PhD

An investigation was carried out at the College
of Horticulture, Vellanikkara during 1992 to
1995 to evaluate the morphological, physical
and chemical characteristics of soils of North
Kuttanad and to assess the extent of toxic
factors that pertained in the soil due to
restricted movement of water under the influ-
ence of Thanneermukkom regulator. The study
was carried out in three parts, viz., (1) Morpho-
logy and physicochemical characteristics, (2)
Fertility characteristics and (3) Toxicity chara-
cteristics. Fifteen soil profile were drawn from
North Kuttanad to study the morphology and
physicochemical characteristics of the area. The
fertility characteristics were studied by
collecting 97 surface soil samples (0-15 cm
depth) from 27 padasekharams of the area
during rainy and summer seasons (before and
after the closure of Thanneermukkom regula-
tor). Toxicity characteristics of the area were
studied by collecting bulk soil samples (0-25
cm depth), surface water and ground water from
the above sites during the same period.
Morphological and physicochemical properties
of the soils showed great degree of variation.
Soils were dark brown to black in colour, sticky
and plastic, subangular blocky in structure and
sandy to clayey in texture, with random
deposits of lime shells and humus. Presence of
faint to prominent reddish yellow or brown
mottles, rice roots and root canals were some of
the special characteristics observed in the soil
profiles.
Soils of the area were highly acidic and mildly
saline. Both soil acidity and salinity increased
with depth. Organic carbon, CEC and ECEC of
the area were higher compared to other parts of
Kerala, but the base saturation was
comparatively lower. The area was rich in
almost all the essential nutrients except P. Fe,
Al and S were present in toxic concentrations.


Potential acidity of the area was very high and
more than 70 per cent of it was contributed by
hydrolytic acidity and the rest by exchangeable
acidity. All the acidity characteristics increased
with depth. The profile IX was grouped under
order Inceptisol and all others under order
Entisol.
On evaluating the fertility characteristics of the
area it was observed that the area experienced
an increase in soil acidity and availability of N,
P, Fe and Zn and a decrease in salinity, CEC,
ECEC and available K, Ca, Mg, \.10 and Cu.
However, the availability of all nutrients except
P was above the deficiency level. Fe was
present in toxic quantities. On a general
comparison with that of pre-barrage period, the
area experienced a reduction in salinity and an
enhancement in soil acidity and availability of
K, Ca and Mg. The Na content was reduced
considerably in response to the reduction in
salinity. The exchangeable and water soluble
cations followed the same trend as that of
available cations. Among the exchangeable
cations Ca was the dominant basic cation
instead of Na which occupied the same place
during pre-barrage period.
Acidity characteristics of surface samples
behaved similar to that of profile samples. Pot-
ential acidity and hydrolytic acidity recorded
higher values during rainy season while
exchangeable acidity was greater during
summer. Among the components of exchange-
able acidity exchangeable Al3+ dominated
during rainy season, and exchangeable H+ dur-
ing summer. The overall influence was greater
for exchangeable A13+ as evidenced from the
higher correlation coefficient (0.862**).
The general soil properties and acidity
characteristics of the bulk soil samples were
similar to that of surface samples, showing a

reduction in pH, EC, CEC and available,
exchangeable and water soluble cations during
summer compared to the rainy season.
Among the different fractions of Fe, free and
available forms were present in large quantities
while exchangeable and water soluble forms
were present in negligible quantities. All the
fractions expressed a higher concentration
during summer indicating more chances for
severe Fe toxicity during that period. Mn was
also present in large quantities. Compared to Fe,
the concentration of different fractions of Mn
were very small. The availability of Cu and Zn
were also above the critical levels. The area was
rich in AI. Reverse to that of Fe the different
fractions of Al showed a lower concentration
during summer. The free Al content was three
times lesser than that of free Fe, while in
exchangeable form Al expressed a higher
concentration. The water soluble AI was very
low.
Surface water and ground water of the area
were mildly acidic and saline during rainy
season and they showed an increase during
summer. The acidity exceeded the permissible
maximum but the salinity was maintained below
the permissible limit for agricultural and
domestic purposes.
Among the various elements present in water,
Na and Cl- were the dominant ions expressing
greater concentrations during summer in both
surface and ground water. Based on SAR they
were rated as moderately unsafe for irrigation
during summer. The concentrations of K, Ca
and Mg were within the permissible maximum
for agricultural and domestic purposes. P was
present only in traces. The Fe content was
greater for ground water than surface water and
it exceeded the permissible limit for drinking
water. Though Mn was absent in ground water,
it has already reached up to the permissible
maximum in surface water. Al content


exceeded the permissible maximum for
domestic purposes. Cu, Zn, Cd and Pb were not
detected in water. SO4-S, NH4-N and NO2+NO3-
N contents of both surface and ground water
were well below the critical levels suggested,
but Cl' contents of both were sufficient to cause
specific toxicity effect.
The chlorinated hydrocarbon pesticides identi _
fied in the area were (X-HCH, y-HCH and
DDT. They showed higher concentration during
summer. Among the chlorinated hydrocarbons,
DDT was present in larger quantities, though it
was banned for agricultural uses, followed by
(X-HCH. The concentration of y-HCH was
comparatively small.
The accumulation of fertiliser residues in the
area was not so negligible. The highest concen-
tration was observed for NH4-N during addi-
tional crop season, at the time of basal dressing,
both in soil and water. During punja season, a
decrease of 55 to 60 per cent in soil and 10 to
12 per cent in water for NH4-N was observed.
The content of N02+N03-N was comparatively
low in soil due to continuous submergence. In
water it was not as low as that of soil,
indicating a major portion of N02+NOrN
retained in water. P content of the area was
very low. Its loss through drainage water was
nil.
A sizable quantity of K was also subjected to
loss through drainage water, though the extent
of loss was well below the level of N. Here also
highest concentration was noted during
additional crop season at the time of basal
dressing both in soil and water.
The study indicated that the area is subjected to
severe pollution due to the accumulation of
native toxic factors as well as residues of
pesticides and fertilisers. The closure of
Thanneermukkom regulator aggravates the
situation by restricting the water movement.