EESC456-CHAPTER2

Question 1

Why no soils on the moon

Answer 1

No organic matter present, absence of life on the moon

Question 2

Weathering of igneous, sedimentary &
metamorphic rocks =

Answer 2

• Primary to secondary minerals
• Typical composition of rocks determining the kind of soil you get from parent material

Question 3

• Mechanical (4) breakdown (weathering)

Answer 3

– Mechanical
* Temperature (wildfire related exfoliation of rocks)
* Pressure – exfoliation
* Abrasion: Water, ice & wind (erosion by flowing water)
* Plant & animal action

Question 4

Biogeochemical weathering breakdown: (6)

Answer 4

• Hydration – addition of water molecule:
• Hydrolysis – action of splitting of water; hydrogen & hydroxyl ions (H20 –> H + HO)
• Dissolution – dissolving soluble minerals = big cave systems
  –> gypson, limestone, dolomite = vulnerable to it
• Carbonation & other acid reactions – action of acids on rock materials
• Oxidation – Reduction (“redox”):
  change in valence state (& ionic radius)
  –>Fe2+ oxidised to Fe3+ (oxidation = loss of
  electron)
  –>Reverse is Reduction (gain electron)
• Complexation – biological processes produce acids contributing to decomposition of rocks

Question 5

Integrated weathering process:

Answer 5

several processes in conjunction

Question 6

5 soil forming factors at work (interacting)

Answer 6

1. parent material (limiting factor, mineral material out of which soil is forming, geological/organic precursors to soil)
2. climate (precipitation + temperature)
3. biota (living ecosystem contribution)
4. topography (relief, elevation, aspect, landscape position, etc.)
5. time (period since p.m. began to undergo soil formation. how much depends on factors above; easily broken p.m. = longer/hot, humid climate = shorter)

Question 7

The nature of the parent material profoundly influences …

The chemical and mineralogical composition of parent material also influences both … and …

Soils are derived from parent materials, but are defined by ….

Characteristic sequences of horizons lead to
…

Answer 7

soil characteristics.

chemical weathering and the natural vegetation

their difference from them (from the environment)

classification

Question 8

4 basic soil forming (genesis) processes

Answer 8

1. Transformations: physical/chemical alterations, synthesis, rearrangement in different ways
2. Translocations: movement of organic/inorganic materials (up/down with water, in solution/suspension, mixing by animals)
3. Additions: organic matter in dust (fall outs from atmosphere) + solutes (with precipitation)
4. Losses: leaching, decomposition, physical erosion, crop removal when harvesting

Question 9

Consequences of factors + soil processes = products (of soil forming)

Answer 9

Master horizons (roughly horizontal layers) develop. (USDA). Master horizons: O, A, E, B, C

A : upper mineral soil, darker from incorporation of o.m., often coarser surfaces (Okanagan = 5-10 cm)

E: (exit). not always there. eluviated, zone of max. removal of clay, Fe, Al-oxides (usually clay minerals); coarser (consequence of high leaching) & paler (due to elluviation process)

B: (bulk) original parent material no longer recognisable; illuviation,
accumulation (soil forming, humus-leached o.m.-, clay minerals of E), transformation; many subdivisions possible (B1, B2, B3, etc).

C: insufficient soil development to qualify as B, but unconsolidated enough to be dug with shovel, retains characteristics of parent
material. Transitional B to P.M. (in between zone)

–>Each may be further sub-divided

Question 10

2 aspects that differ in Canada (CSSC) from USDA

Answer 10

• E is a downgraded to a form of A, Ae
• And underlying rock is a recognized horizon, R (which is subscripted in USDA, e.g. Cr) because it is more important/prominent feature of soil profiles in Canada (shallow soils)

Question 11

O horizon subdivisions why?

Answer 11

division of O horizon because substantial depth of o.m. needed to be divided. Not just accumulation of litter on top, if it is not consistently there formed in o.m. then p.m. is rarely there.

