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Arboriculture > Chapter 3: Soil Science > Flashcards

Chapter 3: Soil Science Flashcards

1
Q

Soil is an ecosystem inhabited by what?

A

insects, earthworths, nematodes, fungi, bacteria, and other microbes all living together in a delicate balance

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2
Q

nematodes

A

microscopic roundworm; many are beneficial organisms, but some feed on plant tissue and may cause disease or damage

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3
Q

parent material

A

soil bedrock or base material from which a soil profile develops

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4
Q

Composition of ideal soil

A

45% mineral solids (sand, silt, and clay) that originate from the parent material; 50% spore space (filled with air or water), and 5% organic matter and organisms

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5
Q

horizon

A

visible layer of soil within the soil profile, oriented parallel to the soil surface

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6
Q

Why do soils develop horizontal layers below the surface?

A

rainfall, leaching, heating/cooling, chemical reactions, biological activities, and accumulation of different elements and materials

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7
Q

soil profile

A

vertical section through the soil and all of the soil horizons

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8
Q

What are the five major soil horizons?

A 
O - O horizon (Organic layer)
A - A horizon
E - E horizon (when it exists)
B - B horizon
C - C horizon
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9
Q

How are soil layers distinguished?

A

by differences in color, texture, and smell which can indicate variations in drainage, organic and mineral content, and other characteristic changes

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10
Q

organic layer

A

top (O) horizon of the profile; thin layer of decomposing organic material at the soil surface; has huge impact on the biological characteristics of the soil; contains materials such as leaves, twigs, bark, and organisms known as the litter layer; very active biologically and is gradually broken up and decomposed by this activity

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11
Q

A horizon

A

contains most of the fine absorbing roots of trees and is very biologically active; composed of inorganic material (sand, silt, and/or clay); normally rich in organic matter which gives this horizon its characteristic dark color

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12
Q

E horizon

A

found below the A horizon; lacks the organic matter found in the A horizon and lighter in color

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13
Q

B horizon

A

below the A (and E if present) horizons; zone of accumulation where materials that have leached from the surface mix with soil particles from the lower parent material

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14
Q

topsoil

A

the uppermost layers (O, A, E, and sometimes the upper part of the B horizon)

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15
Q

C horizon

A

deepest layer of soil, just above the bedrock; composed of partially weathered parent material; soil here is continually forming through the physical chemical, and biological weathering of the parent material

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16
Q

aggregates (in soil)

A

close cluster or mix of small particles of soil and/or organic matter of varying sizes that are bonded together; sand, gravel, or small rocks in the soil; improve soil structure

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17
Q

Positive impacts of soil organisms?

A

their growth and movement through the soil are important for improving aeration, fertility, and the structural components of soils

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18
Q

Soil requirements of roots?

A

space among soil particles, organic materials and essential mineral elements, and adequate oxygen and water; tree roots grow where soil conditions are favorable

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19
Q

soil texture

A

relative fineness or coarseness of a soil due to particle size of the the inorganic, mineral soil particles

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20
Q

sand

A

soil particles with a size between 0.06 and 2.0 mm in diameter; relatively large, resulting in coarser-textured soils; coarse soil dominated by macropores

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21
Q

silt

A

soil particles with a grain size between 0.004 and 0.062 mm; coarser than clay particles but finer than sand; intermediate in size

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22
Q

clay

A

soil particles with a typical grain size less than 0.004 mm; soil predominantly composed of such particles; smallest soil particle, resulting in fine textured soils; fine soil with a high percentage of micropores

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23
Q

Rank the soil particles from finest to coarsest.

A

clay, silt, sand

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24
Q

loam

A

soil texture classification based on a certain ratio of sand, silt, and clay; mix (but not equal mix) of the three different particle sizes and is often considered an ideal soil texture because of the favorable characteristics for plant growth; contains relatively less clay

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25
Q

What determines a soil’s ability to hold water and provide oxygen to the roots?

