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Tea bushes cultivated in Darjeeling mostly
belongs to the 'China jat' and 'China hybrid'.
It is a hardy, multi stemmed, slow growing evergreen
shrub which if allowed to, can grow upto 2.5
metres in height. It takes four to six years
to mature. The leaves are small, dark green,
elliptic-oblong or ovate-oblong, lamina sparsa
appressed and pubescent, midrib densely pubescent,
obtusely serrulate to double serrate, flat to
wavy margin. Under cultivation it is pruned
down and trained as low spreading bush to ensure
that a maximum crop of young shoots can be obtained
and maintained. The root system of a tea bush
can be divided into main roots, subsidiary roots
and feeder roots. The lateral roots give rise
to a surface mat of feeding roots which lack
root hairs when mature. Root system varies in
tea bushes depending on genetic make up and
soil environment. Starch is stored in roots.
Plucking season begins in March and closes by
November, the cold winter months of December
to February are a period of dormancy. Each hectare
yields an average of a mere 500 kgs. of dry
tea, less than a third of the yields of gardens
in plains. A Darjeeling tea bush yields only
100 grams of made tea in a year. Each kilogram
of fine tea consists of more than 20,000individually
hand plucked shoots.
AGRO-CLIMATE |
A 'good growing season' for tea as
one having warm days, long sunshine hours,
high humidity and adequate rainfall, preferably
in overnight showers.
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Air temperature |
Tea is grown under a regime of air
temperature that varies between 80 and 350C. In Darjeeling, the
extension growth stops at monthly mean
maximum and minimum temperatures of 19.40C
and 12.40C respectively in
November and it start flushing during
end of March when mean maximum and minimum
temperatures exceed 210C and
140C respectively. The extension
growth of the tea plant in general ceases
below a minimum temperature of 130C.
In Darjeeling, highest yield was achieved
in June when mean maximum and minimum
temperatures were 23.50C and
18.30C respectively. The rapid
decline in yield in Darjeeling during
October and then stops during November
until end of March indicates that low
temperature is one of the major climatic
variables, limiting yield. It has been
reported that the higher yield in Darjeeling
was achieved during the period from June
to September when the differences between
maximum and minimum temperatures were
least in comparison with the rest of the
year.
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The
relationship between monthly yield and
air temperature at Darjeeling |
Soil
temperature |
In
many instances soil temperature is of
greater importance to plant life than
air temperature and soil temperature influences
to growth and yields of tea. soil temperature
is an important variable, with a lower
limit of about 200C, at 0.3
m under short grass surface (or 160C
beneath a canopy tea), below which shoot
extension rates will be reduced. The corresponding
upper levels are 290C and 250C
respectively.
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Rainfal |
Tea is basically a rain-fed crop. It is
grown well in areas where annual rainfall
varies from 1150 to 6000 mm. Tea should
not normally be grown in areas where the
rainfall is below 1150 mm, unless irrigation
is available. The effect of precipitation
is perhaps more manifested by its influence
on moisture status of the soil and in
inducing vegetative growth. Therefore,
distribution of rainfall over the year
is as vital as the total annual rainfall.
Annual rainfall varies from 2274 (Kalimpong
sub-division) to 4082 mm (Kurseong sub-division)
in Darjeeling where in May, the southerly
winds reaches the hills and cause increased
precipitation which is at times very high.
There is some residual effect of monsoon
in November. But November and December
are almost rainless and the light showers
which fall in January and February occur
when shallow depressions are passing eastward
over the plains. In October, northerly
winds begins, cloud is much less than
in previous months and rainfall occurs,
mainly owing to cyclonic storms which
generally recurve towards north Bengal
at the end of the season.
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The
relationship between monthly yield of
processed tea and rainfall at Darjeeling
gardens |
Humidity
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It
has influence in determining the loss
of moisture by evapotranspiration. The
invisible water content of the air is
expressed as relative humidity (RH), saturation
vapour pressure deficit or dew point.
RH of 80 - 90 % is favourable during the
growth period of tea plants, below 50
%, shoot growth is inhibited and below
40 % growth is adversely affected. In
Darjeeling, even during the driest part
of the year in March and April, mean RH
never drops below 60 % in this region.
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Solar radiation |
It is the source of energy which sustains
organic life on the earth surface. Crop
production is in fact an exploitation
of solar radiation. The intensity and
duration of sunshine has also an important
influence on the growth of tea plant.
The hours of bright sunshine are fewer
in the rainy season of Darjeling hills
due to the overcast clouds.
