11. Soil Systems

Front 1

refers to processes that physically breakdown and chemically alter earth material.

Back 1

weathering

Front 2

also known as mechanical weathering, is the breakdown of large pieces of earth material into smaller ones, without changes in chemical composition.

Back 2

physical weathering

Front 3

There are many ways earth material can be physically weathered...

Back 3

1. When water freezes in rock crevices it expands creating stress in the crevice. As the stress increases, the crevice widens ultimately breaking the rock.
2. Plant roots wedge rocks apart as they grow into rock crevices too.
3. The shrinking and swelling by alternating heating and cooling weakens mineral bonds causing the rock to disintegrate.

Front 4

What happens to the surface area as a large block of material is broken into several smaller ones?

Back 4

surface area increases

Front 5

What is the increase in surface area due to the physical weathering of an object important?

Back 5

having more total exposed surface provides more area upon which chemical reactions can take place to further weather the material.

Front 6

The breakdown of earth material by chemical alteration. This usually means adding a substance like water or air to the material.

Back 6

chemical weathering

Front 7

when oxygen is added to iron bearing minerals, a loose mantle of iron oxide is created (rust).

Back 7

oxidation

Front 8

an exchange reaction involving minerals and water. Free hydrogen (H+) and hydroxide (OH)- ions in water replace mineral ions and drive them into solution. As a result, the mineral's structure is changed into a new form.

Back 8

hydrolysis

Front 9

common process whereby silicate minerals are weathered into a clay mineral.

Back 9

hydrolysis

Front 10

Dry locations tend to be dominated by ______ weathering and moist places by ______ weathering.

Back 10

physical, chemical

Front 11

Soil horizons form as a result of the four horizon development processes...

Back 11

additions, transformation, translocation, and removal

Front 12

...can be materials that are transported into the location where a soil is forming. For instance, dust with a high calcium carbonate content could be blown on to the developing soil adding calcium to the evolving profile. This is one idea as to how soils in the Midwestern part of the United States called mollisols were enriched with CaCO3.

Back 12

additions

Front 13

...of the materials added to the developing soil occur by chemical and biological processes acting on them. For instance, leaves falling on the surface and plant roots dying beneath may decompose into a dark brown, nutrient-rich material called humus.

Back 13

transformations

Front 14

...involves the movement of soil-forming materials through the developing soil profile. Can occur by water running through the soil transferring materials from upper to lower portions of the profile.

Back 14

translocation

Front 15

soil forming materials that are completely removed from the soil profile. Easily dissolved elements like calcium carbonate can be removed from the soil profile under rainy climates.

Back 15

removal

Front 16

refers to the relative proportion of sand, silt and clay size particles in a sample of soil.

Back 16

structure

Front 17

Soil texture effects many other properties like...

Back 17

structure, chemistry, and most notably, soil porosity, and permeability.

Front 18

refers to the amount of pore, or open space between soil particles.

Back 18

soil porosity

Front 19

the way soil particles aggregate together into what are called peds. Peds come in a variety of shapes depending on the texture, composition, and environment.

Back 19

soil struture

Front 20

...or crumb structures, look like cookie crumbs. They tend to form an open structure that allows water and air to penetrate the soil.

Back 20

granular

Front 21

looks like stacks of dinner plates overlaying one another. Type of structure that tends to impede the downward movement of water and plant roots through the soil. Therefore, open structures tend to be better agricultural soils.

Back 21

platy

Front 22

the mass per unit volume of a soil, including the pore space

Back 22

soil bulk density

Front 23

The greater the bulk density the more ______ the soil. Bulk density increases with clay content and is considered a measure of the compactness of the soil.

Back 23

compact

Front 24

How does the use of heavy agricultural equipment impact soil bulk density?

Back 24

The use of heavy agricultural equipment can cause compaction of soil, especially in wet clay soil. Soil compaction results in reduced infiltration and increase runoff and erosion.

Front 25

As plant material dies and decays it adds organic matter in to the soil in the form of...

Back 25

humus

Front 26

Soils with the ability to absorb and retain exchangeable cations have a high...

Back 26

cation exchange capacity

Front 27

Cations such as ______, ______, ______, and ______ are attracted and held to humus. These cations are rather weakly held to the humus and can be replaced by metallic ions like ______ and ______, releasing them into the soil for plants to use.

Back 27

calcium, magnesium, sodium, and potassium

Front 28

Most good agricultural soils have a pH between _____.

Back 28

5 and 7

Front 29

pH range of soils that pose a problem for agriculture due to their lack of nutrients. More common in humid regions.

