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 of hydrology, flood, acidity and salinity. Typical water logged soils
- Kayal soil: It comprises reclaimed areas of Kottayam and Alappuzha districts. Slightly acidic. Medium in organic matter content. Poor in vailable nutrients but rich in Ca.
- Karappadam: Distributed over a large area of upper Kuttanad. River borne alluvial soil 1-2 m. below the sea level. Generally clay loam in texture, high acidity, fair amount of organic matter, poor in available nutrients particularly P. Deficient in lime.
- Kari soil: Acidity is due to the presence of different forms of S. Kari soil resemble Peat soil.
9. Black soil:
Seen in Chittur area of Palakkad district. Low in Organic matter, calcareous, moderately alkaline, high in clay content. CEC is high. Medium in P and K content and low in N.
10. Forest soil:
A product of weathering of crystalline rocks under forest cover. Rich in organic carbon. PH acidic. Rich in N and poor in P. Major problems of Kerala soils are acidity, salinity water logging and poor physical properties. 88% of soils are acidic. 60% of the area is medium in available N, 65% of the area is low in available P and 75% is low in available K.