Soil

Factors affecting soil formation:

1. type of parent material/bedrock

2. climatic conditions(temperature and rainfall)

3. presence of living organisms(plants and animals)

4. Relief and topography

pedogenesis - process of soil formation

Alluvial soil: formed by sediments of alluvium eroded from rocks and transported over a long distance by rivers(riverine or ex situ/transported soil)

Alluvial soil - extremely fertile(found in Northern Plains of India, basin of Indus and tributaries Jhelum, Chenab, Ravi, Sutlej and Beas, Basin of Ganga and tributaries Yamuna, Gomati, Ghaghara, Gandak, Kosi, Brahmaputra basin and tributaries, valleys and deltas of rivers)

Alluvial soil is formed by sediments(alluvium) eroded from rocks and transported over long distances through rivers

Riverine soil(mostly found in river basins)

Ex situ/transported soil - sediment deposition far from parent rock

Riverine alluvium - sand, silt and clay(loam) in varying proportions

45% of total land surface of India is alluvial soil

Classification of Alluvial soil:

Bhangar:

Older alluvium

Found: 30 m above flood level in river terraces

Coarse in texture

Less fertile

Khadar:

Newer alluvium

Found in deltas along the banks of its rivers in its floodplains

Finer in texture

More fertile, gets replenished b y floods every year

Classification of alluvial deposits:

Coastal alluvium - found in narrow strips along eastern and western coasts of india

Deltaic alluvium - Deposited at the mouth of rivers(predominant in Ganga-BP delta along with deltaic areas of eastern floodplains)

Rivers of eastern floodplains - mahanadi, godavari, krishna, cauvery

Inland alluvium - dry sandy, coarse and porous soil(found on pains of ganga and tributaries)

Characteristics of alluvial deposits:

Extremely fertile; suitable for both rabi and kharif crops

Rich in potash and lime

Deficient in nitrogen, phosphoric acid, and sometimes also lacks humus

Varied greatly in texture from coarse to fine(sediments are finer near river approaching mouth)

Colour varied from yellow to brown(Deccan coastal strips: darker soil because the rivers flow over black lava soil)

Found upto depth 500m

Crops: rice, wheat, cotton, oilseed, sugarcane, jute

Black cotton soil

Black cotton/regur soil - volcanic origin(disintegrated sheets of lava/basalt)

Black cotton soil is found in gujarat, maharashtra, up, madhya pradesh, andhra pradesh, tn

Characteristics of black cotton soil:

Fine grained and clayey

Colour varies from black to chestnut brown

Rich in iron, potash, lime calcium, alumina, magnesium, carbonates and humus

Moisture retentive, sticky when wet

Self ploughing

Crops - cotton, sugarcane, wheat, tobacco

Red soil - residual soil formed by weathering of old crystalline igneous rocks(like granite) and metamorphic rocks(like gneiss)

Distribution of red soil - tn, karnataka, andhra pradesh, chhattisgarh, madhya pradesh, jharkhand, odisha

Characteristics of red soil -

Red due to high iron oxide content; colour may vary from chocolate brown to yellow

Mixture of clay and sand

Deficient in nitrogen, lime, phosphoric acid and humus; not a fertile soil; becomes productive when fertilisers are added

Rich in potash

Porous; cannot retain moisture(irrigation essential)

Easy to till

Crops - maize, wheat, rice, millets, tea, cotton, sugarcane, cashew nut

Laterite soil - residual soil formed by leaching of lateritic rocks under high conditions of temperatures and heavy rainfall with alternating dry and wet periods

Leaching - process by which water soluble nutrients in soil like lime and silica percolate down soil profile during rains

Leaching renders the topsoil infertile as it is left with only oxides of iron and aluminium

Laterite soil - building material =(can be cut with spade, hardens like iron when exposed to air)

Distribution of laterite soil - summits of western ghats and eastern ghats in peninsular india, rajmahal ranges, vindhya and satpura, malwa plateau, summits of garo and Khasi hills in north east, various parts of andhra pradesh tn, west bengal, odisha, karnataka and goa

Characteristics and composition of laterite soil:

Infertile soil due to leaching of essential minerals

Poor in nitrogen , potassium, phosphorus and lime

Rich in iron

Red due to high content of iron oxide

Coarse texture; friable

Highly acidic, unsuitable for agriculture

Porous; bad water retention

Crops : cashew nut and tapioca(tea, coffee, rubber, etc. with help of irrigation)

Soil erosion - detachment and transportation of soil by agents of denudation such as weathering, running water and wind.

Causes for soil erosion:

Vegetation cover removed due to deforestation removes binding agent(roots) and exposes soil to weathering agents

Anthropogenic factors like faulty agricultural practices, overgrazing, contour ploughing, and mining

Pattern of rainfall changes leading to heavy rainfall in short span of time

topography(hill slopes more prone to erosion than level surfaces)

Types of soil erosion:

Erosion by running water

(i) Sheet erosion - torrential downpour in hilly regions with no vegetative cover leading to erosion of topsoil. Occurs in himalayas, nilgiri hills, etc.

(ii) Rill erosion - fast streams of water cutting narrow channels or grooves under high velocity and detaches soil

Rill - narrow channel

(iii) gully erosion:

Ravines - deeper and wider rills

Exposed bedrock in ravines forming rugged features - badland topography(river valley of chambal in malwa region of madhya pradesh and south eastern rajasthan)

(iv) Stream bank erosion - erosion and deposition of soil due to overflowing of river banks

(v) Erosion by waves/coastal erosion - strong waves erode sediments from cliffs and shorelines and carry them back to sea

Erosion by wind: occurs mostly in deserts and dry areas where there is no vegetative cover. It blows away dry sand and deposits it in other areas, making both unproductive. It has led to progression of deserts to the east from the deserts of western rajasthan and southern punjab

Human factors : civilisation, deforestation, mining, faulty agriculture methods