Soil Formation, Composition, and Conservation

Posted on Jan 15, 2025 in Geology

Soils: Formation and Composition

Soils: are formed from the superficial layer of the crust. This process is called pedogenesis.

Formation of Horizon C: Mainly due to temperature changes, the rocks undergo physical weathering, disintegrating into pieces. Chemical weathering alters some minerals in the rocks.
Appearance of Horizon A: Living organisms are established on horizon C. First, lichens and mosses, then bacteria, fungi, and finally more evolved living organisms. Living organized matter is added to the soil, forming horizon A.
Development of Horizon B: This horizon develops between A and C. Materials drawn from the wash water descend by gravity.

Factors involved in pedogenesis (soil formation):

The bedrock gives rise to the soil, provides most of its mineral components, and influences its early formation based on how easily it can be altered.
The time it takes to form a soil varies from hundreds of years in hot, humid climates to thousands of years in cold or dry climates.
Weather is a major factor in soil development, influencing the type of weathering, the introduction of vegetation, and the amount of vegetation.
Living things, especially plants, contribute to soil organic matter and mineral salts extracted from deeper soil zones, deposited on the surface as leaves, fruits, or flowers.
Topography is very important in soil formation. On plains, soils form where weathered rock remains in place, while in areas with slopes, erosion processes predominate.
Human action is decisive in the evolution of soils, as it can quickly remove soils formed over thousands of years through over-farming, livestock production, deforestation, fires, urbanization, and pollution.

Soil compounds include inorganic material, organic matter, air, and water.

Inorganic material is derived from bedrock weathering and transformation.
Organic matter consists of living organisms and organic debris that generate raw humus and developed humus.
- Raw humus has undergone little change and contains recognizable living organisms.
- Developed humus forms through the total decomposition of young organic matter and involves many soil microorganisms. It is black, rich in ammonia, nitrites, and humic acids, and mixed with clay, forms an organo-mineral complex.
Pores between the solid particles of organic and inorganic components may occupy up to 50% of the soil. They are filled with air and salt solutions. If the liquid fraction predominates, the environment tends to be greenish; if air prevails, the soil color tends to be reddish-brown.

Soils of good quality, or loam soil, should contain all components in balanced proportions.

Soil horizons are structured. The sequence of all these horizons is called a soil profile.

The A horizon is called the washing horizon because it contains salts that are dragged into the lower horizons by water. Its color is dark because it contains organic matter.
The B horizon, called the precipitation horizon, is formed from the precipitation of salts and other compounds from the A horizon. Its color is lighter than A due to the lack of organic matter and the abundance of mineral salts.
The C horizon is formed by the weathering of bedrock.

The soil is a very fragile system that can degrade easily. Strategies for its conservation should aim to prevent both contamination and loss.

The contamination of agricultural soils can be avoided by the rational use of fertilizers and herbicides.
Soil loss is reduced by preventing erosion through building terraces on sloping land, promoting plant cover, acting to prevent fires, and promoting afforestation.