Soil

Soil is a natural body consisting of layers (soil horizons) that are primarily composed of minerals which differ from their parent materials in their texture, structure, consistency, color, chemical, biological and other characteristics. It is the unconsolidated or loose covering of fine rock particles that covers the surface of the earth. Soil is the end product of the influence of the climate (temperature, precipitation), relief (slope), organisms (flora and fauna), parent materials (original minerals), and time. In engineering terms, soil is referred to as regolith, or loose rock material that lies above the ‘solid geology’. In horticulture, the terms ‘soil’ is defined as the layer that contains organic material that influences and has been influenced by plant roots and may range in depth from centimetres to many metres. Soil is composed of particles of broken rock (parent materials) which have been altered by physical, chemical and biological processes that include weathering (disintegration) with associated erosion (movement). Soil is altered from its parent material by the interactions between the lithosphere, hydrosphere, atmosphere, and biosphere. It is a mixture of mineral and organic materials in the form of solids, gases and liquids. Soil is commonly referred to as “earth” or “dirt”; technically, the term “dirt” should be restricted to displaced soil. Soil forms a structure filled with pore spaces and can be thought of as a mixture of solids, water, and gases. Accordingly, soils are often treated as a three-state system. Most soils have a density between 1 and 2 g/cm³. Little of the soil of planet Earth is older than the Pleistocene and none is older than the Cenozoic, although fossilised soils are preserved from as far back as the Archean.

There are ten soil groups in Kerala. 1. Red soil: The red colour is due to the presence of Fe2O3.Localised in southern parts of Thiruvananthapuram. The soil is almost homogeneous. Acidity ranges from 4.8 to 5.9. The gravel content is comparatively less. Low in essential nutrients and organic matter. 2. Laterite soil: Majority of area comprises this type of soil. Heavy rainfall and high temperature are conducive for laterisation. Laterites are poor in available N and P. Low in Water Holding Capacity and CEC is low. 3. Coastal alluvial soil: Seen in the coastal tracts along the west. They have been developed from recent marine deposits. Permeability is more. Low organic matter content. Low CEC. Water Holding Capacity is less. 4. Riverine alluvial soil: Seen along the banks of rivers. Shows wide variation in physico-chemical properties depending on the nature of alluvium and the characteristic of the catchment area through which the river flows. Organic Matter, N and K are moderate. 5. Greyish Onattukara soil: Sandy soil confined to the Onattukara region. They occur as marine deposits and extends to the interior upto the laterite soil. Extremely deficient in plant nutrients. CEC is also poor. 6. Brown hydromorphic soil: Localised in river valleys. Mostly confined to the valley bottoms of undulating topography in the mid lands and low lying areas of coastal strips. Exhibits wide variation in physico-chemical and morphological properties. Drainage is the major problem. Moderately supplied with organic matter, N and K. Deficient in lime. 7. Hydromorphic saline soil: Found in the coastal tracts of Ernakulam, Thrissur and Kannur districts. During rainy season the fields are flooded leaving the area almost free of salt. Maximum accumulation of salts occur during summer. 8. Acidic saline soil: Seen in Kuttanad region covering about 875 sq.km. Soil face with serious problems …