| The
south Indian tea soil is classified as latosols.
It extends along the western ghats, which run
in north to south direction parallel and close
to the west coast of the peninsula. The six major
tea districts vary in elevation from 300 to 2500
m above MSL and the minfall varies from 900 to
7500 mm per annum. In geological origin, the soils
are mainly derived from gneissic rocks. The soils
have undergone considerable weathering as shown
by their acidity and low calcium content. They
are abundant in sesquioxides. The soils of High
Ranges, Anamallais, central and south Travancore
are light in texture, coarse and fine sand fractions
comprising 62 to 67 per cent of soil. The soils
of Wynaad and Nilgiris are of clay loam type with
the clay fraction prepondering. The disadvantage
of higher clay content at Nilgiris is offset to
certain extent by the presence of higher amount
of organic matter in the soil. Chemically, all
the soils are poor and the organic matter helps
in building structure and microbial activity.
About 50 per cent of the total cation exchange
capacity of soils is contributed by organic matter
fraction. On an average about 40-60 kg N/ha will
be released from organic matter.
Kaolinite is the dominant clay mineral, which
has a very weak bonding for potassium and low
cation exchange capacity. Therefore, the leaching
loss of potassium is considerable and it increases
with decrease in pH of soils. Because of the
base deficiency created by low CEC of soils
in comparison to root CEC of tea plant, absence
of fixation and decreased binding energies due
to acidity, tea roots are placed in an unfavourable
environment as far as cationic nutrition (ammonium
and potassium in particular) is concerned. Hence,
there is a need for regular and frequent application
of nitrogen and potassium to evenout the above
effects. Thus splitting the application can
increase the agronomic efficiency of nitrogen
and potassium. As the tea soils have no fixation
sites for potassium and the clay fraction is
of non-expanding type, there is good percolation
of water. The broadcasted fertiliser is therefore
leached down to the root zone with ease. There
is also a risk of leaching down of nitrogen
and potassium below the root zone if the nitrogen
and potassic fertilisers are placed in the subsoil.
Hence nitrogenous and potassic fertilisers are
recommended to be applied by broadcast method.
Tea soils of south India contain large amount
of free sequioxides, which results in strong
P fixation.
South Indian tea soils contain low calcium content,
which is preferable for tea growth. In soils
with pH above 6.0, accumulation of calcium interferes
with uptake of potassium. In soils with pH below
4.0, the H+ and Al3+ ions are likely to interfere
with potassium uptake. Nitrogen efficiency is
the maximum in soils between pH 4.5 and 5.0
and hence liming once or twice in a pruning
cycle is recommended to maintain the soil pH
around 4.8. As kaolinite and sesquioxide colloids
present in tea soils are of non-expanding type,
the retentivity of moisture of the colloids
are comparatively lower. But the availability
of water to the plants will be longer in heavy
soils of Wynaad, Nilgiri- Wynaad, Nilgiris and
Karnataka in comparison to lighter soils of
other districts. The cation exchange capacity
on an average varies between 4 and 10 meq% for
Anamallais, Central Travancore and High Range
and 8 and 15 meq% for Wynaad, Nilgiri-Wynaad
and Nilgiris. Based on the texture, the infiltration
rate is slow (5-12.5 mm/hr) for Wynaad, Nilgiri-Wynaad
and Nilgiris and moderate (15-25 mm/hr) for
Anamallais, Central Travancore and High Range.
The major problem of tea soils of south India
is severe soil erosion due to intense rain and
steep slopes. Contour cultivation and bench
terracing are found effective techniques against
soil erosion.
| SOIL
PROFlLE AND LANDSCAPE OF TEA GARDENS OF
SOUTH INDIA |
|
