SOIL : Geography Notes & Important Concepts for UPSC

Soil is a complex living system that covers the land. It is made up of minerals, organic matter, water, and air. Soil is essential for life on Earth, as it provides plants with the nutrients they need to grow. Soil also plays an important role in the water cycle and the carbon cycle.

There are many different types of soil, each with its own unique properties. The type of soil in a particular area is influenced by a number of factors, including climate, vegetation, and topography.

Soil is important for a number of reasons. It provides plants with the nutrients they need to grow, and it also plays an important role in the water cycle and the carbon cycle. Soil is also the foundation of agriculture, and it supports a wide variety of ecosystems.

Soil conservation is important because soil is a valuable resource that is easily lost. Soil erosion can be caused by a number of factors, including wind, water, and human activities. Soil conservation practices can help to reduce soil erosion and protect our soil resources.

"Finally, we'll also talk about something super important: how to take care of our soil. We'll find out ways to keep it healthy and safe from being worn away or damaged. This way, our soil can keep on helping plants grow and supporting life on our planet for a really, really long time."

Topics Discussed

What is Soil?

Soil is defined as the upper layer of the earth composed of loose surface material. It is a mixture of many substances including an endless variety of minerals, remnants of plants and animals, water and air. It is the end product of continuing interaction between the parent material, local climate, plant and animal organisms, and elevation of land. Since each of the elements varies over space, soils also differ from place to place. Soil is an important segment of our ecosystem, as it serves as an anchorage for plants and a source of nutrients. Thus, the soil is the seat, the medium, and the fundamental raw material for plant growth. Through its relative fertility, it affects man's economic activities and shapes the destiny of our country. When the soil is lost, property and culture are also lost. Therefore, it is a valuable national and fundamental earth resource of the country.

How is Soil Formed? 

Soil formation, also known as pedogenesis, is a complex and gradual process that takes place over thousands to millions of years. It results from the interaction of various physical, chemical, biological, and environmental factors. Here's how soil is formed:

• Weathering of Parent Material: Soil formation begins with the weathering of the parent material, which can be rocks, minerals, sediments, or organic materials. Weathering occurs due to physical (e.g., temperature changes, frost action) and chemical (e.g., dissolution, oxidation) processes that break down the parent material into smaller particles.

• Addition of Organic Matter: Organic matter, including decaying plants, animals, and microorganisms, is added to the surface. This organic material enriches the soil and provides essential nutrients.

• Biological Activity: Soil organisms, such as earthworms, bacteria, fungi, and plant roots, play a crucial role in soil formation. They help decompose organic matter, mix soil layers, and release nutrients through their activities.

• Leaching and Eluviation: Water percolating through the soil carries away soluble substances (a process called leaching) and moves them downward. This can lead to the accumulation of minerals and nutrients in lower soil horizons (eluviation).

• Illuviation: The deposition of leached materials into lower soil horizons is called illuviation. This process contributes to the development of distinct soil layers or horizons with varying properties.

• Climate: Climate, including temperature, rainfall, and humidity, influences the rate of weathering and the types of soil formed. Tropical regions, for example, tend to have more weathered soils than arid regions.

• Topography: The landscape's shape and slope affect soil formation. Steep slopes may lead to erosion, while flat areas can accumulate sediments and organic matter.

• Time: Soil formation is a gradual process that takes thousands to millions of years to develop mature soils. The longer the process continues, the more developed and fertile the soil becomes.

• Parent Material Composition: The chemical and mineral composition of the parent material influences the properties of the resulting soil. For example, limestone parent material leads to alkaline soils, while granite parent material produces acidic soils.

• Biological Activity: Soil microorganisms and plants contribute to the breakdown of organic matter and the release of nutrients, affecting soil fertility.

• Human Activities: Human activities like agriculture, deforestation, and urbanization can significantly impact soil formation. Improper land use and management practices can lead to soil degradation and erosion.

 

Over time, these factors interact and lead to the development of distinct soil profiles with characteristic horizons, such as the O horizon (organic layer), A horizon (topsoil), B horizon (subsoil), C horizon (weathered parent material), and R horizon (bedrock).

