M. K. V.; Mizambwa, F. C. S.; Nixon, D. J.; Lugusi, J.; Kimambo, E. I.
    Over an eight-year period, harvesting methods based on simple mechanical aids (blade and shear) were evaluated against hand harvesting on mature morphologically contrasting tea clones in Southern Tanzania. The effects of shear step height (5-32 mm) and the harvest interval (1.8-4.2 phyllochrons) were also examined. Except in the year following pruning, large annual yields (5.7- 7.9 t dry tea ha[minus sign]1) were obtained by hand harvesting at intervals of two phyllochrons. For clones K35 (large shoots) and T207 (small shoots), the mean harvested shoot weights were equivalent to three unfurled leaves and a terminal bud. The proportions of broken shoots (40-48 %) and coarse material (4- 6 %) were both relatively high. Using a blade resulted in similar yields to hand harvesting from K35 but larger yields from T207 (+13 %). The yield increase from clone T207 was associated with the harvest of more shoots and heavier shoots, smaller increases in canopy height, and a higher proportion (7-9 %) of coarse material compared to hand harvesting. On bushes, which had been harvested by hand for two years following pruning, using flat shears (no step) supported on the tea canopy resulted, over a three year period, in yields 8-14 % less than those obtained by hand harvesting and, for clone K35, a reduction in the leaf area index to below 5. The development of a larger leaf area index is made possible by adding a step to the shear. However, since annual yields were reduced by 40-50 kg ha[minus sign]1 per mm increase in step height, the step should be the minimum necessary to maintain long-term bush productivity. As mean shoot weights following shear harvesting were about 13 % below those obtained by hand harvesting, there is scope, when using shears, to extend the harvest interval from 2 to 2.5 phyllochrons.
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    Responses of Young Tea (Camellia Sinensis) Clones to Drought and Temperature II: Dry Matter Production and Partitioning
    (Cambridge University Press, 1996-01-01T00:00:00Z) Burgess, Paul J.; Carr, M. K. V.
    The physiological basis for differences in yields from well-watered and droughted plants of four contrasting clones of tea were studied in terms of light interception, dry matter production and partitioning at a high altitude site in Southern Tanzania where there are marked seasonal variations in rainfall and temperature. The plant dry weights, including roots, were measured eight months after field planting and subsequently at intervals of three to four months, corresponding to the different seasons, during the following two years. Fully irrigated plants of one clone (S15/10) were also harvested after four years in the field. Clones differed in the rates of canopy spread and hence in their capacity to intercept solar radiation. The ‘radiation use efficiency’ (the net total dry matter production per unit of intercepted short-wave solar radiation) was similar for the four well-watered clones and ranged from 0.40 to 0.66 g MJ -1 , which corresponds closely to values reported for other woody tropical plants. A 16-week drought treatment imposed two years after planting reduced the mean light interception of the four clones by about 25% and the mean radiation use efficiency by 78% to 0.09 g MJ -1 . Clone S15/10, a cultivar from Kenya which produces large yields, partitioned a greater proportion of dry matter to leaves and harvested shoots than the other clones, and correspondingly less to large structural roots. This resulted in a maximum harvest index of 24%, substantially greater than other values reported in the literature. There were seasonal differences in partitioning with more dry matter being diverted to roots and less to shoots during the cool season. Although the drought treatments had no significant effect on root growth, the amount of dry matter partitioned to leaves, stems and harvested shoots declined by 80-95%. The roots of all four clones extended in depth at similar rates (about 2 mm d -1 ), those of Clone S15/10 reaching 2.8 m after four years. The results are discussed in terms of appropriate field cultural practices and possible selection criteria for high yielding clo
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    Responses of Young Tea (Camellia Sinensis) Clones to Drought and Temperature. I. Yield and Yield Distribution
    (Cambridge University Press, 1996-07-01T00:00:00Z) Burgess, Paul J.; Carr, M. K. V.
    The yield responses to drought and temperature of six contrasting tea clones were studied in a line-source irrigation experiment in Southern Tanzania. The selected clones, all commercially and/or scientifically important in eastern Africa, embrace a range of morphological and physiological types. The bushes were planted in August 1988 and differential drought treatments were imposed for 16 and 13 weeks towards the end of the dry seasons in 1990 and 1991 respectively. The resulting soil water deficits were successfully simulated using a water balance model. Under well-watered conditions Clone S15/10 (from Kenya) gave the highest yield of dry tea reaching 5600 kg ha-1 in the fourth year after planting (1991/92) compared to 3640-4420 kg ha-1 for the other five clones. During the cool season Clone SFS150 (from Malawi) yielded more than Clones 1, 207, 6/8 and K35. Although annual yields decreased curvi-linearly as the maximum soil water deficit increased, single values for the drought sensitivity of each clone could be derived by using stress time as an index of drought. On this basis Clones S15/10 and 207 were identified as being the most sensitive to drought; Clones SFS150 and 1 were drought resistant. The reasons for these differences in yield responses and the importance of determining drought sensitivity over an appropriate time period are discussed.