Soil Structure

Soil Structure

• Individual sand silt and clay particles will form together into specified shapes.

• These shaped structural peds – are given names based on their appearance.

Peds are formed in the soil by wetting, drying, freezing and thawing and are held by clay and organic matter

Kinds of Soil Structure

• Granular• Platy• Sub-angular Blocky• Prismatic• Good structure

promotes healthy soil

Soil Structure

• Soil separates do not act in the soil as individuals, but as partners, or aggregates. Aggregates are the clumps of soil separates.

• When aggregates are bound together into larger masses they are called PEDS.

• soil structure is relatively easy to change or alter especially when the soil is being cultivated.

• Soil clods can be broken apart by wetting and drying, and by freezing and thawing.

• Cementing agents which bind soil separates together include microbial gums, iron oxides, organic matter, and clay.

Types of Structure

1. Granular Structure

Granular Structure• Granular structure is the most beneficial form of soil

structure for plant growth.• Granular structure aggregates are formed by the

breaking apart of larger aggregates through the physical processes of wetting and drying, and freezing and thawing.

• These aggregates are then cemented together by the by-products of the microbial decomposition of organic matter, which are called microbial gums.

• The more microbial gums, the greater the aggregate stability. The way to obtain microbial gums is by adding organic matter to the soil; thus, plant residues contribute indirectly to better soil structure

2. Platy Structure

Platy Structure

• Platy structure is often found in the E horizon (below the A) where water moves laterally through the soil.

• Platy structure can be detrimental because it restricts root and water penetration.

3. Blocky Structure

Blocky Structure

• Blocky structural peds are found most frequently in the B horizons.

• They have been created by the wetting and drying and freezing and thawing cycle of the B horizon.

• The clay films also act as a binding agent for the blocky aggregates.

• The B horizon can often be determined in a profile by looking for the location of blocky peds which can be readily seen.

• Blocky can be either angular (sharp ped edges) or sub-angular (rounded ped edges).

4. Prismatic or Columnar Structure

Prismatic or Columnar Structure

• Where the blocky peds are longer than they are wide, the prismatic or columnar structure is identified (common only in B horizons).

• They are often the first structure formed in a soil, because their formation only requires vertical cracking in the soil.

5. Structureless

Structureless

• C horizons generally lack any structural aggregation.

• Their lack of structure is termed "massive." • Massive structure is hard to break apart

and appears in very large clods. • Where very sandy soils lack aggregation,

or the soil particles don't stick together the structureless condition is termed "single-grained." Single grained always accompanies a loose consistence.