Practice Flashcards
Soil forms from which two main inputs/processes?
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All Flashcards in Topic 5.1
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5.1.110 cards
Soil forms from which two main inputs/processes?
Weathering of rock plus the addition of organic matter over time (humus formation).
Rock + organic matter.
What are the main components of healthy soil (approximate proportions)?
About 45% minerals (sand/silt/clay), 25% air, 25% water, 5% organic matter (humus and organisms).
Think: minerals, air, water, organic matter.
Define weathering in the context of soil formation.
Weathering is the breakdown of parent rock into smaller particles by physical, chemical, or biological processes.
Rock → particles.
List the three types of weathering.
Physical weathering, chemical weathering, biological weathering.
Three categories.
Name the three main types of weathering and give one example of each.
Physical: freeze–thaw or temperature changes; Chemical: dissolution or oxidation; Biological: roots or burrowing organisms breaking rock.
Physical / chemical / biological.
Which CLORPT factor refers to slope and drainage?
Relief (topography).
R = relief.
What part of soil composition is usually ~5% but crucial for fertility?
Organic matter (humus and soil organisms).
Small % but high impact.
What does CLORPT stand for in soil formation?
Climate, Organisms, Relief (topography), Parent material, Time.
Mnemonic for soil-forming factors.
Why is soil considered effectively non-renewable on human timescales?
Because soil forms extremely slowly (around 1 cm per 100–1000 years), so lost topsoil cannot be replaced within human lifetimes.
Rate of formation is very slow.
Exam-style point: how should you describe soil as a resource?
Soil is technically renewable, but the renewal rate is so slow that degraded soil is effectively non-renewable on human timescales.
Renewable vs timescale.
5.1.210 cards
Define soil texture.
Soil texture is the proportion of sand, silt, and clay particles in a soil.
Sand–silt–clay mix.
Texture is defined by which three particle types?
Sand, silt, and clay.
Three particle sizes.
Give two properties of sandy soil.
Sandy soil has large particles, drains quickly, is well aerated, but has low water and nutrient retention.
Large particles → fast drainage.
Which soil drains fastest: sand or clay?
Sand drains fastest.
Large pores drain quickly.
Give two properties of clay soil.
Clay soil has very small particles, drains poorly and can become waterlogged, but holds water and nutrients well.
Tiny particles → poor drainage.
What pH range do most crops prefer?
Around pH 6–7.
Near neutral.
Why does pH matter for plant growth?
pH affects nutrient availability and microbial activity, influencing how easily plants can absorb nutrients.
Availability changes with acidity.
What is loam and why is it ideal for agriculture?
Loam is a balanced mix of sand, silt, and clay, giving both good drainage and good nutrient/water retention.
Balance = best for crops.
How does high humus content increase productivity (cause-effect chain)?
Humus improves structure and water-holding capacity and increases nutrient availability (higher CEC), so plants grow more, increasing NPP.
Structure + nutrients + water → growth.
Exam-style: when asked about productivity, what must you always do?
Link soil property to productivity using a clear cause-effect chain (property → plant growth → higher NPP).
Cause → effect.
5.1.310 cards
What does the O horizon contain?
Leaf litter and decomposing organic matter.
Organic layer.
What is a soil profile?
A vertical cross-section of soil showing all horizons from the surface down to bedrock.
Vertical cross-section.
List the main soil horizons in order from top to bottom.
O (organic), A (topsoil), B (subsoil), C (parent material), R (bedrock).
O-A-B-C-R.
Which horizon tends to accumulate materials washed down from above?
The B horizon (subsoil) through illuviation.
B = build-up.
Which horizon is usually most important for plant growth and why?
The A horizon (topsoil) because it contains humus, roots, and most biological activity and nutrients.
Topsoil = life + nutrients.
What is the C horizon?
Weathered parent material with little organic matter.
Broken rock fragments.
Define leaching.
