SOIL

Soil formation, or pedogenesis, is a complex process influenced by various factors interacting over time. The primary factors responsible for soil formation include:

• Parent Material: The type of rock or unconsolidated material from which the soil forms is known as the parent material. The mineral composition and physical characteristics of the parent material influence soil properties.

• Climate: Climate is a crucial factor in soil formation. Temperature, precipitation, humidity, and wind affect the rate of weathering of rocks, decomposition of organic matter, and the overall development of soil profiles. For example, tropical climates with high temperatures and rainfall typically result in more rapid soil formation.

• Organisms: Soil formation involves the activities of living organisms, including plants, animals, bacteria, fungi, and other microorganisms. Plant roots contribute to the physical breakdown of rocks, while microbial activity decomposes organic matter, releasing nutrients.

• Topography (Relief): The slope and shape of the land, known as topography, influence soil development. The movement of water down slopes affects erosion, deposition, and the distribution of soil particles. Steep slopes may have thinner soils due to erosion, while valleys may accumulate sediments.

• Time: Soil formation is a time-dependent process. It takes thousands to millions of years for soils to develop from parent material through weathering, organic matter accumulation, and other processes. Older soils tend to exhibit more distinct horizons or layers.

• Biological Activity: The activities of organisms, particularly plant roots and soil microorganisms, play a crucial role in soil development. Plants contribute organic matter through litter and root turnover, and their roots physically break down rocks. Microorganisms aid in organic matter decomposition and nutrient cycling.

• Humification: This refers to the process of organic matter decomposition, where complex organic materials are transformed into humus. Humus contributes to soil structure, nutrient availability, and water retention.

• Illuviation and Eluviation: These processes involve the movement of materials within the soil profile. Illuviation is the deposition of dissolved or suspended materials in a lower soil horizon, while eluviation is the removal of materials from a horizon.

• Parent Material Alteration (Weathering): The physical and chemical breakdown of rocks into smaller particles is called weathering. Weathering processes, including physical disintegration and chemical alteration, contribute to the formation of soil particles.

The interplay of these factors, known as the "CLORPT" factors (Climate, Organisms, Relief, Parent Material, and Time), determines the unique characteristics of soils in different regions. Understanding these factors is essential for soil scientists, geologists, and agronomists to manage and utilize soils effectively for various purposes

Stages of Soil Formation

Soil formation, also known as pedogenesis, occurs through a series of stages over an extended period. These stages are not always distinct, and the process is dynamic, influenced by various factors. The general stages of soil formation include:

1. Weathering of Parent Material:

   • Physical weathering breaks down rocks into smaller particles through processes like freeze-thaw cycles, abrasion, and root action.
   • Chemical weathering involves the alteration of minerals in rocks due to reactions with water, acids, or other chemical agents.

2. Soil Accumulation (Translocation):

   • Soil materials undergo translocation or movement within the soil profile through processes like eluviation (downward movement) and illuviation (upward or lateral movement).
   • This movement results in the development of soil horizons, with distinct layers exhibiting different characteristics.

3. Horizon Formation:

   • Over time, soil horizons develop as a result of the accumulation and translocation of materials. The main soil horizons, from top to bottom, are O (organic), A (topsoil), E (eluviation), B (subsoil), C (parent material), and sometimes R (bedrock).
4. Decomposition of plant and animal residues contributes organic matter to the soil. This organic material enhances soil fertility, structure, and water-holding capacity
5. The layering of horizons forms a soil profile. The combination of climate, organisms, relief, parent material, and time (CLORPT factors) influences the development of distinct soil profiles
6. With time, soils mature and exhibit well-developed horizons. Mature soils have distinct layers, and the physical and chemical properties stabilize
7. A climax soil represents the final stage of soil development under specific environmental conditions. It is in equilibrium with the surrounding ecosystem and is influenced by factors such as climate, vegetation, and topography
8. Soil scientists classify soils based on specific criteria such as texture, color, structure, and other properties. Classification helps in understanding soil behavior and suitability for various uses

Soil forming processes, also known as soil genesis or pedogenic processes, encompass a variety of physical, chemical, and biological activities that contribute to the development and evolution of soil. These processes occur over long periods of time and are influenced by factors such as climate, parent material, topography, organisms, and time. Here are the key soil forming processes:

• Weathering:

  • Physical Weathering: Breakdown of rocks into smaller particles through processes like freeze-thaw cycles, abrasion, and root action.
  • Chemical Weathering: Alteration of minerals in rocks due to reactions with water, acids, or other chemical agents.

• Translocation (Erosion and Deposition):

  • Eluviation: The process of leaching and removal of materials from the upper soil horizons, often involving the movement of minerals and nutrients downward.
  • Illuviation: The deposition of leached materials in lower soil horizons, leading to the development of distinct soil layers.