Back 29

acidic soils

Front 30

pH range of soils that may contain appreciable amounts of sodium that exceed the tolerances of plants, contribute to high bulk density and poor soil structure. These soils are common in semiarid regions.

Back 30

alkaline soils

Front 31

Soil formation begins first with...

Back 31

the break down of rock into regolith.

Front 32

At the top of the soil profile. Horizon that is primarily composed of organic matter. Fresh litter is found at the surface, while at depth all signs of vegetation structure has been destroyed by decomposition. The decomposed organic matter, or humus, enriches the soil with nutrients (nitrogen, potassium, etc.), aids soil structure (acts to bind particles), and enhances soil moisture retention.

Back 32

O horizon

Front 33

Located at the top or beneath the O horizon. This horizon marks the beginning of the true mineral soil. In this horizon organic material mixes with inorganic products of weathering. This horizon typically is a dark colored horizon due to the presence organic matter. Eluviation occurs in this horizon.

Back 33

A horizon

Front 34

the removal of inorganic and organic substances from a horizon by leaching. It is driven by the downward movement of soil water.

Back 34

Eluviation

Front 35

generally is a light-colored horizon with eluviation being the dominant process. Leaching, or the removal of clay particles, organic matter, and/or oxides of iron and aluminum is active in this horizon. Under coniferous forests, this horizon often has a high concentration of quartz giving the horizon an ashy-gray appearance.

Back 35

E horizon

Front 36

Beneath the E horizon. This horizon is a zone of illuviation where downward moving, especially fine material, is accumulated. The accumulation of fine material leads to the creation of a dense layer in the soil.

Back 36

B horizon

Front 37

In some soils the B horizon is enriched with calcium carbonate in the form of nodules or as a layer. How does this occur?

Back 37

This occurs when the carbonate precipitates out of downward moving soil water or from capillary action.

Front 38

Eluviation is significant in what climates? Why?

Back 38

humid climates, with ample precipitation to move soil materials downward through the soil profile.

Front 39

In arid or semi-arid climates where does the zone of illuviation exist in the soil profile?

Back 39

Because precipitation is scarce, the zone of illuviation is closer to the surface.

Front 40

This horizon represents the soil parent material, either created in situ or transported into its present location. Beneath this horizon lies bedrock.

Back 40

C horizon

Front 41

Newly formed "immature" soils may only have what sequence of horizons?

Back 41

O-A-C horizons

Front 42

Soil research has shown that soil profiles are influenced by five separate, yet interacting, factors:

Back 42

parent material, climate, topography, organisms, and time.

Front 43

the material that soil develops from, and may be rock that has decomposed in place, or material that has been deposited by wind, water, or ice. The character and chemical composition plays an important role in determining soil properties, especially during the early stages of development.

Back 43

parent material

Front 44

How does the influence of parent material on soil change over time?

Back 44

Over time, the influence of parent material on soil decreases as it is altered and climate becomes more important.

Front 45

Three ways in which climate influences soil properties.

Back 45

1. Energy and precipitation strongly influence physical and chemical reactions on parent material.
2. Climate also determines vegetation cover which in turn influences soil development. 3. Precipitation also affects horizon development factors like the translocation of dissolved ions through the soil.

Front 46

Describe the conditions of desert region soils as they are influenced by climate.

Back 46

Hot, dry desert regions have sparse vegetation and hence limited organic material available for the soil. The lack of precipitation inhibits chemical weathering leading to coarse textured soil in arid regions.

Front 47

Describe the conditions of tundra region soils as they are influenced by climate.

Back 47

Bacterial activity is limited by the cold temperatures in the tundra causing organic matter to build up.

Front 48

Describe the conditions of tropical region soils as they are influenced by climate.

Back 48

In the warm and wet tropics, bacterial activity proceeds at a rapid rate, thoroughly decomposing leaf litter. Under the lush tropical forest vegetation, available nutrients are rapidly taken back up by the trees. The high annual precipitation also flushes some organic material from the soil. These factors combine to create soils lacking much organic matter in their upper horizons.

Front 49

Topography has a significant impact on soil formation as it determines:

Back 49

erosion, deposition and soil texture, and microclimates which affect vegetation which in turn ifluences the soil.

Front 50

The amount of water increases in the down slope direction as water is contributed from upslope segments. The velocity of the water increases as well as it moves towards the base of the slope. Which segments on the slope experience the highest amounts of erosion?

Back 50

Erosion increases downslope and is greatest at the base.

Front 51

How does slope erosion influence the development of soils?

Back 51

At the top of the slope, stable conditions prevail, soils are deeper and more developed. At mid to lower slope areas, erosion strips away parent material before it can be developed into a soil. Thus, we should find weakly developed soils towards the middle and near bottom of the slope.