O (organic)
Oi – fibric (=litter)
Oe – hemic (=fermentation),
Oa – sapric (=humus, amorphous residues) = most broken down

Question 12

5. time (factors influencing soil formation)

Answer 12

– Rates of weathering (biogeochemical)

– Interaction with parent materials
–> basalt (volcanic) needs less time

– Chrono-sequence (sequence overtime)
–>alluvial terraces-layering
–>coastal dune soils; inlands = older, coastal sand deposits = newer

more time = more forming

Question 13

4. topography/landscape (factors influencing soil formation)

Answer 13

– Slope steepness
–> top = loose material (gravity, water, collovial move)
–> bottom = accumulate materials (washed/leached down)

– Position in landscape: accumulation & wetness, catena

– Interaction with vegetation

– Slope aspect (Pole + Equatorial aspects)
–>East/North facing slopes = less sun –> higher moisture, more vegetation
–>West/South facing slopes = more sun –>
less vegetation is supported

– Salt build-up

– Parent material interactions = varying conditions of soil forming

Question 14

Catena

Answer 14

characteristic sequence of profiles down toposequence

Natural sequences of soil types
–> soil mapping; fairly consistent soil profiles (same repeating patterns) across landscape

different sequences of soil forming depending on where you are in the landscape (aspect/slope) = sequences of soil horizons differ

Question 15

3. Biota (factors influencing soil formation)

Answer 15

– O.M. accumulation
–>maintains integrity of aggregates
–> fosters aggregation of soil particles

– Bio-geo-chemical weathering
^linked
– Nutrient cycling (released, mineral breakdowns)

– Profile mixing - within soil profile (animals mixing soil around)

– Aggregate stability (o.m.)

– Soil forming = 1/erosion rate (effect of vegetation cover)
–>inverse
–>erosion rate is higher in the absence of vegetation
–> higher vegetation cover = less erosion = more build up of soil

Question 16

Role of biota (3)

Answer 16

1. Type of vegetation: e.g. grassland vs forest
   –>grassland soil; thich, deep, o.m. enriched A horizon. o.m./A horizon transfered through soil profile
2. Role of animals:
   -mixing (animal burrowing induces mixing)
   -aggregation (earthworms process soils),
   -aeration (earthworms tunnel through = pores)
   -movement of soil
3. Human influences: tillage, cover type,
   degradation, mining
   –>different color/vegetation = different soil forming
   –>Cultivation plowing (turning over soil)

Question 17

2. Climate (factors influencing soil formation)

Answer 17

most influential of the four factors acting on parent material because it determines the nature and intensity of the weathering that occurs over large geographic areas. Both below affect the rates of chemical, physical, and biological processes.

-Effective precipitation: residual that leaches profile

-Temperature: rate of biogeochemical reactions more than 2x for each 10C increase in T. Temperature and moisture both influence the organic matter content of soil through their effects on the balance between plant growth and microbial decomposition
–> influences weathering
–>influences potential vegetation:

Humid climates = trees.
subhumid and semiarid = grasses
arid = shrubs and brush

Okanagan soil forming = slow (heat, no water, cold, altitude)

Question 18

1. Parent material (factors influencing soil formation)

Answer 18

A. Colluvial debris (colluvium);
-detached from the heights above and carried downslope, mostly by gravity, assisted in some cases by frost action or water
-Poorly sorted rock fragments (varying grain sizes)
-angular (not traveled far from p.m.)
-coarse- physical weathering = dominant
-Stones, gravel, and fine materials are interspersed (not layered), and the coarse fragments are rather angular

–>bottom of mountain
–> easy drainage + tendency to be unstable, prone to slumping/landslides,

B. Alluvial Stream deposits (alluvium):
1. floodplains:
2. alluvial fans
3. deltas:
-Sorted
-rounded (transported by water)
-layered (each layer = particles same size) due to varying available energy in flows in water suspension to transport materials
–> seasonal, multiseasonal = sequences of sorting
–> layering more horizontal when water, more angular if transported by wind

C. Marine deposits
-Sorted, rounded, layered
–>ocean deposited in marine

D. Glacial & meltwater: glacial ice pushed forward, it swept away the existing regolith with its soil mantle, rounded the hills, filled in the valleys, severely ground and gouged underlying rock. Thus, the glacier became filled with rock and all kinds of unconsolidated materials, carrying great masses of these materials as it pushed ahead. ice melted (glacier retreats) so glacial debris/drift remained. =new regolith and fresh parent material for soil formation.

