Soil

 

• Most important layer of the earth’s crust. mixture of rock debris and organic materials.
• Factors affecting the formation of soil are relief, parent material, climate, vegetation and other life-forms and time also human activity.
• Components of the soil are mineral particles, humus, water and air.

Soil Profile / Horizon

• ‘Horizon A’ is the topmost zone, where organic materials have got incorporated with the mineral matter, nutrients and water, which are necessary for the growth of plants.
• ‘Horizon B’ is a transition zone between the ‘horizon A’ and ‘horizon C’, and contains matter derived from below as well as from above. It has some organic matter in it, although the mineral matter is noticeably weathered.
• ‘Horizon C’ is composed of the loose parent material. This layer is the first stage in the soil formation process and eventually forms the above two layers.

Factors of soil Formation

• Soil formation are the nature of the parent rock and climatic factors.
• Topography, role of organic material and time taken for the composition of soil formation.

Classification of Soil

• Ancient Time – Urvara and Usara (fertile and sterile).
• 16th centrury A.D - classified on the basis of their inherent characteristics and external features such as texture, colour, slope of land and moisture content in the soil.
• Based on texture
• sandy, clayey, silty and loam, etc.
• Based on Colour
• Red, yellow, black, etc.
• Basis of genesis, colour, composition and location
1. Alluvial soils
2. Black soils
3. Red and Yellow soils
4. Laterite soils
5. Arid soils
6. Saline soils
7. Peaty soils
8. Forest soils.

Soil Survey of India, established in 1956. The National Bureau of Soil Survey and the Land Use Planning an Institute under the control of the Indian Council of Agricultural Research (ICAR).

Classified the Indian soils on the basis of their nature and character as per the United States Department of Agriculture (USDA) Soil Taxonomy – Inceptisols, Entisols. Alfisols, Vertisols, Aridisols, Ultisols, Mollisols, Others.

Alluvial Soil

• Northern plains and the river valleys. Depositional soils.
• 40 per cent of the total area.
• Narrow corridor in Rajasthan, they extend into the plains of Gujarat. deltas of the east coast and in the river valleys.
• Nature from sandy loam to clay. Rich in potash but poor in phosphorous.
• Upper and Middle Ganga plain, two different types of alluvial soils have developed, viz. Khadar (New Alluvium) and Bhangar (Older Alluvium). both contain calcareous concretions (Kankars).
• Loamy and clayey - lower and middle Ganga plain and the Brahamaputra valley.
• Sand content decreases from the west to east.
• Colour - grey to ash grey. Alluvial soils are intensively cultivated.

Black Soil

• ‘Regur Soil’ or the ‘Black Cotton Soil’
• Deccan Plateau - parts of Maharashtra, Madhya Pradesh, Gujarat, Andhra Pradesh and some parts of Tamil Nadu.
• Upper reaches - Godavari and the Krishna, North western part of the Deccan Plateau.
• Clayey, deep and impermeable. Sticky when wet and shrink when dried.
• ‘self-ploughing’ - Slow absorption and loss of moisture.
• Rich in lime, iron, magnesia, alumina & potash. But they lack in phosphorous, nitrogen and organic matter.
• Colour - deep black to grey.

Red and Yellow Soil

• Crystalline igneous rocks. Areas of low rainfall in eastern and southern part of the Deccan Plateau.
• Odisha and Chhattisgarh and in the southern parts of the middle Ganga plain.
• Reddish colour due to a wide diffusion of iron in crystalline and metamorphic rocks. looks yellow when it occurs in a hydrated form.
• Normally fertile. Poor in nitrogen, phosphorous and humus.

Laterite Soil

• Areas with high temperature and high rainfall. Rich in iron oxide and aluminium.
• Humus removed fast by bacteria.
• poor in organic matter, nitrogen, phosphate and calcium, while iron oxide and potash are in excess.
• Not suitable for cultivation. Application of manures and fertilisers are required for making the soils fertile for cultivation.
• Red laterite soils in Tamil Nadu, Andhra Pradesh and Kerala are more suitable for tree crops like cashew nut.
• Develop higher areas of the Peninsular plateau. Karnataka, Kerala, Tamil Nadu, Madhya Pradesh and the hilly areas of Odisha and Assam.
• Used for Brick Making.

