What is a soil concept?...(Soil Concepts and Characteristics)

 

Soil Concepts and Characteristics

Introduction

• Soil: Covers most of the earth’s land surface and is a natural medium for plant growth.
• Definition: According to Joffe (1949), soil is a natural body of mineral and organic materials differentiated into horizons.

Concepts and Viewpoints of Soil

• Mining Engineer: Sees soil as debris covering rocks or minerals.
• Highway Engineer: Considers soil as the material for road beds.
• Homeowner: Views soil as a seed bed for gardens.
• Farmer: Regards soil as a habitat for plants.
• Soil Chemist: Thinks of soil as a storehouse for plant nutrients.
• Geologist: Defines soil as weathered rock.
• General Perspective: Soil is essential for food, clothing, and shelter.

Etymology

• The word "soil" comes from the Latin word solum, meaning floor.
• Related terms in French (sol) and Spanish (suelo) also mean soil or floor.

Definition of Soil

• Edaphologist: Defines soil as a mixture of mineral and organic matter capable of supporting plant life.
• Pedologist: Defines soil as a natural product formed from weathered rock by climate and living organisms.

Modern Concept of Soil

• Soil is a three-dimensional dynamic natural body on the earth's surface.
• Soil Material: Often referred to as weathered rock or "soil parent material."
• Regolith: Includes all loose material above the rock bed.

Functions of Soil

• Acts as a natural medium for plant growth.
• Provides mechanical support to plants.
• Supplies essential nutrients and water to plants.

Parent Material

• Refers to the consolidated material that is chemically weathered mineral or organic matter from which soil develops.
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Soil vs. Regolith

• Soil:
• Higher organic matter.
• Abundant plant roots and microorganisms.
• Intense weathering.
• Characteristic soil horizons and profiles.

Soil Profile

• A vertical section of soil layers.
1. O Horizon: Organic material at various decomposition stages.
2. A Horizon (Top Soil): Rich in organic matter, darker in color.
3. E Horizon: Heavily leached subsurface horizon, light in color.
4. B Horizon (Subsoil): Accumulates minerals leached from above.
5. C Horizon: Least weathered, known as saprolite.
6. Bedrock: Solid rock underlying soils and regolith.

Top Soil and Subsoil

• Top Soil: Major zone for plant development, rich in organic matter, exposed to weathering.
• Subsoil: Lies beneath the topsoil, less fertile than topsoil.

Soil Composition

• Major Components:
• Mineral Matter
• Organic Matter
• Soil Water
• Soil Air
• An ideal soil consists of 50% solid space and 50% pore space.

Mineral Soil

• Inorganic portion of soil, variable in size and composition.
• Composed of small rock fragments and minerals.
• Clay: Chemically active, stores available plant nutrients.

Organic Components of Soils

• Soil Organic Matter: Partly alive and partly dead decomposed residues of plants and animals.
• Constitutes 1% to 6% of the topsoil weight.

Soil Composition and Properties

Organic Soils

• Soils with more than 20% to 30% organic matter are called organic soils.
• Decomposing organic matter is a key source of:
• Phosphorus
• Sulfur
• Functions of organic matter in soil:
• Supplies plant nutrients.
• Binds mineral particles into aggregates, improving soil structure and aeration.

Humus

• The decomposed organic residues present in soil are known as humus.

Soil Water

• Water in soil is essential for:
• Plant growth.
• Physiological processes.
• Nutrient supply in solution.
• Water Holding Capacity: The amount of water a soil can store.
• Most soil profiles can store between 2.0 and 10.0 inches 5to 25 cm) of available water.
• Soil Solution: The water in soil that contains dissolved salts.
• Soil Porosity: The water held within the soil pores.

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Soil Air

• Soil air differs from atmospheric air:
• Not continuous due to soil composition.
• Generally has higher moisture content.
• Contains more carbon dioxide and less oxygen than the atmosphere.
• Soil air composition is influenced by soil water relationships.
• Soil air occupies larger pores, and as soil dries, pore sizes decrease.

Important Gases in Soil

• Dissolved oxygen
• Carbon dioxide
• Methane
• Hydrogen sulfide
• Nitrogen

Soil Particle Sizes

• Clay:  0.002   mm
• Silt:  0.002 - 0.05   mm
• Sand:  0.05 - 2    mm