-Till: deposited by ice; unsorted, unstratified, boulders to clay, more rounded than colluvium, less than alluvium, compacted deposits.
–> transported + dumped all at same place by glaciers close to it

-Outwash: sorted gravels and sands
–> traveled further with glacial water

-Lacustrine deposits: coarse deltaic deposits, as water flow slows; fine silts and clay particles in still water (no energy)

E. Residual

Question 19

Residual parent material:

Answer 19

underlying rock forms soil on site (saprolite) or broke down/transported forming away from site (regolith)

develops in place from weathering of the underlying rock.

Where the climate is warm and very humid, residual parent materials are typically thoroughly leached and oxi- dized, and they show the red and yellow colors of various oxidized iron compounds.

In cooler and especially drier climates, the color and chemical composition of residual parent material tends to resemble more closely the rock from which it formed

A great variety of soils occupy the regions covered by residual debris because of the marked differences in the nature of the rocks from which these materials evolved. The varied soils are also a reflection of wide differences in other soil-form- ing factors, such as climate and vegetation

Question 20

Mixed glacial deposits:

Answer 20

various episodes of glacial melt, different things deposited overtime

Compacted (previous + new materials)
Coarser (like concrete, poor rankage) to finer as go down profile

–> does not drain easily

Question 21

Aeolian deposits:

Answer 21

Wind-transported (eolian) materials important as parent material for soil formation include, from largest to smallest particle size: dune sand, loess and aerosolic dust and windblown volcanic ash from erupting volcanoes.

Materials transported by wind (sand dunes, loess, aerosolic dust, volcanic ash)
–> Wind can most effectively pick up material from soil or regolith that is loose, dry, and unprotected by vegetation. Dry, barren landscapes have served, and continue to serve, as sources of parent material for soils forming as far away as the opposite side of the globe. The smaller the particles, the higher and farther the wind will carry them.

dust transported
= nutrients too
= atmospheric variance (visible gps)

–> ex. Sahara desert to Amazon, Mobile sands Namibia

Question 22

Organic deposits

Answer 22

wetlands where rate of accumulation
exceeds decomposition (peats)

Organic material accumulates in wet places where plant growth exceeds the rate of residue decomposition. In such areas residues accumulate over the centuries from wetland plants.

• Types of Wetlands (Canada)
• Types of peat materials:
  o Moss peat (mostly sphagnum)
  o Herbaceous peat – sedges, reeds, cattails
  o Woody peat – includes tree & shrub material
  o Sedimentary peat – aquatic plants & faecal
  material (finer materials)

Question 23

Weathering

Answer 23

breaks up rocks and minerals

modifies or destroys their physical and chemical characteristics

carries away the finer fragments and soluble products

synthesizes new minerals that influence important properties in soils.

Weathering is a biochemical process that involves both destruction and synthesis. the original rocks and minerals are destroyed by both physical disintegration and chemical decomposition.

Question 24

The nature of the rocks and minerals being weathered determines the rates and results of the … and …

Answer 24

breakdown and synthesis

Question 25

Earth’s rocks

Answer 25

Igneous, sedimentary, and metamorphic.

Question 26

Igneous rocks

Answer 26

formed from molten magma
composed of such primary minerals (light-colored quartz, muscovite, and feldspars and dark-colored biotite, augite, and hornblende).

The mineral grains in igneous rocks interlock and are randomly dispersed,

include such common rocks as granite and diorite

Question 27

Primary minerals
Secondary minerals

Answer 27

have not been altered chemically since they formed as molten lava solidified.

are recrystallized products of the chemical breakdown and/or alteration of primary minerals.

Question 28

Sedimentary rocks

Answer 28

form when weathering products released from other, older rocks col- lect under water as sediment and eventually reconsolidate into new rock.

The resistance of a given sedimentary rock to weathering is determined by its particular dominant minerals and by the cementing agent.

