Soil Composition, Types, and Land Pollution Issues

Posted on Apr 7, 2025 in Geology

Understanding Soil Composition and Structure

Soil is the loose material on the Earth’s surface situated above solid rock.

Soil Layers (Horizons)

Soil is typically composed of three main layers or horizons:

  • Topsoil (A horizon): The uppermost layer, which gains organic material from the decomposition of plants and animals.
  • Subsoil (B horizon): Located beneath the topsoil, this layer accumulates materials leached from the horizons above.
  • Weathered Bedrock (C horizon): This layer contains loose pieces of rock, broken off from the parent rock below by weathering (the process where rock is broken down by elements like wind and water).

Soil’s Four Basic Constituents

Soil consists of four fundamental components:

  • Organic matter
  • Mineral matter
  • Water
  • Air

Approximately half of the soil volume is pore space, filled with varying amounts of air and water.

Topsoil is arguably the most crucial layer for life, as it is where humans live and most plants grow. Organic matter within the topsoil significantly increases fertility because these materials are mixed near the surface and are continually recycled through decomposition.

Leaching is the process where water dissolves and removes soluble minerals and organic matter from the topsoil, potentially carrying them deeper into the soil profile or into rivers.

Different Types of Soil

Soil texture, determined by the balance of mineral particles, leads to different soil types:

Loamy Soils

  • Good balance between sand, silt, and clay.
  • Contains both large and small pore spaces.
  • Retains adequate moisture while allowing excess water to drain.
  • Contains enough clay to hold essential nutrients.
  • Considered the best soil type for general farming.

Clayey Soil

  • Characterized by very small pore spaces.
  • Offers little aeration due to particle density.
  • Water is often trapped, leading to poor drainage.
  • Generally nutrient-rich.
  • Can be heavy and difficult to break up or cultivate.
  • Good for grass growth but may require expensive drainage work for other crops.

Sandy Soil

  • Features large pore spaces.
  • Allows for a large amount of air (good aeration).
  • Does not hold water well; drains very quickly.
  • Often referred to as ‘hungry soils’ because they require frequent and large applications of fertilizers to maintain nutrient levels.

Mineral particles (sand, silt, clay) are formed by the weathering of the parent rock beneath the soil. Soils are often classified based on the dominant particle size (e.g., sandy, clayey, loamy).

Texture refers to the relative proportions of these mineral particles in the soil.

Factors Influencing Plant Growth and Farming

Several soil properties influence its suitability for plant growth and farming:

  • Pore space: The spaces between mineral particles, affecting water and air holding capacity.
  • Aeration: The amount of air present in the pore spaces, crucial for root respiration.
  • Drainage: The soil’s ability to allow excess water to pass through.
  • Nutrients: The soil’s capacity to supply essential nutrients to plants.
  • Workability: How easily the soil can be ploughed and cultivated.

Land Pollution Concerns

Human activities can negatively impact soil health and lead to land pollution.

Fertilizers and Pesticides

While fertilizers and pesticides can increase food output, their repeated application over long periods can be detrimental.

  • Excessive pesticide use can kill vital soil organisms (like earthworms and beneficial microbes).
  • This reduces the rate of decomposition of organic materials.
  • Consequently, the natural release of plant nutrients into the soil slows down.

Eutrophication

Eutrophication occurs when excess nutrients (often from fertilizer runoff) enter water bodies, causing algal blooms. When these algae die and decompose, the process consumes large amounts of dissolved oxygen, starving the water of oxygen needed by other aquatic plants and animals.

Salinization

In some areas, particularly arid and semi-arid regions, human activities like large-scale irrigation can increase the salt content in soils. As irrigation water evaporates, salts are left behind, accumulating over time and reducing crop productivity.

Types of Waste Contributing to Land Pollution

Domestic Waste

  • Originates from food preparation, cooking, serving, and discarded items like cartons, plastics, and boxes.
  • The extent of land pollution depends on the efficiency of waste collection and disposal systems.
  • Improper disposal poses health dangers and can contribute to outbreaks of disease.

Toxic Waste

  • Generated from industrial processes involving food, wood, metal, chemicals, etc.
  • Causes pollution when disposed of improperly into the ground or water, especially in high concentrations.
  • Wastes containing heavy metals like mercury and arsenic are particularly hazardous to human health and ecosystems.

Nuclear Waste

  • Produced by nuclear power stations and related activities.
  • Poses risks not only through potential air pollution but primarily through the emission of radioactivity and the challenge of long-term waste disposal.
  • Has significant long-term environmental implications and health risks, including increased rates of cancer and leukaemia.
  • Requires extremely secure and safe long-term storage solutions.