Understanding Soil: Formation, Properties, and Conservation

What is Soil? An Introduction to Pedology

Soil is the interface between the geosphere, biosphere, and atmosphere. The study of soil is known as Pedology (Soil Science).

Soil Formation: The Three Stages

Soil formation is a complex process divided into three main stages:

Stage 1: Formation of the C Horizon

Rocks experience both chemical and physical weathering, leading to a more or less altered bedrock. This altered material is also known as the mantle of alteration or the C horizon.

Stage 2: Development of the A Horizon

This stage involves the establishment of a progressive living horizon, with contributions from:

• Pioneer settlers (lichens, mosses, etc.)
• Microorganisms and heterotrophic organisms
• Higher plants and animals

These organisms contribute to soil organic matter (humus), leading to the formation of the A horizon.

Stage 3: Formation of the B Horizon

Due to rainwater, a solution of mineral salts is produced and leaches from the A horizon to deeper layers, resulting in the formation of the B horizon.

Key Soil Properties

Physical Properties of Soil

• Texture: Refers to the proportion of sand, silt, and clay particles.
• Porosity: The ratio of soil pore space to total volume, affecting water and air movement.
• Color: Depends on the proportion of different soil components, such as organic matter and minerals.

Chemical Properties of Soil

• pH: Measures the acidity or alkalinity (levels of H⁺ ions) in the soil.
• Useful Water Reserve: The quantity of groundwater that can be absorbed by vegetation.
• Ion Exchange Capacity: The ability of soil to hold various ions through absorption.

Soil Composition: The Three Phases

Soils consist of three distinct phases: solid, liquid, and gas.

The Solid Phase

This represents the most stable, representative, and widely studied phase of soil.

• Formed by minerals (90-99%) and organic matter (1-10%).
• Young Humus: Organic debris that has undergone little or no decomposition.
• Mature Humus: Organic matter resulting from the total decomposition of humus, involving large numbers of organisms.

The Liquid Phase

The liquid phase consists of soil water and soil solutions, which are derived from the alteration of minerals and organic matter.

The Gas Phase

Gases are present in the soil pores. The numerous pores in the soil (up to 50% by volume) can be filled with:

• Liquids: Water with dissolved salts.
• Gases: Atmospheric air enriched with CO₂.

A healthy soil must be balanced and contain all components in appropriate proportions.

Soil Conservation and Restoration

Sustainable agricultural and livestock practices are crucial for soil health. Key measures include:

• Use of organic fertilizers.
• Fallowing (leaving land uncultivated for a period).
• Adequate stocking rates for livestock.
• Firefighting and prevention.
• Rational use of forests to prevent degradation of unprotected areas.
• Measures to prevent erosion, such as the construction of terracing in hilly farming areas.

A terrace is a horizontal surface on steep terrain, created by human work, supported by a wall or embankment, and used for farming. Terracing significantly reduces erosion processes.