EESC456-CHAPTER1.2

Question 1

Soil profile

Answer 1

The vertical section exposing a set of horizons in the wall of soil pits (large hole, deep)

Question 2

Parent material

Answer 2

Original regolith (deepest layers). The unconsolidated and more or less chemically weathered mineral or organic matter from which the solum of soils is developed by pedogenic processes.

Question 3

Horizons within a soil may vary in thickness and have irregular boundaries, but generally they … the land surface.

Answer 3

parallel

–> this alignment is expected since the differentiation of the regolith into distinct horizons results from air/water/solar radiation/plants influences originating at the soil-atmosphere interface.

Question 4

Because the weathering of the regolith occurs first at the surface and works its way down, the uppermost layers have been …, while the deepest layers are most similar to the original regolith, which is referred to as …

Answer 4

changed the most

the soil’s parent material

Question 5

In places where the regolith was originally rather uniform in composition, the material below the soil ….

In contrast, where wind, water, or glaciers have transported and deposited the parent material on top of dissimilar material, the regolith found below a soil may be

Answer 5

may have a similar composition to the parent material from which the soil formed. I

quite different from the upper layer of regolith in which the soil has formed.

Question 6

O horizon- Organic horizon of mineral soils.

Answer 6

organic layers at the soil surface are designated the O horizons

In undisturbed ecosystems, especially forests, organic remains of fallen leaves and other plant and animal materials tend to accumulate on the surface. There they undergo varying degrees of physical and biochemical breakdown and transformation so that layers of older, partially decomposed materials may underlie the freshly added debris.

Question 7

A horizons

Answer 7

The surface horizon of a mineral soil having maximum organic matter accumulation, maximum biological activity, and/or eluviation of materials such as iron and aluminum oxides and silicate clays.

Layers nearest the surface, dominated by mineral particles but have been darkened by the accumulation of organic matter.

Soil animals and percolating water move some of these organic materials downward to intermingle with the mineral grains of the regolith. These join the decomposing remains of plant roots and microbes to form organic materials that darken the upper mineral layers.

Also, because weathering tends to be most intense nearest the soil surface, in many soils the upper layers lose some of their clay or other weathering products by leaching to the horizons below.

–>An A Horizon begins to differentiate as materials (such as organic matter) are added to the upper part of the profile.

Question 8

B horizons

Answer 8

A soil horizon, usually beneath the A or E horizon, that is characterized by one or more of the following:

(1) a concentration of soluble salts, silicate clays, iron and aluminum oxides, and humus, alone or in combination;

(2) a blocky or prismatic structure;

3) coatings of iron and aluminum oxides that give darker, stronger, or redder color.

–> Accumulated materials (silicate clays, iron, aluminum oxides, gypsum, calcium carbonate) washed down from horizons above or formed in place due to weathering process = B horizons

–> The B horizon forms as other materials (such as salts and clays) are translocated and accumulate in deeper zones.

Question 9

C horizon

Answer 9

A mineral horizon, generally beneath the solum, that is relatively unaffected by biological activity and pedogenesis and is lacking properties diagnostic of an A or B horizon. It may or may not be like the material from which the A and B have formed.

–>least weathered part of soil profile

–>plant roots + micro-organisms often extend below the B horizon (humid regions) = chemical changes in soil water
= biochemical weathering of regolith
=formation of C horizons

Question 10

Layers underlying the A + O horizons contain comparatively less…. than the horizons near the surface.

Answer 10

organic matter

Question 11

E horizons

Answer 11

Horizon characterized by maximum illuviation (washing out) of silicate clays and iron and aluminum oxides; commonly occurs above the B horizon and below the A horizon.

–>usually lighter color than adjacent horizons above/below

–> Intensely weathered and leached horizons that have not accumulated organic matter occurring in upper part of profile (just below A usually).

