Soils of India: Formation, Types, Erosion, and Conservation Guide
Introduction to Soil and Pedology
Soil Definition: Soil is a critical natural resource that covers a significant portion of the Earth's land surface. It is the foundation upon which all forms of life depend, either directly or indirectly, as a primary source of food.
Dynamic Nature: Soil is considered a dynamic layer because it sustains vegetation cover, serves as a storage for groundwater used by plants and humans, and acts as a natural resource for agricultural crop cultivation.
Pedology: This is the scientific study of soil within its natural environment.
Pedogenesis: This refers to the specific process of the formation and development of soil.
Soil Composition: Soil consists of various components in varying proportions:
Fine particles.
Silica.
Clay.
Chalk (Calcium carbonate).
Humus: This is formed by the decomposition of plant remains, animal manures, and dead animals. It is identified as the most essential element for determining the fertility of the soil.
In-Situ vs. Transported Soils
In-Situ Soils:
Definition: These are soils that are formed in their original place of origin.
Formation Process: Weathering is the primary process involved in their formation.
Examples: Black Soil, Laterite Soil, and Red Soils.
Transported (Ex-Situ) Soils:
Definition: These are soils formed as a result of transportation by natural agents such as wind and water.
Formation Process: Both weathering and erosion are involved in their formation.
Example: Alluvial Soil.
Alluvial Soil
Origin: The name 'Alluvial' refers to soils formed on alluvium deposits brought by rivers and streams. The parent material comes from the deposition of erosional products. These are categorized as Transported or Ex-situ soils.
General Characteristics:
Depth: These soils are found to depths of up to .
Color: Ranges from yellow and light brownish to light and dark grey.
Chemical Composition: Rich in Potash, humus, and lime; deficient in nitrogen and phosphoric acid.
Texture: Varies significantly from coarse to fine.
Classification by Location:
Inland Alluvial Soil: Found in the Indus, Ganga, and Brahmaputra regions. It is sandy, coarse-textured, porous, and dry. Commonly found in parts of Uttar Pradesh (UP) and Bihar. It notably lacks humus.
Deltaic Alluvial Soil: Formed by fine silt and clay deposited by rivers at their mouths near the sea. It is fine-textured, compact, and has high moisture retention. Found in West Bengal (WB) and the deltas of the Mahanadi, Krishna, Godavari, and Kaveri rivers. It contains humus.
Coastal Alluvial Soil: Found along the Western coastal plain (Gujarat to Kerala) and the Eastern coastal plain (Odisha to Tamil Nadu). It is generally sandy, coarse, and has less humus.
Note on Color: Alluvial soils in the valleys and deltas of the Godavari and Krishna rivers are dark in colour because they are mixed with regur (black) soil.
Khadar vs. Bhangar:
Khadar (Newer Alluvium):
Found near rivers, on flood plains, and deltas.
Finer in texture, light brown, loamy, porous, and clayey.
High fertility as it is replenished by silt deposited during floods.
Bhangar (Older Alluvium):
Found away from rivers on piedmont plains.
Characterised by coarse texture and contains kankar (lime nodules).
Dark grey in colour, sandy, and non-porous.
Generally infertile.
Distribution:
States: Parts of Punjab, Haryana, Uttar Pradesh, Bihar, West Bengal, and Odisha.
Regions: Coast of Gujarat, Brahmaputra valley, and coastal strips of Peninsular India.
Crops Grown:
Suitable for both Rabi and Kharif crops.
Food Crops: Rice, wheat, and cereals.
Cash Crops: Cotton, oilseeds, sugarcane, and jute (specifically in the Lower Ganga Valley).
Black Soil (Regur Soil)
Formation: Evolved from the weathering of basalt rock, which is volcanic in nature. This is an in-situ soil.
Color: Its characteristic black colour is due to the presence of iron (specifically magnetite ore).
Characteristics:
Deep and fine-grained.
Color varies from black to chestnut brown.
Composition (LIMCAP): Rich in Lime, Iron, Magnesium, Calcium, Aluminium, and Potash.
Hydration Properties: Highly moisture retentive and becomes very sticky when wet. It requires tilling immediately after the first rain.
Self-ploughing: During dry conditions, the soil hardens and develops deep cracks. These cracks aid in aeration and air circulation.
Distribution:
Regions: The Deccan Trap.
States: Parts of Gujarat, Maharashtra, Madhya Pradesh (MP), Chhattisgarh, Southern parts of UP, North-west Odisha, and Southern Tamil Nadu.
Crops Grown:
Food Crops: Wheat, jowar, fruits, and vegetables.
Cash Crops: Cotton (the primary crop), sugarcane, linseed, and gram.
Red Soil
Formation: Created by the weathering of crystalline and metamorphic rocks. It consists of a mixture of clay and sand.
Characteristics:
Color: Red due to high iron oxide content (haematite ore).
Composition: Deficient in nitrogen, lime, phosphoric acid, and humus.
Texture: Porous and friable, but notably not moisture retentive.
Vulnerability: Extremely prone to soil erosion.
Productivity: While naturally limited, the soil becomes productive with the addition of fertilizers.
Distribution:
Regions: Southern parts of the Peninsular region and the Chotanagpur Plateau Region.
States: Tamil Nadu, Karnataka, North-Eastern parts of Andhra Pradesh (AP), Chhattisgarh, and Odisha.
