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PLS 366 > Final > Flashcards

Final Flashcards

1
Q

What are the 6 key functions of soils in ecosystems?

A

a medium for plant growth, determines the fate of water, nature’s recycling system, provides habitat for living organisms, influence the atmosphere, a medium for building

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2
Q

How does the pedosphere interact with the lithosphere?

A

The minerals present in soil are also the minerals that reach further down to make up the lithosphere

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3
Q

How does the pedosphere interact with the hydrosphere?

A

Water travels through the soil or flows over its surface therefore any pollution in the pedosphere ends up in the hydrosphere, soil channels rain water to rivers

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4
Q

How does the pedosphere interact with the atmosphere?

A

Soil releases gases into the atmosphere such as carbon dioxide, oxygen, and nitrogen and removes gases

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5
Q

How does the pedosphere interact with the biosphere?

A

Soil affects the biosphere by decomposing organic matter and biomass from plants animals and microbes and allowing it to be reused in the life cycle

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6
Q

surface horizon with lots of organic material

A

O horizon

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7
Q

horizon nearest the surface, has lots of mineral particles but is darker due to organic matter

A

A horizon

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8
Q

the bleacher horizon where things are being leached out

A

E horizon

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9
Q

underlying layers that have accumulated materials washed down from above or formed from weathering with little organic matter

A

B horizon

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10
Q

the least weathered soils horizon

A

C horizon

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11
Q

topsoil

A

organically enriched, majority of plant roots found here

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12
Q

subsoil

A

where most water is stored, roots can’t really grow here, it’s hard to modify subsoil

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13
Q

Minerals make up what persent of the soil and what are their purpose?

A

Minerals make up 45% of the soil (loam soil good for growing plants), sand silt and clay are the main particles, they are essential for plant growth

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14
Q

Air makes up what percent of the soil and what is its purpose?

A

Air makes up 20-30%, air content is related to water content, the composition of soil air varies from place to place and soil air has a higher moisture content. The content of CO2 is usually high and O2 lower

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15
Q

Organic matter makes up what percent of the soil and what is its purpose?

A

Organic matter makes up 5%, made up of biomass, remains of organisms, and organic compounds. A continues cycle of matter being gained from residues or death of plants and animals, and lost by releasing of CO2

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16
Q

Water makes up what percent of soil and what is its purpose?

A

Water makes up 20-30%, water is held in pores so it can’t flow like we think of water flowing, it’s never pure it contains dissolved substances so is more accurately called a solution than water

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17
Q

What is root interception?

A

It is when roots continually grow into new, undepleted soil.

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18
Q

What is diffusion?

A

It is when nutrient ions continually move from areas of greater concentation toward the nutrient-depleted areas of lower concentration around the root surface.

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19
Q

What is mass flow?

A

When dissolved nutrients are carried along with the flowing soil water toward a root that is actively drawing water from the soil.

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20
Q

Diagram the ways soil provides nutrients to growing plant roots

A
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21
Q

List five ways that human activity can diminish soil quality

A

mismanagement of forests, farms, and rangeland. Accumulation of salts due to improper irrigation. Cultivating without returning organic residues. Contamination from chemical spills nd industrial processes

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22
Q

What is Hydrolysis?

A

adding water across a bond

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23
Q

What is hydration?

A

adding water to a chemical structure

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24
Q

What is carbonation?

A

Co2 dissolving in water

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25
Q

What is dissolution?

A

minerals dissolving in water

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26
Q

What is oxidation-reduction?

A

loss and gain of electrons (moving from Fe2 to Fe3)

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27
Q

What is complexation?

A

It’s the equation that looks really complex, it is mediated by soil biological processes

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28
Q

What is physical weathering?

A

disintegration caused by temeprature, water, wind, ice, and organisms. The minerals and textures partly determine the rate it is weathered.

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29
Q

What is chemical weathering?

A

Chemical weathering is the chemical composition of the rock is altered.

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30
Q

Five soil forming factors?

A

climate, biota, parent materials, topography, time

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31
Q

describe the relationships between residual, transported and organic parent materials

A

Residual materials are formed in place, organic form in wet places where plant growth exceeds the rate of decomposition (commonly referred to as peat), and transported materials are materials that move places due to various factors.

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32
Q

How does temperature and rainfall influence soil formation?