Soil profile

A soil profile is a vertical cross-section of the soil with many layers running parallel to the surface. These layers are known as soil horizons. The earth is arranged in many layers or horizons during its formation process.

Soil profiles typically comprise six horizons, each with distinct characteristics.

Note: The six soil horizons from top to bottom are: O, A, B, C, and R. represented below

• The O Horizon is the uppermost layer, primarily composed of leaf litter and fresh organic matter.
• The A Horizon is rich in decomposed organic matter and hosts various microorganisms like earthworms, fungi, and bacteria.
• The B Horizon contains less organic matter (humus) but has more mineral content.
• The C Horizon consists of broken bedrock fragments.
• The R Horizon is the compacted bedrock layer found at the bottom of the soil profile.

Types of Soil

Soil is not uniform across the globe; it varies from place to place. NCERT classifies the soils of India broadly into the following six types based on their properties and formation processes. The primary soil types discussed are:

soil resources in India map

1. Alluvial Soils

• Alluvial soil is the most important soil type in India.
• It covers vast areas like the valleys of the Sutlej, Ganga, and Brahmaputra rivers, as well as parts of the southern peninsula.
• This soil varies in texture from sandy loam to clay and is rich in potash but lacks nitrogen and organic matter.
• Its color generally ranges from grey to reddish brown.
  Alluvial soils are formed from deposits of silt and sand carried by rivers from the Himalayas and the Great Indian plateau.
• These soils are young and don't have well-developed profiles.
• They are highly productive and crucial for Indian agriculture.
• Alluvial soil in India can be divided into two types: newer alluvium (khadar) and older alluvium (bangar).
• Newer alluvium(Khadar) is a light, crumbly soil found in river valleys and floodplains.
• Older alluvium(Bangar), found on interfluves, has more clay and poor drainage.
• Almost all types of crops can be grown on these soils due to their productivity.

 

2. Black Soils (Regur)

• Black soils are mainly found in the Deccan lava region, covering parts of Maharashtra, Gujarat, Madhya Pradesh, Karnataka, Telangana, Andhra Pradesh, and Tamil Nadu.
• They form from volcanic basaltic lava disintegration, giving them their black color due to compounds of aluminum and iron.
• These soils are locally known as "regur" and cover about 64 million hectares.
• Black soils are typically clayey, with low permeability and impregnability, but their depth varies across regions.
• Notably, they retain moisture well, even during dry seasons, and develop cracks in summer when they lose moisture.
• When saturated, the soil becomes sticky, maintaining aeration and oxidation, which helps retain fertility.
• This sustained fertility is beneficial for crops like cotton, sugarcane, wheat, onions, and various fruits, making it valuable for agriculture, especially in regions with low rainfall.

3. Red Soils

• Red soils are found in the Peninsular upland regions of India, including Tamil Nadu, Karnataka, Goa, Maharashtra, Telangana, Andhra Pradesh, Orissa, Chotanagpur Plateau, and Meghalaya Plateau.
• They surround the black cotton soil zone and cover around 72 million hectares of arable land.
• These soils develop on crystalline rocks like granite and gneisses.
  Due to abundant iron compounds, red soils have a reddish color but lack organic matter.
• They are generally less fertile compared to black and alluvial soils.
• However, their productivity can be improved through irrigation and fertilizer use.
• Red soils are suitable for growing crops such as rice, millet, maize, groundnut, tobacco, and various fruits.

4. Laterite Soils

• Found in high-altitude areas with heavy rainfall in several states.
• Develop in hot and humid climates.
• Often found on high flat erosion surfaces.
• Prone to nutrient loss through leaching, making them infertile.
• Characterized by a hard, pebbly crust formed due to wet and dry periods.
• Features include chemical decomposition of parent rock, leaching of silica, reddish-brown color from aluminum and iron oxides, and lack of humus.
• Suitable for crops like rice, millets, and sugarcane in lowlands, and tropical plantations like rubber, coffee, and tea in the uplands.

