Science U1 L5 Flashcards
Definition of soil
loose mixture of small rock fragments, organic matter, water, and air that can support the growth of vegetation.
What is the first step of soil formation?
weathering of parent rock
What is a parent rock?
the source of inorganic soil particles
How is soil made?
weathering breaks down parent rock into smaller and smaller pieces. Pieces of rock eventually become very small particles that are mixed in with organic matter to form soil.
What do you call the remains of decayed organic matter?
Humus
Give two examples of decomposers.
bacteria and fungi
Where is humus found?
in the top layer of soils
Why is humus important?
it contains nutrients that plants need to grow.
Define humus
dark, organic material formed in soil from the decayed remains of plants and animals
Explain the role of decomposition.
When plants or animals die, they are broken down by decomposers, and the nutrients are returned to the soil
Define the role of larger animals such as earthworms and moles that live in soil.
They loosen and mix the soil as they burrow through it. Mixing increases the amount of air in soil and improves the ability of soil to drain water.
Soil formation takes a long time. What are the four main factors in determining exactly how long these processes take.
- Rock type
- Climate
- Topography
- Plants and animals
How does rock type affect how long soil takes to develop?
the rate of weathering depends on the structure of the rock and minerals that make up the rock
How can climate affect soil development?
Soil develops more quickly in warm, wet areas than in cold, dry areas.
How does topography affect soil development?
Soil usually develops faster in flatter areas where sediments are not easily eroded. The sediments usually erode faster on steep slopes.
How do plants and animals affect soil development?
Plant roots hold sediments in place, allowing soil to develop quickly. Areas teaming with life have higher rates of decomposition and mixing. Soil tends to develop more quickly in these areas. Plants and animals help soil to develop quicker.
What do you call a vertical section of soil that shows all different layers of soil?
Soil profile
What is soil horizon?
Each layer in the soil profile that has different physical properties
What are the three main horizons?
Horizon A, B, C
Describe Horizon A
- top of soil profile
- layer where decomposers live
- contains the most decayed organic matter
- Dark color caused by humus
What Horizon would you find dead leaves, branches, and other organic matter.
Horizon A
Which Horizon has the most developed soil?
Horizon A
What is leaching?
When water carries material, such as iron minerals and clay from one Horizon to another.
In which Horizon does leaching cause a reddish or brownish color?
Horizon B
What is another name for the soil in Horizon A?
topsoil
Which Horizon is the least developed?
Horizon C
Which Horizon contains the largest rock fragments and usually no organic matter?
Horizon C
Which Horizon contains mostly weathered rock from which soil is formed?
Horizon C
What is the term that describes the relative amounts of different sized soil particles
soil texture
soil texture
What is the term that describes the relative amounts of different sized soil particles
What are the different soil particles?
sand
silt
clay
Which particles are the largest?
sand
Which particles are the smallest?
clay
What type of soils form in warm, wet regions, with fast development of soil?
Tropical Soils
What type of soils form in dry regions and are shallow, containing little organic matter? In areas of low rainfall and slow soil development?
Desert Soils
What soils form in regions with moderate rainfall and temperatures.
Temperate Soils
What soils form in cold, dry regions where chemical weathering is slow? Typically with no well-developed horizons. May have many rock fragments?
Arctic Soils
What is the pH of soil?
measurement of how acidic or basic soil is
What is an acidic pH?
pH less than 7
What is a basic pH?
pH greater than 7
What is pore space?
the spaces between soil particles
What is found in pore spaces of soil?
air and water
What pore space ratio do most plants grow?
the best soil for growing most plants has about a 50 % of its volume as pore space, equally divided between water and air.
What is soil fertility?
how well soil can support plant growth
What affects the quality of soil fertility?
climate humus minerals nutrients topography
Where are most fertile soils found?
areas with moderate rainfall and temperatures
soils with lots of humus
