Soil Science Final

The underlying reason why the Mesopotamian civilization died out is _____.

salinity caused by over-irrigation 

The Greek, Roman, and other Mediterranean civilizations declined primarily due to _____.

Soil Erosion

Much of the southeastern Piedmont of the US lost in excess of four inches of top soil as a result of European colonization.

True

a) Define what is meant by the Agricultural Transformation [1 point]

b) List two distinct ways in which it was pivotal to human civilization [2 points]

Agricultural Transformation refers to the change humans made from a hunter/gatherer lifestyle to a sedentary one. Over 5,000 years ago, agricultural practices started to be used by humans and it domesticated us in many ways. Human civilization developed social classes and working heirachry as a result of this tranformation. Health also improved in many ways because of the abundance and variety of food. 

Which three of the following contribute the development of saline seeps?

Answer: Fertilizers, excess irrigation, shallow rooted crops. Do not select erosion

Soils are central to terrestrial ecology and interact with four other ecosystem components, making five in total.  Which of the following is the name used to refer to the soil component?

Pedosphere

Six fundamental functions of soils were described in lecture.

One function is use as an engineering material.  The remaining five functions are ecological in nature. 

Name other five ecological functions. 

• medium for plant growth

• recycling system for nutrients and organic waster

• modifier of the atmosphere

• habitat for soil organisms

• system for water supply and purification

"E" horizons develop when a soil's zone of eluviation extends deeper in the profile than the depth of organic matter incorporation.

True

Natural mineral soils in humid regions with considerable rainfall generally have pHs in which range?

4-7

Approximately what percentage of an ideal soil's volume should be occupied by air?

25%

Which three of the following soil properties are associated with clays?  Select all correct answers.

• water retention

• soil cohesiveness

• nutrient retention

which of the following is not an essential plant nutrient

cadmium- Cd

List the five soil forming factors.  I will consider only your first five answers.

Climate, parent material, topography, biota, time

As opposed to the five soil-forming factors, soil development can be viewed with respect to four types of soil-forming processes.  List these four types of processes

Compared with basalt, granite has which of the following characteristics?

• Granite is more likely to produce a sandy soil.

• Granite contains greater amounts of potassium.

• Granite is more likely produced by magma that cooled underground.

Dark colored minerals are particularly rich in which two plant nutrients?

Iron- Fe and Magnesium- Mg

In general, light-colored minerals weather more readily than do dark-colored minerals.

False

Physical weathering is generally more important in soil formation than is biogeochemical weathering.

False

Compared with soils forming on level uplands, soil formation on slopes is retarded by which two  of the following? 

• reduced effective rainfall

• erosion

The parent material deposited by the melting of glaciers after the last Ice Age is called _____.

Till

Which of the following best characterizes the progression of soil moisture regimes as one moves from the eastern to western US, e.g., Delaware to California?

[east] udic - ustic - aridic - xeric [west]

Soils forming from hard rock parent material are estimated to take 10,000 to 100,000 years to become fully mature.

True

Forest soils tend to have a thinner A horizon than do prairie grassland soils.

True

List three distinct ways in which soil biota affect soil formation.  List four for a bonus point. 

• break down OM

• Nutrient cycling

• Physical Mixing

• Biological weathering

A soil's subgroup name also tells you the suborder name.

True

Like the taxon names at other levels of soil classification, soil series names are composed of formative elements.

False

For each soil order name, select the corresponding description. 

Alfisols: argillic subsoil; moderate fertility; not too acid; typically forest soil

Vertisols: high percentage of shrink/swell clays; cracks when dry

Mollisols: grassland soil; thick, dark A horizon; subsoil varies

Inceptisols: typical horizonation: A/Bw/C; "adolescent" soils

Ultisols: argillic subsoil; low fertility; low pH; typically forest soil

Entisols: very young soils; no B horizon

For each diagnostic horizon, select the corresponding description. 

argillic: subsoils with illuvial clay accumulation; Bt

cambic: inception of subsoil horizon; Bw

mollic: thick, dark A horizon; high in organic matter

ochric: relatively thin, less dark A horizon

calcic: accumulation of illuvial lime (carbonate minerals); Bk

A soil is classified as an Argiaquoll.  Which of the following is true regarding this soil? 

• It is water-saturated for a significant portion of the year.

• It has a thick dark A horizon

• The subsoil has a relatively high clay content.

• It was probably probably formed under prairie/grassland vegetation.

Which of the following is a nonsensical ("imaginary") soil, i.e., one that cannot logically exist?

Argent

Soil color has little direct effect on soil and is most useful for providing clues regarding soil properties and/or development.

True

Which of the following statements regarding soil color is most likely not correct?

