Agricultural Soil Composition, Structure, and Quality Factors

Soil Composition and Particle Size Classification

• Gravel: Fragments of bedrock, minerals, and organic matter (M.organica).
• Sand and Silt: Gravel that has been physically disintegrated.
• Clay (Arcilla): Inorganic matter (M.inorganica) and colloidal material resulting from soil chemical processing.

Loam and Silt: Ideal Cultivation Soils

Loam (or silt) is composed of sand, silt, clay, and humus, making it one of the best soils for cultivation.

• Excessive water retention without proper absorption limits nutrient profit for roots.
• Soil texture is defined by the percentage equivalent of sand, silt, and clay.
• The number of pores per unit volume of soil determines the displacement rate of water and air permeability.

Soil Behavior Based on Composition

Soil particle size directly influences key properties like porosity, permeability, and retention capacity:

Structural Types and Characteristics

Soil structure is heavily influenced by the interaction between clay and organic matter (MO) colloids:

• Soils Rich in Clay and Organic Matter (MO)

  Colloids act as Binders (4:1 ratio mixture of MO and inorganic clay/humus, featuring unlike charges). Structure is typically lumpy, resulting in medium permeability.

• Soils Rich in Clay but Poor in MO

  Colloids act as Dispersants (colloids with a single charge, clay + clay). Structure is often asphyxiant, leading to low permeability.

• Soils Low in Clay and Organic Matter

  Without colloids, the structure is characterized by individual grains, resulting in high permeability.

Factors Influencing Farm Soil Quality

• Quality of Drainage and Nutrients: Depends on the pores that hold minimal water.
• Depth: Each layer must be uniform to properly absorb inorganic and organic nutrients.
• Structure: Depends on the structure of the colloids, which possess an electric charge on their surface.
• Texture: Determined by whether the grain size is coarse (thick) or fine (thin).

Chemical Properties of Soil

Ion Exchange

Ion exchange involves charged atoms moving between the surface of colloidal material and the soil solution. This results in a dynamic equilibrium, driving chemical alteration of minerals, mineralization of organic matter (OM), and the absorption of nutrients by plants.

Soil Acidity (pH)

Soil acidity is characterized by its pH level, which determines the type of ions absorbed by the colloids (e.g., Ca, Mg, K, Na). Acid soils are typical of wetlands, while basic soils are common in arid regions.

Redox Potential

Redox potential measures the oxidizing or reducing properties of a soil. This is particularly important when the soil has low oxygen content, which decreases due to plant and microbial respiration. A high-oxygen soil is highly oxidized.

Mechanisms of Soil Deterioration

1. Pollution: Introduction of any waste, most commonly non-biodegradable materials.
2. Erosion: Loss of moisture and nutrients, which generates cracking and breaking of the soil structure.
3. Desertification: Severe soil loss where the land becomes desert.
4. Deforestation: Excessive felling of trees.
5. Overgrazing: Excessive presence of animals leading to vegetation loss and compaction.