Which property affects the water retaining capacity of soil and factors affect soil permeability and water holding capacity?
Respected Sir, Rk Naresh
The water-retaining capacity of soil is primarily influenced by its texture, while soil permeability and water-holding capacity are affected by a combination of factors, including texture, structure, and organic matter. Let's explore these aspects:
Water-Retaining Capacity - Influenced by Soil Texture:
Clay Soil: Clay soils have small particles with high surface area, creating fine pore spaces that can hold a significant amount of water. They generally have a high water-retaining capacity, but their drainage can be slow.
Silt Soil: Silt soils have intermediate-sized particles, offering a moderate water-retaining capacity.
Sand Soil: Sandy soils have larger particles and, consequently, larger pore spaces. While they have a low water-retaining capacity, they allow for faster drainage.
Factors Affecting Soil Permeability:
Soil Texture: As mentioned earlier, soil texture plays a significant role. Sandy soils with larger particles generally have higher permeability, allowing water to move more quickly, while clay soils with smaller particles tend to have lower permeability.
Soil Structure: Soil structure refers to how individual soil particles are grouped together. Well-structured soils with good aggregation tend to have higher permeability because of the presence of larger pores between aggregates, facilitating water movement.
Organic Matter: Organic matter can improve soil structure and increase water-holding capacity. It enhances permeability by promoting the formation of stable aggregates, which improves pore spaces in the soil.
Compaction: Compaction, often caused by heavy machinery or foot traffic, can reduce soil permeability by compressing soil particles and decreasing pore spaces. Compacted soils may have reduced water infiltration rates.
Factors Affecting Water-Holding Capacity:
Soil Texture: Soil texture is a key factor. Clay soils with smaller particles have a higher water-holding capacity, while sandy soils with larger particles have a lower water-holding capacity.
Organic Matter: Organic matter acts like a sponge, enhancing water retention in the soil. It improves soil structure, creating more stable aggregates and increasing the availability of water to plants.
Soil Structure: Well-structured soils have better water-holding capacity due to improved pore spaces that can retain water against the force of gravity.
Depth of Soil: Deeper soils generally have a higher water-holding capacity as they provide a greater volume for water storage.
Soil texture is a fundamental factor influencing both water-retaining capacity and permeability. Other factors, such as soil structure, organic matter content, compaction, and soil depth, also play roles in determining these properties. A balanced combination of these factors contributes to optimal soil conditions for plant growth and water management.
To resume, it’s affected by permeability and porosity which depend on particles size and type of soil.
Generally speaking, clay-rich soils have the largest pore space, hence the greatest total water holding capacity. Soil water retention capacity, hydraulic conductivity, and permeability are primarily determined by texture (sand, silt, clay contents), structure (bulk density and porosity), and organic matter content. Cohesion and adhesion forces: These two basic forces are responsible for water retention in the soil. The cohesion is the attraction of molecules for each other. The adhesion is the attraction of water molecules for the solid surface of soil. The quantity of water that soil can retain after flowing down of the gravitational water is called its field capacity or water holding capacity. It depends on chemical composition of the soil which means types of ions present and hence pH of the soil. Size of soil particles and their aggregation form pores in soil.Soil water retention curves (SWRC) as soil water content as a function of soil matric potential (Ψm), is a critical soil hydraulic property. A number of factors affect the permeability of soils, from particle size, impurities in the water, void ratio, the degree of saturation, and adsorbed water, to entrapped air and organic material. Water-holding capacity is controlled primarily by soil texture and organic matter. Soils with smaller particles (silt and clay) have a larger surface area than those with larger sand particles, and a large surface area allows a soil to hold more water. Permeability describes how quickly water may pass through the earth. Clay, for example, has high porosity and less permeability. The gravity of the earth determines the direction and the rate of flow of water as gravity pulls the water downwards from a high to a low hydraulic gradient. A number of factors affect the permeability of soils, from particle size, impurities in the water, void ratio, the degree of saturation, and adsorbed water, to entrapped air and organic material.
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