Soil Aggregates Flashcards
What is soil aggregate?
Soil aggregates are clumps of soil particles that adhere together by clay fragments, roots and microbial residue.
What are considered microaggregates?
< 0.25mm
What are considered macroaggregates?
> 0.25mm
What is aggregate stability?
A measure of the ability of soil aggregates to resist degradation when exposed to external forces such as water erosion, wind erosion, shrinking and swelling processes and tillage.
What is aggregate stability an indicator of?
Organic matter content, biological activity, and nutrient cycling in soil.
What are some ecological functions of soil aggregates?
- Provides soil stability
- Improves soil carbon sequestration and reduces GHG emissions.
- Allows water infiltration and drainage.
- Has higher levels of OM that contribute to moisture retention.
What are the two processes involved in aggregate formation?
- Flocculation
- Cementation
What is Flocculation?
It is when primary particles stay together due to interactive forces (electrostatic) and form microscopic floccules.
What is cementation?
Clay binds with SOM. SOM acts as a nucleus for aggregate formation. Bacteria and Fungi produce polysaccharides that help bind soil particles and stabilize soil aggregates. Roots and fungal hyphae also hold soil particles together.
How can bacteria and fungi be a part of the soil formation process?
Bacteria create electrostatic charges that attractes clay particles. They produce polysaccharides that can produce aggregates. Hyphae form cross links between soil particles.
What are the two types of factors affecting aggregate formation and stability?
Inherent and Dynamic.
What is an example of an inherent factor?
Type and amount of clay
What are some examples of dynamic factors?
Organic matter and biological activity.
Physical disturbance destroys aggregates.
Return of plant residue
How does diverse crop rotation improve aggregate stability?
Diverse plant species contribute to soil aggregation. The different root systems help with the formation of aggregates.
How does fertilizer and manure application improve soil aggregate stability?
Fertilizer application increases root biomass and exudate but can also cause soil acidity.
Manure increases OM inputs and bacteria produce more polysaccharides.
Is 2:1 clay better at forming aggregates or is 1:1 clay better at forming aggregates?
2:1 clay is more likely to form aggregates than 1:1 clay because it has a higher CEC and, therefore, a higher negative charge.
What is Liming?
It is adding CaCO3 to acidic soil to balance out pH.
Is liming an example of flocculation or cementation?
Folcculation
How does liming help with aggregate stability?
Liming can increase aggregate stability but only till the soil reaches the pH of 7.8 if there is still more CaCO3 being added to the soil after that then the aggregate stability starts to decrease.
How does prescribed grazing help with or disrupt aggregate stability?
Urine and manure can increase SOM which can help with aggregate stability but on the other hand animals walking on the field can lead to compaction and reduces soil stability but overall, low intensity of grazing is better that no grazing in terms of aggregate stability.
How does tillage and residue management affect aggregate stability?
Tillage decreases aggregate stability. Residue management increases aggregate stability.
How does salinity affect aggregate stability?
Sodium causes soil aggregates to collapse.
How does irrigation management affect aggregate stability?
Furrow and flood irrigation causes aggregation slacking (soil particles break down).
What properties of water affect soil aggregate stability?
Water electric conductivity (EC) and sodium adsorption ratio (SAR) affect aggregate stability.
How does sodium adsorption ratio (SAR) affect aggregate stability?
As SAR increases, aggregate stability decreases.
What are some solutions to SAR problems in the soil?
- Change irrigation source
- Blend irrigation water with water lower in sodium levels.
- Apply sulfur or gypsum.
