Question Discussion & Solution

Alluvial soil

• Alluvial soil contains silt, sand, clay, and gravel as well as humus, lime, and organic matter. 
• It is usually most extensive in the lower part of a river's course, forming floodplains and deltas, but they may form at any point where the river overflows.
• Major characteristics of alluvial soil are it is made by the deposition of the river load as it flows from its upper to its lower.
• On the basis of its ages alluvial soil is divided into Bhangar (Old alluvium) and Khadar (New alluvium). 
• It is porous as well as light, so it is easily tillable.
• They are generally rich in potash but poor in phosphorous. 
• Alluvial soil is widespread in northern plains and river valleys.
• Wheat, rice, maize, sugarcane, pulses, oilseed are mainly cultivated in alluvial soil.

Yellow soil

• It develops on crystalline igneous rocks in areas of low rainfall.
• Especially in Eastern and Southern Deccan.
• It is reddish-yellow in colour.
• Red colour due to wide diffusion of iron in crystalline and metamorphic rocks.
• Yellow colour when it is in hydrated form.
• These soils are fine-grained and fertile.
• It is poor in nitrogen, phosphorus and humus.
• It is suitable for the cultivation of rice, wheat, sugarcane, maize/corn, groundnut, ragi (finger millet) and potato, oilseeds, pulses, millets, and fruits.

Black soil

• It has a pH of  6.8.
• The parent material for most of the black soil is the volcanic rocks that were formed in the Deccan Plateau.
• Black soil covers most of the Deccan Plateau.
• This includes parts of Maharashtra, Madhya Pradesh, Gujarat, Andhra Pradesh and some parts of Tamil Nadu. 
• These soils are also known as the ‘Regur Soil’ or the ‘Black Cotton Soil’.
• The colour of the soil ranges from deep black to grey.
• The black soils are generally clayey, deep and impermeable.
• They swell and become sticky when wet and shrink when dried.
• So, during the dry season, this soil develops wide cracks.
• They retain moisture for a very long time which helps crops to sustain even during the dry season.
• Chemically, the black soils are rich in lime, iron, magnesia and alumina.
• But they lack phosphorous, nitrogen and organic matter.

• The pH of red soil is more than 5.
• Red soil area extends into and includes the greater part of Jharkhand and West Bengal.
• Red soils have originated from weathering of the ancient crystalline, and metamorphic rocks.
• These are porous, friable and neutral to acidic in nature.
• These soils are poor in nitrogen, phosphate, lime and humus. 
• Suitable for the cultivation of ragi, groundnut, millet, potato, tobacco, paddy, wheat, and sugarcane.