Soil Formation Factors Flashcards

Questions and Answers

What are the five factors of soil formation?

Parent materials, Climate, Biota, Topography, Time.

Do the five factors of soil formation act independently?

False

What are the two types of weathering?

Physical (mechanical) and chemical.

What is physical weathering?

The breakdown of rock or mineral into smaller pieces with no change in the chemical composition. Signup and view all the answers

What is chemical weathering?

The breakdown of rocks by chemical agents. Signup and view all the answers

What is the chief chemical agent?

Water. Signup and view all the answers

Why is climate considered to be the most influential factor acting on parent material?

It determines the nature and intensity of the weathering process that occurs over large geographic areas. Signup and view all the answers

The principle climatic variables influencing soil formation are __ and _.

Temperature and effective precipitation. Signup and view all the answers

What type of biome has the most amount of litter accumulation?

A boreal forest. Signup and view all the answers

What biome has the least amount of litter accumulation?

A tropical rain forest. Signup and view all the answers

What are the methods of mechanical weathering?

Expansion and contraction (due to heating and cooling cycles). Signup and view all the answers

What is frost action?

The process where water freezes at night and expands because the solid occupies a greater volume. Signup and view all the answers

What does frost action require?

An adequate supply of moisture, moisture must be able to enter rock or soil, temperature must move back and forth over freezing point. Signup and view all the answers

How do plants cause physical weathering of rocks?

The rocks are cracked by the plant's roots. Signup and view all the answers

What is exfoliation?

The process in which curved plates of rock are stripped from a larger rock mass. Signup and view all the answers

Many reactions proceed more quickly as temperature ________.

Increases. Signup and view all the answers

With biological processes, for every ______ rise in temperature, the rates of biochemical reactions double.

10ºC. Signup and view all the answers

How do temperature and moisture influence the organic matter content of soil?

Through their effects on the balance between plant growth and microbial decomposition. Signup and view all the answers

If warm temperatures and abundant water are present in the profile at the same time, the processes of weathering, leaching and plant growth will be ________.

Maximized. Signup and view all the answers

Increasing effective annual precipitation generally leads to:

Increased clay and organic matter contents, Greater acidity, Lower ratio of Si/Al. Signup and view all the answers

High temperatures result in faster __________ rates.

Organic matter decomposition. Signup and view all the answers

How do waves physically weather rock material?

By smashing big shells into smaller pieces of shell and eroding rocks creating sediments to be deposited elsewhere. Signup and view all the answers

Smaller particles have a greater surface area, resulting in more rapid _________.

Chemical weathering. Signup and view all the answers

How do plants cause chemical weathering?

By CO2 evolution and carbonic acid formation, leakage of organic acids. Signup and view all the answers

_______ is essential for all the major chemical weathering reactions.

Water. Signup and view all the answers

To be effective in soil formation, water must ________ into the regolith.

Penetrate. Signup and view all the answers

What determines how effectively precipitation can influence soil formation?

Seasonal rainfall distribution, Evaporative demand, Soil permeability. Signup and view all the answers

The greater the depth of water penetration, the greater the depth of _______.

Weathering soil and development. Signup and view all the answers

What does percolating water stimulate?

It stimulates weathering reactions and helps differentiate soil horizons. Signup and view all the answers

How does the deficiency of water affect soils in dry regions?

Soluble salts are not leached from these soils, so they build up to levels that curtail plant growth. Signup and view all the answers

Increasing water ________ chemical weathering rates.

increases. Signup and view all the answers

What is effective precipitation?

The amount of water that moves through the regolith. Signup and view all the answers

What does increasing effective precipitation do?

It increases the rate at which clays and other materials are translocated within the soil profile. Signup and view all the answers

How does oxidation and reduction relate to the aeration of soils?

Well-drained soils tend to be aerobic (oxidized) and poorly drained soils tend to be anaerobic (reduced). Signup and view all the answers

How does water affect the decomposition rate of organic matter in soil?

More water means slower decomposition because the oxygen supply is cut off. Signup and view all the answers

Organic decomposition is faster when the conditions are ________.

Aerobic. Signup and view all the answers

What are characteristics of desert soils?

Relatively shallow, influenced by mechanical weathering. Signup and view all the answers

What are characteristics of the humid tropics?

Deep and well developed, most primary minerals have been destroyed by intensive weathering. Signup and view all the answers

A increase in rainfall results in increased ________.