–> Under certain conditions, usually associated with forest vegetation and high rainfall, a leached E horizon forms between the A and B horizons. If sufficient rainfall occurs, soluble salts will be carried below the soil profile, perhaps all the way to the groundwater (and eventually out to sea).

Question 12

Topsoil

Answer 12

Organically enriched a horizon at soil surface

Cultivated soils; majority of plant roots found in topsoil (zone enhanced, loosened, irrigated)

The layer of soil moved in cultivation. Presumably fertile soil material used to top-dress roadbanks, gardens, and lawns.

Question 13

Plow layer

Answer 13

Plowing + cultivating a soil homogenizes/modifies the upper 10-25 cm of the profile.

The soil ordinarily moved when land is plowed; equivalent to surface
soil.

Question 14

Subsoil

Answer 14

That part of the soil below the plow layer.

Soil layers underlie topsoil.

–> can greatly influence land-use
–>stores much of water needed by plants
–> supplies important quantities of some plant nutrients

if too dese/acidic/wet ; can impede plant growth. Hard, expensive to modify (physically or chemically) subsoil

Question 15

Surface soil

Answer 15

The uppermost part of the soil, ordinarily moved in tillage, or its equivalent in uncultivated soils. Ranges in depth from 7 to 25 cm. Frequently designated as the plow layer, the Ap layer, or the Ap horizon.

Question 16

The properties of the topsoil are commonly far more conducive to plant growth than those of …. In cultivated soils, therefore, productivity is often correlated with the thickness of the …

Answer 16

the subsoil
topsoil layer

Question 17

Many of the chemical, biological, and physical processes that occur in the upper soil layers also take place to some degree in the …, which may extend deep into the underlying saprolite or other regolith material.

Answer 17

C horizons

Question 18

Traditionally, the lower boundary of the soil has been considered to occur at the greatest rooting depth of the …., but soil scientists are increasingly studying layers below this in order to understand ecological processes of the …, such as groundwater pollution, parent material weathering, and biogeochemical cycles

Answer 18

natural vegetation
critical zone

Question 19

Phytotoxic substances

Answer 19

in soils may result from human activity (such as chemical spills or herbicide application), or they may be produced by plant roots, by microorganisms, or by natural chemical reactions.

Question 20

A fertile soil will provide a … in amounts and relative proportions appropriate for optimal plant growth.

Answer 20

continuing supply of dissolved mineral nutrients

Question 21

C.B. HOPKiNS CaFé— Closed Monday Morning and Night— See You Zoon, the Mg

Answer 21

Carbon
Boron
Hydrogen
Oxygen
Phosphorus
Potassium
Nitrogen
Sulfur
Calcium
Iron
Chloride
Manganese
Molybdenum
Nickel
Selenium
Copper
Zinc
Magnesium

Question 22

Soils have the capacity to assimilate great quantities of organic waste, turning it into … converting the mineral nutrients in the waste to forms that can be utilized by plants and animals, and return- ing the …to the atmosphere as …, where it again will become a part of living organisms through plant photosynthesis

Answer 22

beneficial soil organic matter

carbon

carbon dioxide

Question 23

Of the solid material, typi-ally most is mineral matter derived from the rocks of the Earth’s crust. Only about 5% of the volume in this ideal soil consists of organic matter. Since it is far less dense than mineral matter, the organic matter accounts for only … of the weight of this soil.

Answer 23

about 2%

–>However, the influence of the organic component on soil properties is often far greater than these small proportions would suggest.

Question 24

Soils with much more than … of their volume in solids are likely to be too compacted for good plant growth. It is in these pore spaces that … + …. circulate, roots grow, and microscopic creatures live. The rela- tive proportions of water and air fluctuate as water is added or lost.

Answer 24

50%
air and water

Question 25

In an optimum condition for most plants, the pore space will be divided ….

If there is much more water than this, the soil will be waterlogged. If much less water is present, plants will suffer from drought.

Answer 25

roughly equally among the two, with 25% of the soil volume consisting of water and 25% consisting of air.