Question 29

Metamorphic rocks

Answer 29

are formed from other rocks by a process of change termed “meta- morphism.”

These movements (continental plates) subject igneous and sedimentary rock masses to tremendous heat and pressure. These forces may slowly compress and partially remelt and distort the rocks, as well as break the bonds holding the original minerals together.

Recrystallization during metamorphism may produce new (usually larger) crystals of the same minerals, or elements from the original minerals may recombine to form new minerals.

The particular minerals that dominate a given metamorphic rock influence its resistance to chemical weathering

Question 30

physical disintegration

Answer 30

Without appreciably affecting their composition, physical disintegration breaks down rock into smaller rocks and eventually into sand and silt particles that are commonly made up of individual minerals.

–> physical weathering is accentuated in very cold or very dry environments,

Question 31

Chemical decomposition

Answer 31

Simultaneously, the minerals decompose chemically, releasing soluble materials and synthe- sizing new minerals, some of which are resistant end products. New minerals form either by minor chemical alterations or by complete chemical breakdown of the original mineral and resynthesis of new minerals. During the chemical changes, particle size continues to decrease, and constituents continue to dissolve in the aqueous weathering solution. The dissolved sub- stances may recombine into new (secondary) minerals, may leave the profile in drainage water, or may be taken up by plant roots.

–> chemical re-actions are most intense where the climate is wet and hot.

Question 32

Three groups of minerals that remain in well-weathered soils

Answer 32

1) silicate clays, (2) very resistant end products, including iron and alumi- num oxide clays, and (3) very resistant primary minerals, such as quartz.

–> In highly weathered soils of humid tropical and subtropical regions, the oxides of iron and aluminum, and certain silicate clays with low Si/Al ratios, predominate because most other constituents have been broken down and removed.

Question 33

1. temperature (physical weathering-desintegration)

Answer 33

Rocks exposed to sunlight heat up during the day and cool down at night, causing alternate expansion and contraction of their constituent minerals.

As some minerals expand more than others, temperature changes set up differential stresses that eventually cause the rock to crack apart.

Because the outer surface of a rock is often warmer or colder than the more protected inner portions, some rocks may weather by exfoliation—the peeling away of outer layers. This process may be sharply accelerated if ice forms in the surface cracks. When water freezes, it expands, disintegrating huge rock masses and dislodging mineral grains from smaller fragments.

Question 34

2. abrasion by water/ice/wind (physical weathering-desintegration)

Answer 34

When loaded with sediment, water has tremendous cutting power. The rounding of riverbed rocks and beach sand grains is further evidence of the abrasion that accompanies water movement.

Windblown dust and sand also can wear down rocks by abrasion (Grand Canyon).

In glacial areas, huge mov- ing ice masses embedded with soil and rock fragments grind down rocks in their path and carry away large volumes of material.

Question 35

3. plants/animals (physical weathering-desintegration)

Answer 35

Plant roots can enter cracks in rocks and pry them apart, resulting in some disintegration.

Burrowing animals may also help disintegrate rock somewhat.

–>such influences are of little importance in producing parent material compared to other 2

Question 36

Examples of how both types of weathering occur together, and each tends to accelerate the other.

Answer 36

physical abrasion (rubbing together) decreases the size of particles and therefore increases their surface area, making them more susceptible to rapid chemical reactions.

Question 37

Chemical weathering is enhanced by such …. as the presence of water and oxygen, as well as by such … as the acids produced by microbial and plant-root metabolism.

The various agents act in concert to convert primary minerals to secondary minerals and ….

**importance of ….in each of the six basic types of chemical weathering reactions discussed in the following.

Answer 37

geological agents

biological agents

release plant nutrient elements in soluble forms.

water

Question 38

1. Hydration (biogeochemical weathering)

Answer 38

Intact water molecules may bind to a mineral. Hydrated oxides of iron and aluminum =common products of hydration reactions.

Question 39

2. Hydrolysis (biogeochemical weathering)

Answer 39

Water molecules split into their hydrogen and hydroxyl components, and the hydrogen often replaces a cation from the mineral structure.

