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Clays:
To be designated clay a soil must contain at least 35% of the clay separate and in most cases not less than 40%. In such soils the characteristics of the clay separates are distinctly dominant, and the class names are clay, sandy clay and silty clay. Sandy clays may contain more sand than clay. Likewise, the silt content of silty clays usually exceeds clay fraction
Particle size less than 0.002 mm
Plate like or needle like in shape
Belong to alumino silicate group of minerals
Some times considerable concentration of fine particles which does not belong to alumino silicates. (eg). iron oxide and CaCO3
These are secondary minerals derived from primary minerals in the rock
FLESH of the soil
Importance of clay
Clay particles play a very important role in soil fertility.
Clayey soils are difficult to till and require much skill in handling. When moist clayey soils are exceedingly sticky and when dry, become very hard and difficult to break.
They have fine pores, and are poor in drainage and aeration.
They have a high water holding capacity and poor percolation, which usually results in water logging.
They are generally very fertile soils, in respect of plant nutrient content. Rice, jute, sugarcane can be grown very successfully in these soils.
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