Question 26

Compared to surface soil layers, subsoils tend to contain less … + less … and a larger proportion of its pore space is made up of small pores (micropores), which tend to be filled with water rather than with air.

Answer 26

organic matter, less total pore space,

Question 27

Except in organic soils, most of the soil’s solid framework consists of …The larger soil particles (stones, gravel, and coarse sands) are generally …. Smaller particles tend to be made of a …

Answer 27

mineral particles.

rock fragments consisting of several different minerals

single mineral.

Question 28

texture has a profound influence on many soil properties, and it affects the …

Answer 28

suitability of a soil for most uses

Question 29

Clayey soils, such as those high in …clays, make very unstable material on which to build because … This shrink–swell action can easily crack foundations and cause retaining walls to collapse. These clays also become … + …when they are wet. Other types of clays, formed un- der different conditions, can be very stable and easy to work with.

Answer 29

smectite

they swell when wet and shrink when dry.

ex- tremely sticky and difficult to work with

Question 30

primary minerals: They are prominent in the sand and silt fractions of soils and contain many of the nutrient elements needed by plants.

Secondary minerals: tend to dominate the clay and, in some cases, silt fractions.

Answer 30

Minerals that have persisted with little change in composition since they were extruded in molten lava (e.g., quartz, micas, and feldspars)

Other minerals, such as silicate clays and iron oxides, were formed by the breakdown and weathering of less resistant minerals as soil formation progressed.

Question 31

Soil structure

Answer 31

describes the way these building blocks (from which soil is constructed) are associated together in aggregates of various sizes and shapes (nature of the soil “clumps”)

the way particles are arranged together

Soil structure is just as important as soil texture (the relative amounts of different sizes of particles) in governing how water and air move in soils.

Question 32

Both … + … fundamentally influence many processes in soil, including the growth of plant roots.

Answer 32

structure and texture

Question 33

When people cultivate soils and harvest the crops without returning organic residues and mineral nutrients, the soil’s …. becomes depleted. Degrading soil quality can be reflected in diminished capacity to ….

Answer 33

supply of organic matter and nutrients

produce food

Question 34

Contamination of a soil with toxic substances from industrial processes or chemical spills can degrade its capacity to …(3). Degradation of soil quality by pollution is usually localized, but the environmental impacts and costs involved are very large.

Answer 34

provide habitat for soil organisms
to grow plants that are safe to eat
or to safely recharge ground and surface waters

Question 35

first priority =

it is often necessary to attempt to restore the quality of soils that have already been degraded. Some soils have sufficient …. to recover from minor degradation if left to regenerate on their own. In other cases, more effort is required to restore degraded soils.

the science of …has rapidly evolved to guide managers in restoring plant and animal communities to their former levels of diversity and productivity. The job of soil restoration, an essential part of these efforts, requires in-depth knowledge of all aspects of the soil system.

Answer 35

protecting soil quality

resilience

restoration ecology (soil restoration)

Question 36

In their optimal state, these organisms work together to function in … + … Healthy soils function more efficiently with less need for expensive human interventions and inputs than unhealthy, degraded soils.

Answer 36

a self-regulating and perpetuating manner.

Question 37

Soil quality

Answer 37

is a measure of the ability of a soil to carry out particular ecological functions

Soil quality reflects a combination of chemical, physical, and biological properties.

Question 38

Soil properties that cannot be significantly changed by management. rela- tively unchangeable, inherent properties that help define a particular type of soil (2)

Changeable soil properties can indicate the status of a soil’s quality relative to its potential (2)

Answer 38

Soil texture, mineral makeup

structure and organic matter content

Question 39

Soil is a basic resource underpinning all terrestrial ecosystems. Managed carefully, soils are a … resource, but in the scale of human lifetimes they cannot be considered a … resource.