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Day length |
There are remarkable variations in day
length between 9 and 15 h prevailing in
Darjeeling. In Darjeeling, highest yield
was recorded during June when average
day length was 13 h 49 m. In fact, 50
% annual crop is produced in Darjeeling
during June to August when day length
obtained in between 12-13.5 h is a factor
contributing to high productivity during
this period.
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Altitude
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The China variety in particular and
the hybrids in general produce very fine,
flavoury tea when they are grown above
an altitude of about 1100 m as in the
case of Darjeeling. China hybrid bushes
from Darjeeling fails to reproduce the
full hill muscatel flavour if grow in
the plains of Assam and Dooars. It may
thus be stated that the Darjeeling teas
owe their unique flavour partly to the
type of bush and partly to the climate.
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Hail
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It is unpredictable and of a localized
nature. Hail in Darjeeling is almost a
regular phenomenon every year during spring
and cause severe losses. Hailstroms occur
in one valley or other during March to
May, but end of March to early April is
the period when it occurs most. The severity
of damage ranges from shattering of leaves
to peeling of bark in trunks, young stems
breaks and bushes aredefoliated. It can
be particularly
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harmful when the bushes are recovering
from the effect of a severe drought
and are refoliating after pruning. In
Darjeeling hills, loss of higher priced
quality crop during first and second
flush due to hail damage is actually
the real damage in terms of income.
Despite destruction of current crop
it damage stems which lead to disease
and pest problems.
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PHYSIOLOGY |
Tea is an evergreen small tree by habit,
but is trained as a bush through the periodic
management practices like pruning and
plucking. It is a C3 plant.
Tea plant adapt well to different terrain
and climatic conditions. The crop needs
acid soil and humid tropical environment.
Tea bushes in commercial production are
planted closely and pruned to a low surface
for ease of plucking and to stimulate
fresh shoot growth to be harvested in
sequence as tender growing shoots form
the economic yield. Management practices
like pruning, tipping, plucking, shade
management are interrelated and leniency
of one compensates for severity of others.
Field management practices of this crop
are based on some important physiological
capabilities of the plant. Understanding
the physiology and biochemistry of the
tea plant holds the key for sustained
productivity, quality of product and cost
effective management.
Crop distribution
and components of yield
Tea is cultivated in 31 countries,
scattered from 450 N to 330 S of the equator. These latitudinal variations
are reflected on the physiological behaviour
of tea plant. One such gross change is
the crop distribution. Peaks and troughs
of crop productions are more sharply defined
as we go away from the equator towards
North or South. In Darjeeling, the crop
peak is reached during June-August. Annual
yield distribution, and hence potential
yield, is largely influenced by seasonal
fluctuations in weather variables. The
potential production and distribution
of yields throughout the year depend on
four factors: (1) the number of buds per
unit area that are contributing to the
dynamics of the shoot population, (2)
the fraction of these that are actively
growing (that is, not dormant), (3) the
rates of development and extension of
these actively growing shoots, and (4)
the mean weight of the harvested shoots.
The crop distribution in a year depends
also on the pruning time which, in turn,
is decided by the prevailing seasonal
conditions.
Shoot Growth and
regeneration
Like many tropical crops, tea exhibits
periods of intensive leaf growth alternating
with periods of dormancy. The amount of
growth made between two states of dormancy
is known as flush. In Darjeeling, the
number of such flushes in a year is four.
A vegetative shoot that is allowed to
grow uninterruptedly unfolds leaves in
a normal manner until leaf production
ceases with the appearance of banjhi bud.
A fully developed bud has the initials
of the full flush within it. The bud swells
and after a variable period of time it
breaks. First the outermost appendage
breaks free and produces a cataphyll (janam).
This is followed by the unfolding of a
second janam. After unfolding of the second
janam the tip of a new leaf becomes visible.
A persistent leaf with unserrated margin
known as fish leaf or gol-pat often exists
between the janam at the base of the shoot
and the first normal leaf. The gol-pat
is the same new leaf that is visible at
the time of unfolding of second janam
but was displaced from the original place
due to elongation of shoot. Thereafter,
the bud continues to grow and unfold to
produce the normal leaves with the latter
eventually becoming mature leaves with
elongated internodes. When a tea bush
is pruned, primaries develop from the
dormant buds on the stubs. When they reach
a certain predetermined height, they are
tipped to make a pluckable table. This
operation extends over a few weeks and
depending on tipping height, some primaries
become dormant below the tipping level.