5. Desert Soils

• Occur in western Rajasthan, Saurashtra, Kachchh, western Haryana, and southern Punjab.
• Associated with arid and semi-arid conditions, with water scarcity for six months.
• Sandy to gravelly texture, low organic matter, humus, and infrequent rainfall.
• Limited chemical weathering, with soil colors ranging from red to light brown.
• In general, not suitable for agriculture due to water scarcity, but some crops like cotton, rice, and wheat can be grown with adequate irrigation and fertilizers.

6. Mountain Soils

• Complex and diverse, varying with altitude, topography, geology, vegetation, and climate.
• Different types of soils are found in various regions, from deep alluvium in river basins and lower slopes to immature gravel at higher altitudes.
• Steep relief areas often have little to no soil.
• Crops vary by region, including rice in valleys, orchards on slopes, and potatoes in many areas.

Soil Composition 

1. Mineral Particles:

   • Soil is primarily composed of mineral particles, including sand, silt, and clay.
   • Sand particles range in size from 0.05 to 2.0 millimeters.
   • Silt particles are smaller, measuring between 0.002 and 0.05 millimeters.
   • Clay particles are the smallest, less than 0.002 millimeters in size.

2. Organic Matter:

   • Organic matter in soil typically makes up about 5% of its composition.
   • This organic matter includes decomposed plant and animal material, providing nutrients and improving soil structure.

3. Water Content:

   • Soil can contain varying amounts of water, depending on factors like precipitation and drainage.
   • Soil can hold water in its pore spaces, with the water content ranging from 25% to 50% by volume.

4. Air Content:

   • Air fills the spaces between soil particles.
   • Soil should ideally contain about 25% air to allow for proper aeration and root respiration.

5. Microorganisms:

   • Soil is home to a diverse community of microorganisms, including bacteria, fungi, and protozoa.
   • A teaspoon of healthy soil can contain billions of microorganisms.

6. Nutrients:

   • Soil contains essential plant nutrients, including nitrogen (N), phosphorus (P), and potassium (K).
   • Nutrient levels vary by soil type, but nitrogen often makes up about 0.1% of soil composition.

7. pH Level:

   • Soil pH measures its acidity or alkalinity on a scale of 0 to 14.
   • A pH of 7 is considered neutral. Soils with pH values below 7 are acidic, while those above 7 are alkaline.

8. Salts and Minerals:

   • Soils may contain various salts and minerals, depending on their geological origin.
   • Common minerals found in soils include quartz, feldspar, and mica.

9. Microbial Decomposition Products:

   • The decomposition of organic matter by soil microbes results in the formation of stable organic material called humus.
   • Humus contributes to soil structure and nutrient retention.

10. Soil Texture:

    • Soil texture refers to the relative proportions of sand, silt, and clay in the soil.
    • Loam, a balanced mixture of sand, silt, and clay, is considered ideal for most crops.

11. Soil Horizons:

• Soil is often divided into distinct horizons, each with unique properties.
• The O horizon contains organic matter, the A horizon is topsoil rich in nutrients, the B horizon contains minerals leached from above, and the C horizon consists of weathered parent material.

Data & Importance of Soil

The importance of soil cannot be overstated, as it plays a vital role in sustaining life on Earth, supporting agriculture, and contributing to various ecosystems. Here are key points highlighting the importance of soil, along with relevant data:

1. Foundation of Agriculture:

   • Data: Approximately 95% of the world's food is produced directly or indirectly from the soil.
   • Importance: Soil provides the essential substrate for crop growth, serving as the foundation for agriculture, which feeds the global population.

2. Nutrient Cycling:

   • Data: Soil contains a vast reservoir of essential nutrients, with the global soil nitrogen stock estimated at around 94,000 teragrams (Tg).
   • Importance: Soil acts as a reservoir and regulator of nutrients, allowing for their cycling and availability to plants, which are crucial for food production.

