Lecture 29- Soils Flashcards
What are the three key macro nutrients for plant growth
Nitrogen, potassium, phosphorous
Why are micronutrients important?
To help plants carry out key enzyme functions
Why are carbon, oxygen and hydrogen not considered major soil macro nutrients?
They are predominantly gathered from atmospheric and water sources by plants, and not the soil
What is a cation and what is an anion?
A cation is a negatively charge ion, a cation is a positively charged one
Saplings the yield response to micronutrient contamination?
Stage 1. Deficiency. This is where increasing concentrations cause an increase in plant weight/ growth
Stage 2. Adequate. The concentrations are in sufficient quantities that any increases do not have an impact on plant growth
Stage 3. Toxicity. Concentrations get too high and cause toxic conditions, causing a decrease in plant weight
Explain the yield response to micro contaminants
As the plants don’t rely on them for growth, increases in the concentrations of micro contaminants have no impacts until reaching toxicity levels
Why are cancerous soils often micronutrient deficient?
The high ph and cancerous content cause micronutrient deficiencies. These micronutrient deficiencies result from less h+ ions biding to colloid surfaces, meaning micronutrients can
Where are alkaline soils and associated micronutrient deficiencies most common?
Middle East, North Africa, south west USA, Australia
What is PH?
A measure of the H+ ion concentration in solution. More hydrogen atoms means a more acidic solution
Why is ph considered a master variable in chemical reactions?
Many chemical and biological reactions are dependant on it
What is the ph range for mineral dominated soils?
4.0 to 10.0
What is the common ph range for humid regions?
5-7
How do soils act as a buffer zone?
They act as a buffer between the atmosphere and groundwater, retaining nutrients and supply them in a steady flow
Within soil, what absorbs ions, molecules and gas?
Clay minerals and organic matter
What causes soil to have its sorptive properties?
Large surface area of clay and hummus, electrical charges
What properties cause greater sorptive properties?
- Divalent ions are more preferable than mono charged ones
2. Large cations are preferred over smaller ones of the same charge, due to their greater surface area
What is cation exchange capacity?
A sum of the total cations that a soil can absorb
What is cation exchange capacity dependant on?
- Negative charge density
- Number of exchange sites
- Soil ph
How does cec impact a soils buffering capacity?
Soils with a greater cec have a greater buffering capacity
What are the three types of acidity in soils?
- Active acidity
- Reserve acidity
- Exchangeable acidity
What is active acidity in soils?
Quantity of H+ ions in soil water solution
What is the reserve activity in soils?
The amount of H+ ions held on soil surfaces via adsorption. This has a greater capacity than soil water.
What is the exchangeable acidity of soils?
The proportions of H+ and aluminium ions held within the soils diffuse layer. These can easily move into solution
How does the addition of acid to soils impact ions on cation exchange sites? Refer to active and reserve acidity
The addition of little acid will cause displacement of the cations bound to the soil surface (by H+ ions). This means there is no change in the soil water PH (which is the measured part) as the H+ ions are held on colloid surfaces and not in solution. When the reserve acidity is full, H+ ions are then encore rates into active acidity, altering PH.