Low chromas often indicate well-aerated oxygen-rich conditions.

Describe the loam textural class with respect to each of the following:

a) the approximate relative percentages of sand, silt, and clay on a weight basis [1 pt]

b) the relative degree to which the three soil separate influence soil properties [1 pt]

a) The loam textural class has relative percentages of 40% sand, 40% silt, and 20% clay. 

b) Even though the percentage of clay is lower, it still has an equal impact on the soil properties. So, the three soil seperates all influence the soil properties relatively equally. 

The vast majority of clays are far smaller than the size of bacteria.

True

On a weight basis, clay-sized particles have roughly twice the surface area as do silt-sized particles.

False

Which three of the following are likely direct benefits attributable to good soil structure?  [select all correct answers]

• Reduced soil erosion

• Improved soil aeration

• Better root penetration

Match each description with the corresponding structural classification

typical of subsoil horizons, roughly cubical aggregates: blocky

structureless condition of soils high in clay and/or silt; breaks irregularly: massive

generally in A horizons, roughly spherical aggregates, loose arrangement: granular

Which of the following promote good soil structure? 

Addition of fresh organic matter

Plant rooting, esp. roots of grasses

Divalent cations such as Ca²⁺

Microbial growth and activity

Burrowing by earthworms and insects

Which of the following statements regarding soil structure is/are likely correct?

• Compared to blocky structure, granular structure is more "open" (loosely packed).

• Formation of granular structure is encouraged by the abundance of plant roots and insect/earthworm activity in topsoils.

List three distinct reasons why it is beneficial to "feed the soil", i.e., add fresh, undecomposed organic substances.  I will consider only your first three answers.

1) Reduces soil erosion by adding non decomposed organic matter, like leaf litter, to the surface. 

2) Promotes water retention

3) Increases organic matter of the soil when it eventually breaks down, which is good for plants and other organisms.

Soil tillage has which three of the following long-term effects on soils? 

• Reduces aggregate stability

• Promotes loss of soil organic matter

• Reduces macroporosity

Plant rooting first becomes severely impeded at a bulk density of approximately _____ g cm^-3.

1.6

The bulk density of a highly compacted soil can exceed particle density.

False

With respect to soil porosity, tillage has which of the following long-term effects? 

• Decreased macroporosity

• Increased microporosity

• Decreased overall soil porosity

In general, clay-rich soils benefit more from soil structure than do sandy soils.

True

Macropores provide which of the following? 

• Aeration

• Drainage

• Root penetration

• Water infiltration

After a soil drains following a thoroughly wetting rainstorm, all of the remaining water-filled pores contain plant-available water.

False

Very sandy soils generally have greater bulk densities than do soils high in clay.

True

Dividing a soil's bulk density by particle density gives a measure of the relative presence of soil solids.

true

Compaction preferentially destroys macroporosity.

True

Plow pans form immediately below the depth to which plows penetrate soil.

True

Which of the following help reduce compaction and/or ameliorate plow pans?  Select all correct answers.

• Planting forage radish

• Using wide tires on vehicles

• Using boards to distribute human weight

• Subsoil rippers

Mulches and crop residues left on the soil surface have which of the following effects?  Select all correct answers.

• Increased water infiltration

• Reduced erosion

• Increased biological activity

If bulk density decreases, porosity must also decrease.

False

a) Define soil tilth.  Be precise. [1 pt]

b) List two distinct and practical ways of enhancing soil tilth. [2 pts]  List three for a bonus point.

1) Soil tilth is the physical state and health of a particular soil based on practices of using and caring for it. 

2) Soil tilth can be enhanced by using no till practices when farming the soil and covering the soil in mulch or other non-decomposed organic substances. Another good practice to enhance tilth is selecting proper timing when walking or driving on the soil, such as when it isn't soaking wet. 

Which of the following statements is true regarding water molecules?

The partial negative charge on a water molecule is associated with the oxygen atom.

Which of the following statements is true regarding the behavior of soil water?

Hydrogen bonding occurs both between adjacent water molecules and between water molecules and soil surfaces.

Capillary rise from a free water surface is both greater (in height) and more rapid in fine-textured soil than in coarse-textured soil.

False

Water "balls up" on waxy leaf surfaces due to cohesive forces being greater than adhesive forces.

True

The potential of water at a free water surface is considered to be zero.

True

In normal (non-salty) soils that are actively (currently) draining after a rainfall event, which of the following types of water potential are significant?

• Gravitational potential

• Matric potential

If significant, osmotic potential of soil water is always ______ and therefore ______ water uptake by plants.

Negative… decreases

Regardless of texture, soils can be expected to be fully drained approximately two days after a thoroughly wetting rainfall.