A

The greater the depth of water penetration, the greater the depth of weathering soil and development. Salts can build up in areas that do not receive enough rainfall and can kill plants. For every 10 C raise in temp, the rates of biochemical reactions more than double. Weathering is maximized in areas with warm temperatures and abundant water.

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33
Q

How do plants and animals influence soil formation?

A

vegetative over reduces natural soil erosion rates, organic acids produced from some plants bring iron and aluminum into the soil, the nutrient cycling of trees greatly affects the soil acidity, earthworms and the like effectively mix the soils to make the nutrients better distributed-pedoturbation

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34
Q

Describe the four basic processes of soil formation

A

Redistribution/Translocation: Eluviation, exit, Illuviation, into, Additions (dust carried by the wind, plant materials), Transformations (decomposition, chemical and physical weathering), and Loss of materials (leaching, erosion)

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35
Q

Relate the four basic processes of soil formation to a hypothetical tall grass prairie soil

A

When plants get established they begin to provide additions of litter and root residues on and in the surface layers of the parent material. The plant residues are transformed by soil organisms into humus and other new organic substances. Earthworms , ants, termites, and other smaller animals come live in the soil and accelerate the organic transformations as well as promote the translocation of plant residues. Where rainfall is great enough to cause significant drainage to the groundwater, some of the dissolved materials may be completely removed from the developing soil profile (losses).

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36
Q

strong gleying (mottles caused by iron)

A

g

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37
Q

illuvial accumulation of OM (caused by rain water flowing from one layer to another)

A

h

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38
Q

accumulation of Fe and Al oxides

A

o

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39
Q

plow layer

A

p

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40
Q

illuvial (caused by rain water flowing from one layer to another) accumulation of sesquioxides (free iron oxides)

A

s

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41
Q

silicate clay accumulation

A

t

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42
Q

distinctive color without clay

A

w

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43
Q

fragipan

A

x

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44
Q

What defines a mollic epipedon?

A

A surface horizon, dark, thick (725 cm), high OM, > or = 50% base saturation

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45
Q

What defines an umbric epipedon?

A

A surface horizon, acidic Mollic, base saturation = 50%,

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46
Q

What defines an ochric epipedon?

A

A surface horizon, light colored, low OM, too thin for plants

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47
Q

What defines a histic epipedon?

A

O surface horizon, surface organic horizon, saturated as some time in year, 12-18% organic C

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48
Q

What defines a melanic epipedon?

A

A surface horizon, surface mineral horizon, black from high OM, high in allophane, developed from volcanic ash, >6% organic C, < 30 cm, thick and fluffy

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49
Q

What defines a cambic horizon?

A

weakly developed B horizon, evidence of color and/or struction development w/o clay accumulation (Bw)

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50
Q

What defines and Argillic horizon?

A

illuvial accumulation of silicate clays, clay films on peds, in pores, called clay skins or cutan (Bt)

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51
Q

What defines a spodic horizon?

A

illuvial accumulation, h-humus, s-sesquioxides, in coarse textured soils and cool climates (Bh, Bs, Bhs)

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52
Q

What defines a fragipan?

A

weakly cemented, dense horizon, > 50% of upland soils in the loess region, usually loamy textured (Bx, Cx)

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53
Q

What defines an oxic horizon?

A

highly weathered, accumulation of low activity clays, Fe & Al oxides, very low % BS (Bo)

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54
Q

moisture regime - saturated w/ water for sufficient periods of the year

A

Aquic

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55
Q

moisture regime - humid climate, no water constraints

A

Udic

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56
Q

moisture regime - part of the growing season may be dry, plants might have problems finding water

A

Ustic

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57
Q

moisture regime - dry, desert, very limited growing season

A

Aridic

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58
Q

moisture regime - Mediterranean style, cool wet winter and dry hot summers

A

Xeric

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59
Q

temperature regime - < 8 degrees C, cool summer

A

Cryic

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60
Q

temperature regime - > 8 degrees C, warmer in summer

A

Frigid

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61
Q

temperature regime - 10-15 degrees C

A

Mesic

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62
Q

temperature regime - 15-22 degrees C

A

Thermic

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63
Q

List, from order to series, the classification categories of soil taxonomy

A

Order

Suborder

Great Group

Subgroup

Family

Series

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64
Q
A
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65
Q

ent

A

Entisols

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66
Q

ept

A

Inceptisols

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67
Q

and

A

Andisols

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68
Q

el

A

Gelisols

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69
Q

id

A

Aridisols

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70
Q

ert

A

Vertisols

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71
Q

oll

A

Mollisols

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72
Q

alf

A

Alfisol

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73
Q

ult

A

Ultisols

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74
Q

od

A

Spodosols

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75
Q

ox

A

Oxisols

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76
Q

ist

A

Histosols

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77
Q

Entisols (ent)

