PhD

An investigation was carried out at College of Agriculture, Vellayani during
2001- 2004 to delineate acid sulphate soils of Kuttanad and to develop sustainable
land use plan for the area based on land evaluation and crop suitability rating with the
help of GIS technology. The study consists of generation of detailed soil maps of
acid sulphate soils of Kuttanad, various thematic maps of acid sulphate soils of
Kuttanad, interpretation of soil maps, qualitative and quantitative evaluation of land
use systems of the area, and development of a sustainable land use model taking into
account the climatology, productivity and socio- economic constraints of the area.
Kuttanad is a lowlying deltaic region lying 0.6 to 2.2 m below mean sea level.
The reconnaissance soil survey of the area was conducted according to the principles
envisaged in IARI (1970). Two profile pits were dug from each series identified and
morphological features were described and surface as well as subsurface samples
were drawn for detailed laboratory examination. Soil classification was done based
on field survey, soil correlation and laboratory investigation and soil map of acid
sulphate soils of Kuttanad was prepared based on GIS technique. Land capability
classification was done based on inherent soil characteristics, degree of limitations
etc. Soil site suitability classificatio~ was done to find the suitability of different
crops in the region and fertility capability classification was also done for evolution
of sustainable agricultural management. These soils were thoroughly evaluated to
study the present land use, its suitability and to suggest alternate land use plan for the
area.

The morphological and physico- chemical characteristics of the area showed
great degree of variation. The soils were deep with a hue of7.5 YR to 10 YR, sticky
and plastic, angular blocky to sub angular blocky in structure with textural variation
from sandy to clayey with random deposits of lime shells and humus. Presence of
faint to prominent reddish yellow or brown mottles in most of the soil layers. Some
of the special characteristics observed were partially burned wooden logs and reddish
brown root channels.
The soils were extremely acidic with high organic carbon content. The CEC,
ECEC and available nutrients except phosphorous were high for these soils. Due to P
fixation, phosphorous deficiency is widespread. However the base saturation was
below 50 per cent.
As per USDA classification, the entire study area was classified under the
order Entisols, with suborder Aquent, great group Sulfaquent, subgroup Typic
Sulfaquent with six soil series viz., Ambalapuzha, Purakkad, Thotapally, Thuravur,
Kallara and Thakazhi. As per FAO classification, these soils were included under
Thionic Fluvisols.
The region enjoys a humid tropical climate. Based on soil mapping of the
area it is revealed that acid sulphate soils of Kuttanad cover an area of 14277.51 ha
comprising of six soil series. Kallara series occupied the largest area of 6860.17 ha.
The soils of the region were deep, poorly drained loamy soils in control section and
are very gently sloping with slight erosion.
Land capability classification of the area showed five soil senes ViZ.,
Ambalapuzha, Purakkad, Thuravur, Kallara and Thakazhi covenng an area of
13099.60 ha came under the class IV sw. The Thotapally series was grouped under

III sw. While considering the soil site suitability for paddy, Thotapally and Thuravur
series come under subclass S2 xf ie these are moderately suitable for paddy
cultivation with limitations due to fertility and pH. For coconut cultivation, all the
series except Thuravur are grouped under S2 xf. Soil site suitability for mango
cultivation revealed that Ambalapuzha, Purakkad and ThotapalJy senes are
moderately suitable with limitations due to excess wetness, low pH and fertility
limitations. As per Fertility Capability Classification, the soils belong to the units
Lgac, Lgac, LCgac, Cgaics, Lgac and LCgaic respectively for Ambalapuzha,
Purakkad, Thotapally, Thuravur, Kallara and Thakazhi series. The modifiers that are
relevant to the acid sui phate soi I condition are "g" which defi nes wet land soi Is, "a"
aluminium toxicity, "i" denotes high P fixation by iron, "c" denotes the acid sulphate
soil condition.
Socio - economic, cultural and ecological traits were also taken in to account
along with land, crop and climatological characteristics of the area for the
development of a probable land use model. Based on the study the land use models
that can be suggested for the area are rotational farming involving paddy, fish and
livestock.