Soil Profile
Soil Profile (Soil Horizons)
The loose material or the upper layer of the mantle rock (regolith – a layer of loose, heterogeneous material covering solid rock) consisting mainly of very small particles and humus which can support the growth of plants is known as “soil”. Soil mainly consists of mineral/rock particles, portions of decayed organic matter, soil water, soil air and living organisms. The major factors that influence the formation of soil are parent material, relief, climate, vegetation, life forms and time.
- What is Soil?
- Soil is the loose material or the upper layer of mantle rock (regolith) that supports plant growth.
- It consists of very small particles and humus.
- Contains mineral/rock particles, decayed organic matter, soil water, soil air, and living organisms.
Khadar, Bangar, Bhabhar, and Terai
- Soil is the loose material or the upper layer of mantle rock (regolith) that supports plant growth.
- Major factors influencing soil formation include:
- Parent material
- Relief
- Climate
- Vegetation
- Life forms
- Time
- Four Main Components of Soil:
- Inorganic or mineral fractions
- Organic matter (decayed plants and animals)
- Air
- Water
- Soil forms under specific natural conditions through a process known as *pedogenesis*.
- Each element of the natural environment contributes to this complex process.
- A soil profile is a vertical cross-section of soil made up of layers called *horizons*.
- Horizon A (Topsoil): Contains organic materials mixed with mineral matter, nutrients, and water essential for plant growth.
- Horizon B (Subsoil): Rich in minerals and less humus, represents a transition zone between Horizons A and C.
- Horizon C: Composed of weathered and decomposed parent rock material, the initial stage of soil formation.
- Alluvial Soil
- Alluvial soils are widespread in the northern plains and river valleys, covering about 40% of the total land area of India.
- These soils are derived from debris brought down by the Himalayas, and in the Peninsular region, they are found in deltas of the east coast and in river valleys.
- The colour of alluvial soil ranges from light grey to ash grey, and it varies in texture from sandy loam to clay.
- They are rich in potash but poor in phosphorus.
- There are two types of alluvial soils:
Khadar: The new alluvium found in floodplains, enriched with fresh silt deposits each year.
Bhangar: The old alluvium found away from the flood plains, contains concretion (kankars) of impure calcium carbonate.
- These soils are suitable for crops like wheat, maize, sugarcane, pulses, and oilseeds.
- Red and Yellow Soil
- Found in the regions with low rainfall, such as the eastern and southern parts of the Deccan Plateau, this soil covers about 18.5% of the total land area.
- The red color comes from iron in the crystalline and metamorphic rocks, while the soil appears yellow when hydrated.
- The soil is usually fertile if fine-grained but less fertile when coarse-grained.
- Wheat, cotton, oilseeds, millets, tobacco, and pulses are mainly cultivated in this soil.
- Black or Regur Soil
- Black soil, also known as Regur Soil, covers about 15% of India’s land area, mainly in the Deccan Plateau.
- The soil is rich in iron, lime, magnesium, and potassium but lacks nitrogen, phosphorus, and organic matter.
- These soils are perfect for crops like cotton, pulses, millets, sugarcane, citrus fruits, and linseed.
- Black soils have a clayey texture and shrink and form cracks when dry, which makes them suitable for cotton cultivation.
- Desert Soil
- Desert soil covers 4.42% of the total land area of India, mostly found in western Rajasthan.
- The soil is sandy to gravelly, with low moisture content and low water-retaining capacity.
- Desert soils are saline, and in some areas, the salt content is high enough to extract common salt.
- Watering through irrigation makes the soil more suitable for plant growth.
- Laterite Soil
- Laterite soil is found in areas with a monsoon climate and is formed by leaching of lime and silica.
- This soil is low in organic matter, nitrogen, and phosphate but high in iron oxide and potash.
- Laterite soil is commonly used for tree crops like cashew nuts in Kerala, Tamil Nadu, and Andhra Pradesh.
- Mountain Soil
- Mountain soils are found in forest regions with sufficient rainfall and have varied textures, ranging from coarse-grained on the upper slopes to loamy and silty in the valleys.
- These soils are generally acidic with low humus content in snowbound areas and more fertile in lower valleys.
- Peaty and Marshy Soil
- Found in areas of heavy rainfall and high humidity, these soils are rich in humus and organic matter.
- They are heavy, black in color, and often alkaline, making them suitable for the growth of vegetation in southern Uttarakhand, northern Bihar, and coastal areas of West Bengal, Odisha, and Tamil Nadu.
- Saline and Alkaline Soils
- Saline soils are found in arid, semi-arid, and waterlogged regions and are high in sodium, magnesium, and potassium, making them infertile.
- These soils are suitable for growing salt-resistant crops like berseem and dhaincha.
- Saline soils are found in western Gujarat, deltas of the eastern coast, and areas near the Rann of Kutch in Gujarat and Rajasthan.
- The ICAR classified Indian soils based on USDA taxonomy:
- Inceptisols: 39.74%
- Entisols: 28.08%
- Alfisols: 13.55%
- Vertisols: 8.52%
- Aridisols: 4.28%
- Ultisols: 2.51%
- Mollisols: 0.40%
- Others: 2.92%
- Soil erosion refers to the removal of the topsoil.
- Occurs when natural processes or human activities disturb the balance between soil formation and removal.
