Q. The black cotton soil of India has been formed due to the weathering of (UPSC Prelims 2021)
Answer:
fissure volcanic rock
Notes: The correct answer is
[B] fissure volcanic rock. Black cotton soil, also known as
Regur soil, is characteristic of the Deccan Trap region in India.
- Parent Material (Formation): This soil is formed from the weathering of solidified lava (basaltic rocks) that spread over the Deccan Plateau during volcanic eruptions through fissures (cracks) millions of years ago.
- Characteristics: It is highly argillaceous (clayey), deep, and impermeable. It develops wide cracks during the dry season, which allows for "self-plowing" by oxygenating the deeper layers.
- Mineral Composition: It is rich in calcium carbonate, magnesium, potash, and lime, but generally poor in phosphorus, nitrogen, and organic matter. The black color is often attributed to the presence of titaniferous magnetite or iron and aluminum silicates.
- Agricultural Importance: It is exceptionally fertile and retains moisture for a long period, making it ideal for rain-fed agriculture. It is most famous for cotton cultivation, hence the name "Black Cotton Soil."
- Distribution: It covers most of the Deccan Plateau, including parts of Maharashtra, Madhya Pradesh, Gujarat, Andhra Pradesh, and some parts of Tamil Nadu.
Why other options are incorrect:- Brown forest soil [A]: Found in Himalayan regions, formed under coniferous and deciduous forests.
- Granite and schist [B]: These are the parent materials for Red Soil, which forms through the weathering of crystalline igneous rocks in areas of low rainfall.
- Shale and limestone [D]: These sedimentary rocks usually give rise to different soil types; for example, limestone weathering often leads to Terra Rossa or rendzina soils.