The Soils of India: Characteristics, Erosion, and Conservation

Definition and Fundamentals of Soil Resources

• Basic Definition: Soil is the topmost layer of the Earth’s land surface. It is a thin, loose layer consisting of a mixture of small rock particles and decayed organic matter.

• Ecological Role: Soil acts as the medium on which plants grow and serves as a primary platform for supporting human and animal life. Directly or indirectly, all human needs are derived from soil.

• Composition: Soil is a complex mixture of mineral matter, including:

  • Silica: A major component of most soils.

  • Clay: Fine-grained natural soil material.

  • Chalk: Also known as calcium carbonate ($CaCO_3$).

  • Humus: This is decayed vegetable and animal remains. It is critical for soil fertility.

• Origin and Formation:

  • Soil is derived from parent rock material through an ongoing process of wear and tear, breakup, and disintegration.

  • Pedogenesis: This technical term refers to the process of soil formation.

  • External Factors: Factors affecting the composition and character of the top layer include changing temperatures (causing cracking in summer months like March, April, and May), wind, running water, and human interference.

Soil Fertility and Profile

• Soil Fertility: This is defined as the strength of the soil to support plant life. A soil is considered productive (fertile) or non-productive (infertile) based on its ability to sustain crops.

• Conditions for Fertility:

  • Moisture Content: Adequate moisture (often referred to as "nummy" in Hindi) is required to supply essential nutrients to plants.

  • Nutrient Richness: Fertility depends on the presence of nitrogen ($N$), potassium ($K$), and phosphorus ($P$).

  • Organic Matter: Presence of humus.

  • Soil Depth: Sufficient depth is needed for roots to grow downward and bind the plant to the soil, preventing it from being uprooted by strong winds.

  • Fertilizers: Soil fertility can be manually improved by adding chemicals or organic matter designed to enhance productivity.

• Soil Profile: The vertical cross-section of different layers of soil. It generally consists of:

  • Top Soil: The most important layer containing humus, bacteria, worms, insects, and decayed plant life. It takes many years to form but is easily washed away by floods.

  • Subsoil: Found below the topsoil, consisting of the parent rock material, moisture, and mineral constituents.

  • Bedrock: The hard rock material found below the subsoil that has not yet been broken up.

Classification based on Location

• Residual Soil (In situ): Soil formed in its original position by the breaking up of the parent rock. Examples include red, black, laterite, and desert soils.

• Transported Soil (Ex situ): Soil transported from its place of origin by agents of erosion such as wind or water.

  • Aluvial Soil is the primary example of transported soil.

  • These soils typically do not have a clear soil profile compared to $In\,situ$ soils because they are deposited as sediments from other locations.

Aluvial Soil

• General Characteristics:

  • It is an $Ex\,situ$ (transported) soil formed by sediments brought down by rivers.

  • Also known as Riverine soil.

  • Covers approximately $40\%$ of India, primarily in the Indus, Ganga, and Brahmaputra basins.

  • Found to depths of up to $500\,m$.

  • Color: Faint yellow.

  • Texture: Consists of sand, silt, and clay. A mixture of these three is called Loam ($LOAM$).

• Nutrient Composition: Rich in lime, potash, and humus. It is deficient in nitrogen and tends to be phosphoric.

• Regional Textural Differences:

  • Upper Ganga: Texture is rougher or more coarse ($COARSE$).

  • Lower Ganga (West Bengal): Texture is finer and contains more moisture.

• Sub-Types of Alluvium:

  • Bhangar: The older alluvium; occupies a large part of the Northern Plains. It is less fertile and contains lime nodules with a clayey nature.

  • Khadar: The younger alluvium; highly fertile and contains fine silt and clay.

• Regional Distribution:

  • Inland Alluvium: Found in the plains of major rivers.

  • Deltaic Alluvium: Found in the deltas of the Mahanadi, Godavari, Krishna, and Cauvery.

  • Coastal Alluvium: Found along the coasts of Peninsular India and the plains of Gujarat.

• Associated Crops: Rice, cotton, sugarcane, oilseeds, and tobacco. It is highly important for Jute cultivation in the Bengal region.

Black Soil

• Nomenclature: Also referred to as Black Cotton Soil, Regur Soil, or Lava Soil.

• Origin: $In\,situ$ volcanic origin. It is formed by the disintegration of basalt through the denudation of volcanic rocks.

• Physical Properties:

  • Black in color.

  • Fine texture with up to $50\%$ clay content.

  • Highly moisture-retentive, which is essential for cotton growth.

• Nutrient Profile: Rich in lime, iron, magnesium, humus, alumina, calcium, and potash.

• Distribution: Found in the Deccan region, including Maharashtra, Madhya Pradesh, Northern Karnataka, Gujarat, Telangana, and parts of Andhra Pradesh (specifically the Guntur region).

