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SOIL TYPES

The soil map of Kerala is compiled from the map obtained from the Soil Survey Unit of the Department of Agriculture, Kerala State and the Soils of India map published by the National Bureau of Soil Survey and Land Use Planning. In general, the soils are dominated by lateritic soils and forest loams. Other soil types have developed in certain areas due to local physiographic factors. Based on the physico-chemical properties and morphological features, they are classified into ten broad groups, which could be identified with thirteen 'general groups' of soil taxonomy. Brief description of these soil groups are presented (Centre for Earth Science Studies, 1984).

Coastal Alluvium (Tropopsamments Tropofluvents)

This soil has originated from recent deposits, predominantly marine, with some fluvial sediments along the coast line. The soil is immature with high sand content and low water holding capacity with pH value less than 6.5 in most of the areas.

Riverine Alluvium (Tropofluvents - Eutropepts - Dystropepts)

This type of soil, developed along river valleys, occurs throughout the State cutting across the extensive laterite soils. The soil is very deep with surface texture ranging from sandy loam to clay. It is very fertile having high water holding capacity and plant nutrients which are regularly replenished during floods. It supports cultivation of paddy, arecanut, pepper, tapioca and a wide variety of vegetables.

Red Loam (Tropudalfs - Eutropepts)

This occurs mainly as colluvial deposits in isolated patches in foothills and hillocks being associated with laterites. The red colour is due to the presence of iron oxides. The soil being highly porous and friable is not fertile.

Lateritic Soil (Eutrorthox - Haplorthox -Dystropepets)

This soil, a typical weathering product under humid tropical conditions, occurs throughout the State. It shows the development of AB(c) profiles, which are deep to very deep. The B horizon is well developed in most cases with abundant ferruginous and quartz gravels. Though this soil, in general, is acidic and poor in available nitrogen, phosphorus, potash and organic matter, it is well drained, widely cultivated and responds to management practices. A variety of crops like coconut, tapioca, rubber, arecanut, pepper, cashew etc, can be successfully grown by the proper application of fertilizers and irrigation.

Greyish Onattukara (Troporthents)

This soil with its characteristic grey colour occurs in the districts of Alleppey and Quilon. It is generally coarse grained, highly porous with limited capacity for retaining water and fertilizers. These soils are acidic and are extremely deficient in major plant nutrients. Additions of sufficient organic matter and irrigation facilities improve the water holding capacity for cultivation of paddy, tapioca and other seasonal crops in addition to coconut.

Acidic Saline (Tropaquepts -FIuvaquents)

This soil is found mainly in the Kuttanad region. Developed under hydromorphic conditions, these include the Kari soil (black soil with high organic content developed in low lying water logged areas), kayal soil (in reclaimed areas with high clay content) and karappadam soil (soil along river courses with high silt content). Salinity and waterlogging have put limitations to crop culture but with careful management, these soils can sustain good crop production. Paddy is successfully grown in this soil.

Brown Hydromorphic Soil (Tropaqualfs -Tropaquepts)

This is commonly found in areas of wetlands and is moderately rich in organic matter, nitrogen and potash and deficient in lime and phosphate. Acidity is a problem in some places. For poorly drained areas, provision for drainage is essential.

Hydromorphic Saline Soil (Tropaqualfs)

The saline soil of this group is observed along the coastal strip where inundation by sea causes salinity. The problem of acidity is also observed within this soil group in some areas.

Black Soils (Chromuderts)

Black soil is found in the north-eastern part of Palghat district adjacent to Coimbatore district of Tamil Nadu. This soil is dark in colour, low in organic matter, calcareous, moderately alkaline and high in clay content. This higher proportion of clay makes it sticky and plastic in character. The shrinking-swelling capacity is also high. As this soil promotes cotton cultivation, it is often referred to as black cotton soil. Due to low organic matter and high clay percentage, it is found suitable for a limited variety of crops.

Forest Loam (Hapludolls - Tropudalfs -Tropeptic -Eutrorthox)

This soil is developed in the eastern part. of the State within forest area on the weathered crystalline rocks. The upper layer is highly enriched with organic matter derived from the decomposed leaves. Due to the presence of excessive organic matter, the soil is dark reddish brown to black in colour. It is rich in nitrogen, but poor in bases. The soil is quite fertile under forest cover and promotes prolific undergrowth. In denuded areas, protection against soil erosion is recommended.

The preceding description of the soils of Kerala is quite generalised. The State is yet to be covered by detailed soil survey. At present, these broad soil groups have been identified in terms of their principal characteristics.

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