Soil acidity
decrease (become more acidic)
What are three characteristics of ion exchange reactions?
Reversible
Rapid
Stochiometric
What are exchangeable cations?
Those cations which are readily displaced, by mass ion effect, from negatively charged colloids on which they are absorbed (They are on the DDL)
What are some key physical and chemical properties of SOM?
Higher water retention (Very high SSA, functional groups)
More porous than mineral soil (aprox. 90%)
About 58% C concentration
What are organic soils?
Soils that developed largely from organic deposits. In the Canadian System of Soil Classification these soils have >17% C (or >30% organic matter) by weight and organic horizon must extend to a depth of ≥40cm
What influences soil acidification?
Climate
Parent Material
Vegetation
What is the Law of Mass Action?
The greater the number of Na+ ions in solution the higher the probability that Na+ will displace K+
What is the Cation exchange capacity?
The number of exchangeable cations which the soil solids can adsorb
What is mineralization and Immobilization?
Mineralization is the process of conversion of an organic form of an element to an inorganic state as a result of microbial decomposition
Immobilization is the conversion of an element from the inorganic to organic form in microbial (or plant) tissues, thus rendering the element unavailable to plants
Briefly explain the formation of a bog
Pond -> OM accumulates in the bottom -> Starts to cover more of the depression, smaller shurbs and plant organisms cover the surface
Two main processes that promote soil acidification
Hydrolisis (production of H+ ions)
Leaching of non-acidic ions
What is a pH-Buffer?
A material that contributes tot he system's resistance to change in pH when acids or bases are added.
Which has a higher CEC Kaolinite or Montmorillonite? What about Organic Matter?
OM has a higher CEC in comparison. Kaolinite, compared with Montmorillonite, has a more stable structure, less isomorphic substitution, a lower number of negative charges, thus a lower CEC
What are chelates?
Chelates are organo-mineral complexes in which a metallic ion is bonded to an organic molecule by means of multiple bonds (at least 2), thus forming a ring structure
Valence is important (Bonds)
Metal ion surrounded by an organic molecule forming a ring structure. Positive charge will be neutralized
small, mobile, increase nutrient availability
What are organic soil horizons? (Poorly vs well drained sites)
Of, Om, Oh
L, F, H
What is the role of aluminum (Al3+) in soil acidity?
Aluminum (Al3+) reacts with water (hydrolysis) and can produce up to 3 Hydrogen Ions (H+). Aluminum is very common in phyllosilicates (aluminosilicates)
What is the buffering capacity of a soil?
The capacity of a soil to resist change in pH when acids/bases are added
What is base saturation?
Base saturation (BS) is the fraction of cations on the cation exchange site occupied by base cations rather than H+ and Al3+
What are base cations?
Why is the Carbon - Nitrogen ratio significant? What is an ideal ratio?
What are forest humus forms? Give the three broad categories.
Forest humus forms classification is based on the sequence, properties, and inferred origin of organic horizons (usually just H) and the Ah horizon
Mor
Moder
Mull
What are the pools of soil acidity?
Residual acidity
Exchangeable acidity
Active acidity
The more charged particles the soil has, the more ions it has in its DDL or exchange complex. A higher number of ions in the DDL means a higher probability they engage in reactions with acids & bases added to the soil solution, increasing the resistante to pH change
Plant nutrition benefits of a high or low CEC?
Preferred to have a high CEC to safely keep nutrients. It is good to have base-forming cations that counterbalance the acidity increase
What is the relationship between C/N and Microbial activity?
Decomposition is mediated by microbes under aerobic conditions. Soil bacteria need a 8C:1N ratio
When cacteria are happy & meet the requirement, there is surplus that plants can pick up
Why is it important to recognize the different humus forms?