R2102 1.2 Describe the properties of soil that contribute to the healthy growth of plants

Question 1

Topsoil: Aeration and pore space (5)

Answer 1

1. Naturally more open. High % of large pores so good aeration
2. Can be maintained at 50%+
3. Can be improved by cultivating
4. Plants have roots into topsoil and increase the amount of air in the soil by creating channels through the soil as they grow.
5. Larger pore spaces allow organisms to survive in topsoil on the nurtrients they find from living and dead plant materials.

Question 2

Topsoil: Organic matter (4)

Answer 2

1. 2-5%
2. Lots of living organism especially near surface
3. As organisms die they contribute to soil fertility
4. Plant roots grow and die in the topsoil, and surface litter breaks down, so their is a high level of humus or organic material in the soil

Question 3

Topsoil: Water (2)

Answer 3

1. Depends on soil texture
2. Humus holds water well making in available for plant roots to take up in this layer instead of draining through topsoil and eventually down to the water table.

Question 4

Topsoil: Nutrient content (3)

Answer 4

1. Humus also hold some nutrients well, allowing plant roots in the topsoil to reach them
2. Plants only take up nutrients held in solution in the water in soil, so if topsoil holds water nutrients will be accessible.
3. Enriched by addition of fertilisers

Question 5

Topsoil: colour (3)

Answer 5

1. Dark brown / black, lighter if high chalk content
2. High level of organic matter means topsoik is usually darker than subsoil
3. Darker colour holds onto heat well

Question 6

Topsoil: Suitability for plant growth and damage

Answer 6

1. Best possible option for plants growing in open soil
2. Can be damaged by wrong treatment e.g. compaction
3. If construction work skims off topsoil it can be replaced. However its replacement can conceal problems - e.g. concealled debris left over from construction.

Question 7

Subsoil: Aeration and pore space (4)

Answer 7

1. Few roots penetrate the subsoil, mainly taproots and large shrubs
2. Soil is less crumbly and more compressed.
3. Limited large pores so poorer aeration
4. Generally too deep for cultivation

Question 8

Subsoil: Organic matter (2)

Answer 8

1. Less than 1%
2. Much less organic matter from the decay of plant roots, dead plant material and organisms

Question 9

Subsoil: Water content (3)

Answer 9

1. Depends on soil texture
2. Possible layers of compaction or pans - so subsoil may drain well or become water logged
3. The few roots that penetrate this deep can sometimes access water when the topsoil has dried out. This can be an important water reserve.

Question 10

Subsoil: Nutrient content (4)

Answer 10

1. Low nutrient content, generally below main feeding roots
2. Some of the minerals in the subsoil are what a plant requires
3. Forms of nitrogen leach easily from the topsoil into the subsoil
4. Very little dead organisms and no humus

Question 11

Subsoil: Colour (3)

Answer 11

1. Light browns or greys
2. Generally paler than topsoil. It is one of the ways to distingiush the two when you dig a profile pit.
3. Colour difference is due to lack of organic matter

Question 12

Subsoil: Suitability for plant growth (4)

Answer 12

1. Less suitable for plant growth than topsoil
2. Do not mix subsoil with topsoil when you are digging. The poorer quality subsoil will reduce the quality of the topsoil
3. Possible exception to planting of trees in subsoil -meaning subsoil may need cultivation