Introduction of Black Soil
- Metals such as iron, magnesium, and aluminum are abundant in India’s black soil. It is, however, nitrogen, potassium, phosphorus, and humus deficient. The iron oxide component in black soil gives it a red color.
- This soil accounts for 15% of all soil types in India. Volcanic boulders and lava flow make up these soils. It is primarily found in the Deccan Lava Tract, which spans Maharashtra, Chhattisgarh, Madhya Pradesh, Gujarat, Andhra Pradesh, and Tamil Nadu.
- Swelling (during rainy periods) and shrinking are two common properties of this dark soil (dry period). It generates incredibly deep cracks of more than 30-45 cm when dry. Cracks in the Kovilpatti (Tamil Nadu) area might be 2 to 3 meters long and 1 to 6 cm wide. In comparison to other soils, field preparation takes longer. The soil is only suitable for crop cultivation after secondary tillage.
- The fine-grained soils have a high concentration of calcium and magnesium carbonates. Black soil retains more moisture for a longer period of time. Black soils in Tamil Nadu have a high pH (8.5 to 9) and are high in lime (5-7 percent), as well as low permeability.
- The soils have a higher capacity for cation exchange (40-60 m.e./100 g). Rice, Ragi, Sugarcane, and Cashew Nuts, among other crops, are grown on this type of soil. This type of soil forms as a result of excessive leaching and is seen in locations with a lot of rain.
Black soil in India
“The organic and inorganic components on the Earth’s surface that create the medium for plant growth can be characterized as soil.”
Soil is a natural body made up of solids (minerals and organic matter), liquids, and gases that occurs on the land surface, occupies space, and is distinguished from the initial material by one or both of the following: horizons, or layers, that are distinguishable from the initial material as a result of additions, losses, transfers, and transformations of energy and matter or the ability to support rooted plants in a natural environment.
The barrier between soil and air, shallow water, live plants, or plant materials that have not begun to disintegrate is the top limit of soil. If the surface is continually covered by water that is too deep (usually more than 2.5 meters) for the growth of rooted plants, the area is not regarded to have soil.
The lowest boundary between soil and non-soil beneath the soil is the most difficult to identify. Soil is made up of horizons near the Earth’s surface that have been transformed over time by climate, relief, and living organisms, as opposed to the underlying parent material. Soil commonly grades to hard rock or earthy materials at its lower limit, devoid of animals, roots, or other signs of biological activity. The bottom boundary of soil is arbitrarily defined at 200 cm for classification reasons.
The Indian Council of Agricultural Research (ICAR) set up an All India Soil Survey Committee in 1953 which divided the Indian soils into eight major groups. They are:
(1) Alluvial soils
(2) Black soils
(3) Red soils,
(4) Laterite and Lateritic soils
(5) Forest and Mountain soils
(6) Arid and Desert soils
(7) Saline and Alkaline soils
(8) Peaty and Marshy soils
This is a very logical classification of Indian soils and has gained wide acceptance.
Properties of Black Soil
- Cotton is the most significant crop farmed on these soils, they’re also termed regur (from the Telugu word Reguda) and black cotton soils. Several theories have been proposed to explain the formation of this category of soils, but most pedologists believe that they were generated thousands of years ago by the solidification of lava dispersed across huge areas during volcanic activity in the Deccan Plateau.
- The Deccan and Rajmahal traps, as well as ferruginous gneisses and schists found in Tamil Nadu, are responsible for the majority of the black soils. While the former is appropriately deep, the latter is often shallow.
- According to Krebs, the regur is simply a mature soil formed by relief and climate rather than a specific type of rock. This soil, he claims, can be found when yearly rainfall is between 50 and 80 cm and wet days are between 30 and 50. He considers the existence of this soil in the west Deccan, where rainfall averages approximately 100 cm and wet days exceed 50, to be an outlier.
- The genesis of black cotton soils is attributed to old lagoons in which rivers deposited sediments transported down from the interior of the Peninsula covered in lava in some sections of Gujarat and Tamil Nadu.