Front 52

How does hillslope orientation affect the microclimate of a place?

Back 52

As the slope of the surface increases, so does the local sun angle, up to a point. As the local sun angle increases, the intensity of heating increases, causing warmer surface temperatures and, likely, increased evaporation. Orientation of the hill slope is certainly important too. Those slopes which face into the sun receive more insolation than those facing away. Thus inclined surfaces facing into the sun tend to be warmer and drier, than flatter surfaces facing away from the sun. The microclimate also impact vegetation type.

Front 53

how do living organisms benefit the soil?

Back 53

1. add organic matter
2. nutrient cycling
3. aid in decomposition
4. weathering process

Front 54

What would happen to the nutrient content of the soils if not for the cycling of nutrients by soil organisms?

Back 54

Nutrients that find their origin in the soil would be leached out without soil organisms to bring them upwards through the soil profile. Soil nutrients would diminish, and so would the soils ability to support life.

Front 55

Broadleaf, deciduous trees like oak and maple generally have high nutrient demand creating surface litter rich in nutrients when leaves die and fall to the forest floor. Decomposition of the litter releases the nutrients back into the soil for the tree to take back up. How could one decribe the nutrient content of soils in this type of ecosystem?

Back 55

soils under these kinds of forests tend to be high in soluble bases and nutrients.

Front 56

Pine trees generally have low nutrient demands. The decaying litter that falls to the forest floor is poor in nutrients.

Back 56

under pine forests there is little cycling of soluble nutrients like calcium, magnesium, sodium, and potassium and these nutrients are thus leached creating an acidic soil environment.

Front 57

The degree to which nutrients are cycled depends on...

Back 57

the needs of the organism occupying a particular place.

Front 58

How does time influence the development of soil?

Back 58

As time passes, the weathering processes continue to act on soil parent material to break it down and decompose it. Horizon development processes continue to differentiate layers in the soil profile by their physical and chemical properties. As a result, older more mature soils have well-developed sequence of horizons, though some may undergo so much weathering and leaching that visually distinct layers may be hard to see.

Front 59

How do burrowing animals influence the nutrient cycling and weathering of soils?

Back 59

Burrowing animals create passage ways through the soil to help aerate and allow water to infiltrate into it. Burrowing animals help translocate materials and fertilize the soil at depth

Front 60

How does climate interact with time to influence soil development processes?

Back 60

Soil development proceeds much more rapidly in warm and wet climates thus reaching a mature status sooner. In cold climates, weathering is impeded and soil development takes much longer.

Front 61

five soil forming (pedogenic) processes

Back 61

laterization, calcification, podzolization, salinization, gleization

Front 62

The soil forming process of the deep red to bright orange-red soils of the topics. Occurs in the hot, rainy tropics where chemical weathering proceeds at a rapid rate. Soils subject to this process tend toward the acidic and lack much organic matter as decomposition and leaching is extreme. Exposure of the soil to the hot tropic sun by deforestation bakes the soil dry, reducing infiltration, increasing runoff, and reducing fertility.

Back 62

laterization

Front 63

This soil forming process occurs in warm, semi-arid environments, usually under grassland vegetation. Soil tends to be rich in organic matter and high in soluble bases. The B horizon of the soil is enriched with calcium carbonate precipitated from water moving downward through the soil, or upward by capillary action of water from below.

Back 63

calicification

Front 64

This soil forming process occurs in warm and dry locations where soluble salts precipitate from water and accumulate in the soil. These soils are common in desert and steppe climates. Salt may also accumulate in soils from sea spray. The rapid evaporation of salt-rich irrigation water has devastated thousands of acres of land world-wide.

Back 64

salinization

Front 65

Gleization occurs in regions of high rainfall and low-lying areas that may be naturally waterlogged. Bacterial activity is slowed in the constantly wet environment thus inhibiting the decomposition of dead vegetation allowing it to accumulate in thick layers. Peat is found in the upper portion of the soil. Decaying plant matter releases organic acids that react with iron in the soil. The iron is reduced rather than oxidized giving the soil a black to bluish - gray color.

Back 65

gleization

Front 66

Soils are classified on the basis of ______ ______,

Back 66

diagnostic horizons that are different from the O, A, B, and C horizons.

Front 67

Soil order that is found in southwestern Wisconsin. Soils lacking horizons because their parent material has only recently accumulated. These soils also form where the parent material is quartz sand, in which horizons do not easily form. They have a wide geographic distribution and can be found in any climate and under any vegetation. These soils and Inceptisols are often found on floodplains, delta deposits, or steep slopes where parent material has difficulty accumulating.