• Historical Anecdote: During Nitish Kumar's tenure as Railway Minister (Vajpayee administration), black soil areas were linked to rail derailments because the soil tended to sag or sink under the tracks.

• Associated Crops: Cotton, Jowar, sugarcane, vegetables, coffee, and tobacco.

Red Soil

• Origin: $In\,situ$ soil formed by the prolonged weathering of crystalline and metamorphic rocks of the Peninsular Plateau.

• Characteristics:

  • Red in color due to the presence of Iron Oxide ($Fe_2O_3$). It may occasionally appear chocolate brown or yellow.

  • Consists of a mixture of clay and sand.

  • Rich in potash but deficient in lime and nitrogen.

• Distribution: Covers Jharkhand, Odisha, Karnataka, Tamil Nadu, parts of Kerala, Goa, and stretches from Bundelkhand down through the peninsula.

• Agricultural Use: Ideal for dry farming as it needs irrigation support.

• Special Geography: Includes Anantapur district in Andhra Pradesh, noted as the second-largest desert region in India after parts of Rajasthan.

• Associated Crops: Groundnut and millets (crops that do not require high water levels).

Laterite Soil

• Formation Process: Formed $In\,situ$ due to Leaching (also called de-silication) under conditions of heavy tropical rainfall.

• Leaching Definition: The loss of soluble substances and nutrients from the top layer of soil due to excessive rain, making the layer extremely infertile.

• Physical Characteristics: Red in color (due to iron oxide), coarse in texture, and high in acidity.

• Utility: Generally unsuitable for mass cultivation of staples like paddy or sugarcane. Widely used in the construction industry (brick-making).

• Distribution: Small portions in the Northeast, Jharkhand, Madhya Pradesh, Tamil Nadu, and the Western Coast (Kerala and Karnataka).

• Associated Crops: Cashew, tobacco, and Tapioca (a major crop in Kerala). The Spices Board of India is headquartered in Kochi, Kerala, reflecting the region's agricultural profile.

Soil Erosion: Types and Causes

• Definition: The removal of the topsoil cover by water, wind, or human activity. It occurs when the rate of removal of soil particles exceeds the rate of soil formation.

• Causes: Faulty agricultural practices, pollution, drought, and floods.

• Erosion by Running Water:

  • Sheet Erosion: The slow removal of a thin layer of soil when vegetation is destroyed (common in the Himalayas and Nilgiris).

  • Gully Erosion: Occurs when water gushes in deep paths called Rills, which deepen to form Ravines (e.g., the Chambal Valley in Madhya Pradesh, known as "Badlands").

  • Stream Bank Erosion: Flash floods cause rivers to cut into banks and deposit silt load in agricultural fields across UP, MP, and Rajasthan.

• Sea Erosion: Powerful coastal waves eat away land.

  • Case Study: In the Krishna District of Andhra Pradesh (near Machilipatnam), islands known as Lanas shrunk significantly over 20 years due to the sea "eating" the land.

• Wind Erosion: Primarily seen in the Thar Desert (Rajasthan). Wind blows fine particles/nutrients away and deposits them elsewhere (desertification), making land unproductive.

• Human Factors:

  • Improper cultivation practices.

  • Overgrazing: Cattle eat away plant life, leaving nothing to bind the soil.

  • Deforestation: Cutting trees removes the root systems that hold soil together.

  • Population Pressure: Construction and infrastructure projects.

  • Infrastructure: Laying railway lines disturbs local topography.

• Annual Loss: Rainwater washes away approximately $18\,cm$ of fertile topsoil every year.

Soil Conservation and Prevention Techniques

• Soil Conservation Definition: The prevention of soil loss due to erosion and the prevention of reduced soil fertility.

• Objectives: Avoid loss of topsoil, prevent the lowering of the water table, avoid silting of canals, and prevent landslides (e.g., Uttarakhand).

• Mechanical and Agricultural Methods:

  • Terrace Farming: Creating level steps on hilly slopes that act as bunds to stop water and soil from running down. Popular in USA and Japan.

  • Contour Plowing: Using the natural contours of the land as bunds. It differs from terrace farming in the way water flow is controlled (using ridges and furrows). Popular in China and Japan.

  • Shelter Belts: Planting several rows of trees to act as "windbreaks" to check wind erosion.

  • Strip Cropping: Growing crops in alternate strips of land to reduce the impact of wind.

  • Afforestation: Increasing tree cover to bind the soil.

  • Crop Rotation: Alternating crops (e.g., planting pulses between cycles of paddy or sugarcane) to maintain soil health.

  • Leguminous Plants: Growing pulses to naturally restore soil nutrients.

  • Fallowing and Jhuming: Shifting cultivation (Jhuming) is legally banned due to the creation of barren land.

  • Physical Infrastructure: Constructing dams to control water flow and plugging gullies with silt deposition.

  • Management: Limiting the time allowed for cattle grazing.