Of these, some remain permanently dormant
while others throw out new flush of growth
above the tipping level and they are plucked.
After a primary shoot has been tipped,
new shoots originating from the axillary
buds of maintenance leaves (first order
of laterals) and these shoots are plucked
when grow above the tipping level. Plucking
of the laterals again stimulates production
of new generation of shoots of the next
higher order and the process continues
till the end of plucking season. Normally,
seven to eight orders of laterals are
produced in a year. The maximum quantum
of yield is possible to harvest only up
to the fourth order of laterals, and the
fifth laterals onwards do not contribute
much towards yield. The dynamics of leaf
production in tea is dependent on the
production rate of bud. However, some
factors viz. vigour, water availability,
intensity of light, temperature, pathogens
and herbivores influence production of
buds and unfurling of the leaves. The
period needed for unfurling may also vary
according to the characteristics of the
cultivars and site qualities.
Rhythmic
growth in unpruned tea
Unpruned tea is having a rhythmic pattern
of shoot growth. Most of the tea growing
regions in the world experienced periods
of drought or cool winters which inhibit
shoot growth. These climatic restrains
synchronize the flushing cycle. Although
changes in the environment might synchronize
the cycles between bushes, but despite
wide fluctuation of temperature, the period
of the cycle remains constant throughout
the year. In free growing tea, the leaf
primordia for an ensuing cycle of flush
are laid with the bud in the apparent
dormant period and scale leaf primordia
are initiated during flushing period,
with the rate of primordia formation being
consistent in both dormant and active
periods, while the rate of shoot elongation
and expansion is sigmoidal in nature.
Further, in any one cycle different numbers
of leaves expand on different shoots.
The rhythmic cycle is independent of the
plastochron and is related to the rate
of shoot extension. In unpruned tea, the
shoots at the top of the bush start flushing
a little early than the shoots of the
side branches and the flushing shoots
lower down the bush goes dormant much
early than the apical shoots. Despite
the differences in shoot activity, the
rhythmic growth patter however is maintained
over the tea bush as a whole.
Role
of maintenance foliage
All mature leaves, including fish leaves,
left on bush below the plucking surface
are the maintenance foliage. Productivity
and health of the tea bushes are governed
by the interaction between the 'source'
and 'sink' which have diametrically opposite
functions. The canopy of maintenance foliage
is the 'source' of carbohydrates, while
the proliferating and expanding organs
of the plant are the 'sinks' or the sites
of their utilization. The products of
photosynthesis move from the 'source'
to 'sinks'. Young growing shoots at the
plucking table are reported to be the
strongest 'sinks' and their presence results
in an upward movement of photosynthates.
The young shoots on a tea bush develop
at the expense of photosynthates produced
by the maintenance foliage. Growth and
development of shoots is largely dependent
on the size and efficiency of the maintenance
leaf canopy. Therefore, retention of an
optimal amount of photosynthetically active
healthy mature leaves on the bush is of
paramount importance in promoting the
growth of crop shoots. The depth of maintenance
foliage in a tea bush is regulated by
the tipping height. It has been established
that the maintenance layer should not
be less than 20 cm to 25 cm in depth.
Maintenance leaves reach peak efficiency
within a month of their unfolding and
remain photosynthetically active up to
six months and its capacity for photosynthesis
gradually declines after about six months
. The life of the maintenance foliage
on a tipped and plucked shoot does not
exceed eighteen months. Leaves in the
maintenance layer will age and becomes
less efficient. Therefore, it is necessary
to add new leaves to this layer periodically
in replacement of the very old and dropped
leaves.
Winter
dormancy
Tea cultivated near the equator
produces almost the same yield every month,
but further from the equator winter harvest
gradually declines and at latitude beyond
about 160, there is almost
complete winter dormancy. It has been
observed that tea bushes go dormant when
the average day length remains approximately
below 11 h 15 min for a period of about
six weeks and this happens beyond 160 N or S latitudes. It has been postulated
that low temperatures have a definite
role in bud dormancy.
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SOIL |
The tea soils of Darjeeling belongs
to the Daling series which rests under
a variety of foliated and banded metamorphic
rocks, partly sedimentary and partly
igneous in origin. These rocks are generally
known as Darjeeling gneiss and composed
of mica-schists and gneisses. Some of
the gneisses have been formed by injections
of granite fluid along the micaceous
layers of the schists. Where soaking
has been through, the gneisses approach
granites in composition and are made
of biotite muscovite, quartz and foldspars.