A

soil structure and texture; which have a profound influence on the chemical and biological properties of the soil; thus texture plays an important role in determining which species of trees will do well in a given site

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26
Q

soil structure

A

arrangement of soil particles into aggregates; formed of shape, size, strength, and arrangement of soil aggregates; root growth, freezing and thawing, and burrowing insects and other animals also contribute to changes

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27
Q

macropore

A

relatively large space between soil particles (mainly aggregates) that is usually air filled and allows for water movement and root penetration

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28
Q

micropore

A

relatively small space between soil particles that is likely to be water filled; source of available water to plants between rainfalls

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29
Q

Why are macropores generally filled with air?

A

Because macropores are too large to hold water against the force of gravity, therefore they become filled with air as water drains from the soil

30
Q

What determines the amount of macropore and micropore space in soil?

A

the size and shape of soil aggregates and the soil texture

31
Q

bulk density

A

mass of soil per unit volume, often used as a measure of compaction; weight of dried soil per unit of undisturbed volume; used to assess whether adequate pore space exists, if soil texture is known

32
Q

soil compaction

A

compression of the soil, often as a result of vehicle or heavy-equipment traffic, that breaks down soil aggregates and reduces soil volume and total pore space, especially macropore space; an increase in bulk density and a decrease in total pore space; difficult to correct, especially around established trees

33
Q

What are the different soil types susceptibilities to compaction?

A

Clay: high percentage of fine particles - easily compacted
Sand: high percentage of sand - less prone to compaction
high moisture content: more easily compacted
dry soil: less easily compacted

34
Q

Effects of compacted soil?

A

restricted root growth, reduced water infiltration and availability, limited movement of oxygen and carbon dioxide in the root zone, limited biological component of soil by reducing the large pores required by larger organisms to move through the soil, develop surface crusts when aggregates are destroyed and the fine soil particles at the surface orient themselves like shingles on a roof, inhibiting water infiltration and gas exchange with the air above

35
Q

pH

A

unit of measure that describes the alkalinity or acidity of a solution, negative log of the hydrogen ion concentration, measured on a scale from 0 to 14, greater than 7 is alkaline, less than 7 is acidic, and 7 is neutral (neither acidic nor alkaline, pure water); logarithmic function

36
Q

What pH is favorable for most trees?

A

6.0-6.5; although quite variable for different species

37
Q

Why does pH effect tree growth?

A

by effecting mineral nutrient because some essential elements are available for uptake within a relatively narrow pH range

38
Q

How can you alter the soil pH?

A

adding sulfur temporarily lowers the pH, adding lime raises the pH; this is easy on the superficial layers of the soil; altering the subsurface pH is more difficult

39
Q

buffering capacity

A

ability of a soil to maintain or resist change in its pH; especially true in soils that are high in clay or organic matter

40
Q

ions

A

atom or group of atoms with a positive or negative charge

41
Q

anions

A

ion that carries a negative charge

42
Q

cations

A

ion that carries a positive charge

43
Q

Most abundant cations in soil?

A

calcium (Ca), magnesium (Mg), potassium (K), sodium (Na), and aluminum (Al)

44
Q

cation exchange capacity (CEC)

A

ability of a soil to adsorb and hold cations, affected by soil pH, measures (gauge of) soil fertility, clay composition, and engineering characteristics; a measure of the soil’s capacity to attract, retain, and exchange positively charged cations

45
Q

Do soils have a net charge?

A

Yes, negatively charged sites outnumber positively charged sites, thus soils have a net negative charge; organic matter and clay particles normally have a negative charge density which attracts and holds cations giving soils high in clay and organic matter a high cation exchange capacity

46
Q

leach

A

tendency for elements or compounds to wash down through the soil or tendency for elements or compounds to wash into the soil

47
Q

Possibility of leaching in soil types?

A

sandy soils have a greater possibility of leaching than clay soils

48
Q

saline soils

A

soil with a high concentration (excess levels) of soluble salts; can cause poor plant growth

49
Q

sodic soils

A

soil with relatively low levels of soluble salts and a concentration of sodium high enough to adversely affect soil structure (symptoms include waterlogging, erosion, soil surface crusting, and poor plant growth) soils with less than 12 sodium absorption ratio

50
Q

soil food web

A

complex network of interconnected food chains in an ecosystem, in the soil in this case

51
Q

rhizosphere

A

soil area immediately adjacent to, and affected by, plant roots; typically has a high level of microbial activity; microzone of intense biological activity surrounding actively elongating roots; altered environment (pH may be 1 or 2 units higher or lower compared to bulk soil) within the soil where many organisms flourish

