Effect of thermal time on shoot growth and development of low grown Tea [Camellia sinensis (L.) O. Kuntze] in Sri Lanka
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Date
2015
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Journal ISSN
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Publisher
Uva Wellassa University of Sri Lanka
Abstract
Tea [Camellia sinensis (L.) O. Kuntze] is an important beverage crop in Sri Lanka and it is a sector
where the country can take a lot of pride. The young, light green leaves, usually, the bud and the first
two to three leaves are harvested for tea production. Study the shoot growth pattern of tea is an
important element in tea physiology. It is difficult to predict leaf expansion and growth, based on
calendar days, because leaf initiation and expansion are highly temperature dependent (Ritchie and
Ne Smith, 1991). Because of the dependency on temperature, rate of shoot growth varies with
elevation. Therefore, growing degree days based on actual temperature is a simple and accurate
method to predict the occurrence of a certain developmental stage. Thus, thermal time can be used to
predict the developmental stage of a leaf, extension of a tea shoot and Leaf Area (LA) expansion of
shoot accurately.
This study was aimed to assess the variation in number of shoots at different developmental stages
in the bush with thermal time, estimate shoot extension of a developing and harvestable tea shoot as
a function of thermal time, estimate the Leaf Area (LA) of a developing and harvestable tea shoot as
a function of thermal time and estimate the number of days taken to reach different leaf
developmental stages of cultivar TRI 2025. This will provide an opportunity to estimate the shoot
extension and Leaf Area (LA) expansion of harvestable tea shoot and it will help to adjust field
management practices and to determine correct harvesting policies.
Materials and Methods
The field experiments were carried out at Field No 01, St. Joachim Estate, Tea Research Institute,
Ratnapura, Sri Lanka (latitude : 6 40’ N; longitude : 80 25’ E ) during mid of May to July 2014.
Elevation of the study location is 29 m amsl and belongs to Agro ecological region of WL2. The soil
group of the site belongs to Red Yellow Podzolic (Panabokke, 1996). The total rainfall was about
711 mm with a mean temperature of 28.5 C during the experimental period. TRI 2025 was used as
the planting material. Daily sunshine hours, rainfall, minimum maximum temperature was obtained
from the meteorological station at St. Joachim Estate, Ratnapura. In addition, soil moisture was
measured during the experimental period at weekly. Data analysis was done using MS-Excel and
Minitab 16 software.
In the first experiment, field observations were made for TRI 2025 using 1m sample size of plucking
table with ten bushes at homogeneous location. The numbers of shoots at different shoot
developmental stages in the bush (i.e. buds, bud with fish leaf, bud with one normal leaf, bud with
two normal leaves, bud with three normal leaves and banjies) were counted at seven days interval.
The accumulation of Thermal Time (TT) over the growing period was calculated using equations
developed by Robertson et al., 2002. It was considered that Tbase of 12.5 C (Carr and Stephens,
1992), TOpt 22 C (Amarathunga et al., 1999) and Tce 40 C (Carr, 1972) for TRI 2025.
In the second experiment, with the appearance of each leaf, length of the shoot was measured at seven
day intervals from randomly selected five axillary buds per bush that tagged immediately after
plucking. The length of the new shoot was measured from the base of the shoot to the base of the
bud. All measurements were taken until individual shoots reached their acceptable harvesting stage
(bud with three normal leaves). Weather records obtained at experiment 01 were used in experiment
02.
In third experiment, Length (L) and width (W) of the individual leaves in a tea shoot (i.e. fish leaf,
first, second, third normal leaf and bud) were measured at seven day intervals. Leaf length (L) was
measured from lamina tip to the point of intersection of the lamina along the mid-rib, while leaf width
(W) was measured from end to end between the widest lobes of the lamina perpendicular to the
lamina mid-rib. The equation for TRI 2025 developed by (Jayasinghe et al., 2013) was used in
estimating the Leaf Area (LA) at each day. In addition to that, record the number of days it was taken
to unfolding of each appendage from the date of tagging and time it was taken to reach a acceptable
harvesting stage having bud with a three leaf stage.
Description
Keywords
Agriculture, Export Agriculture, Crop Production, Tea Industrials, Tea Technology