- Black soils are found between 15°N and 25°N latitudes and 72°E and 82°E longitudes, covering 5.46 lakh sq km (or 16.6% of the country’s entire geographical area). This is a hot and dry region. As a result, it belongs to the Peninsula’s dry and hot soil groups.
- Maharashtra, Madhya Pradesh, and sections of Karnataka, Andhra Pradesh, Gujarat, and Tamil Nadu are the most common locations for these soils.
- Some scientists attribute the black color of these soils to the presence of a small amount of titaniferous magnetite, or perhaps iron and black components in the parent rock. The soil’s dark color could come from crystalline schists and basic gneisses found in Tamil Nadu and Andhra Pradesh. This category of soils can be found in several shades of black, including deep black, medium black, shallow black, and even a blend of red and black.
- Moisture is retentive in the black soil. When wet during the rainy season, it swells and gets sticky. Because the plough gets caught in the muck in such conditions, working on the soil is nearly impossible.
- During the hot dry season, however, liquid evaporates, the soil shrinks, and broad and deep fractures, up to a meter deep, appear. This allows for adequate soil oxygenation and exceptional fertility.
- The soil “swallows” itself and maintains soil moisture after being “self-ploughed” by loose particles falling from the ground into the fissures. For ages, this soil has been utilized to grow a variety of crops without the use of fertilizers or manures, and it has even been used for fallowing with little or no signs of exhaustion.
- A typical black soil is argillaceous, with a high clay content of 62 percent or more, and no gravel or coarse sand. Alumina is 10%, iron oxide is 9-10%, and lime and magnesium carbonates are 6-8 percent. Potash levels are fluctuating (less than 0.5%), and phosphates, nitrogen, and humus levels are low. The structure is cloddish, yet it can be brittle on occasion.
- A layer rich in kankar nodules formed by segregation of calcium carbonate at lower levels exists in all regur soils in general, and in those derived from ferromagnesian schists in particular. Black soils in the uplands are generally low in fertility, but in the valleys they are darker, deeper, and richer.
- The black soils are widely used for producing several important crops due to their high fertility and moisture retentivity. Cotton, wheat, jowar, linseed, Virginia tobacco, castor, sunflower, and millets are some of the main crops grown on the black soils. Where irrigation facilities are available, rice and sugarcane are equally important. On the black soils, a wide range of vegetables and fruits thrive.
Important features of Black Soil:
- Regur means cotton – best soil for cotton cultivation.
- Most of the Deccan is occupied by Black soil.
- Mature soil.
- High water retaining capacity.
- Swells and will become sticky when wet and shrink when dried.
- Self-ploughing is a characteristic of the black soil as it develops wide cracks when dried.
- Rich in: Iron, lime, calcium, potassium, aluminum and magnesium.
- Deficient in: Nitrogen, Phosphorous and organic matter.
- Colour: Deep black to light black.
- Texture: Clayey.
Characteristics and Constraints of Black Soil
The soils developed on schists and gneisses and are moderately shallow (50-75 cm) to moderately deep (75-100 cm) where as those developed on basalt are deep (100-150 cm) to very deep (>150 cm). These soils are highly argillaceous with clay content varying from 30-80%.
The clay of Black soil has a high coefficient of expansion and contraction, and it is predominantly smectitic in nature, resulting in gilgai micro-relief, deep and wide fractures, and closely intersecting slicken sides.
The CaCO3 content of the members grown on calcareous clay parent material is high and grows unevenly with depth. The pH of black soils ranges from 7.8 to 8.7, with sodic soils reaching up to 9.4.
Cation exchange capacity (35-55 c mol (p+) kg -1) and base status are both high in black soils. Despite the fact that black soils have a high moisture holding capacity (150-250 mm/m), water is not available to plants due to the tenacious hold of the smectitic clay.
When wet, black soils are exceedingly sticky, and when dry, they are incredibly hard. Because it shrinks when it dries, it has a low permeability and a high bulk density (1.5 to 1.8 Mg m -3).
During droughts, black soils are subjected to moisture stress. Organic carbon, nitrogen, sulfur, and phosphorus are all deficient in these soils. In shallow soils, water retention capacity is a crucial issue. When watered, deep soils are more susceptible to salt and sodicity, especially in the subsoil.