13: Neutralizing Soil pH

Question 1

Active acidity

Answer 1

Represented by the H+ concentration of soil solution

Question 2

Exchangeable acidity (reserve):

Answer 2

H+ and Al3+ on the cation exchange complex
Related to the CEC of the soil
Can buffer changes in soil pH

Question 3

Consideration of reserve acidity effect on amount of pH nuetralizer needed

Answer 3

Soils with high reserve acidity will need more pH neutralizers to change the acidity.

Question 4

Liming neutralization reaction

How many H+ ions does each molecule of carbonate neutralize?

Answer 4

2H+ + CO32- → CO2 + H2O

Each molecule of carbonate (CO32-) neutralizes two H+ ions

Question 5

Agricultural liming materials

What are they and give some information about them

Answer 5

Calcitic limestone and dolomitic limestone
- Most common

Burned lime and hydrated lime
- Rapid reaction but expensive

Basic slag and wood ashes
- Lower grade materials

Question 6

How much liming to apply?

Answer 6

Soil dependent factors:
- Current soil pH
- Target soil pH
- Soil buffer capacity
- Amount of soil to ameliorate

Lime dependent factors:
- Chemical composition of the liming material (purity)
- Fineness of the liming material

Question 7

Soil buffering capacity

What pH range is adding charge most effective?
When is pH buffered by different compounds? What compounds are those?

Answer 7

At pH of 4-7, changes depend on CEC and pH dependent charge sites

Low pH is buffered through aluminum compounds, high pH is buffered through carbonates

Question 8

Amount of charge needed for different soil textures

Answer 8

You need more charge to finer-textured soils because they have a higher buffering capacity. For example, you’d need to add much more lime to clay loam than sand to change pH by the same amount