Understanding Soil: Formation, Horizons, and Conservation

What is Soil? An Essential Ecosystem

Much of the land surface is covered by a layer of loose material called soil, where plants are or may be rooted. It is a habitat for a variety of organisms. The soil is an ecosystem.

Soil Components

• Organic Matter: Formed by many organisms, traces of undecomposed organisms, and humus (partially decomposed organic matter).
• Inorganic Material: Fragments of rocks, minerals, air, and water that occupy the holes left by the solid materials.

Factors Influencing Soil

The characteristics of soils are influenced by several factors: climate, the original rock, the topography of the area, and the organisms that use it as a habitat. In mature soil, we find different soil horizons, also known as edaphic horizons. Each one has a specific texture. A cross-section of these horizons is called the soil profile.

The Process of Soil Formation and Its Horizons

Stages of Formation

• Initial Stage (Parent Rock): Changes in temperature, water, and air fragment the rocks. Lichens settle on the surface, begin to decompose, and start adding organic matter.
• Young Soil: Hundreds of years later, the action of water, air, and living organisms like lichens and mosses allows herbs and grasses to establish themselves.
• Mature Soil: After a few thousand years, the alteration will affect deeper layers of the parent rock. The land has been fortified with organic matter.

Soil Horizons

The distinct layers of soil are called horizons:

• O Horizon: Composed of leaves and partially decomposed organic debris.
• A Horizon: Dark in color due to a large amount of humus.
• B Horizon: Lighter in color, with no humus. Materials dragged from higher layers are deposited here.
• C Horizon: Altered bedrock.
• R Horizon: Unaltered parent rock (bedrock).

Materials are drawn from upper to lower horizons by rainfall in a process called leaching.

Soil Evolution: Formation vs. Erosion

Soils are constantly evolving. They are formed and also destroyed by erosive processes.

• If formation processes predominate: The soil increases its thickness and complexity. In the upper part, much plant debris accumulates, and there is an increased decomposing activity from fungi. At the bottom (below 2 meters), the layers cease to be considered soil.
• If erosion processes dominate: The soil loses thickness. This can end with the bedrock being exposed.

Soil Degradation and Destruction

Human activities can modify, degrade, and destroy soil. These activities include:

• Felling of trees
• Over-cultivation
• Overuse of fertilizers
• Overgrazing
• Salinization

The expansion of deserts, or desertification, is often caused by human actions.

Measures for Soil Conservation

To conserve soil, several measures can be taken:

• Soil Conditioners: Adding organic matter or lime.
• Windbreaks: Techniques to dampen the effect of the wind.
• Contour Farming: Terracing and tilling according to the contour lines of the land.