Example = is the action of water on microcline (potassium-containing feldspar.)
–>The potassium released is soluble and is subject to adsorption by soil colloids, uptake by plants, and removal in the drainage water.

Example = silicic acid (H4SiO4) is soluble. It can be removed slowly in drainage water, or it can recombine with other compounds to form secondary minerals such as the silicate clays.

Question 40

3. Dissolution (biogeochemical weathering)

Answer 40

Water is capable of dissolving many minerals by hydrating the cations and anions until they become dissociated from each other and surrounded by water molecules.

Example = Gypsum dissolving in water

Question 41

4. Acid reactions (biogeochemical weathering)

Answer 41

Weathering is accelerated by the presence of acids, which increase the ac- tivity of hydrogen ions in water.

Example = carbon dioxide dissolves in water (a process enhanced by microbial and root respiration) the carbonic acid (H2CO3) produced hastens the chemical dissolution of calcite in limestone or marble.

Example = Soils also contain nitric acid (HNO3), sulfuric acid (H2SO4), and many organic acids and hydrogen ions associated with clays—all of which can react with soil minerals.

Question 42

5. Oxidation-Reduction (biogeochemical weathering)

Answer 42

Minerals that contain iron, manganese, or sulfur are especially susceptible to oxidation–reduction reactions.

When rocks containing such minerals are exposed to air and water during soil formation, the iron is easily oxidized (loses an electron) and becomes triva- lent Fe(III) (ferric). If iron is oxidized from Fe(II) to Fe(III), the change in valence and ionic radius causes destabilizing adjustments in the crystal structure of the mineral.

In other cases, Fe(II) may be released from the mineral and almost simultaneously oxidized to Fe(III).

=The oxidation and/or removal of iron during weathering is often made visible by changes in the colors of the resulting altered minerals

Question 43

6. Complexation (biogeochemical weathering)

Answer 43

Soil biological processes produce organic acids such as oxalic, citric, and tartaric acids, as well as larger organic acid molecules. In addition to providing H+ ions that help solubilize aluminum and silicon, they also form organic complexes with Al3+ ions from within the structure of silicate minerals, causing these minerals to further disintegrate.

Example = oxalic acid forms a soluble complex with aluminum from the mineral, muscovite. As this reaction proceeds to the right, it destroys the muscovite structure and releases dissolved ions of the plant nutrient, potassium.

Question 44

The various chemical weathering processes occur …and are …

Answer 44

simultaneously
interdependent

Question 45

Soils are often defined in terms of these factors as dynamic natural bodies having properties derived from the combined effects of …. and …, as modified by …, acting on …. over ….

Answer 45

climate and biotic activities
topography
parent materials
periods of time

Question 46

Contrasting climatic regimes are likely to be associated with contrasting types of vegetation, and perhaps differing topography and parent material as well.

Nonetheless, in certain situations one of the factors has had the dominant influence in determining differences among … (lithosequence, climosequence, biosequence, toposequence, or chronosequence).

Answer 46

a set of soils

Question 47

Classification of Parent Materials

Answer 47

Inorganic parent materials can either be formed in place as residual material weathered from the rock below, or they can be transported from one location and deposited at another.

In wet environments (such as swamps and marshes), incomplete decomposition may allow organic parent materials to accumulate from the residues of many generations of vegetation.

Although it is their chemical and physical properties that most influence soil de- velopment, parent materials are often classified with regard to the mode of placement in their current location.

parent material properties vary widely within each group and because the effect of parent material is modified by the influence of climate, organ- isms, topography, and time.

Question 48

Packing voids (colluvium)

Answer 48

spaces created when tumbling rocks come to rest against each other (sometimes at precarious angles), help account for the easy drainage of many colluvial deposits and also for their tendency to be unstable and prone to slumping and landslides, especially if disturbed by excavations.

Question 49

Floodplains (alluvial stream deposits)

Answer 49

flood waters deposit sediments on the floodplain, laying down the coarser materials near the river channel where the water flows deeper, faster and with more turbulence.