Leaching is the washing of soluble nutrients downward through soil by water.
Nutrients washed down.
What is leaching and what is one consequence in wet climates?
Leaching is nutrients being washed downward; it can make topsoil nutrient-poor and reduce fertility.
Wet → nutrients move down.
What is a soil profile in one sentence?
A soil profile is the full set of horizons seen in a vertical section from surface to bedrock.
One-sentence definition.
In tropical rainforests, where are most nutrients stored and why?
Mostly in the biomass because heavy rainfall causes rapid decomposition and strong leaching, leaving soils relatively nutrient-poor.
Wet climate → leaching.
5.1.410 cards
Soil quality directly affects which productivity measure?
Net primary productivity (NPP).
Plants/biomass.
Define net primary productivity (NPP).
NPP is the rate at which plants produce biomass after accounting for respiration.
Photosynthesis minus respiration.
Name three key factors linking soil to productivity.
Nutrients, water availability (water-holding capacity), and aeration (oxygen for roots).
Nutrients + water + oxygen.
Name two soil factors that can limit productivity.
Low nutrient availability (e.g., N or P limiting) and low water-holding capacity (drought stress) can limit productivity.
Think nutrients + water.
Why does soil aeration affect productivity?
Roots need oxygen for respiration; poor aeration (waterlogging/compaction) reduces root function and plant growth, lowering NPP.
Roots need O2.
Name one soil organism group and its function.
Decomposers (bacteria/fungi) break down dead matter and release nutrients.
Decomposers = recycling.
How do decomposers increase soil fertility?
Decomposers break down dead organic matter and release mineral nutrients back into the soil for plants to absorb.
Recycle nutrients.
How do mycorrhizae help plant productivity?
They increase root surface area and improve uptake of water and mineral nutrients, supporting plant growth and NPP.
Fungi help roots.
What is the role of nitrogen-fixing bacteria in productivity?
They convert atmospheric N2 into plant-available nitrogen compounds (often in legume root nodules), reducing nitrogen limitation and increasing plant growth.
N2 → usable nitrogen.
Exam technique: what must each point include in a 4–7 mark “soil and productivity” answer?
A clear cause-effect link from a soil property to plant growth to increased NPP.
Property → growth → NPP.
5.1.510 cards
Which is generally faster: soil formation or soil loss from erosion?
Soil loss from erosion is usually faster than soil formation.
Forms slowly.
Define soil degradation.
Soil degradation is the decline in soil quality due to processes such as erosion, nutrient depletion, compaction, salinization, or contamination.
Decline in quality.
Name four types of soil degradation.
Erosion, salinization, compaction, nutrient depletion (also contamination and desertification).
List processes.
Name two impacts of soil degradation on society.
Lower crop yields and reduced food security (also higher costs and greater vulnerability to drought).
Food supply.
How can irrigation lead to salinization?
In arid areas, irrigation water evaporates and leaves dissolved salts behind, which accumulate and can become toxic to plants.
Evaporation leaves salt.
Name two impacts of soil degradation on the environment.
Increased sedimentation/water pollution and biodiversity loss (also reduced carbon storage).
Water + ecosystems.
Give two human activities that increase soil erosion.
Deforestation (removes roots that bind soil) and overgrazing (removes vegetation cover), increasing runoff and wind erosion.
Loss of vegetation cover.
Give two common human causes of soil degradation.
Deforestation and intensive agriculture (also overgrazing, irrigation, urbanization).
Human land use.
Why is prevention usually better than restoration for soil?
Because soil takes centuries to form and restoration is slow and uncertain compared with preventing erosion and fertility loss.
Time factor.
Why is soil degradation a major sustainability issue?
Soil forms very slowly but can be lost quickly; degradation reduces food security, harms water quality, reduces biodiversity, and lowers carbon storage.
Slow to form, fast to lose.
Topic 5.1 study notes
Full notes & explanations for Soil systems
ESS exam skills
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