False

Which of the following statements is/are true regarding fully-drained soils at field capacity?  [select all correct answers]

• Both gravitational and hydrostatic potentials are zero.

• The matric potential of the soil water is approximately -10 kPa.

• The largest water filled pores have diameters of approximately 30 um.

• Water films on the soil particles are approximately 15 um in thickness

At the permanent wilting point, fine-textured soils hold more water than coarse-textured soils because they _____. 

• have more surface area

• have more pores  <0.2 um in diameter.

At any given soil water content, a sandy soil will always have a higher (less negative) water potential than a clay-rich soil.

True

Within water films on soil particles, which two of the following statements is/are true?  [select all correct answers]

• Water molecules near the particle surface experience greater adhesive forces than those farther away.

• Water potentials decrease (become more negative) as one approaches the particle surface.

Drawing on your knowledge of how water moves in unsaturated soils (unsaturated flow), explain the common phenomenon of plants wilting in the late afternoon but subsequently recovering by morning.  Specifically, answer these two questions: 1) what happens in the soil overnight that allows the plants to recover, 2) what causes this to happen?  [+2 pts]

Plants that wilt in the late afternoon are able to recover over night for a few reasons. During the day, due to the strong sunlight, plants are constantly transpiring and using up the water around/near their roots in the soil and water is evaporating from the soil surface simoltaneously. Eventually, they don't have as much water available to them and they begin to wilt. At night, there is no sunlight causing constant evaporation from the soil and unsaturated flow of water deeper in the soil is occuring. This means that the water in the bulk soil, away from the plant roots, is beginning to move toward the dry areas around the roots because it is in the chemical nature of water to move from wet areas to dry areas. The roots can then take up this water and the plant becomes no longer wilted. 

Given the following moisture values for a soil (percentages by weight):

   55% when saturated

   45% at field capacity

   15% at permanent wilting point

   5% when air dry

   0% when oven dry

What is the soil's percent plant-available water holding capacity on a weight basis?  (Note that a calculator is available.)

30%

A 10-cm layer of soil has a plant-available water holding capacity of 20% by weight and a bulk density of 1.5 g cm^-3.  Which two of the following statements is/are true?  [select all correct answers] (Note that a calculator is available)

• The soil holds a total of 3 cm of plant available water at field capacity.

• The soil holds a total of 30% plant-available water on a volume basis at field capacity.

Which of the following statements is true regarding the effect of soil organic matter (SOM) on soil water properties? 

As SOM increases, plant-available water holding capacity generally increases.

A moderately permeable soil horizon would probably have a K_sat of around _____ cm hour^-1.

2

Which two of the following is/are true statements regarding preferential flow (PF)?

• PF is almost entirely restricted to those continuous macropores that are open at the soil surface.

• Tillage destroys most PF paths.

Preferential flow can have both negative and positive consequences. 

Positive: quickly supplying deep roots with water and nutrients, enhancing microbial activity in these hotspots, improving soil structure (aggregation), controlling runoff by moving water deeper, and boosting soil carbon cycling by transporting young carbon

Negative: causing rapid water and pollutant transport, bypassing soil filtration to contaminate groundwater with pesticides/nutrients, accelerating erosion, harming slope stability, and reducing water availability in the root zone, which degrades soil quality and food production

Water infiltration rates under no-till agriculture are equal to those under native forest vegetation.

False

Why are rates of unsaturated water flow in soils lower relative to those for saturated flow? 

• Not all pores are water-filled.

• Water films may be discontinuous.

During water infiltration from a localized water source (e.g., an irrigation furrow), lateral (horizontal) movement of water is greater in sandy soils than in fine-textured soils.

False

Which two of the following statements are true regarding water infiltration into a dry soil?

• Infiltration is initially rapid but eventually decreases to a steady state.

• The rate of infiltration once the soil is fully wetted is equal to its Ksat.

In the video(s) on water movement you were assigned, water in an upper fine-textured soil layer did not move readily into an underlying coarse-textured layer.  Answer the following two questions:
a) Give a concise explanation for this phenomenon that includes the water potential principles involved. [up to 2 bonus pts]

b) What conditions must be present for water movement into the coarse-textured layer to occur? [1 bonus pt]

a) Water in the upper fine-textured soil layer did not move readily into an underlying coarse-textured layer because the water in the fine textured soil layer was held too tightly by the pores and the soil was not saturated enough for gravity to force it to move. The pores in the fine textured soil are much smaller than in the coarse-textued soil. This means that water in the small pores have a high capillary action with strong cohesive and adhesive forces keeping the water inside. So by the chemical nature of water, it will not move readily into an empty big pore from a small pore, which is why it did not move from the upper fine textured soil layer to the lower coarse textured one. 

b) The water will move into the coarse textured layer if the soil is completely saturated. In this case, the cohesive and adhesive forces wouldn't be strong enough to resist the force of gravity, which means the water would have to move from the small pores in the fine textured soil down into the large pores in the coarse textured soil. 

