MSc

An investigation was undertaken in Eruthavoor watershed comprising an area
of 472.1 ha in Western Ghats region coming under the agro ecological unit (AEU 8) of
southern laterites of Thiruvananthapuram district. The main objective was to conduct
land evaluation and land use planning in Eruthavoor watershed of Western Ghats region
of Thiruvananthapuram district, utilizing soil survey techniques, GIS and remote
sensing.
A total of 20 soil mapping units (SMU) were demarcated in the watershed. Three
soil series were identified and mapped. Vizhinjam series and Neyyatinkara series come
under garden land soils and Marukil series come under lowland soils. Vizhinjam series
accounts for 64.95% of total area (306.65 ha), followed by Neyyatinkara series with
14.54% of the total area (68.64 ha) and Marukil series accounts for 13.54% of the total
area (63.87 ha). The study showed that 19.95% (15.92 ha) of wet land soils, which were
originally Marukil series, have permanently been converted for other land uses viz.,
rubber, coconut and arecanut. They were classified under miscellaneous soils. The soils
of the watershed fall into two orders, Ultisol and Entisol. Garden land soils namely,
Vizhinjam series (Sub group-Typic Plinthustults) and Neyyatinkara series (Sub group-
Typic Kandiustults) series falls under Ultisol and wet land soil series namely, Marukil
(Sub group- Aquic Quartipsamments) fall under the order Entisol.
Two profiles were examined for each series identified during field survey and
from around each profile ten surface samples were collected for analysis and geo-
referenced using GPS for further validation. Chemical, physical and biological analysis
of the samples were carried out to assess the general fertility status of the study area.
The investigations revealed that the soils are very strongly acidic to very slightly acidic
with medium to high organic matter content. N and K status were low to medium and P
was high. Calcium Magnesium and Sulphur were generally deficient. Overall
micronutrient status also showed sufficient availability except Zinc and Boron.
Bulk density values showed that Vizhinjam series had high BD followed by
Marukil series and Neyyatinkara series. Water holding capacity was high for
Neyyatinkara series followed by Vizhinjam series. Lowland series Marukil showed
lowest values amoung all. Microbial population and dehydrogenase activity of surface
samples revealed that Vizhinjam series had high values compared to other two series,
owing to the high organic matter content.
Land capability classification revealed that the area falls under four subclasses,
viz., IIw, IIws, IIIe, and IVes associated with erosion, wetness and soil limitations. IVes
was the dominant category in garden lands and IIw in lowlands. As per the land
irrigability classification, the mapping units were classified as 2d, 2ds, 3t and 4st, based
on drainage, soil and topographic limitations. Among this, 4st and 2d classes accounted
for the largest area in garden lands and lowlands respectively. Soil conservation priority
maps indicated the need for immediate soil and water conservation activities in an area
of 110.07 ha under conservation priority class II, 265.21 ha under conservation priority
class III and 79.79 ha under the priority class IV.
Soil suitability evaluation was performed for eighteen crops for each mapping
unit coming under three soil series. Major suitability limitations in the study area were
climate, soil physical characteristics (slope and texture), fertility (pH), topography and
wetness with varying degrees of impingement on different crops. Neyyatinkara series
was moderately suitable (sub class- S2) for most crops evaluated. Pineapple, sapota,
cowpea, elephant foot yam and green gram fall under the marginally suitable sub class
(S3) owing to climatic, soil physical and fertility (pH) limitations. Gravelly nature of
soils in Vizhinjam series restricted the choice of most of the crops in suitability
evaluation procedures. In Vizhinjam series, arecanut and pepper were moderately and
marginally suitable in an area of 264.09 ha and 42.56 ha respectively. Rubber, coconut,
papaya, pineapple and sweet potato were only marginally suitable in the soil mapping
units of Vizhinjam series. Due to topographic limitations mapping unit no 11 (area
42.56 ha), was found non suitable for rubber and papaya. Marukil series are highly
suitable (sub class S1) for paddy in an area of 63.87 ha. Pineapple, banana, brinjal,
bhindi, tomato, cassava, sweet potato, elephant foot yam and green gram were
evaluated as moderately suitable for Marukil series, the important limitations being
wetness, soil and fertility (pH). Since the converted wetlands exhibit heterogeneity in
properties as they were reclaimed wet lands, soil site suitability evaluation procedures
were not applied in them.
The soil mapping units or land parcels which have similarity in land capability,
land irrigability, soil conservation priorities and soil site suitability evaluations were
categorized to derive homogenous units or land utilization types (LUT) for which
management recommendations are the same. Five LUTs were identified in the
watershed. The land use appropriateness and allocation is as follows: 14.54% of the
total area (68.64 ha) for LUT-1, 55.94%(264.09 ha) for LUT-2, 9.01%(42.56ha) for
LUT-3, 13.54% (63.87 ha) for LUT-4 and 3.37% (15.92 ha) for
LUT-5. Based on the
land evaluation, resource inventory and prevalent socio economic status of the study
area, the management practices which can be adopted for each soil series for attaining
sustainable agricultural development and livelihood security are suggested in the study
including, soil test based fertilizer applications, soil and water conservation measures,
crop suitability, strategies for ground water recharge, live stock development etc