A

only A horizon over C, found on or within parent materials, poor climatic conditions, considered other soils

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78
Q

Inceptisols (ept)

A

immature, ochric, no Bt, resistant parent material

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79
Q

Andisols (and)

A

young, high porosity, formed from volcanic ash, highly productive soils, wind and erosion problems, Melanic, low bulk density

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80
Q

Aridisols (id)

A

short wet periods, little leaching of cations, low OM, salt accumulations

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81
Q

Gelisols (el)

A

frozen, permafrost, little development

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82
Q

Vertisols (ert)

A

must have >30% expanding clays, high expansion and contraction, self mising, big cracks, deep A, poor horizonation

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83
Q

Mollisols (oll)

A

Mollic epipedon, >50% base saturation, very fertile and productive

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84
Q

Alfisols (alf)

A

ochric or umbric (acidic mollic), well developed A, (E) B, C, Bt, >35% base saturation, generally forested soils

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85
Q

Ultisols (ult)

A

ochric or umbric, Bt, well developed horizon hoizons, acidic,

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86
Q

Spodosols (od)

A

high sand content, ochric, usually have E, Bhs or Bs, highly leaches, very acidic, low base saturation, very infertile, forested areas (sand +pine) = ?

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87
Q

Oxisols (ox)

A

very highly weathered, tropicl, ochric or umbric, oxic subsurface horizons, low activity 1:1 clays, Fe and Al oxides, Bo, very low % base saturation

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88
Q

Histosols (ist)

A

organic soil, histic, 12-18% organic matterial, saturated part of year, high water and nutrient holding capacity, low bulk density

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89
Q

Select items likely to be found in the standard format of a soil description

A

horizon designation, diagnostic horizon, horizon boundaries, description of horizon in typical pedon

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90
Q

Explain what content a county soil survey includes

A

a. general soil map – two parts, color map at approximate scale that shows the soil associations grouped into the main physiographic regions and an index map for the detailed map sheets
b. detailed map sheets – detailed soil map consisting of many individual map sheets
c. interpretive information – descriptive information from the over laying of the geographic information on the map so it can be used for land use of site planning. Usually soil profile descriptions and soil characterization date

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91
Q

What does sand influence soil properties?

A

high drainage rate, good aeration, rapid decomposition of organic matter, low susceptibility to water erosion, high pollutant leaching potential and low resistance to pH change and poor ability to store plant nutrients.

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92
Q

How does silt influence soil properties?

A

high water holding capacity, medium of most things, high susceptibility to wind and water erosion

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93
Q

How does clay influence soil properties?

A

high water holding capactity, poor aeration, very slow draingage, high soil organic matter level, high compactibility, low suceptability to erosion, shrink-swell, good sealing, low leaching potential, high ability to store plant nutrients and resit pH change

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94
Q

What can soil color determine?

A

drainage, weathering, OM, and soluble constituents

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95
Q

What darkens soils?

A

soil organic matter

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96
Q

What provides brown, red yellow, and orange colors?

A

Iron oxides

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97
Q

What color does carbonates produce?

A

whitish colors

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98
Q

What color do reduced Fe oxides give soils?

A

gray and green colors

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99
Q

The more weathered a soil the more likely its color will be___ under oxidizing conditions

A

red

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100
Q

What does a dominant grey color mean?

A

gleying

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101
Q

What does gleying indicate?

A

highly reduced and poorly drained soils.

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102
Q

What are the four types of soil structures?

A

granular, platy, blocky, and prism

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103
Q

What soil structure is most prevalent in a B horizon?

A

blocky

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104
Q

What soil structure is most prevalent in an E horizon?

A

platy

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105
Q

Where is granular soil structure most prevalent?

A

A horizon

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106
Q

What is a granular structure?

A

circleish aggregates that are separated from each other in a loosely packed arrangement. Usually from less than 1 to as large as 10mm in d.

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107
Q

What is a platy structure?

A

relatively think horizontal peds or plates. can be inherited from PM

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108
Q

What is a blocky structure?