3. Carbon Storage:

   • Data: Soil stores a significant amount of carbon, with estimates of global soil organic carbon stocks exceeding 2,400 gigatons (Gt).
   • Importance: Soil sequesters carbon, helping mitigate climate change by reducing atmospheric carbon dioxide levels when managed sustainably.

4. Biodiversity Support:

   • Data: Soil ecosystems are incredibly diverse, with an estimated 10,000 to 50,000 species per square meter in some soils.
   • Importance: Soil provides habitat and sustenance for a multitude of organisms, including microorganisms, insects, and plant roots, contributing to overall biodiversity.

5. Water Filtration and Regulation:

   • Data: One hectare of forest soil can retain over 36,000 liters of water.
   • Importance: Soil acts as a natural filter, purifying water as it percolates through, while also regulating water flow, reducing flooding, and replenishing groundwater.

6. Erosion Control:

   • Data: Soil erosion costs billions of tons of topsoil annually, impacting agricultural productivity.
   • Importance: Healthy soil with good structure and vegetation helps prevent erosion, protecting fertile topsoil and minimizing sedimentation in water bodies.

7. Waste Decomposition:

   • Data: Soil decomposes organic waste, with decomposition rates varying based on soil conditions.
   • Importance: Soil aids in the decomposition of organic matter, recycling nutrients and reducing the burden of waste disposal.

8. Medicinal Resources:

   • Data: Many medicinal plants and fungi rely on specific soil conditions for growth.
   • Importance: Soil provides the substrate for the cultivation of medicinal plants and the development of pharmaceutical resources.

9. Cultural and Historical Significance:

   • Data: Soil has cultural and historical importance, with many civilizations, traditions, and archaeological sites linked to specific soils.
   • Importance: Soil is an integral part of human culture and history, influencing art, agriculture, and architecture.

10. Sustainable Land Use:

    • Data: Sustainable land management can lead to increased agricultural yields, food security, and reduced environmental degradation.
    • Importance: Recognizing the importance of soil in sustainable land use practices is essential for long-term food production and ecosystem health.

In conclusion, soil is a precious natural resource that provides a foundation for agriculture, supports biodiversity, regulates water, and helps mitigate climate change. Recognizing its importance and practicing responsible soil management is critical for the well-being of current and future generations.

Problems of Soil Resources

1. Soil Erosion:

   • Soil erosion is the process of soil being carried away by natural elements like water, wind, glaciers, and waves.

2. Natural Causes:

   • Gravity can move soil slowly (soil creep) or rapidly (landslides) down slopes over thousands of years, shaping the land as we know it.

3. Environmental Problem:

   • Soil erosion is a major environmental issue and a significant constraint for agricultural production.

4. Factors Influencing Soil Erosion:

   • Physical factors include the erosivity of rainfall, erodibility of soil, severity of periodic floods, and the length and steepness of slopes.
   • Social factors include deforestation, overgrazing, land use practices, and cultivation methods.

5. Serious Forms of Soil Erosion:

   • Ravines, gullies, and landslides are highly visible and severe forms of soil erosion.
   • Sheet erosion caused by rains and wind erosion, although less visible, are equally serious threats to topsoil.

6. The extent of Ravine and Gully Erosion:

   • Ravine and gully erosion affect significant areas in India, damaging approximately 3.67 million hectares of soil.
   • Major ravine and gully areas are found in regions like Yamuna-Chambal, Gujarat, Punjab Siwalik foothills, and Chhotanagpur.

7. Sheet Erosion and Landslides:

   • Sheet erosion is widespread in various regions, including sloping deforested terrain, terraced uplands, plains, coastal areas, Western Ghats, and NorthEastern hills.
   • Landslides occur, particularly in earthquake-sensitive belts like the Siwaliks, triggered by heavy rainfall and slope disturbances from human activities.

8. Other Types of Erosion:

   • Glacial erosion is limited to the high Himalayas, and sea erosion occurs primarily in coastal areas.

9. Threats to the Thar Desert:

   • In the last 50 years, the Thar desert has encroached upon approximately 13,000 hectares of land in Rajasthan, Gujarat, Haryana, and Uttar Pradesh.

