5.1 Soil (DP IB Environmental Systems & Societies (ESS): HL): Flashcards

The process by which water moves downward through soil layers is called percolation.

False.

Leaching is a transfer process because it involves the movement of dissolved minerals through the soil.

Decomposition in soil systems is the breakdown of organic matter by microorganisms, releasing nutrients, carbon dioxide, and water.

The accumulation of soluble salts in the soil, which can harm plant growth, is called salinisation.

Biological mixing is the movement of soil particles and materials by soil organisms, such as earthworms, which helps mix organic matter and minerals.

Soil acts as a reservoir for water and nutrients, which are both essential for plant growth.

A soil function is an essential role that soils perform in terrestrial ecosystems, such as supporting plant growth, biodiversity, and biogeochemical cycles.

Soils support plant growth by providing a medium for seed germination, storing water, and supplying essential nutrients such as nitrogen, phosphorus, and potassium.

Soils act as a natural seed bank, providing a substrate for germination and root development.

True.

Soils store water that plants use for hydration, nutrient uptake, and photosynthesis.

A biogeochemical cycle is the process by which essential elements like carbon, nitrogen, and phosphorus are recycled between living organisms and the environment, often involving soils.

Soils provide habitats and niches for a wide range of species, supporting high biodiversity including microorganisms, animals, and fungi.

Soils can act as carbon sinks, stores, or sources depending on environmental conditions, storing or releasing carbon through the decomposition of organic matter.

Tropical forest soils generally have low carbon storage because decomposition is rapid.

Soil texture describes the physical make-up of soils based on the proportions of sand, silt, clay, and humus present.

The main components of soil texture are sand, silt, clay, and humus.

Soil that feels sticky when wet contains a high proportion of clay.

The laboratory method mixes soil with water, allows it to settle into layers, and measures the thickness of sand, silt, and clay to calculate their proportions.

True.

Humus increases nutrient retention in soils, while less humus leads to more nutrient leaching.

Sandy soils drain quickly and may not retain enough moisture for some plants.

Compaction of clay soils limits aeration, which can hinder root growth and beneficial microbial activity.

A soil profile is the vertical section of soil that displays its distinct layers (horizons) formed by long-term interactions within the soil system.

Soil profiles develop as a result of long-term interactions within the soil system, forming distinct horizons.

A horizon is a distinct layer within the soil profile that differs in composition and characteristics from layers above and below it.

False.

Soil profiles usually have more organic-rich layers near the surface and become more mineral-rich deeper down.

Climate, vegetation, parent material, and time are all factors that influence the development of a soil profile.

The O horizon is the uppermost layer of soil, composed mainly of organic matter such as leaf litter and decaying plant material.

The A horizon is also called the topsoil or mixed layer, and it is essential for plant growth due to its high nutrient content.

The E horizon is a soil layer where leaching or removal of minerals and nutrients occurs, often appearing lighter in colour.

The B horizon is the layer where minerals and nutrients leached from upper horizons accumulate, often called the subsoil.

The C horizon represents the weathered parent material from which the soil has formed and often contains partially weathered rock.

The R horizon is the unweathered bedrock that forms the base of the soil profile, largely unaffected by biological activity.

The O horizon is most rich in organic matter.

In undisturbed natural systems, all horizons (O, A, B, and C) are typically present, allowing rich, stable ecosystems to develop.

True.

Losing the organic-rich O and A horizons leads to lower soil fertility and greater need for fertilisers.

Using cover crops or crop rotation are methods that help maintain soil fertility and reduce erosion.

The B horizon is higher in clay, iron, and aluminium compounds compared to the layers above, and is often called the subsoil.

Soil profile diagrams show the composition, nutrient content, water-holding capacity, and drainage characteristics of the soil, helping farmers and land managers make informed decisions about land use and soil conservation.

Soil formation is the process by which soil develops over time due to the interaction of factors such as climate, organisms, geomorphology, geology, and time.

The five main factors influencing soil formation are climate, organisms, geomorphology, geology, and time.

The physical features of the landscape, such as slope, aspect, and drainage, are referred to as geomorphology.

In tropical regions, high temperatures and humidity promote rapid weathering and decomposition, resulting in deep, nutrient-rich soils such as oxisols.

In polar regions, low temperatures slow down biological processes, leading to thin, poorly developed soils.

Leaching is the process by which water removes nutrients and minerals from the topsoil, often resulting in nutrient-poor and acidic soils.

In areas with high rainfall, leaching can lead to the formation of acidic soils such as podzols.

Soils in arid regions often experience salinisation, leading to dry, nutrient-poor soils called aridisols.

Organisms such as plants, animals, and microorganisms contribute to soil formation by breaking down parent material, adding organic matter, aerating the soil, and recycling nutrients.

Soils derived from limestone or chalk, called rendzinas, are typically rich in calcium carbonate.

Andosols are fertile soils formed from volcanic ash, rich in minerals and nutrients, and typically found in areas with recent volcanic activity.

True.

Older soils undergo more weathering and biological activity, leading to well-defined horizons and greater fertility than younger soils.

Soil composition is the proportion of mineral particles, organic matter, water and air in soil.

The four main components of soil are mineral particles, organic matter, water, and air.

Organic matter in soil comes from decomposed plants and animals.

Mineral particles are sand, silt, and clay fragments in soil that vary in size and chemical properties.

Water and air in soil are essential for plant growth and microbial activity.

True.

Organic matter comes from decomposed plants and animals and helps improve soil fertility.

Cation-exchange capacity (CEC) is a measure of how well soil holds and exchanges nutrient ions like potassium, calcium, and magnesium.

Sand particles are less than 2 mm in diameter and have low cation-exchange capacity.

Clay has the highest cation-exchange capacity among soil particle types.

Loam soil is a balanced mixture of sand, silt, and clay that is ideal for cultivation due to its good drainage, nutrient retention, and workability.

The soil texture triangle is a tool used to classify soils based on the relative proportions of sand, silt, and clay.

The three sides of the soil texture triangle represent the proportions of sand, silt and clay.

False.

Sandy soils have a low water holding capacity and drain quickly.

Bulk density is the mass of soil per unit volume, indicating the degree of compaction and suitability for plant growth.

Most plants grow best in soils with a pH between 6 and 7.

A soil carbon store refers to the large amount of carbon held in soils as organic material and carbon compounds, which is roughly twice as much as in the atmosphere.

True.

Soils contain about twice as much carbon as the atmosphere, making them a major carbon store.

When soil organic matter breaks down, both carbon dioxide (CO₂) and methane (CH₄) can be released into the atmosphere.

Soil decomposition releases carbon dioxide (CO₂) when oxygen is present, but methane (CH₄) in waterlogged conditions.

Global warming raises soil temperatures, accelerating decomposition and causing faster release of CO₂ and CH₄, which can further increase warming.

Tilling soil increases decomposition rates and leads to more CO₂ release.

Draining wetlands introduces oxygen to previously waterlogged soils, speeding up decomposition and releasing both CO₂ and CH₄ into the atmosphere.

A tipping point is when rising temperatures cause rapid and uncontrollable carbon emissions from soils, potentially leading to a self-reinforcing cycle of global warming.

Permafrost thawing in the Arctic releases large amounts of CO₂ and CH₄, which can greatly accelerate global warming due to the large carbon stores in frozen soil.

Methane clathrates are ice-like structures containing trapped methane and are found in permafrost and under the ocean floor.