Arid Soils

• Red to brown in colour.
• Salt content is so high that common salt is obtained by evaporating the saline water.
• Dry climate, high temperature and accelerated evaporation. Lake moisture and humus.
• Nitrogen is insufficient & Phosphate content is normal.
• ‘Kankar’ layer formation in the bottom horizons restricts the infiltration of water.
• Western Rajasthan characteristic arid topography contain little humus and organic matter.

Saline Soils

• Usara soils - larger proportion of sodium, potassium and magnesium, - they are infertile & Poor drainage. sandy to loamy.
• In arid and semi-arid regions in waterlogged and swampy areas.
• lack in nitrogen and calcium.
• western Gujarat, deltas of the eastern coast and in Sunderban areas of West Bengal.
• In Rann of Kuchchh - Southwest Monsoon brings salt particles.
• Areas of intensive cultivation with excessive use of irrigation.
• Punjab and Haryana, farmers are advised to add gypsum to solve the problem of salinity in the soil.

Peaty Soil

• Heavy rainfall and high humidity. Good growth of vegetation.
• large quantity of dead organic matter accumulates, rich humus and organic content to the soil.
• Organic matter – 40-50%. Heavy and black in colour.
• Many places, they are alkaline.
• Northern part of Bihar, southern part of Uttarakhand and the coastal areas of West Bengal, Odisha and Tamil Nadu.

Forest Soil

• Sufficient rainfall is available depending on the mountain environment.
• Loamy and silty on valley sides and coarse-grained in the upper slopes.
• Snow-bound areas of the Himalayas, Acidic with low humus content - lower valleys are fertile.
• Germination and growth of plant and vegetation including crops.

Soil Degradation

• Decline in soil fertility - nutritional status declines and depth of the soil goes down due to erosion and misuse.
• Deforestation, overgrazing, overuse of chemical feritilisers or pesticides, rain wash, landslides and floods.

Soil Erosion

• Destruction of the soil cover.
• Balance between Rate of removal of fine particles from the surface is the same as the rate of addition of particles to the soil layer.
• Sometimes, Balance is disturbed by natural or human factors, leading to a greater rate of removal of soil.
• Wind and water are powerful agents of soil erosion. Wind erosion is significant in arid and semi-arid regions.
• heavy rainfall and steep slopes, erosion by running water is more significant.
• Main form in India -  sheet and gully erosion (Common in steep slope).
• Gullies deepen with rainfall, cut the agricultural lands into small fragments and make them unfit for cultivation. Large number of deep gullies or ravines is called a badland topography.
• Ravines common in Chambal basin, found in WB, TN. losing about 8,000 hectares of land to ravines every year.
• Deforestation - Plants keep soils bound in locks of roots, and thus, prevent erosion. They also add humus to the soil by shedding leaves and twigs.
• Fairly large area of arable land in the irrigated zones of India is becoming saline because of over irrigation.
• Unless the soil gets enough humus, chemicals harden it and reduce its fertility in the long run. Half of the total land of India is under some degree of degradation.

Soil Conservation

• To maintain soil fertility, prevent soil erosion and exhaustion, and improve the degraded condition of the soil.
• Soil erosion is essentially aggravated by faulty practices.
• Slope gradient of 15 - 25 per cent should not be used for cultivation.
• Land used for agriculture, terraces should carefully be made.
• Avoid Over-grazing and shifting cultivation.
• Contour bunding, Contour terracing, regulated forestry, controlled grazing, cover cropping, mixed farming and crop rotation are some of the remedial measures which are often adopted to reduce soil erosion.
• Finger gullies can be eliminated by terracing, bigger gullies - Series of check dams.
• Series of check dams - protect cultivable lands from encroachment by sand dunes through developing shelter belts of trees and agro-forestry.
• Lands not suitable for cultivation should be converted into pastures for grazing.
• Stabilize sand dunes in western Rajasthan by the Central Arid Zone Research Institute (CAZRI).
• Central Soil Conservation Board - prepared a number of plans for soil conservation in different parts of the country.
• Integrated land use planning is best technique for proper soil conservation.

Other Conservation Measures

• Mulching: bare ground between plants is covered with a layer of organic matter like straw.
• Contour Barriers: build barriers along contours.
• Rock dam: Slow down the flow of water. Prevents gullies and further soil loss.
• Terrace farming: steps or terraces, reduce surface run off and soil erosion.
• Intercropping: grown in alternate rows, sown at different times
• Contour ploughing: parallel to the contours of a hill slope to form a natural barrier
• Shelter belts: coastal and dry regions, rows of trees are planted to check the wind movement protect soil cover