Back 67

Entisols

Front 68

Soils just starting to show horizon development because the soil is quite young. You can see the differentiation of layers in these soils formed on colluvium in West Virginia on the right. These soils like Entisols, are found in any type of environment and are commonly found forming in alluvium on floodplains and delta deposits.

Back 68

Inceptisols

Front 69

These soils have a very high content of organic matter in the dark upper layer of the profile. Found in many different environments from the tundra to the tropics, These soils form in places where organic matter is slow to decompose and thus accumulates over time such as bogs and swamps. They are often "mined" for peat which is dried and burned as fuel.

Back 69

Histosols

Front 70

Soils of arid and semiarid environments where moisture is scarce. They are typically light in color as there is little vegetation to add organic matter to the soil profile. A negative moisture balance in these soils inhibits eluviation. Calcification and salinization are important soil forming processes acting in these soils. Soil horizons are weakly developed and sodium is often high in concentration making them alkaline. The coarse texture of these soils makes it difficult to retain much moisture. These soils can be quite fertile soil if irrigation is properly used. Used improperly, a salt crust can form on the soil. Most are used for grazing.

Back 70

Aridisols

Front 71

Soils developing in parent material containing at least fifty percent volcanic ash. The layers of ash can be seen in this soil from Hawaii. Naturally fertile soils, they support a dense natural cover in moist climates. These soils occur around individual volcanoes created from andesite-rich magma. They are common on the volcanic islands and mountains of "The Ring of Fire", that encircles the Pacific Ocean from North America through Japan.

Back 71

Andisols

Front 72

Dark black soils rich in expandable clay minerals. The clay readily swells upon wetting and shrinks when dried. Though found in every type of climate, they are often found in steppe and wet/dry tropical climates where the soil develops deep cracks as it dries. Surface fragments fall into the cracks and are "swallowed" when the soil swells upon wetting. The soil then develops an "inverted profile" with organic material that is typically located near the surface of the profile is now found at depth.

Back 72

Vertisols

Front 73

These soils are among the most fertile on the Earth. Born under grassland vegetation, these soils are well-known for their dark brown to black organic rich surface layers. These soils have a granular structure and soft consistency when dry. These soils are rich in calcium and others nutrients, and generally posses high moisture retention. Calcium nodules are found near the base of the soil as calcium carbonate precipitates out of soil water. These soils are found in the drier portions of the humid continental climate through the steppe climate.

Back 73

Mollisols

Front 74

These soils are commonly found in cool, moist environments under coniferous forest vegetation. Surface litter composed of pine needles breaks down in the presence of water to form a weak organic acid. Acidic soil water removes base ions in solution to create an acidic soil. Easily dissolved materials are leached from surface layers leaving behind the most resistant material like quartz, creating an ashy-gray near-surface layer. Layers at depth are stained with iron and aluminum oxides.

Back 74

Spodosols

Front 75

Soils developed under temperate forests of the humid midlatitudes. Eluviation is moderate and base status is fairly high in these soils. Common to the humid continental (like the one in Michigan on the left) and humid subtropical climates, these soils are well-developed and contain a subsurface layer of clay called an argillic horizon. Some alfisols are found in the wet/dry tropical climate of Africa, South America, Australia, and Southeast Asia. Having a favorable moisture balance and good fertility, they are very productive soils for agriculture. In fact, they have been successfully used for farming in China and Europe for thousands of years. These soils are abundant on older glacial deposits in the United States, and loess deposits in and near the Mississippi embayment.

Back 75

Alfisols

Front 76

These soils share many of the same properties as Oxisols. Highly weathered soils, they are often red/yellow in color reflecting the oxidation of iron and aluminum. Found in the moister portions of the Humid Subtropical climate, they have a illuvial clay layer which distinguishes them from Oxisols which do not.

Back 76

Ultisols

Front 77

Soils found in warm, rainy climates under broadleaf, evergreen vegetation like that found in the rain forest. Chemical weathering (especially oxidation) in the presence of warm temperatures combined with heavy rainfall creates a soil rich in iron and aluminum oxides called "sesquioxides". A rich diversity of decomposers, rapid uptake by vegetation, and heavy precipitation quickly removes nutrients from the soil. What is left is a nutrient poor soil, not well-suited for agriculture. Cleared of vegetation, the exposed surface is easily eroded.

Back 77

Oxisols

Front 78

Soil that develops on permafrost and common to the tundra. These soils consist of mineral or organic material, or both and have experienced cryoturbation (frost churning) due to annual freeze-thaw cycles.

Back 78

Gelisols