• Addition of Organic Material:

  • Decomposition of plant and animal residues contributes organic matter to the soil. This process is essential for the development of the O horizon (organic horizon) and improves soil fertility.

• Humification:

  • The decomposition of organic matter into humus, a dark, stable, and nutrient-rich material that improves soil structure and nutrient holding capacity.

• Mineralization:

  • The conversion of organic nitrogen into inorganic forms, making nutrients available for plant uptake.

• Podzolization:

  • The leaching of iron and aluminum compounds from the upper soil horizons (illuviation) and their accumulation in the lower horizons, resulting in the formation of spodic horizons.

• Pedoturbation:

  • The mixing and displacement of soil materials by various soil organisms, including earthworms, ants, and burrowing mammals. This process enhances soil aeration and nutrient distribution.

• Clay Illuviation:

  • The movement of clay particles downward through the soil profile, contributing to the development of clay-rich horizons.

• Hydration and Swelling:

  • The absorption of water by certain minerals, leading to their expansion and contraction, which can affect soil structure and porosity.

• Cementation:

  • The binding together of soil particles by substances like iron oxides, silica, or calcium carbonate, forming aggregates and contributing to soil structure.

• Laterization:

  • The process where leaching removes silica, leaving behind iron and aluminum oxides in tropical soils, resulting in the formation of laterite soils

 

 

Soil Profiles and Horizons

 

 

A soil profile is a vertical section of soil from the surface down to the bedrock or unweathered parent material. The soil profile is divided into layers called horizons, each of which has distinct physical and chemical characteristics. These horizons are labeled with letters, and the arrangement of horizons forms the soil profile. The main soil horizons, from top to bottom, are:

• O Horizon (Organic Horizon):

  • Composed mainly of organic material such as decomposed plant and animal residues.
  • Dark in color due to the presence of humus.
  • Often found in forested or well-vegetated areas.

• A Horizon (Topsoil):

  • Also known as the topsoil.
  • Rich in organic matter, minerals, and microorganisms.
  • The zone where most plant roots are active.
  • Darker in color due to organic matter.

• E Horizon (Eluviation Horizon):

  • The eluviation or leaching horizon.
  • Characterized by the removal of minerals and nutrients through leaching.
  • Lighter in color than the A horizon.

• B Horizon (Subsoil):

  • Accumulation of leached materials (clays, iron, aluminum) from above horizons.
  • Often referred to as the subsoil.
  • May contain minerals leached from above horizons (illuviation).
  • Various subtypes based on mineral content, color, and structure.

• C Horizon (Parent Material):

  • Also known as the parent material.
  • Composed of weathered rock material.
  • Unconsolidated and lacks the structure seen in higher horizons.
  • Provides the source material for soil development.

• R Horizon (Bedrock):

  • The unweathered rock layer that lies beneath the soil.
  • Sometimes included in the soil profile, but not always considered a true soil horizon.

 

 

 

Soil Classification

 

Soil classification is the process of categorizing soils into groups or classes based on their common characteristics. The classification helps in understanding and communicating information about soils, making it a crucial tool for agriculture, engineering, land use planning, and environmental management. Various soil classification systems are used worldwide, but the two most widely recognized systems are the USDA Soil Taxonomy and the World Reference Base for Soil Resources (WRB). Here's an overview of these systems:

1. USDA Soil Taxonomy:

   • Developed by the United States Department of Agriculture (USDA).
   • Based on soil properties such as texture, color, structure, and mineral composition.
   • Hierarchical classification system with six categorical levels:
     1. Order
     2. Suborder
     3. Great group
     4. Subgroup
     5. Family
     6. Series
   • The system recognizes 12 soil orders, each with distinct characteristics, such as Entisols, Inceptisols, Aridisols, Mollisols, and others.

2. World Reference Base for Soil Resources (WRB):

   • Developed by the International Union of Soil Sciences (IUSS).
   • A global soil classification system intended for international use.
   • Focuses on soil properties and processes that are relevant at the global scale.
   • Uses qualifiers to describe soil characteristics and includes reference soil groups.
   • Divides soils into major reference groups, such as Ferralsols, Andosols, and Podzols.

3. FAO Soil Classification (FAO World Soil Resources Report 103):

   • Published by the Food and Agriculture Organization (FAO) of the United Nations.
   • Provides a framework for global soil classification.
   • Based on soil properties and criteria relevant for land use planning and sustainable land management.
   • Classifies soils into groups such as Ferralsols, Acrisols, and Nitisols.

