Soil aggregate stability
[8] Without access to oxygen, plant roots and aerobic microorganisms are unable to respire, and can die.
The calcium ion (Ca2+), through its cationic bridging effect on flocculation of clay and organic matter compounds, has a crucial role in the formation and stability of soil aggregates.
[14] Sesquioxides act as stabilizing agents for aggregates because iron and aluminum in solution act as flocculants (i.e., bridging cations between negatively charged soil particles), and sesquioxides have potential to precipitate as gel on clay particles.
[16] Soil clay particles have varying effects on aggregate formation, depending on its type.
Soil with 2:1 type of phyllosilicate clay minerals (e.g., montmoriollinite) typically have high cation exchange capacity (CEC), which allows them to bind with polyvalently charged organic matter complexes to form microaggregates.
[3] On the other hand, in soils with oxides and 1:1 type of phyllosiliacte clay minerals (e.g., kaolinite), soil organic matter is not the only binding agent and aggregate formation is also due to electrostatic charges between and among oxides and kaolinite particles.
[20][21] To help explain these contradictory results, it was hypothesized that soils will maintain a state of aggregate stability equilibrium.
[16] This is because 2:1 type phyllosilicate minerals swell and increase their volume with changing water content; meaning these soils expand when wet, and contract as they dry out.
It was found that with higher water content in the soil at the time of freezing had a reducing effect on aggregate stability overall.
Earthworms, termites, and ants are some of the most important invertebrates that are capable of having an effect on soil structure.
[24] Some microarthropods, including mites and collembola, although they are small, because there are large numbers of them, they are able to improve soil structure.
Roots can act as a binding agent themselves, and produce large amounts of exudates that supply carbon to the rhizosphere organisms and soil fauna.
Fungal hyphae can serve as binding agent that stabilizes macroaggregates and they also secrete polysaccharides that contribute to microaggregation.
[12] Tillage can disrupt soil aggregation in several ways: (i) it brings subsoil to the surface, thereby exposing it to precipitation and freeze-thaw cycles, and (ii) it changes soil moisture, temperature, and oxygen level, thereby increasing decomposition and carbon loss.
Higher amounts of precipitation and irregular rainfall events can decrease aggregate stability and increase erosion.
[16] Soil aggregate stability can be measured in several ways, since: In most cases, the wet aggregate stability method is more relevant, because this method mimics the effects of water erosion, which is the driving force of erosion in most environments.
[30] used a method whereby aggregates were subjected to different internal swelling pressures from different concentrations of sodium chloride (NaCl).
[33] To calculate the mean weight, the following formulae can be used: For formulas: A dry sieving rotary cylinder described by Chepil[34] can be used in combination with a nested sieve design, as described by the following procedure by Metting and Rayburn:[35] The slaking method used to measure soil aggregate stability is a measure of how well a soil aggregate sticks together when submersed in water.