Chemical weathering. Signup and view all the answers

A decrease in temperature results in increased ________.

Mechanical weathering. Signup and view all the answers

What is the cycle that nutrients take in the ecosystem?

Absorbed from the soil by plants, returned to the soil surface in plant residues, returned to the soil when soil organisms decompose the plant residues. Signup and view all the answers

What are characteristics of a grassland?

Rapid cycling, annual return of above-ground biomass to soil; soils of grasslands tend to have higher organic matter contents. Signup and view all the answers

In the grassland, much of the organic matter added to the soil is from ______.

The deep, fibrous, grass root systems. Signup and view all the answers

What is the source of most organic matter in a forest?

Tree leaves falling on the forest floor. Signup and view all the answers

What other characteristic about grasslands leads to organic matter formation?

Grasslands experience fires that destroy large amounts of aboveground material but stimulate even greater contributions from roots. Signup and view all the answers

The soils under grasslands generally develop a thicker _______ horizon.

A. Signup and view all the answers

Where do forests store most of their organic matter?

In the forest floor (O horizon). Signup and view all the answers

The microbial community in a typical grassland is dominated by _______.

Bacteria. Signup and view all the answers

Forest soil is dominated by ______.

Fungi. Signup and view all the answers

What horizon is commonly found in forested areas that is typically not found in grasslands?

The leached E horizon. Signup and view all the answers

How does the leached E horizon form?

It results from the action of organic acids generated mainly by fungi. Signup and view all the answers

Tree leaves, especially conifers, have ________ acids that promote weathering.

Fulvic organic. Signup and view all the answers

What are characteristics of a deciduous forest?

Intermediate cycling, wood tissue stays but leaves drop; some humus in soil. Signup and view all the answers

What are characteristics of an evergreen forest?

Slow cycling - plants hold nutrients, not returned to soil; little humus in soils; soils under pine forests are generally more acid than those formed under deciduous forests. Signup and view all the answers

Litter falling from coniferous trees will recycle only ______ quantities of calcium, magnesium, and potassium compared to those recycled by litter from some deciduous trees.

Small. Signup and view all the answers

What are the anthropogenic effects (human effects) on soil?

Plowing, irrigating, mining, clearing, disposing, leveling. Signup and view all the answers

Earthworms, termites, and rodents act as _______, moving weathered materials and organic matter up and down the soil profile.

Mixing agents. Signup and view all the answers

Large animals _______ the soil, which reduces air space.

Compact. Signup and view all the answers

Vegetation is the ______ for most microorganisms thus influences soil microbial populations.

Food source. Signup and view all the answers

Natural vegetation helps to _______ the soil and protect it from the ravages of soil erosion.

Stabilize. Signup and view all the answers

What does the topography of a landscape influence?

Rate of runoff, rate of erosion, infiltration of water. Signup and view all the answers

Gravity results in a general trend for water to flow from to .

Higher elevations to lower elevations. Signup and view all the answers

Which is deeper, soils on hillsides or soils on flat terrains?

Soils on flat terrain. Signup and view all the answers

Level areas on summits have high _________ generally.

Leaching. Signup and view all the answers

Level areas on foot-slopes have higher ____ and higher _ and lower _______.

Higher water tables, higher effective moisture, lower leaching. Signup and view all the answers

Systems that contain a lot of ridges tend to absorb ______ than systems that are flat.

More energy. Signup and view all the answers

A convoluted surface dilutes solar energy over _______ surface area than does a smooth surface.

More. Signup and view all the answers

In the northern hemisphere, a north-facing slope will be ______ than a south-facing slope.

Cooler. Signup and view all the answers

Depressed areas can have accumulation of water leading to the formation of and in turn .

Peat bogs, organic soils. Signup and view all the answers

The longer a soil parent material stays in place for the soil-forming processes to act upon it, the _ the horizon development and the ___ it forms.

Greater, deeper. Signup and view all the answers

Clays are _______ minerals.

Secondary. Signup and view all the answers

What are characteristics of clays?

They form in the soil, change forms, move downward with leaching rainwater. Signup and view all the answers

What are characteristics of organic matter?

Forms on the surface, moves downward with rainwater, declines after reaching a maximum. Signup and view all the answers

Residual parent materials have generally been subjected to soil-forming processes longer than transported parent materials.

True Signup and view all the answers

Recently deposited alluvium alongside a stream has had too little time for __________ to take place.