Readily available fresh water present as groundwater, lakes, and rivers combined constitutes approximately which percentage of water globally?

<1%

In the water balance equation, discharge consists of which of the following? 

Drainage (leaching) and runoff

Under a given type and amount of vegetation, a site's estimated potential evapotranspiration (PET) will be influenced by which three of the following?  [select all correct answers]

Wind speed, temp, relative humidity

a) In one or two sentences, explain why rates of potential evapotranspiration are always less than that for water evaporation from a free water surface.  Be precise.

b) Potential evapotranspiration for a well vegetated site is generally considered to be what percentage of the rate of water evaporation from a free water surface?

a) Rates of potential evapotranspiration (PET) are always less than or equal to that for water evaporation from a free water surface under the same weather conditions because a vegetated surface, even a well-watered reference crop, offers greater aerodynamic and surface resistance to the flow of water vapor compared to an open water body. The stomatal resistance of the plants and the complex canopy structure inherently limit the rate of water loss compared to the completely free, constantly saturated surface of a water body. 

b) Potential evapotranspiration for a well-vegetated site is generally considered to be 70% to 85% of the rate of water evaporation from a free water surface, typically represented by pan evaporation measurements. This adjustment is often applied using a pan coefficient, which typically ranges from 0.64 to 0.81. 

Which two of the following statements are true regarding soil water deficit?

• Lower (more negative) soil water potentials increase soil water deficit.

• Soil water deficit can be thought of as a measure of plant moisture stress.

Both potential and actual evapotranspiration are high in hot deserts on a annual basis.

False

Which two of the following statements are likely true with regard to water discharge? 

• Increasing soil cover (e.g., mulch, crop residues) will both increase soil leaching and simultaneously reduce runoff and erosion.

• A soil at field capacity will likely experience greater runoff than a drier soil, particularly at the beginning of the rainfall event.

a) Name one management practice that farmers can adopt to reduce runoff from their agricultural fields.

b) Explain precisely how the practice given in "a)" functions to reduce runoff.

Optional: List a additional distinct practice (and explanation) for bonus points. 

a) Runoff can be reduced by using efficient irrigation practices, such as drip/microirrigation.

b) Drip/microirrigration reduces runoff by being extremely specific about where the water is being applied and applying it a little bit at a time. It is 80-90% efficient because the soil has time to fully absorb the water instead of too much being applied at once and half of it running off the surface as a result. 

C) Planting cover crops:)

Impervious surfaces have which three of the following effects on a given site's hydrology?  [select all correct answers]

• Infiltration decreases.

• Overall evapotranspiration is lower, but evaporation is increased relative to transpiration.

• Groundwater recharge decreases.

Which two of the following generally occur following a timber harvest ?

• discharge increases

• nearby streams exhibit greater "flashy" behavior

Artificial drainage enhances crop yields primarily due to lowering of water tables during the _____ months.

Spring

The melting of snowfall on a frozen soil is more harmful than snowfall melting on unfrozen soil.

True

During transpiration, water is pulled through a plant due to water potential gradients (differences in water potential).

True

Which of the following is least likely to influence water use efficiency (WUE)?

Type of irrigation

There is no relationship between irrigation (field water) efficiency and water use efficiency (WUE).

True

In general, increasing leaf area index will increase plant yield more than it will increase water usage.

True

Which two of the following statements is/are true regarding the various irrigation methods discussed in lecture?  [select all correct answers]

• Furrow irrigation has field water efficiencies as low at 20%.

• Furrow irrigation almost always leads to either over- or under-application of water to crops.

List two distinct benefits of artificial drainage.  

improved crop yield/health by preventing waterlogging for better root growth and earlier planting access, and enhanced property safety/usability by eliminating slippery, muddy, or damaged areas for recreation, sports, or structural protection

List two distinct detriments (harmful consequences) of artificial drainage.  

Two distinct consequences of artificial drainage are increased nutrient pollution in waterways (like nitrogen and phosphorus leading to algal blooms) and significant wetland loss/habitat destruction, altering natural water cycles and harming aquatic ecosystems by removing water storage and filtration

Soils used for golf putting greens often consist of a sandy-textured rooting zone underlain by a thick layer of gravel.  What is the primary purpose of the gravel layer with respect to soil water relations?

It is present to increase water storage in the overlying sandy layer.

Which of the following make a soil unsuitable for a septic system?  [select all correct answers]

• shallow to bedrock

• steep slope

• high water table

• rapid permeability