Crops Grown:
Food Crops: Pulses, millets, rice, and wheat.
Cash Crops: Cotton and sugarcane.
Laterite Soil
Formation: Formed via leaching of lateritic rocks under conditions of high temperature and heavy rainfall with alternate dry and wet periods. It develops in-situ.
The Leaching Process: This occurs when nutrients are washed away by heavy rains. This reduces the proportion of lime and silica while increasing the proportion of iron and aluminium compounds in the upper soil layers.
Characteristics:
Red in colour and rich in iron.
Acidic in nature.
Coarse and crumbly in texture; not moisture retentive.
Composition: Negligible amounts of nitrogen, potassium, and organic matter.
Agricultural Utility: Generally not suitable for agriculture in its natural state but supports pasture and scrub forests. With the use of manure, it can be cultivated. Its hard nature makes it useful as a building material.
Distribution:
Regions: Summits of the Western and Eastern Ghats, and the Malwa Plateau.
States: Tamil Nadu, Andhra Pradesh, West Bengal, Odisha, Karnataka, Goa, and Kerala.
Crops Grown:
Due to high acidity and poor moisture retention, it is unsuitable for most cereals or pulses.
Food Crops: Tapioca and cassava.
Cash Crops: Cashew (grows well), tea, coffee, and rubber.
Soil Erosion: Causes and Types
Definition: The destruction and removal of unconsolidated soil particles by agents of erosion like rain and wind.
Causes:
Lack of vegetation cover.
Anthropogenic (human) factors.
Patterns of rainfall.
Topography of the land.
Types of Erosion:
Running Water Erosion:
Sheet Erosion: Occurs when torrential rainfall removes the entire top layer of soil. Common in hilly areas like the Himalayas, North Eastern Hills, and the Nilgiris. Rivers like the Brahmaputra, Kosi, Chambal, Damodar, and Ganga cause massive damage during overflows, creating rugged topography.
Rill Erosion: Finger-like rills appear on the landscape. These eventually increase in number, depth, and width, hampering cultivation.
Gully Erosion: Occurs when water gushes in distinct paths, deepening into ravines or gullies reaching the bedrock. This creates "badland topography." A primary example is the Chambal Valley.
Stream Bank Erosion: Flowing water erodes river banks, widening the river bed over time.
Wind Erosion: Predominant in deserts and dry regions with little vegetation. Wind blows away fine sand particles and deposits them elsewhere.
Human (Anthropogenic) Factors: Includes human settlement, improper cultivation techniques, overgrazing, and deforestation.
Regional Distribution of Soil Erosion
Running Water: Parts of Assam, Bihar, Manipur, and West Bengal. Slopes of the Western Ghats and Shillong Plateau are also affected.
Sheet Erosion: Chotanagpur plateau and the slopes of the Himalayas.
Gully Erosion/Ravines: Parts of Jharkhand, Maharashtra, Karnataka, and Kerala. Extensive ravine tracks exist along the Chambal and Yamuna rivers in Madhya Pradesh, and the sub-Himalayan lower slopes in Punjab and Himachal Pradesh.
Flood Erosion: Northern Uttar Pradesh, Northern Bihar, parts of West Bengal, and Assam.
Wave Erosion: Maximum along the coasts of Kerala, Karnataka, and Goa during the monsoon.
Landslides: Western slopes of Western Ghats and Eastern Himalayas during heavy monsoon rainfall.
Wind Erosion: Limited to desert districts of Rajasthan and Gujarat.
Soil Conservation: Need and Methods
Necessity for Conservation:
To prevent the loss of fertile topsoil and plant nutrients to maintain crop yields.
To facilitate groundwater recharge; without vegetation, rainwater cannot percolate (seep) into the soil.
To reduce "run-off" (rainwater that flows down slopes instead of seeping in), which increases river discharge and causes devastating floods.
To combat desertification caused by deforestation and the falling groundwater table.
Afforestation: Planting trees and vegetation is fundamental. Roots hold the soil, while shrubs and trees reduce water flow velocity and wind speed.
Agronomic Measures:
Nutrient Management: Adding organic matter, fertilizers, and growing leguminous plants.
Crop Management: Replacing slash-and-burn (jhooming) with crop rotation or multiple cropping to prevent leaching.
Reclamation: Fixing waterlogged and saline soils. Developing ravine areas (e.g., Central India).
Grazing Control: Moving herds over different pastures to prevent overgrazing.
Shelterbelts: Rows of trees planted perpendicular to wind direction to check sand dune migration (e.g., Thar Desert) and coastal erosion.
Mechanical Measures:
Terrace Farming: Converting slopes into a series of steps (common in Himalayas and peninsular areas).
Bunds: Low walls constructed parallel to contours at the edge of steps to reduce erosion.
Contour Ploughing: Ploughing parallel to contours to arrest rainwater in furrows.
Strip Cropping: Dividing fields into strips with different crops grown transverse to wind direction.
Gully Plugging: Building small dams or plugs in deep gullies and planting fast-growing bushy plants on the gully floors.
Government Schemes:
Integrated watershed management.
Reclamation of ravines and badlands.
Vanamahotsava (Afforestation) and restriction of overgrazing.
Schemes to control shifting cultivation.
Rural development and ecological awareness programmes.