Environmental Geology 12

How does water move through the pore spaces in soil?

A droplet of water moves downward when gravity overcomes the cohesive and the stronger adhesive forces that hold droplets to soil particles.

Why is the salinization of a field a problem for agriculture?

The salinity of the soil water gets to the point that plant growth is reduced.

Which of the following are true about the soil classification system used by soil scientists?

There are 12 different soil orders, and they are based on the five soil-forming factors. It is based, in part, on the characteristics of the soil horizons. The temperature and moisture regime of the soil is considered in soil classification.

Why do scientist and engineers classify soils differently?

They are interested in different soil characteristics.

How do organisms control soil development?

They create passages in the soil that increase gas and fluid exchange. They contribute organic matter to the soil. Some organisms move materials within the soils.

Which of these climates would experience the highest or fastest weathering rates?

Tropical climate

A rock that has been physically weathered has ______.

been broken into smaller pieces by mechanical means

Since they define soils differently and are interested in different soil properties, scientists and engineers ______.

classify soils differently

Silicate rocks are abundant at Earth's crust. As the minerals in these rocks chemically weather, they form the abundant ______ minerals found in soils. This also concentrates the chemically resistant mineral ______ in the soil as others weather.

clay; quartz

One soil-forming factor is the parent material (earth materials) from which the soil develops; the other four soil-forming factors are , , , and .

climate organisms topography time

As a wet but saturated clay-rich soil starts to dry out, its plasticity will ______.

decrease to nearly zero as the soil completely dries out

The drainage characteristics of the soil affect plant growth because ______.

different species of plants prefer different levels of soil moisture

The mineral composition of the soil and the dipolar nature of the water molecule affect the soil's ability to hold water. This soil property is called ______ resistance.

drought

The 12 different soil orders devised by soil scientists are related to the ______.

five soil-forming factors

Permeability is the ability of a ______.

fluid to flow though the interconnected pore spaces within a material

Useful for growing rice but otherwise harmful to agriculture, ______ limit movement of water and gases into and out of the soil.

hardpans

How are expanding clays used?

how engineers design the supports for heavy structures soil drainage

The compressibility of soils affects ______.

how engineers design the supports for heavy structures soil drainage

A(n) ______ in the ______ content of a soil increases its capacity to shrink and swell.

increase; clay

Farmers try to limit soil compaction because ______.

it makes it more difficult for roots to penetrate the soil it is essentially irreversible

The best agricultural soils are soils with ______.

lots of surface area on particles to store water but not so much clay that strong cohesive forces make it too hard for plants to extract the water

Weathering that results in the physical degradation of rocks with no compositional changes is called weathering.

physical

Soils are important to humans because they ______.

play a critical role in the production of food. provide the raw materials to make aluminum influence construction projects

The amount of void space in a soil relative to the total volume of the soil is called soil ______.

porosity

Sediment pollution from soils is likely to result when the ______.

rate of soil erosion increases and soil loss occurs

How are soils derived from rocks? Soils develop as ______.

rocks are weathered, form sediment, and then plants and other organisms thrive on it and help to form soil

Soils with an abundance of clay minerals capable of incorporating a large number of water molecules within their structure can ______.

significantly shrink and swell as the volume of the water changes

Geologists call any type of fragment material that has been transported a sediment, or they call it regolith if it has not been transported. Engineers classify all of these earth materials as ______, whether they can support life or not.

soil

The general term for the loose material at the surface of Earth is dirt. However, if that loose material can support life, it is called ______ by scientists. If the loose material has been transported, it is called ______; if not, it is called ______.

soil; sediment; regolith

Soil fertility is the ability of a soil to ______.

supply the elements necessary for plant growth

The contrasting crystalline structures of quartz and clay minerals cause them to have different soil properties, including ______.

surface electrical characteristics; quartz is neutral, whereas clay is not shape; clay minerals are sheetlike size; clay minerals are smaller

How does the definition of soil used by soil scientists and engineers differ? Scientists use a more restrictive definition limiting soils to ______.

the narrow zone of fragment materials where soil horizons have developed, whereas engineers simply view soils as any type of fragment material

Soil development is influenced by the parent material because ______.

the parent materials differ in composition different parent materials weather at different rates and in different ways soils are derived from their weathered by-products

What is the difference between saturated and unsaturated soils? Saturated soils have ______.

their pores completely filled with water, whereas unsaturated soils do not

If the pore spaces in a soil are filled with both water and air, it is described as ______; once those pore spaces are filled completely with water, the soil is described as ______.

unsaturated; saturated

Comparing climates, chemical weathering will occur faster in places with more and higher temperatures than in dry climates with low temperatures.

water

Soils rich in organic matter are often black in color, whereas soils lacking organic matter tend to be in color (Use just one word for your answer.)

white

Which of the following statements accurately relates soil strength to soil sensitivity?

Soils sensitive to disturbances can experience rapid changes in soil strength as the cohesion between soil particles changes.

Why are soils composed primarily of quartz and clay minerals?

The rocks that break down to form soils are mostly composed of silicate minerals that weather and form clay minerals. Quartz is both abundant in Earth's crust and resistant to chemical weathering.

Which of the following soils would be the most prized for its agricultural potential?

A soil with a high percentage of silt and a moderate percentage of clay and sand

Which of the following changes to a soil would be likely to increase its plasticity?

Adding clay minerals to the soil

Which of the following are soil-forming factors?

Climate Parent material Topography Organisms Time

If a soil is described as "drought resistant," what does that mean?

It does not lose water from its pore spaces easily.

Which of the following are essential soil nutrients for plant growth?

Magnesium Sulfur Calcium Nitrogen Phosphorous

______ influence soil development by adding organic matter to soil, creating passageways in the soil that allow for the exchange of oxygen and water, and sometimes by moving particles upward in the soil.

Organisms

Which of the following statements are true about the movement of water in the pore spaces of soil?

The adhesive forces between water and clay are stronger than the cohesive forces between water and quartz sand. The electrical properties of soil particles affect the movement of water molecules since water molecules have a different charge on each side.

Which of the following are influenced by soil permeability?

The flood characteristics of a drainage basin The occurrence of mass wasting events Crop health related to soil drainage

What is soil porosity?

The fraction of void space in a soil

Which of the following is true about soil?

The nutrients released as water and organisms interact with rocks and minerals help to form the soil on which plants and other organisms depend. Need help? Review these concept resources.

Which of the following characteristics of a soil affect its compressibility?

The orientation of the particles in the soil The amount of soil moisture or water The compressibility of the minerals in the soil

Which of the following accurately describe a difference in soil properties of quartz and clay minerals?

The outer surface of clay minerals has a negative electrical charge, whereas the outer surface of quartz grains is electrically neutral. Particles of clay minerals are exceedingly small compared to sand and silt-sized grains of quartz.

How does the parent material control the types of soil that develop?

The parent material supplies the weathered material from which soils develop.

The ability of a fluid to flow through interconnected pore space within a material is referred to as ______.

Why is soil permeability important?