What is Vertisol?
Heavy clay soils with a high proportion of swelling clays are being churned by vertisols. When these soils dry out, which occurs most years, they develop deep large cracks from the surface downward. Alternate shrinking and swelling, known as argillipedoturbation, induces self-ploughing, in which the soil material consistently mixes itself, resulting in some Vertisols having an exceedingly deep A horizon and no B horizon. (An A/C soil is one that lacks the B horizon.) Gilgai is a microrelief created by the heaving of the underlying material to the surface.
[Image will be Uploaded Soon]
In climates that are seasonally humid, subject to erratic droughts and floods, or that have impeded drainage, vertisols usually form from highly basic rocks, such as basalt. They can vary from grey or red to the more familiar deep black, depending on the parent material and environment.
Between 50°N and 45°S of the equator, vertisols can be found. Eastern Australia (particularly inland Queensland and New South Wales), India's Deccan Plateau, and parts of southern Sudan, Ethiopia, Kenya, Chad (the Gezira), South Africa, and South America's lower Paraná River are all major Vertisol hotspots. Southern Texas and neighboring Mexico, central India, northeast Nigeria, Thrace, New Caledonia, and parts of eastern China are also home to Vertisols.
Vertisols have grassland, savanna, or grassy forest as their natural vegetation. Many tree species find it difficult to grow due to the heavy texture and unstable behavior of the soil, and the forest is rare. Vertisols are dark-colored soils with a moderate humus content, as well as salinity and well-defined layers of calcium carbonate or gypsum layers.
The shrinking and swelling of Vertisols can cause extensive subsidence in buildings and roads. Vertisols are typically used for cattle or sheep grazing. Animals have been known to be harmed by falling through cracks during dry times. Many wild and domestic ungulates, on the other hand, avoid moving on this soil when it is flooded. The shrink-swell operation, on the other hand, allows for fast compaction recovery.
Cotton, wheat, sorghum, and rice can all be grown when irrigation is available. Since vertisols are almost impermeable when saturated, they are ideal for rice. Vertisols can only be worked under a very limited range of moisture conditions: they are very hard when dry and very sticky when wet, making rainfed farming extremely difficult. Vertisols, on the other hand, are highly regarded in Australia because they are one of the few soils that are not severely deficient in usable phosphorus. When dry, some "crusty Vertisols" have a thin, hard crust that can last for two to three years before crumbling enough to allow seeding.
Division of Vertisols
In the USA Soil Taxonomy, Vertisols are Further Divided:
Aquerts are vertisols that have been exposed to subdued aquic conditions for a period of time in most years and have redoximorphic characteristics. The permeability is slowed by the high clay content, and aquic conditions are likely to develop. Ponding can occur when precipitation exceeds evapotranspiration in general. Iron and manganese are mobilized and reduced in wet soil moisture conditions. The dark color of the soil profile may be due in part to manganese.
Cryerts: They have a microclimate in their soil. Cryerts are most common in the Canadian Prairies' grassland and forest-grassland transition areas, as well as at similar latitudes in Russia.
Xererts: Their soil temperature regime is thermic, mesic, or frigid. They reveal cracks that are open for at least 60 days during the summer and closed for at least 60 days during the winter. The eastern Mediterranean and portions of California have the most Xererts.
Torrerts: When the soil temperature at 50 cm is above 8°C, their cracks close for less than 60 days in a row. These soils are found mainly in West Texas, New Mexico, Arizona, and South Dakota in the United States, but they are the most widespread suborder of Vertisols in Australia.
Uderts: They have cracks that are open for at least 90 days a year on average. The tropics and monsoonal climates of Australia, India, and Africa are covered by this suborder of the Vertisols order, which is the world's highest. In the United States, Usterts can be found in Texas, Montana, Hawaii, and California.
They have cracks that are open for fewer than 90 days a year on average and for less than 60 days in a row during the season. Only during drought years do cracks appear in some regions. Uderts can only be found in a few areas around the world, with the highest concentrations in Uruguay and eastern Argentina, as well as parts of Queensland and the Mississippi and Alabama "Black Belt."
FAQs on Vertisol
1. What is Vertisol soil?
Vertisol is a type of soil characterized by a high content of expansive clay minerals, such as smectite. These soils undergo significant changes in volume with variations in moisture content, leading to a unique shrink-swell behaviour. When dry, they develop deep, wide cracks, and when wet, they swell and become sticky and plastic. In the USDA soil taxonomy system, Vertisols are recognized as one of the twelve major soil orders.
2. What are the key characteristics of Vertisol soil?
The most prominent characteristics of Vertisols, often studied in the NCERT syllabus, include:
High Clay Content: Typically contains over 30% clay, which is responsible for its shrink-swell properties.
Shrink-Swell Action: The soil mass shrinks and forms deep cracks upon drying and swells to close these cracks when wet.
Color: Usually dark, ranging from dark grey to black, due to the parent material and organic matter content.
Fertility: They are generally very fertile, rich in lime, potash, magnesium, and calcium carbonate, but often poor in phosphorus and nitrogen.
Water Retention: Possess a high water-holding capacity, making them suitable for rain-fed agriculture.
3. What are Vertisols commonly known as in India?
In India, Vertisols are most famously known as 'Regur soils' or 'Black Cotton Soils'. The term 'Regur' is derived from a Telugu word. They are called 'Black Cotton Soils' because their dark colour and high moisture retention make them exceptionally well-suited for cultivating cotton.
4. Where are Vertisol soils primarily found in India and across the world?
Globally, Vertisols are found in regions with distinct wet and dry seasons, such as eastern Australia, Sudan, and parts of South America. In India, as per the geography syllabus, they predominantly cover the Deccan Plateau region. This includes large parts of:
Maharashtra
Western Madhya Pradesh
Gujarat
Andhra Pradesh and Telangana
Northern Karnataka and parts of Tamil Nadu
5. Why do Vertisols develop deep cracks when they dry out?
The formation of deep cracks is a direct result of the soil's mineral composition. Vertisols have a high concentration of smectite clay minerals. These clay particles have a unique lattice structure that allows them to absorb a large amount of water between their layers, causing the soil to expand or swell significantly. During the dry season, as the soil loses moisture through evaporation, these clay particles shrink dramatically. This uniform shrinking across the soil mass pulls it apart, resulting in the formation of deep, wide cracks on the surface.
6. How does the unique shrink-swell nature of Vertisols impact agriculture?
The shrink-swell property of Vertisols presents both challenges and advantages for agriculture. The primary challenge is tillage; the soil is extremely hard when dry and very sticky when wet, making it difficult to plough. Farmers must time their cultivation activities perfectly, usually after the first rains. However, this property also leads to a phenomenon called 'self-mulching' or 'self-ploughing', where loose surface soil falls into the cracks, mixing the soil profile. Furthermore, their high water-holding capacity is a significant advantage, as it allows crops like cotton, jowar, and wheat to thrive under rain-fed conditions by retaining moisture for longer periods.
7. What is the key difference between Vertisols and Alluvial soils found in India?
The primary difference lies in their formation and composition. Vertisols are in-situ soils, meaning they are formed in their original place from the weathering of underlying basaltic rocks of the Deccan Traps. They are clayey, fine-grained, and rich in minerals like lime and potash. In contrast, Alluvial soils are ex-situ soils, formed from sediments deposited by rivers. They are found in the Indo-Gangetic plains and coastal areas and are typically loamy, more permeable, and compositionally varied depending on the river system that deposited them.
