The Five Components of Soil
Soil primarily consists of five main components, each varying in composition, structure, and properties. Although soil may appear to be a static substance, it is dynamic and constantly changing. Factors such as temperature, water levels, nutrient content, and organic residues fluctuate based on environmental conditions and the organisms living within it. Below are the five essential components of soil:
1. Mineral Materials
Mineral materials are substances that make up soil as a result of erosion. The Earth’s crust consists of various rocks, some composed of minerals and others of decomposed organic matter. Rocks are made up of around 100 elements, with ten primary ones, including:
- Oxygen: ~47%
- Silicon: ~28%
- Aluminum: 8%
- Iron: 5.5%
- Magnesium
- Calcium
- Hydrogen
- Potassium
- Sodium
- Titanium
Other elements, such as gold, silver, copper, sulfur, and nickel, make up about 1% of the soil.
2. Organic Materials
Organic materials in soil result from the decomposition of dead organisms. They consist of plant and animal residues broken down into finer particles through decomposition. Over time, these materials further decompose, stabilizing in the environment to form humus. The decomposition process is a chemical reaction influenced by several factors, including temperature, aeration, soil acidity, and alkalinity.
3. Soil Solution
The soil solution comprises dissolved elements such as salts and gases in water. This solution is retained within the soil and is not affected by gravity. It remains balanced with the soil material and contains essential nutrients in low concentrations for plant growth. Factors influencing the concentration of the soil solution include:
- Soil moisture
- Element concentrations in the soil
- Chemical compounds present
- Types and ages of prevalent green plants
4. Soil Air
Soil air occupies the pores in soil, which account for about 35% of its actual volume. There are two types of pores:
- Capillary pores: Determine the water storage capacity after rainfall or irrigation.
- Non-capillary pores: Determine the air content within the soil.
If water saturation in soil increases, both capillary and non-capillary pores fill with water, displacing air. This creates anaerobic conditions, reducing mineral elements, increasing anaerobic microorganism activity, and acidifying the soil due to higher carbon dioxide levels.
5. Microorganisms
Microorganisms in soil include fungi, bacteria, algae, and protozoa. These organisms live in the soil symbiotically, parasitically, or as decomposers. They play a crucial role in making soil fertile and suitable for plant growth. Microorganisms:
- Aggregate soil particles and improve aeration
- Decompose plant and animal residues into simpler materials that plants can use
- Recycle essential nutrients such as phosphorus and nitrogen
Soil Types
Soil types vary depending on the characteristics and composition studied. These types include:
1. Types Based on Properties and Composition
- Loamy Soil: The best type for agriculture, with a mix of clay and sand particles, excellent aeration, and high water retention, allowing roots to absorb moisture efficiently.
- Sandy Soil: Characterized by large pores, making it incapable of retaining water or nutrients, unsuitable for farming.
- Clay Soil: Composed of very small, cohesive particles, retaining water excessively and often causing poor drainage and aeration. In dry conditions, it cracks significantly.
The best soil is a mixture of these types, typically consisting of 55% loamy soil, 30% clay soil, and 15% sandy soil.
2. Types Based on Location
- Residual Soil: Remains in the location where it was formed, with the underlying layer composed of parent rocks.
- Transported Soil: Moves from its place of formation to another location due to various factors. The underlying layer is unrelated to the topsoil. Types include:
- Soil transported by freshwater
- Soil transported by wind
- Soil transported by gravity
- Soil transported by glaciers
- Soil transported by seawater
- Soil formed from accumulated organic materials
