2.1 Soil formation, the mineral soil and cultivation

Question 1

Describe how the formation of a “surface cap” can form in soil (5)

Answer 1

Falling raindrops or over-watering

Over-cultivation, causing soil structure to break down

Lack of organic matter in the soil

Particles in fine and silty soils bond together and form a crust on the surface

As there is nothing to hold the soil crumbs together, particles fall in to the gaps in the soil surface and block them, causing water to run off and not penetrate the soil

Question 2

Ways of reducing soil cap formation (5)

Answer 2

Avoid cultivating when soil is too dry or too wet, or rain is imminent

Use a layer of organic matter to protect the soil surface from rainfall

Hoe regularly around established plants and between rows of seedlings

Dig organic matter into the soil to increase pore space

Water using a fine rose

Question 3

Effects that a soil cap can have on plant growth (3)

Answer 3

Seedlings unable to penetrate the cap

Roots cannot access water (run-off) causing wilting and reduced growth

Roots cannot access oxygen (pore spaces in soil are filled) causing stunted growth

Question 4

Primary soil cultivation - benefits (6)

Answer 4

Soil compaction is alleviated

Annual weeds are controlled by burying them

Rhizomes and roots of perennial weeds can be removed

Exposes pests to predators

Exposes heavy clay soils to the action of frost in winter

Enables the incorporation of various materials (e.g. organic matter or grit)

Question 5

Primary soil cultivation - limitations (6)

Answer 5

Soil structure can be damaged if carried out at the wrong time

Can lead to soil surface capping

Soil pan can be created by continually cultivating to the same depth

Soil can be more prone to erosion

Releases carbon in to the atmosphere

Weeds are brought to the surface or chopped up

Question 6

Ways of minimising the negative effects of soil cultivation (4)

Answer 6

Always cultivate at the correct time (i.e. not too wet)

Reduce the amount of cultivation (e.g. no-dig system of soil management)

Avoid walking on the soil after it has been cultivated

Use bed systems to avoid walking on the soil

Question 7

Name four soil horizons

Answer 7

O - Organic matter/leaf litter

A - Top soil

B - Subsoil

C - Parent material/bedrock

Question 8

Processes of soil formation, and descriptions (3)

Answer 8

Physical -
physical weathering is the expansion and contraction of rocks due to temperature fluctuations and the freezing and thawing of ice in cracks and fissures.

Chemical -
Chemical weathering is when weak acids dissolve rocks. Acids are found in rain and exuded from plant roots. Humic acid is released by decaying organic matter. Sulphuric acid is formed by chemical pollutants.

Biological -
Biological weathering is the result of plant groups growing between cracks in rocks and exerting great pressure. Cracks widen and rocks break into smaller pieces.
Animals can physically break up the parent material by trampling or burrowing.
Growth of moss and lichen on surface can cause cracks.
Exudates from plants and other organisms can erode rock slowly to release soluble nutrients into the soil.

Question 9

Situations where excess water can occur in a domestic garden (6)

Answer 9

Soil texture - e.g. high clay content where water does not drain quickly

Soil structure where the presence of soil compaction or a surface pan impedes drainage

High water table

Sloping site which will be wet at the bottom

Run-off from hard landscaping - e.g. patios

Leaking pipes

Question 10

Ways to deal with excess water in a domestic garden (4)

Answer 10

Cultivation by double-digging if compaction is a problem, to break up the compaction and incorporate organic matter to improve aeration and maintain soil structure.

If soil has a high proportion of small particles (e.g. clay), the soil texture can be improved by cultivating to incorporate coarse sand/grit and bulky organic matter.

Raised beds can be built to keep the root zone out of the wet soil. Soil will need to be well structured to allow it to drain adequately.

Installation of a drain to remove excess water. Soakaway in the lowest area of the garden;
French drains require an outflow.

Question 11

Methods to cultivate soil in a domestic garden (5)

Answer 11

Digging (single or double)

Forking

Raking

Hoeing

Rotary cultivation

Question 12

Benefits of digging (4)

Answer 12

Relieves compaction

Enables incorporation of materials (e.g. organic matter)

Buries weeds

Brings weed seeds to the surface

Question 13

Benefits of forking (4)

Answer 13

Removes lumps in soil

Aerates soil

Brings pests to the surface

Can roughly fork in organic matter

Question 14

Benefits of raking (3)

Answer 14

Levels the soil

Removes large stones and lumps

Creates a fine tilth

Question 15

Benefits of hoeing (2)

Answer 15

Breaks down a surface cap

Removes weeds

Question 16

Benefits of rotary cultivation (4)

Answer 16

Suitable for large areas of land

Breaking new ground

Improves aeration and drainage

Chops up plant debris

Question 17

Limitation of rotary cultivation

Answer 17

A cultivation pan is created when rotavation is repeatedly carried out to the same depth.

Question 18

What is meant by “pore space”?

Answer 18

Spaces between the solid matter of a soil - categorised into three sizes:
Macropores (large) - hold air
Mesopores (medium) - hold available water
Micropores (small) - hold unavailable/hygroscopic water

Question 19

What is meant by “available water content”?

Answer 19

Water that is available for plant uptake and is held in the mesopores. Available water decreases as the volume of air in the soil increases.

Question 20

What is meant by “saturation point”?

Answer 20

The point at which all pore spaces in the soil are filled with water.

Question 21

What is meant by “permanent wilting point”?

Answer 21

This is when there is no more available water in the soil.
Macropores and mesopores are filled with air and the only water present in the soil is tightly bound to the soil particles by hygroscopic action and is not available to the plant.

Question 22

What is meant by “soil moisture deficit”?

Answer 22

Amount of water required to bring the soil back to field capacity.

Question 23

State the meaning of the term “soil texture”

Answer 23

The relative proportions of sand, silt and clay in a given soil.
(the feel of a soil - i.e. gritty, soapy or smooth - enables the texture to be identified)

Question 24

State the meaning of the term “soil structure”

Answer 24

The arrangement of soil particles into aggregates/crumbs as well as the presence of air, water and a small amount of organic matter.

Question 25

Benefits of garden irrigation (4)

Answer 25

Consistent watering process

Larger areas of plants can be watered more effectively

Timers can be used to control the amount of water delivered

Regular system of watering benefits plant growth and development

Question 26

Limitations of garden irrigation (4)

Answer 26

Surface capping of soil as a result of the delivery of water

Leaching of nutrients

Overwatering can occur

Water may not always be delivered to where it is required

Question 27

Benefits of garden drainage systems (3)

Answer 27

Avoids or reduces waterlogging

Improves drainage of e.g. a clay soil which is not free-draining

Reduces the water table in a soil where it is high

Question 28

Limitations of garden drainage systems (3)

Answer 28

Disturbance of the soil when installing a drainage system

Disturbance of soil profile may impact on plant growth

Compaction of the soil due to the use of heavy machinery when installing drainage systems.

Question 29

Benefits of no-dig method of soil management (4)

Answer 29

Soil is left undisturbed and therefore does not affect the microorganisms in the soil

No soil compaction as soil is not stood upon and no heavy machinery is used.

Soil pans are avoided as digging to the same depth does not take place

Avoids weed seeds being brought to the soil surface.

Question 30

Benefits of digging garden soil

Answer 30

Enables soil pans to be broken up

Incorporation of bulky organic matter which improves soil structure

Aerates soil and improves drainage

Exposes pests to predators

Weeds removed by hand or incorporated into the soil