A

peds that are irregular, roughly cubelike, and range from 5 to 50 mm across. molded by the shape of the surrounding blocks

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109
Q

What is a prism like structure?

A

They are vertically oriented prism or pillar like peds that vary in height.

110
Q

Describe the role of adsorbed cations have in flocculation of clays

A

The positively charged cations attract the negative charge of the clay platelets and forms a bridge between them holding the platelets together.

111
Q

. Explain two physical-chemical and two biological processes influencing aggregate formation in soils

A
  1. Mutual attraction of clay particles (flocculation)
    2. shrink-swell of clay particles (vertisols)
    1. Activities of soil organisms, assist in the formation of macroaggregates via bacterial polysaccharides & glomalin
    2. influence of soil organic matter, major agent in temperate soils, provides substrate for microbial activities
112
Q

Characterize a good seedbed

A

a. soil loose enough to allow easy root elongation and seedling emergence
b. firm enough to ensure the seed can easily imbibe water to begin germination
c. relatively free of large clods

113
Q

Describe how soil crusting occurs, how it influences seedling emergence, and how conservation tillage could be helpful

A

The surface soil aggregates are overworked and under protected. When it rains the water splashes off and disperses fine clay particles that clog pores and seal the surface of the soil. This keeps the water out and it makes the seedlings have a hard time busting through. By leaving the materials on there, there is something to absorb the water and the soil is held in tact by the plant materials.

114
Q

List five of the seven general guidelines for managing soil tilth

A
  1. minimize tillage
    2. timing traffic
    3. mulching surface
    4. add crop residues and animal manures
    5. include sod crops
    6. use cover crops and green manure crops
    7. add soil conditioners (gypsum, organic polymers)
115
Q

the hydrogen don’t attach to the water evenly, they make a v-shape instead and this causes the positive charges to cling towards the side weighed down with the two hydrogens therefore causing this property of water

A

polarity

116
Q

one of the hydrogens makes a low-energy bond to an oxygen particle from another molecule of water. this causes water to have a higher boiling point, specific heat, and viscosity

A

hydrogen bonding

117
Q

the attraction of water molecules for each other

A

cohesion

118
Q

the attraction of water molecules for solid surfaces, causes some water molecules to be held rigidly at the surface of soil solids

A

adhesion

119
Q

results from the greater attraction of water molecules for each other than for the air above, causes an inward force at the surface

A

surface tension

120
Q

h = .15cm2<br></br> r

A

capillary rise

121
Q

In what type of soil does capillarity work?

A

All moist soils

122
Q

What is the prime condition for capillarity?

A

medium to large sized capillary pores

123
Q

How does capillarity work in sandy soils?

A

it permits rapi initial rise but limits ultimate height

124
Q

How does capillarity work in clayey soils?

A

friction slows down the rate at which the water moves through the pores because they’re really fine. Slow linitally but in time exceeds that of sand

125
Q

How does capillarity work in loamy soils?

A

they are in the middle of clay and sand

126
Q

force caused by adhesion, reduced the energy state of water near particle surfaces

A

Matric

127
Q

force caused by cohesion, reduces energy state of water in the soil solution

A

osmotic

128
Q

force pulling the water downward

A

gravimetric

129
Q

Interpret Figure

A

The absence of sharp breaks in the curves indicates a continuous range of pore sizes and therefore a gradual change in the water potential with increased soil water content.

130
Q

Differentiate between gravimetric and volumetric water contents

A

Volumetric Water Content – volume of water associated with a give volume of dry soil

Gravimetric – direct measurement of soil water content: weigh it, heat it to get rid of all the water, weigh it again loss=water weight

131
Q

Θv = Db x θm

A

volumetric water content, gravimetric determination of soil water content

132
Q

gravimetric water content

A

mass of water / mass of soil

133
Q

Define saturated hydraulic conductivity

A

Saturated hydraulic conductivity – the water hose for the flowing water, the thing through which the water can flow that controls the amount

134
Q

describe how Ksat is related to soil uses

A

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a. <!--[endif]-->Beach sand – extremely high

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b. <!--[endif]-->Very sandy soil - too rapidly to filter pollutants in wastewater in a

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c. <!--[endif]-->Moderately permeable soil - it is suitable for most agricultural, recreational, and urban uses that require good drainage

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d. <!--[endif]-->Fine-textured, compacted or poorly structured soil - it is too slow for proper operation of septic tank drain fields, most types of irrigation and lost of recreational uses such as playgrounds

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e. <!--[endif]-->Compacted clay – extremely slow, good for wastewater lagoon lining or landfill cover material

135
Q

Compare and contrast the concepts of infiltration and percolation

A

a. Infiltration – process by which water enters the soil pore spaces and becomes soil water, takes place at the soil surface
b. Percolation – process by which water moves downward into the profile, rate is related to the soil’s hydraulic conductivity

136
Q

Explain how diverse surface soil textures influence infiltration rates over time

A

Water enters a dry soil rapidly at first but slows as the soil becomes saturated.

