Chemical Properties of soil

Question 1

Liming

Answer 1

Liming refers to the process of spreading lime (usually ground limestone) on land.
- Calcium lime is most common but Mg lime also used.
- Soil testing should be carried out to determine if lime needs to be spread.
- Lime can take up to 2 years to become full incorporated into the soil.

Ground limestone consists of CACO3, the smaller the particles that are present, the faster they become available and raise pH.
If the particle size is less than 0.1mm it is considered fine lime and is very reactive, providing a faster neutralisation than larger particles.

Question 2

Advantages of liming

Answer 2

• It neutralises the soil.
• Crops & grasses respond better to fertilisers.
• Increases earthworm activity.
• Improves soil structure.
• It promotes flocculation in soils.

Question 3

Qualities of ground limestone

Answer 3

• Must have a total neutralising value of at least 90%
• It must pass through a 3.5mm sieve
• At least 35% of it must pass through a 0.15mm sieve.
• Moisture content must not exceed 2.5%

Question 4

Nutrient availability

Answer 4

Nutrients are present in different forms and not all of these forms can be absorbed by plants.
- If a plant is lacking in one nutrient, this will affect the uptake of other nutrients and crop yield.
- Most nutrients are available between pH 6 and 7. This is the optimum range for crop growth in a wide range of crops.

Question 5

Best particles for cation ion exchange

Answer 5

Colloidal clay and humus are the smallest particles and so they have the highest rate of cation exchange due to the high surface area.

Question 6

Factors that affect cation exchange

Answer 6

SOIL TEXTURE: A soil with a fine texture has a higher surface area, so they have a higher CEC.
CLAY & HUMUS CONTENT: Both colloidal clay & humus have a high CEC. Soils with greater content of these have a higher CEC.
pH: Influences the availability of certain cations.

Question 7

Flocculation (description)

Answer 7

• Flocculation is the clustering together of particles to form groups called floccules/peds
• Particles of clay are small and negatively charged.
• Cations in the soil are positively charged.
• Certain cation (e.g. Ca) can hold the clay particles together creating a stable aggregate. Larger particles such as sand and silt can also become trapped creating larger aggregates.
• By forming these larger aggregates soil structure and soil drainage are improved.
• Flocculating agents can be used to improve this process. E.g. CaCO3.

Question 8

Good soil structure is necessary for

Answer 8

• Drainage of excess water
• Retention of water for plant growth
• Air movement within the soil
• Root penetration
• Emergence of seedling

Question 9

pH

Answer 9

A measure of acidity of a substance, it can be measured by recording the H+ ion concentration.