Week 2 - Topic 3 - Soil Structure & Aggregate Stability Flashcards
What does soil structure describe?
The arrangement of soil particles and the spaces between them
It influences water movement, drainage efficiency, aeration, habitat for soil organisms, root growth potential, and erosion resistance.
What are the two types of pore spaces created by peds?
- Micropores (within peds)
- Macropores (between peds)
Micropores are responsible for water holding capacity, while macropores enable drainage and aeration.
What are peds in soil structure?
Natural clusters of soil particles bound together
Peds form the basic units of soil structure.
What binding mechanisms contribute to soil particle cohesion?
- Organic material
- Physical binding by fungal strands
- Microbial secretions
- Chemical bonding
- Clay particles
These mechanisms help soil particles stick together.
What are Apedal Soils characterized by?
- No peds
- Single grain (e.g., sand dunes)
- Massive (e.g., crusted surfaces)
Apedal soils have quick drainage but low water holding capacity or high water holding capacity but poor drainage.
What percentage of peds defines weakly pedal soils?
Less than 30% peds
Pedal soils can be classified as weakly, moderately, or strongly pedal based on the percentage of peds.
Describe crumb/granular peds.
- Irregular shape
- Loose fitting
- Create large macropores
- Provide good drainage
- Maintain good water holding capacity
Crumb/Granular peds are beneficial for soil health.
What indicates a stable ped in the Aggregate Stability Test?
Ped stays intact and water remains clear
No action is needed for stable peds.
What action should be taken for slaking peds?
Add organic matter
Slaking peds crumble but water remains clear.
What indicates a dispersive ped in the Aggregate Stability Test?
Ped crumbles and water becomes cloudy
Action required: Add gypsum and organic matter.
What does the screwdriver test assess?
Soil compaction
Easy penetration indicates good conditions for root development, while difficult penetration suggests compaction.
List strategies to improve coarse-textured (sandy) soils.
- Add organic material
- Incorporate inorganic material
- Mix in loam
- Add lime
These strategies enhance soil structure in sandy soils.
What is a key prevention guideline for protecting soil structure?
Avoid working with wet soil
Other guidelines include limiting machinery use in wet conditions and confining traffic to designated areas.
True or False: Soil structure cannot be changed.
False
Unlike soil texture, soil structure can be modified.
What is the ideal soil structure for plant growth?
Granular/crumbly structure
This type of structure supports healthy plant growth.
What is a consequence of damage from vehicles and foot traffic on soil structure?
Repairing damaged structure is costly and time-consuming
Prevention is emphasized as better than repair.