Significant soil profile development. Signup and view all the answers

Soils developed from glacial parent materials and coastal plain areas are generally less weathered than those developed from residual materials.

True Signup and view all the answers

How is soil age considered?

Not in time, but how much development the soil has undergone. Signup and view all the answers

Young soils have __ soil development and _ horizons.

Minimal soil development and few horizons. Signup and view all the answers

Old soils have well ________ developed horizons.

Well. Signup and view all the answers

Where are the oldest soils in the United States?

Terraces and alluvial fans of the Sierra Nevada Mountains in California. Signup and view all the answers

Where are the youngest soils in the United States?

The desert soils of Arizona and New Mexico. Signup and view all the answers

Where are the oldest soils in the world?

Australia. Signup and view all the answers

It takes ________ time for surface horizons to develop than subsoil horizons.

Less. Signup and view all the answers

What is steady state?

When a soil's individual horizons and properties change little over long periods of time. Signup and view all the answers

What are soil-forming factors that hasten the rate of soil formation?

Permeable, unconsolidated, parent material; Warm, humid climate; Forest vegetation; Summit or back-slope landscape position that is well drained. Signup and view all the answers

What conditions are prone to retard soil development?

Impermeable, hard, consolidated parent material; cold, dry climate; prairie vegetation; steeply sloping back-slopes or shoulders. Signup and view all the answers

As we go through time, what happens with soil development?

Thicker horizons that sink deeper into the parent material; increased iron accumulation making the soils redder; increased clay content; increased acidity (soils with lower pH); leaching of nutrients so soils are less fertile. Signup and view all the answers

Study Notes

Five Factors of Soil Formation

Parent materials, climate, biota, topography, and time influence soil formation collectively, not independently.
Physical and chemical weathering are the two main types impacting soil formation.
Physical weathering breaks down materials without changing their chemical composition, while chemical weathering alters materials through chemical reactions.

Key Weathering Agents

Water is the primary chemical agent in weathering processes.
Climate is crucial as it dictates the nature and intensity of weathering in specific geographic areas.

Climatic Influence

Temperature and effective precipitation are the main climatic variables influencing soil formation through their effects on weathering, leaching, and biological processes.
A boreal forest biome has the highest litter accumulation due to slow organic matter decay in cold climates.
Tropical rain forests experience rapid organic matter decay, leading to the lowest litter accumulation.

Mechanical Weathering Processes

Mechanical weathering includes expansion and contraction due to temperature changes and frost action, which requires moisture, access for water, and fluctuating temperatures.
Plant roots can physically weather rocks by cracking them, increasing soil formation.

Chemical Weathering Processes

Chemical weathering includes effects from plant processes that release organic acids and CO2, aiding in rock breakdown.
Effective precipitation is pivotal for chemical weathering, enhancing the movement of materials in soil profiles.

Soil Characteristics and Influences

Temperature and moisture together influence organic matter content and decomposition rates, where warm and wet conditions maximize weathering and growth.
Desert soils are shallow and primarily feature mechanical weathering, while humid tropical soils are deeper with extensive chemical weathering.

Nutrient Cycling in Ecosystems

Nutrients cycle from soil to plants, returning to the soil surface via plant residues and decomposition.
Grasslands exhibit rapid nutrient cycling, contributing significant organic matter from deep root systems.

Microbial Populations in Soils

Grasslands are predominantly populated by bacteria, while forest soils have a higher prevalence of fungi.

Soil Horizon Development

Grassland soils often develop thicker A horizons due to organic matter contributions, while forest soils have an E horizon resulting from leaching by organic acids.
Older soils feature well-developed horizons, while younger soils show minimal development with few distinct layers.

Soil Age and Geographic Variation

The oldest soils in the U.S. are found in California's Sierra Nevada, while the youngest are in Arizona and New Mexico deserts.
Globally, Australia's stable landscapes feature some of the oldest soils.

Conditions Affecting Soil Development

Factors that enhance soil formation include warm, humid climates and well-drained landscapes, while cold, dry conditions and impermeable parent materials hinder development.
Over time, soils see an increase in thickness, iron accumulation, clay content, and acidity, while nutrient leaching may reduce fertility.

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Description

Explore the five essential factors of soil formation with these flashcards. Learn about the interplay of parent materials, climate, biota, topography, and time in shaping soil. Ideal for students studying ecology and environmental science.