4. Unified Soil Classification System (USCS):

   • Primarily used in engineering and construction.
   • Classifies soils based on their physical properties, including particle size and plasticity.
   • Divides soils into three primary groups: coarse-grained soils, fine-grained soils, and highly organic soils

5. Indian Soil Classification System (ISSCS):

   • Developed by the ICAR (Indian Council of Agricultural Research)
   • Categorizes soils based on texture, color, structure, drainage, and other physical properties.
   • Divides soils into 8 major groups, further subdivided into classes and families:
     • Alluvial: Young soils deposited by rivers, fertile and well-drained (e.g., Gangetic alluvium)
     • Black: Clayey soils rich in organic matter, ideal for cotton and sugarcane
     • Red: Rich in iron and aluminum oxides, well-drained, suitable for millets and pulses
     • Laterite: Highly weathered soils depleted of nutrients, common in high rainfall areas
     • Mountain & Forest: Shallow soils on slopes, suitable for forestry and limited agriculture
     • Arid & Desert: Sandy soils with low organic matter, limited agricultural potential
     • Saline & Alkaline: High salt content, require reclamation for agriculture
     • Peaty & Marshy: Organic-rich soils in waterlogged areas, suitable for specific crops

 

 

Soil Erosion and Conservation

 

Soil erosion is a natural process, but human activities, such as agriculture, deforestation, and construction, can accelerate erosion rates. Soil erosion poses significant environmental challenges, including the loss of fertile topsoil, degradation of land quality, and sedimentation of water bodies. Soil conservation aims to reduce or prevent soil erosion and promote sustainable land use. Here are key aspects of soil erosion and conservation:

Causes of Soil Erosion:

1. Water Erosion:

   • Splash Erosion: Movement of soil particles caused by the impact of raindrops.
   • Sheet Erosion: Thin layers of soil being removed uniformly across a large area.
   • Rill Erosion: Small channels forming on the soil surface due to the concentration of water flow.
   • Gully Erosion: Larger and deeper channels or gullies carved into the landscape by concentrated water flow.

2. Wind Erosion:

   • Removal of soil particles by wind, especially in areas with loose and dry soils.
   • Common in arid and semi-arid regions.

3. Human Activities:

   • Deforestation: Removal of vegetation reduces the protective cover against erosion.
   • Overgrazing: Excessive grazing by animals can lead to soil compaction and vegetation loss.
   • Improper Agricultural Practices: Practices like monoculture, excessive tillage, and improper irrigation contribute to erosion.

Soil Conservation Techniques:

• Cover Crops:

  • Planting cover crops, such as legumes or grasses, helps protect the soil from erosion, improves soil structure, and adds organic matter.

• Contour Plowing:

  • Plowing along the contour lines of the land helps reduce water runoff and minimizes soil erosion.

• Terracing:

  • Constructing terraces on steep slopes creates flat surfaces that reduce the speed of water runoff and encourage infiltration.

• Windbreaks:

  • Planting trees or shrubs as windbreaks helps reduce wind speed and prevent wind erosion in exposed areas.

• Agroforestry:

  • Integrating trees and shrubs with crops helps improve soil structure, reduce erosion, and provide additional benefits such as shade and nutrient cycling.

• Covering Bare Soils:

  • Mulching, using cover crops, or applying other materials to cover bare soil helps protect it from the impact of raindrops and minimizes erosion.

• Conservation Tillage:

  • Reduced or no-till farming practices help maintain crop residues on the soil surface, reducing erosion and promoting water retention.

• Check Dams and Silt Fences:

  • Constructing check dams and silt fences helps trap sediment in water runoff, preventing it from reaching water bodies.

• Vegetative Buffers:

  • Planting strips of native vegetation along water bodies acts as a buffer, filtering sediment and pollutants before they reach the water.

• Erosion Control Blankets:

  • These are materials applied to slopes to prevent soil erosion and encourage vegetation establishment

 

 

 

 

 

 

World Soil Day   World Soil Day is an international observance dedicated to raising awareness about the importance of soil and promoting sustainable soil management practices. Designated by the United Nations, World Soil Day is celebrated annually on December 5th. This initiative aims to highlight the significance of soil as a critical component of the natural environment and its role in supporting food security, biodiversity, climate change adaptation, and overall ecosystem health. The key objectives of World Soil Day include: Raise Awareness: Educate people globally about the importance of soil for human well-being, food security, and environmental sustainability. Advocate for Sustainable Soil Management: Promote responsible and sustainable soil management practices to prevent soil degradation, erosion, and loss of fertility. Encourage Research and Innovation: Support research initiatives and innovations related to soil science, soil conservation, and sustainable agriculture. Highlight the Link Between Soil and Sustainable Development Goals (SDGs): Emphasize the role of soil in achieving various SDGs, including zero hunger, clean water and sanitation, and climate action. Engage Stakeholders: Encourage governments, non-governmental organizations, scientists, farmers, and the general public to actively participate in activities and discussions related to soil health and conservation. Each year, World Soil Day has a specific theme to focus attention on a particular aspect of soil. Themes in the past have included "Be the Solution to Soil Pollution" and "Keep soil alive, protect soil biodiversity."