Clayey soils that develop deep, wide cracks during part of the year, as they shrink on drying and swell on wetting, belong to which soil order?

Vertisols are clay-rich soils that swell greatly when wet and shrink when dry, developing deep, wide cracks during the dry season. They are one of the 12 soil orders of the USDA Soil Taxonomy.

Origin of the name:

The name comes from the Latin "vertere", meaning "to turn", because these soils are constantly turned and mixed by their shrinking and swelling. Surface material falls into the cracks during the dry season, and the soil expands again when it gets wet, churning the soil. This is sometimes called "self-mulching" or "self-ploughing".

Characteristics of Vertisols:

• High content (usually more than 30 per cent) of swelling clay minerals, mainly montmorillonite (smectite).
• Cracks that can be several centimetres wide and more than 50 cm deep in the dry season.
• Very sticky and plastic when wet, and very hard when dry, which makes them difficult to plough.
• Slickensides: shiny, grooved surfaces formed inside the soil as blocks of soil slide past each other during swelling.
• Usually dark grey to black in colour.
• High water-holding capacity and generally high natural fertility, though often poor in nitrogen, phosphorus and organic matter.

Where they are found:

• India: the black cotton soils (regur) of the Deccan plateau, in Maharashtra, Madhya Pradesh, Gujarat, Karnataka, Telangana and Andhra Pradesh, are mostly Vertisols.
• Other countries: Australia, Sudan, Ethiopia, Texas (USA) and parts of South America.

Crops:

• In India, Vertisols support cotton, soybean, jowar, wheat, chickpea, sugarcane and pulses.
• Crops can often be grown on stored soil moisture after the rains.

Other USDA soil orders (for comparison):

• Aridisols: dry soils of deserts.
• Entisols: young soils without developed horizons.
• Oxisols: highly weathered soils of the humid tropics.
• Inceptisols: young soils with weakly developed horizons (the most widespread in India).
• Histosols: organic soils (peat).

Why not the other options?

• ✗Aridisols are desert soils that rarely have enough clay to crack in this way.
• ✗Entisols are young soils with little horizon development.
• ✗Oxisols are deeply weathered tropical soils with stable, non-swelling clays.