Finer materials settle out in the calmer flood waters farther from the channel. Each major flooding episode lays down a distinctive layer of sediment, creating the stratification that characterizes alluvial soils

change in grade = stream may cut down through its already well-formed alluvial deposits. This cutting action leaves terraces above the floodplain

nutrient-rich materials lost by upland soils are deposited on the river floodplain and delta. Soils derived from alluvial sediments generally have characteristics seen as desirable for human settlement and agriculture. These characteristics include nearly level topography, proximity to water, high fertility, and high productivity. While alluvial soils are often uniquely suited to forestry and crop production, their use for home sites and urban development should generally be avoided

Question 50

Alluvial fans (alluvial stream deposits)

Answer 50

Streams that leave a narrow valley in an upland area and suddenly descend to a much broader valley below deposit sediment in the shape of a fan, as the water spreads out and slows down. The rushing water tends to sort the sediment particles by size, first dropping the gravel and coarse sand, then depositing the finer materials toward the bottom of the alluvial fan.

The soils derived from this debris often prove very productive, although they may be quite coarse-textured.

Question 51

Deltas (alluvial stream deposits)

Answer 51

Much of the finer sediment carried by streams is not deposited in the floodplain but is discharged into the lake, reservoir, or ocean into which the streams flow. Some of the suspended material settles near the mouth of the river, forming a delta.

found at the mouths of only a few rivers of the world. A delta often is a continuation of a floodplain (its front, so to speak). It is clayey in nature and is likely to be poorly drained as well.
Delta marshes are among the most extensive and biologically important of wetland habitats

Question 52

Coastal deposits

Answer 52

Streams eventually deposit much of their sediment loads in oceans, estuaries, and gulfs. The coarser fragments settle out near the shore and the finer particles at a distance. Over long periods of time, these underwater sediments build up.

Changes in the relative elevations of sea and land may later raise these marine deposits above sea level, creating a coastal plain. The deposits are then subject to a new cycle of weathering and soil formation.

The land surface in the lower coastal portion may be only slightly above the water table during part of the year, so wetland forest and marsh vegetation often dominate areas of such parent materials.

variable textures

All of these sediments came from the erosion of upland areas, some of which were highly weathered before the transport took place. However, marine sediments generally have been subjected to soil-forming processes for a shorter period of time than their upland counterparts. so the properties of the soils that form are heavily influenced by those of the marine parent materials.

–>Because seawater is high in sulfur, many marine sediments are high in sulfur and go through a period of acid-forming sulfur oxidation at some stage of soil formation

Question 53

Drift (Glacial till deposits)
Glacial till
Moraines

Answer 53

all material of glacial origin, whether deposited by the ice or by associated waters.

The materials deposited directly by the ice. They are heterogeneous (unstratified) mixtures of debris, which vary in size from boulders to clay. Till (the adjective “glacial” is optional as there is no non-glacial till) may therefore be somewhat similar in appearance to colluvial materials, except that the coarse fragments are more rounded from their grinding journey in the ice, and the deposits are often much more densely compacted because of the great weight of the overlying ice sheets.

irregular ridges where much glacial till is deposited in

Question 54

Outwash plain
lacustrine deposits

Answer 54

The torrents of water gushing forth from melting glaciers carried vast loads of sediment. In valleys and on plains where the glacial waters were able to flow away freely, the sediment formed an outwash plain. Sediments, with sands and gravels sorted by flowing water, are common valley fills. sorted layering of coarse and fine materials in glacial outwash overlaid by mixed materials of glacial till.

When the ice front came to a standstill, where there was no ready escape for the water, ponding began; ultimately, very large lakes were formed. The lacustrine deposits formed in these glacial lakes range from coarse delta materials and beach deposits near the shore to larger areas of fine silts and clay deposited from the deeper, more still waters at the center of the lake. Flat areas of inherently fertile (though not always well drained) soils developed from these materials as the lakes dried.

Question 55

Dune sands

Answer 55

Strong winds pick up medium and fine sand grains and pile them into hills of sand called dunes along beaches, oceans, large lakes, vast barren deserts. Because most other minerals have been broken down and carried away by the waves, beach sand usually consists mainly of quartz, which is devoid of plant nutrients and highly resistant to weathering action.