52
Q

exudates

A

substance or solution that oozes out of injured plant cells or is secreted through membrane pores and is released into the soil; source of organic matter on which microorganisms feed

53
Q

mycorrhizae

A

symbiotic association between certain fungi and the roots of a plant; fungus roots; specialized root structure that is created when fungi infect roots of a suitable host plant

54
Q

symbiotic

A

association of two different types of living organisms that is often, but not always, beneficial to each

55
Q

symbiotic relationship of mycorrhizae

A

roots provide a place for the fungi to live and provide food (sugar); the fungi increase the capacity of the roots to absorb water and essential elements, especially phosphorus, to protect against certain disease-causing fungi, and help the tree survive stressful conditions

56
Q

symbiotic relationship of legumes

A

the bacteria form colonies in nodules on the roots and “fix” or convert nitrogen from the air into forms that can be used by the plants in the bean and pea family

57
Q

nutrient cycling

A

movement of mineral elements (sometimes called nutrients) within an ecosystem as organic matter decompresses, releasing bound nutrients back to plants; as a plant grows, roots absorb essential solution and produce new woody material and leaves and as seasons pass, plants or plant parts die and are returned to the soil where they are broken down and eventually decomposed by soil organisms and weathering processes

58
Q

actinomycetes

A

group of soil bacteria resembling fungi; play a role in the decomposition of organic matter and the release of mineral elements; symbiotic with some species and play a critical role in the decomposition of organic matter to form humus

59
Q

humus

A

dark-colored, stable form of organic matter that remains after most of the plant or animal residues have decomposed

60
Q

mineralization

A

process in which an organic substance is converted to or trapped in inorganic substance; organically bound plant nutrients are converted into inorganic plant available forms

61
Q

water-holding capacity

A

ability of a soil to hold moisture; large percentage of micropores = high water-holding capacity; large percentage of macropores = low water-holding capacity

62
Q

gravitational water

A

water that drains from the larger soil macropores due to the force of gravity

63
Q

field capacity

A

maximum soil moisture content following the drainage of water due to the force of gravity; after gravitational water has drained away

64
Q

capillary water

A

water held in the capillary pores of the soil; much of this water can move in any direction and is readily available to plant roots; the water that remains after a soil is at field capacity once the gravitational water has drained away

65
Q

permanent wilting point

A

point at which a plant cannot pull any more water from the soil and suffers permanent damage; occurs when water stress is prolonged and severe

66
Q

How does gas exchange between the soil and the atmosphere?

A

respiration takes place through diffusion at the soil surface; oxygen levels are higher at the soil surface

67
Q

Problems in urban soil

A
  1. ) compaction - damages soil aggregates, reduces macropore (air-filled) space, increases bulk density, limits gas exchange, reduces water infiltration, and alters soil organism populations
  2. ) lack an organic layer - decreases biological activity, hampers soil structure development and interrupts nutrient cycling
  3. ) lack microorganisms (mycorrhizae)
  4. ) subsurface barriers from buildings
  5. ) altered drainage, elevated pH, chemical contamination
68
Q

structural soils

A

pavement substrate that can be compacted to meet engineering specifications yet remains penetrable by tree roots in the urban environment to allow root growth and development and establishment of trees; composed of angular crushed stone, clay loam, and hydrogel mixed in a weight ration of 100:20:0.03; developed at the Urban Horticulture Institute, Cornell University, Ithaca NY

69
Q

suspended sidewalk

A

sidewalk that is reinforced and supported with piers or other structures so that it does not rely on compacted subgrade or soil for support

70
Q

structural cells

A

modular system consisting of units of soil and integrated support structures that serve as both a foundation for paved surfaces and a hospitable environment for tree root growth

71
Q

Benefits of amending soil with organic matter?

A

improved water filtration, increased water-holding capacity, improved aeration, and enhanced cation exchange capacity

72
Q

Benefits of mulching the soil surface?

A

reduce surface compaction and crusting, thereby improving water infiltration, reduce soil erosion, decrease weed competition, moderate temperature fluctuations, decrease soil surface pH on excessively alkaline soils

Arboriculture (16 decks)

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