SOIL SCIENCE INTRODUCTION— AGRICULTURE OPTIONAL

Also for M.Sc Entrance, AFO, IFFCO, JRF, NABARD, RRB-SO, and STATE Exam.

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What is Soil Science?

The study of soil as a natural resource on the earth's surface is known as soil science. This field encompasses soil formation, classification and mapping, as well as the physical, chemical, biological, and fertility properties of soils. It also examines how these properties relate to the use and management of soils.

Soil Components

Composition of Atmospheric Air

Nitrogen: By Volume (78.08%), By Weight (76.5%)

Oxygen: By Volume (20.9%), By Weight (23.1%)

Carbon Dioxide: By Volume (0.033%), By Weight (0.04%)

Other Gases: By Volume (0.93%), By Weight (1.36%)

Composition of Soil and Atmospheric Air

Nitrogen: Soil Air (79.2%), Atmospheric Air (78.08%)

Oxygen: Soil Air (20.6%), Atmospheric Air (20.97%)

Carbon: Soil Air (0.30%), Atmospheric Air (0.03%)

Types of Soil in India

Major Classification of Indian Soil are:

1. Alluvial Soil
2. Red Soil
3. Black/Regur Soil
4. Arid/Desert Soil
5. Laterite Soil
6. Saline Soil
7. Peaty/Marshy Soil
8. Forest Soil

Twelve Soil Orders:

Major Soils of India and their Orders:

— Alluvial: Entisol, Inceptisols and Alfisols
— Black: Vertisol
— Red: Alfisols
— Laterite: Ultisols
— Desert: Aridisol

Alluvial soil:

• It is the most important type of soil found in India.
• Alluvial soils are deficient in nitrogen, humus and phosphorus therefore it requires fertilizers.
• Highly fertile.
• Indus-Ganga-Brahmaputhra plain, Narmada-Tapi plain etc. are examples.
• They are depositional soil — transported and deposited by rivers, streams etc.
• New alluvium termed Khadar is sandy, light in colour and less Kankar nodules.
• Old alluvium is termed as Bhangar full of clay, dark colour and more Kankar nodules.
• Newly formed alluvium may not have distinct soil horizons while older alluvium may have soil horizons.
• The khadar soil is sandy and light in colour, while the bangar soil is clayey and dark.
• The khadar soil is more fertile but has less organic matter.
• The Bangar soil is less fertile but high in organic matter.
• Alluvial soils of plains are medium in phosphorous content and high in potassium content.
• Rich in: Potash.
• Colour: Light Grey to Ash Grey.
• Texture: Sandy to silty loam or clay
• Alluvial soils are suitable for the production of crops like rice, wheat, maize, sugar cane, tobacco, cotton, jute, oilseeds etc.

Red soil:

• Seen mainly in low rainfall areas, and semi-arid areas.
• pH- 7- 7.5
• Also Called Early soil.
• Well drained with moderate permeability.
• Low cation exchange capacity and low water holding capacity.
• Porous, friable structure.
• Absence of lime, kankar (impure calcium carbonate).
• Red soil is always in acidic nature.
• Highly suitable for groundnut crop cultivation.
• Colour: Red because of Ferric oxide. The lower layer is reddish-yellow or yellow.
• Texture: Sandy to clay and loamy.
• Crops like millets, pulses, oil seeds (ground nut, gingelly, castor) and tuber crops like cassava are commonly cultivated.

Black/Regur Soil

• Regur means cotton — the best soil for cotton cultivation.
• Mature soil, Also Called Late Soil.
• Dark-grey in colour due to clay-humus complex.
• The soil is rich in clay (montmorillonite) particles and has neutral to alkaline reactions.
• the pH of black soil is 7.2–8.5
• Black soil holds more moisture and is available for a long time.
• Black soil contains a high proportion of clay (30–40%), so, the water-holding/retaining capacity is high.
• Typical characteristics of this black soil are swelling (during the wet period) and shrinkage (dry period)
• Self-ploughing is a characteristic of black soil as it develops wide cracks when dried.
• The soils are finely grained and contain a high proportion of Calcium and Magnesium carbonates. They are poor in N, medium in P and medium to high in K (Characteristic feature of typical Indian soil)
• Colour: Deep black to light black.
• Crops Grown: Cotton, Bengal gram, mustard, millets, pulses, oil seeds (sunflower, safflower)
• Texture: Clayey.

Laterite Soil

• Laterite soils are formed due to the process of lateralization. i.e., leaching of all cations leaving Fe and Al oxides.
• Mostly found in hills and foothill areas.
• Self-ploughing is characteristics like black soil (Shrink well potential)
• Name from the Latin word ‘Later’ which means Brick.
• pH- 5–6
• Become so soft when wet and so hard when dried.
• Seen in the areas of high temperature and high rainfall.
• Formed as a result of high leaching, Lime and silica will be leached away from the soil.
• Organic matter in the soil will be removed fast by the bacteria as it is high temperature and humus will be taken quickly by the trees and other plants. Thus, humus content is low.
• Rich in: Iron and Aluminum
• Deficient in Nitrogen, Potash, Phosphorous, Lime, Humus
• Colour: Red colour due to iron oxide.
• Acid-loving crops (Plantation crops) and fruits (pineapple, avocado) are more cultivated.
• Tea, rubber, pepper, and spices are cultivated.
• At lower elevation places, rice is grown.

Desert/Arid Soil

• Desert soil is sandy soil and is found in low-rainfall areas.
• Seen under Arid and Semi-Arid conditions.
• Deposited mainly by wind activities.
• Such soil is alkaline in nature with a high pH value and is unproductive.
• High salt content, Lack of moisture and Humus.
• Impure Calcium carbonate content is high which restricts the infiltration of water.
• Nitrogen is insufficient and Phosphate is normal.
• Texture: Sandy
• Colour: Red to Brown.

Peaty/Marshy Soil

• Peaty soil →50 % OM (Undecomposed)
• Muck Soil- 20–50 %OM (Well decomposed)
• Peaty soil found in Kerala is called Kari.
• These are marshy soils and are a result of water logging and anaerobic conditions (which leads to partial decomposition of organic matter).
• These soils are characterized by a rich humus and organic content.
• These soils are generally acidic in nature.
• Areas of heavy rainfall and high humidity.
• The growth of vegetation is very less.
• Heavy soil with black colour.
• These are generally submerged during the rainy season and utilized for the cultivation of rice.

Forest Soil

• Regions of high rainfall.
• Humus content is less and thus the soil is acidic.
• These soils are very shallow, stony, and less fertile for the production of field crops. However, this type of soil is useful for forest produce such as timber, tropical fruits and fuel.

Chalka Soil

• The red sandy loam soils “Chalka soils” which cover a large area in Andhra Pradesh become very hard on drying with the result that growth of the crops is adversely affected.
• The incorporation of slow-decomposing crop residues and other materials such as powdered ground nutshell, and paddy husk improves these types of soils.

Types of Clay Minerals

• Expanding type: Smectite group (e.g., Montmorillonite) and vermiculite
• Non-expanding type: mica group (e.g.) Muscovite and biotite (illite).
• The sum of the exchangeable cations that a soil can absorb is called cation exchange capacity (CEC).
• CEC: It is also defined as “the number of cationic species bound at pH 7.0