Question 56

Loess

Answer 56

The windblown materials called loess are composed primarily of silt with some very fine sand and coarse clay

–>This input of mineral dust is thought to be an important source of iron for Ocean life.

Question 57

Aerosolic dust

Answer 57

Very fine particles (about 1–10 μm diameter)

can remain suspended in air for thousands of kilometers before being deposited, usually with rainfall.

accumulate at rates that make significant contributions to soil formation.

Question 58

Volcanic ash

Answer 58

During volcanic eruptions, cinders fall in the immediate vicinity of the vol- cano, whereas fine, often glassy, ash particles may blanket extensive areas downwind

The soils formed are uniquely light and porous and tend to accumulate organic matter more rapidly than other soils in the area.

tends to weather rapidly into allophane, a type of clay with unusual properties

Question 59

Peat

Answer 59

organic deposits (collectively) accumulation up to several meters in depth due to residues from decomposition sink into the water, where their decomposition is limited by lack of oxygen.

most extensively in the cool climates and in areas that have been glaciated.

The rate of peat accumulation varies depending on the balance between production of plant material and its loss by decomposition.

Cool climates and acidic conditions favor slow decomposition but also slower plant production.

Warm climates and alkaline conditions favor rapid losses but also rapid plant production.

artificial drainage, used to remove excess water from a peat soil, lets air into the peat and drastically alters the balance between production and decomposition of organic matter, causing a reversal of the accumulation process and a loss or subsidence of the peat soil.

Question 60

4 types of peat materials

Answer 60

Based on the nature of the parent materials, four kinds of peat are recognized:

1. Moss peat, the remains of mosses such as sphagnum
   –>high water-holding capacities
   –>acidic.
2. Herbaceous peat, residues of herbaceous plants such as sedges, reeds, and cattails
3. Woody peat, from the remains of woody plants, including trees and shrubs
   –> succession of plants favors trees as the residues accumulate so woody peats often dominate the surface layers of organic materials.
   –> woody peats tend to make very pro- ductive agricultural soils that are especially well suited for vegetable production (if drained)
4. Sedimentary peat, remains of aquatic plants (e.g., algae) and of fecal material of
   aquatic animals
   –>undesirable as an agricultural soil
   –>material is highly colloidal and compact and is rubbery when wet. Upon drying, it resists rewetting and remains in a hard, lumpy condi- tion.
   –>occurs mostly deep in the profile

Organic deposits generally contain two or more of these kinds of peats, either in al- ternating layers or as mixtures.

Question 61

Peat vs. Muck

Answer 61

The organic material is called peat, or fibric, if the residues are sufficiently intact to permit the plant fibers to be identified.

If most of the material has decomposed sufficiently so that little fiber remains, the term muck or sapric is used. In mucky peats (hemic materials) only some of the plant fibers can be recognized.

Question 62

Wetland areas are important … and natural habitats for wildlife. Drainage of these areas … the benefits of wetlands

Answer 62

environmental buffers

reduces

Question 63

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 …. The very modest profile development characteristic of … contrasts sharply with the …profiles of the humid tropics

Answer 63

maximized
cold areas
deeply weathered

Question 64

water is essential for all the major chemical weathering reactions. how does it need to be effective in soil formation?

Answer 64

To be effective in soil formation, water must penetrate into the regolith.
–>greater the depth of water penetration = the greater the depth of weathering soil and development.

Surplus water percolating through the soil profile transports soluble and suspended materials from the upper to the lower layers. It may also carry away soluble materials in the drainage waters. –>percolating water stimulates weathering reactions and helps differentiate soil horizons.

deficiency of water is a major factor in determining the characteristics of soils of dry regions.
–>Soluble salts are not leached from these soils, can build up to levels that curtail plant growth. Soil profiles in arid and semiarid regions are also apt to accumulate carbonates and certain types of cracking clays.

Question 65

Considering soils with similar temperature regime, parent material, topography, and age:

increasing effective annual precipitation =

Answer 65

increasing clay and organic matter contents
greater acidity
lower ratio of Si/Al (indication of more highly weathered minerals)