Grades of Soil Structure
- Soil structure refers to the arrangement of soil particles into aggregates (peds).
- The grade of soil structure indicates the degree of aggregation and the cohesion within aggregates, as well as the adhesion between them.
- It depends on factors such as moisture content, organic matter (OM), and soil texture.
Factors Affecting Soil Structure Grade:
- Moisture Content: Structure is assessed when the soil is neither too wet nor too dry.
- Organic Matter (OM) Content: Higher OM generally improves aggregation.
- Texture: The proportions of sand, silt, and clay influence the structure.
4 Grades of Soil Structure
- Structureless:
Description: No visible aggregation, often seen in loose sand.
Types:
- Single Grained: Soil particles are independent (e.g., very sandy soil).
- Massive: Soil particles cling together without any weak spots (e.g., compacted or puddled soil).
- Weak Structure:
- Poorly formed aggregates, barely evident in the soil profile.
Characteristics:
- A mixture of some entire aggregates, many broken aggregates, and much unaggregated material.
- Moderate Structure:
- Well-formed, distinct peds that are moderately durable but not distinct in undisturbed soils.
Characteristics:
- A mix of many distinct aggregates, some broken aggregates, and little unaggregated material.
- Strong Structure:
- Well-formed, distinct aggregates that are highly durable and evident in undisturbed soils.
Characteristics:
- Primarily whole aggregates with few broken ones, and minimal unaggregated material.