10. Impact on Soil Productivity:

    • Soil erosion and nutrient loss pose significant threats to efforts aimed at increasing soil productivity faster than population growth.

11. Overgrazing as a Contributing Factor:

    • Overgrazing by livestock, such as sheep and goats, has played a role in soil erosion, particularly in states like Jammu & Kashmir, Himachal Pradesh, Rajasthan, and Karnataka.

Soil erosion is a multifaceted issue influenced by both natural and human factors, with far-reaching consequences for agriculture and the environment.

Soil conservation

It takes thousands of years for a single inch of soil to be formed naturally, but it takes only a few years for that single inch to be eroded by human interference. If the soil is wasted or blown away, it is not easy to replenish it. Soil conservation is the prevention of loss of the topmost layer of the soil from erosion or the prevention of damaged fertility caused by overuse, acidification, salinization, or other chemical soil contamination. The most important step of soil conservation is to hold the soil in place. This is possible by improved agricultural practices in different regions. Contour plowing and terracing are generally practiced on the hill slopes of the Himalayas. They are the simplest conservation methods. Rows of trees or shelter belts are planted to protect the fields from wind erosion in desert regions of Rajasthan. Afforestation of the river catchment areas and steep slopes has been implemented in many parts of India. The important among them are the Himalayas, the Upper Damodar Valley in Jharkhand, the Nilgiri hills in the south,, etc. It reduces the surface runoff and binds the soil. Ravines are noted for their enormous size and depth with vertical sides.

The Central Soil Conservation Board has established 3 research stations: (1) Kota in Rajasthan, (2) Agra in Uttar Pradesh, and (3) Valsad in Gujarat to suggest methods of reclamation of ravine lands. Soil fertility loss can be prevented by the application of manures and fertilizers.

Various methods for soil conservation are:

1. Planting more and more trees.
2. Using new farming methods.
3. Reducing river flooding.
4. Building small check dams in gullies to slow down water run-off.
5. Digging channels across farm slopes to divert water.
6. Protecting areas likely to be eroded.
7. Checking deforestation.
8. Contour plowing terrace farming.
9. Restore wetlands
10. Planting vegetation cover and forest restoration
11. Planting buffer strips along stream banks
12. Windbreaks
13. Proper waste disposal and management

Soil Health Card (SHC):

Soil Health Card (SHC) is a printed report of a particular land holding that gives information on 12 soil parameters along with recommendations in the dosage of nutrients to be utilized for different crops. On 5th December 2015, the Soil Health Card Scheme was introduced by the Ministry of Agriculture and Farmers' Welfare, Government of India. It is being implemented through the Department of Agriculture of all the State and Union Territory Governments in India. Under the scheme, the card is provided to all farmers of the country at an interval of 3 years.

Significant features of the Soil Health Card Scheme are:

• The Government issues individual soil cards to farmers once every 3 years.
• Cards carry crop-wise recommendations of nutrients and fertilizers in the respective individual farms. These recommendations aim at improving productivity through judicious use of inputs.
• To deliver the recommendations Soil samples are collected and tested in various soil testing labs across the country. After testing, various experts analyze the strength and weaknesses of the soil and suggest measures to deal with them. The results and suggestions are displayed on the cards.
• The soil samples are tested for 12 parameters. They are pH, Electrical Conductivity (EC), Organic Carbon (OC), Nitrogen (N), Phosphorus (P), Potassium (K), Sulphur (S), Zinc (Zn), Boron (B), Iron (Fe), Manganese (Mn), and Copper (Cu) of farm holdings.

The benefits of Soil Health Cards are:

• It decreases 8 to 10 percent use of chemical fertilizers
• It increases productivity by 5 to 6 percent.
• It creates jobs for the agrarian youths in terms of laboratory establishment to undertake
  soil testing
• It curbs the overuse of urea which leads to the deficiency of many soil nutrients.
• It gives crop-wise guidance to farmers.

The card displays the farmer's details, soil sample details, soil test results, and general recommendations. The sample of the Soil Health Card is given below.

 

SHC Card