Answer 39

reusable
renewable

–>In all regions of the world, human activities are destroying some soils far faster than nature can rebuild them

Question 40

human population growth = (3)

While soils completely washed away by …+….by urban sprawl are permanently lost, many more soils are degraded in quality rather than totally destroyed.

Answer 40

struggle to feed human population
wildlife populations are deprived of vital habitat
overall biodiversity suffers.

erosion or excavated and paved over

Question 41

Soil organic matter consists of a wide range of organic (carbonaceous) substances, including …+ , …. + ….

Answer 41

living organisms (the soil biomass)

carbonaceous remains of organisms that once occupied the soil,

organic compounds produced by current and past metabolism in the soil.

Question 42

Under conditions that favor … more than …, large quantities of atmospheric carbon dioxide used by plants in photosynthesis are sequestered in the abundant plant tissues that eventually become part of the soil organic matter.

The balance between … and its …has global implications. In fact, more carbon is stored in the world’s soils than in the world’s …+… combined.

Answer 42

plant production more than microbial decay

accumulation of soil organic matter
loss through microbial respiration

plant biomass and atmosphere

Question 43

Organic matter comprises only a small fraction of the mass of a typical soil. By weight, typical well-drained mineral surface soils contain from … organic matter. The organic matter content of subsoils is even smaller. However, the influence of organic matter on soil properties, and consequently on plant growth, is …

Answer 43

1 to 6%

far greater than the low percentage would indicate

Question 44

Organic matter binds … into a granular soil structure that is largely re- responsible for the loose, easily managed condition of productive soils.

Part of the soil organic matter that is especially effective in …. consists of certain glue-like substances produced by various soil organisms, including plant roots

Answer 44

mineral particles

stabilizing these granules

Question 45

Organic matter also increases the amount of ….. and the proportion of ….

In addition, organic matter is a major source of the plant nutrients …. (3). As soil organic matter decays, these nutrient elements, which are present in organic combinations, are released as … that can be taken up by plant roots.

Finally, organic matter, including plant and animal residues, is the main food that supplies … + …. to soil organisms. Without it, biochemical activity so essential for ecosystem functioning would come to a near standstill.

Answer 45

water a soil can hold
water available for plant growth

nitrogen, phosphorus, and sulfur

soluble ions

carbon and energy

Question 46

Soils higher in organic matter are … in color and have greater …capacities than soils low in organic matter. Abundant organic matter, including plant roots, helps create physical conditions favorable for the … +…

Answer 46

darker
water-holding
growth of higher plants as well as microbes

Question 47

Humus

Answer 47

is a collection of organic compounds that accumulate in soil when partially broken down plant and animal residues are protected from complete decay by various factors in the soil environment.

Like clay, much of the soil’s humus is colloidal in size and exhibits highly charged surfaces. Unlike clay, humus may contain components that can make micronutrients more easily used by plants and may even cause hormone-like stimulation of certain plant processes.

All in all, small amounts of humus remarkably increase the soil’s capacity to promote plant growth.

Question 48

Both humus and clay act as … between larger soil particles; thus, both play an important role in the formation of …. The surface charges of humus, like those of clay, attract and hold both … + ….. However, gram for gram, the capacity of humus to hold nutrients and water is far greater than that of clay.

Answer 48

contact bridges

soil structure.

nutrient ions and water molecules

Question 49

The soil moisture regime, often reflective of climatic factors, is a major determinant of …, including agricultural systems. Movement of water, and substances dissolved in it, through the soil profile impacts both the ..+.. of local and regional water resources. … is also a major driving force in soil formation

Answer 49

the productivity of terrestrial ecosystems

quality and quantity

Water moving through the regolith

Question 50

When the soil moisture content is optimal for plant growth, describe water movement through pores

Answer 50

the water in the large- and intermediate-sized pores can move about in the soil and can easily be used by plants.

The plant roots, however, remove water from the largest pores first. Soon the larger pores hold only air, and the remaining water is found only in the intermediate- and small- est-sized pores.

