Soils of India

Soil Composition and Formation

Soil is a composite mixture of rock fragments and organic matter that develops on the Earth's surface. The formation of soil is influenced by several key factors, including the topography, parent material, climate, vegetation, other life forms, and the passage of time. Human activities also exert a significant impact on soil composition. The constituents of soil encompass mineral particles, humus, water, and air, with the relative proportions varying based on the soil type. Some soils exhibit deficiencies in specific components, while others showcase diverse combinations.

It is structured into three distinct layers referred to as horizons. The uppermost layer, known as 'Horizon A,' integrates organic materials with mineral substances, nutrients, and water essential for plant growth. Situated between 'Horizon A' and 'Horizon C,' 'Horizon B' acts as a transitional zone, containing materials derived both from above and below. Although it retains some organic matter, mineral substances have undergone noticeable weathering. Comprising loose parent material, 'Horizon C' constitutes the base layer.

This layer serves as the initial phase in the soil formation process, ultimately giving rise to the preceding two layers. This arrangement of layers constitutes the soil profile. Beneath these three horizons lies the rock formation, commonly known as parent rock or bedrock.

Historically, soil classification was based on fertility – soils were categorized as either 'Urvara' (fertile) or 'Usara' (non-fertile). However, contemporary approaches consider various characteristics, including texture, color, moisture content, and more. In 1956, the Soil Survey of India, a governmental institution, was established to comprehensively study soil and its attributes.

Definition of Soil

Soil is a composite blend of minute rock particles or debris and organic materials, such as humus, that evolves on the Earth's surface and provides a foundation for plant growth.

Soil Classification – Urvara vs Usara

In ancient India, soil classification was rudimentary yet decisive. The division centered on the soil's fertility status, resulting in two categories: Urvara [fertile] Usara [sterile]

Soil Classification – Involved Institutions

In the modern era, with enhanced comprehension of soil attributes, classification factors expanded to encompass texture, color, moisture, and more. The establishment of the Soil Survey of India in 1956 paved the way for an in-depth study of Indian soils and their attributes. The National Bureau of Soil Survey and Land Use Planning, an entity under the Indian Council of Agricultural Research, conducted extensive investigations into Indian soils.

Key Classifications of Indian Soils

1. Alluvial soil [43%]

2. Red soil [18.5%]

3. Black / regur soil [15%]

4. Arid / desert soil

5. Laterite soil

6. Saline soil

7. Peaty / marshy soil

8. Forest soil

9. Sub-mountain soil

10. Snowfields

Alluvial Soil:

Predominant soil type in India, covering about 43% and spanning 143 sq. km. Widespread across northern plains and river valleys. Prominent in peninsular India, particularly in deltas and estuaries. Rich in humus, lime, and organic matter. Highly fertile. Examples include the Indus-Ganga-Brahmaputra plain and the Narmada-Tapi plain. Deposited by rivers and streams, making them depositional soils. Sand content decreases from west to east. New alluvium termed Khadar; old alluvium termed Bhangar. Color: Light Grey to Ash Grey. Texture: Sandy to silty loam or clay. Rich in: Potash Deficient in: Phosphorous. Cultivated crops: Wheat, rice, maize, sugarcane, pulses, oilseeds.

Red Soil:

Common in low rainfall regions. Also known as Omnibus group. Porous and friable structure. Lacks lime and kankar (impure calcium carbonate). Deficient in: Lime, phosphate, manganese, nitrogen, humus, and potash. Color: Red due to Ferric oxide; lower layer reddish yellow or yellow. Texture: Sandy to clay and loamy. Cultivated crops: Wheat, cotton, pulses, tobacco, oilseeds, potato.

Black Soil / Regur Soil:

Regur denotes cotton – ideal for cotton cultivation. Dominates the Deccan region. Mature soil. High water retention. Swells when wet and shrinks when dried, self-ploughing due to wide cracks upon drying. Rich in: Iron, lime, calcium, potassium, aluminum, and magnesium. Deficient in: Nitrogen, phosphorous, organic matter. Color: Deep black to light black. Texture: Clayey. Cultivated crops: Cotton, soybeans, oilseeds.

Laterite Soil:

Named after the Latin 'Later' meaning Brick. Soft when wet, hard when dry. Occurs in high temperature, high rainfall areas. Result of intensive leaching; loss of lime and silica. Low humus due to rapid decomposition by bacteria and plant uptake. Rich in: Iron, aluminum. Deficient in: Nitrogen, potash, potassium, lime, humus. Color: Red due to iron oxide. Cultivated crops: Rice, ragi, sugarcane, cashew nuts.

Desert / Arid Soil:

Found in arid and semi-arid conditions. Deposited by wind action. High salt content. Low moisture and humus. High kankar content restricts water infiltration. Insufficient nitrogen, normal phosphate. Texture: Sandy. Color: Red to Brown.

Peaty / Marshy Soil:

Present in high rainfall, high humidity regions. Sparse vegetation. Abundant dead organic matter makes the soil alkaline. Heavy, black soil.

Forest Soil:

Found in regions with high rainfall. Low humus content, resulting in acidic soil.

Mountain Soil:

Located in mountainous regions. Immature soil, low humus, and acidic properties.

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