The sedimentary varieties of the Darjeeling
gneiss contain such minerals as garnet,
sillimanite. The presence of kainite
and staurolite indicates that the rocks
were subjected to higher temperature
and pressure than the Daling rocks.
The Darjeeling gneiss also carries sub-ordinate
bands of quartzite.Managing
tea soil health
Good
soil health is the precondition for
good plant health. The maintenance of
good soil structure and fertility through
proper husbandry practices are vital
management considerations for tea soils.
Creating a favourable condition for
soil life and plant growth, nutrient
application and soil conservation are
important aspects of soil fertility
management. Soil fertility arises from
complex interactions between the biological,
chemical and physical properties of
soil. Unplanned land use, bad soil structure,
inadequate drainage, soil compaction
etc reflects decline of productive potential
of the tea soils. These adverse conditions
can be checked by adopting proper soil
management practices. These are: water
conservation, drainage, uprooting, soil
rehabilitation, mulching and herbicide
weeding.
Nutrition
Given the impact of soil on the growth
and yield of tea plants, various long
term fertilizer trials have been launched
in this centre since its inception.
Effects of the various major and micronutrients
on plant nutrition have been under study
vis--vis uptake of major nutrients,
yield and quality. Results obtained
so far indicate that there is a positive
response to yield up to 120 kg ha¹
of nitrogen application in the form
of urea. Net uptake of NPK nutrients
has bee studied with various doses of
phosphate (in the form of rock phosphate
only) with the doses of N and K kept
constant at 120 kg ha¹. Nutrient
content in third leaf and the flush
has been analysed over a period of two
years. Nitrogen uptake ranged between
2.40% to 5.42% in the flush and 2.80
to 4.50% in the third leaf. Similarly,
phosphate ranged between 0.091% to 0.305%
and 0.11% to 0.780% in the flush and
third leaf respectively. But the potash
content has been found to be more in
the third leaves than the flush, the
values of which ranged between 0.81
to 1.98% and 1.29 to 3.32% in the flush
and third leaf respectively. There is
a general trend to increasing yield
with increasing uptake of nitrogen.
The same has not been found to true
for phosphate and potash uptake value.
Micronutrients like zinc, magnesium,
boron etc has also been found to have
profound influence on the nutritional
requirements of tea plants. Field trials
with various pure salts of zinc, magnesium,
boron and molybdenum are being investigated
in this centre which indicates their
essentiality in increasing the yield
of tea. A 2% mixture of zinc and magnesium
along with 1% of boron has been found
to have considerable influence in boosting
the yield of tea. However, the effect
of molybdenum alone or in combination
with other micronutrients has not been
found to increase the yield as that
of a mixture of zinc, magnesium and
boron.
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Service functions
The soil division offers various facilities to the tea estates and small tea growers. Among these services, the most important
is soil testing and fertilizer recommendation. Soils are tested for various parameters viz. pH, organic carbon, available nitrogen, phosphate, potash, sulphur, calcium, magnesium, zinc, boron, aluminium etc. C.F.C, mechanical
analysis and other specific parameters are also tested on exceptional cases. Remedial measures are offered on the basis of test results. The green leaf and, or made tea are also analysed for identifying mineral deficiencies. Water samples are also analysed on specific requests. Beside the above, the analysis of organic manures, fertilizers, de-oiled cakes, and weeds (for nutrient content only) is also done. The details are presented below.
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Sl.No |
Service |
Charge
in Rupees |
| 1. |
i)
Soil sample for pH, organic carbon,
available N, P and K
ii) Soil eelworm count, mechanical
analysis, C.E.C., available sulphur
(on specific request) |
100=00
per sample (a maximum of any 6 (six)
parameters mentioned in (i) & (ii) |
| 2. |
Soil
micronutrient like mobile calcium,
magnesium, copper, zinc, boron, molybdenum,
manganese, iron, aluminium, silicon
etc. |
100=00
per sample per micronutrient |
| 3. |
Organic
manures and fertilizers for pH, moisture
percent and N, P, K. |
400=00
per sample |
| 4. |
Organic
manure and fertilizer for zinc, magnesium,
calcium, sulphur etc. |
400=00
per sample |
| 5. |
Green
leaf (tea) for N, P, K |
100=00
per sample |
| 6. |
Green
leaf (tea) for any other nutrient |
100=00
per sample |
| 7. |
Water
analysis (about 8 parameters) |
100=00
per sample |
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