The water in the intermediate-sized pores can still move toward plant roots and be taken up by them. However, the water in the smallest pores is so close to solid particles that it may be so strongly held that plant roots cannot pull it away.

Question 51

Depending on the soil, ….of the water may remain in the soil after plants have wilted or died for lack of moisture.

Answer 51

one-sixth to one-half

Question 52

Two main factors help explain soil water concept

Answer 52

1. Water is held within soil pores where the attraction between water and the surfaces of soil particles greatly restricts the ability of water to flow
2. Because soil water is never pure water, but contains hundreds of dissolved organic
   and inorganic substances, it = soil solution. An im- important function of the soil solution is to serve as a constantly replenished, dilute nutrient solution bringing dissolved nutrient elements to plant roots.

Question 53

The soil solution contains small but significant quantities of … +…., including the plant nutrients.

The soil solids, particularly the fine organic and inorganic colloidal particles (clay and humus), release ….from which they are taken up by plant roots.

Answer 53

soluble organic and inorganic sub-stances

nutrient elements to the soil solution

Question 54

soil buffering capacity

Answer 54

This ability to resist change. The soil solution tends to resist changes in its composition even when compounds are added or removed from the soil.

–>dependent on many chemical and biological reactions, including the attraction and release of substances by colloidal particles.

Question 55

Many chemical and biological reactions are controlled by the relative amounts of acidity caused by a dominance of … and alkalinity caused by a dominance of …in the soil solution.

Answer 55

hydrogen ions (H+)
hydroxyl ions (OH−)

Question 56

The pH is a

Answer 56

logarithmic scale used to express the degree of soil acidity or alkalinity . The pH is considered a master variable that influences most chemical processes in the soil and is of great significance to nearly all aspects of soil science.

Question 57

If we think of the network of soil pores as the … connecting airspaces to the atmosphere, we can understand that when pores are filled with water the ventilation system becomes clogged.

Answer 57

ventilation system of the soil

Question 58

Soil air differs from atmospheric air in several respects. (3)

Answer 58

1. the composition of soil air varies greatly from place to place in the soil. In local pockets, some gases are consumed by plant roots and by microbial reactions, and others are released, thereby greatly modifying the composition of the soil air.
2. soil air generally has a higher moisture content than the atmosphere; the relative humidity of soil air approaches 100% unless the soil is very dry.
3. the content of carbon dioxide (CO2) is usually much higher, and that of oxygen (O2) lower, than contents of these gases found in the atmosphere. Carbon dioxide in soil air is often several hun- dred times more concentrated than the 0.035% commonly found in the atmosphere. Oxygen decreases accordingly and, in extreme cases, may be 5–10%, or even less, compared to about 20% for atmospheric air. In extreme cases, lack of oxygen both in the soil air and dissolved in the soil water may fundamentally alter the chemical reactions that take place in the soil solu- tion. This is of particular importance to understanding the functions of wetland soils.

Question 59

The amount and composition of air in a soil are determined to a large degree by the …. of the soil. When … enters the soil, it displaces air from some of the pores; the air content of a soil is therefore ….

Answer 59

water content

water

inversely related to its water content.

–>As the soil drains from a heavy rain or irrigation, large pores are the first to be filled with air, followed by medi- um-sized pores, and finally the small pores, as water is removed by evaporation and plant use. This explains the tendency for soils with a high proportion of tiny pores to be poorly aerated.

Question 60

Soil moisture, which directly meets the needs of plants for water, simultaneously controls much of the …+… to the plant roots. The mineral particles, especially the finest ones, attract …, thus determining its …+…

Answer 60

air and nutrient supply
soil water
movement and availability to plants.

Question 61

Organic matter, because of its physical binding power, influences the … and, in so doing, increases the number of …, thereby influencing the ..+.. relationships.

Answer 61

arrangement of the mineral particles into clusters

large soil pores

water and air