Aluminum in Soil
Used as a plan for the background information for my chemistry EE.
- Created by: KyraBing
- Created on: 28-03-14 20:40
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- Aluminum
- pH
- Low soil pH (acidic conditions)
- Low pH increases exposure of avian species to toxic metals, such as aluminum
- Effects on plants
- Cherry seedling investigation
- Concentration of Al increased with decreasing pH
- Al increased from approx. 0.1 to 2.4 meq per 100g with pH decreasing below 5.5
- Recommended pH range: 6.5-7.0
- Levels of Al in root system were proportional to it's availability in the soil
- Al increased from approx. 0.1 to 2.4 meq per 100g with pH decreasing below 5.5
- Levels of Mg and Ca in roots decreased while Mn and Zn increased significantly with increasing Al concentrations
- Seedling mortality increased with increasing Al concetrations
- Overall the investigation suggested that a low soil pH could result in seedling death in part by increasing the absorption of Al into plants at toxic levels
- Concentration of Al increased with decreasing pH
- Roots:
- Stunted roots
- Reduced root zone of susceptible plants such as clover, brassica, ryegrass and most crop plants. This leads to reduced drought tolerance
- General
- Reduced availability of phosphorous through formation of Al-P complexes
- Dominance of tolerant species such as browntop in pastures
- Reduced availabilty of cation nutrients (K, Mg, Ca) through competitive interaction
- Cherry seedling investigation
- Effects on avian species
- Aluminum found in bone marrow of wild pied flycatchers, especially individuals with impaired breeding
- Characteristic impairments of aluminum effected birds
- Production of small clutches
- Defective eggshell formation
- Intrauterine bleeding
- Impairments agree with symptoms of aluminum intoxication in mammals, including humans
- Effects on soil
- Amorphous and crystalline aluminum and iron oxide minerals play a major role in stabilizing soil structure
- Al and Fe oxide interactions with clays are pH dependent
- Low pH, oxides carry a sufficient positive charge, they precipitate on clay surfaces
- These coatings, once formed, are stable at higher pHs.
- Precipitation of oxides at high pH occurs as phases separate from the clays
- Low pH, oxides carry a sufficient positive charge, they precipitate on clay surfaces
- Al and Fe oxide stabilize clay minerals by:
- Decreasing
- Critical coagulation concentration
- Clay dispersion
- Water uptake
- Clay swelling
- Increasing
- Microaggregation
- Micro aggregates:
- Soil aggregates less than 250 micro-meters in size
- Consist of __ cemented together:
- Primary particles
- Plant roots
- Humin:
- Typically found in disturbed or cultivated soils
- Micro aggregates:
- Microaggregation
- Decreasing
- Presence of Al and Fe oxides has a favorable effect on soil physical properties
- Increasing
- Aggregate stability
- Permeability
- Passage or diffusion of a gas, vapor, liquid or solid through a substance without physically or chemically effecting it
- Friability
- Porosity
- Hydraulic conductivity
- Reducing
- Swelling
- Clay dispersion
- Bulk density
- Modulus of rupture
- Increasing
- Soils with significant clay content have an increased risk of Al toxicity at low pH
- In general for soils with medium to high ASC (phosphate retention):
- pH < 5.0: Soluble aluminum almost certainly a problem
- 5.0 < pH < 5.5: soluble aluminum may be a problem
- 5.5 < pH < 6.0: Soluble aluminum not likely to be a problem
- pH > 6.0: Soluble aluminum almost certainly not a problem
- New Zealand soils
- Lower North Island (area of Zealandia and Ian Galloway Park) has a Brown Soil type
- Brown soil type
- Brown or yellow-brown subsoil
- Brown color due to thin coatings of iron oxides
- Precipitation usually >1000mm per year
- Soils usually:
- Strongly leached
- Acid
- Low levels of calcium and other basic cations
- Most extensive soil type in NZ (43% of land)
- Brown or yellow-brown subsoil
- Average NZ soils range from:
- < 0.1 - 20mg/kg Al (0.02M CaCl2)
- But generally levels are less than 3mg/kg if soil pH is above 5.5
- Most soils used for agricultural purposes have a pH higher than 5.5
- pH
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