2.1 Soil formation, the mineral soil and cultivation Flashcards
Understand the physical and chemical properties of soils.
Describe how the formation of a “surface cap” can form in soil (5)
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
Ways of reducing soil cap formation (5)
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
Effects that a soil cap can have on plant growth (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
Primary soil cultivation - benefits (6)
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)
Primary soil cultivation - limitations (6)
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
Ways of minimising the negative effects of soil cultivation (4)
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
Name four soil horizons
O - Organic matter/leaf litter
A - Top soil
B - Subsoil
C - Parent material/bedrock
Processes of soil formation, and descriptions (3)
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.
Situations where excess water can occur in a domestic garden (6)
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
Ways to deal with excess water in a domestic garden (4)
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.
Methods to cultivate soil in a domestic garden (5)
Digging (single or double)
Forking
Raking
Hoeing
Rotary cultivation
Benefits of digging (4)
Relieves compaction
Enables incorporation of materials (e.g. organic matter)
Buries weeds
Brings weed seeds to the surface
Benefits of forking (4)
Removes lumps in soil
Aerates soil
Brings pests to the surface
Can roughly fork in organic matter
Benefits of raking (3)
Levels the soil
Removes large stones and lumps
Creates a fine tilth
Benefits of hoeing (2)
Breaks down a surface cap
Removes weeds
Benefits of rotary cultivation (4)
Suitable for large areas of land
Breaking new ground
Improves aeration and drainage
Chops up plant debris
Limitation of rotary cultivation
A cultivation pan is created when rotavation is repeatedly carried out to the same depth.
What is meant by “pore space”?
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
What is meant by “available water content”?
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.
What is meant by “saturation point”?
The point at which all pore spaces in the soil are filled with water.
What is meant by “permanent wilting point”?
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.
What is meant by “soil moisture deficit”?
Amount of water required to bring the soil back to field capacity.
State the meaning of the term “soil texture”
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)
State the meaning of the term “soil structure”
The arrangement of soil particles into aggregates/crumbs as well as the presence of air, water and a small amount of organic matter.
Benefits of garden irrigation (4)
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
Limitations of garden irrigation (4)
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
Benefits of garden drainage systems (3)
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
Limitations of garden drainage systems (3)
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.
Benefits of no-dig method of soil management (4)
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.
Benefits of digging garden soil
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