        Sandy soils have the least decline.

        Soils with high amounts of expansive clays have a high initial infiltration rate when cracks are open but very low when the clay swells with water and closes the cracks.
137
Q

explain how soil stratification affects water movement

A

The water is attracted to the fine-textured soil only when the water content is raised a bunch will the water begin to move to the sand.

138
Q

What is maximum retentive capacity?

A

– all soil pores are filled with water, matric potential is close to zero, the soil will remain here only so long as water continues to infiltrate

139
Q

What is field capacity?

A

when water addition stops the largest pores will drain downward rapidly, when this flow becomes negligible it is at field capacity. Soil is holding the maximal amount of water useful to plants, it is near its lower plastic limit, and sufficient pore space is filled with air to allow optimal aeration for most aerobic microbial activity and the growth of most plants

140
Q

What is the wilting coefficient?

A

the rate of plant water removal fails to keep up with the plant needs so the plant wilts. At first they can keep up by absorbing a lot at night when water isn’t being lost through leaves but eventually they loose so much they can’t catch up and are wilted night and day

141
Q

What is the hygroscopic coefficient?

A

soil moisture is lowered below the wilting point, the water molecules that remain are very tightly held, most are absorbed by colloidal soil surfaces the water is held so rigidly that most of it can only move in the vapor phase

142
Q

Describe how soil texture and organic matter content influence available water holding capacity

A

As fineness of texture increases there is an increase in available moisture storage. Sand to loam to silt loam. But clay soils have a higher wilting coefficient so they tend to provide less water. OM has a very high water-holding capacity. It also affects it indirectly because of its influence on soil structure and total pore space.

143
Q

Describe how vegetation type influences the fate of precipitation and irrigation

A

grasslands and forests protect the soil from the raindrops and enourage water infiltration and decrease likelihood of runoff

144
Q

Describe how stem flow influences the fate of precipitation and irrigation

A

water is directed down the plant to the stem and flows downward in this way, increases the opportunity for saturated flow to occur

145
Q

Describe how soil management influences the fate of precipitation and irrigation

A

– Enhance soil surface storage to allow more time for infiltration. Maintain dense vegetation during period of high rainfall (cover crops). Maintain soil structure by minimizing compaction.

146
Q

Describe how urban watersheds influence the fate of precipitation and irrigation

A

curtailed infiltrating capacity and saturate hydraulic conductivity because of heavy equipment use in preparing land increases surface runoff. Leads to erosion and severe environmental problems

147
Q

Identify the two major points of resistance to water movement in the soil-plant-atmosphere continuum

A
  1. the rate at which water is supplied by the soil to the absorbing roots
    2. the rate at which water is transpire from the plant leaves
148
Q

Explain how vegetative, paper and plastic mulches, along with crop residues and conservation tillage not only reduce surface evaporation but also provide other benefits

A

Vegetative mulches – most practical for small areas, provides clean path for foot traffic, reduces weed growth, moderate soil temperatures prevent overheating, increase in water infiltration, provides organic matter and plant nutrients, encourages earthworm populations, reduces soil erosion

        Paper and Plastic Mulches – widely used for vegetable and small fruit crops, increases in plant growth,

        Crop Residue and Conservation Till – increase infiltration,
149
Q

explain why a deep well would be more likely to provide high quality drinking water than a shallow well

A

It would not come into contact with the pollution plume because the water wouldn’t be moving very much or coming into contact with extraneous things

150
Q

Identify three principal factors which regulate soil aeration

A

soil macroporosity, soil water content, and O2 consumption by respiring organisms

151
Q

Contrast the composition of soil air with that of the air above the soil

A

soil air has lower amounts of O2, higher CO2, is much higher in water vapor, and under waterlogged contions the concentrations of gases such as methane and hydrogen sulfide are much higher

152
Q

Describe how (and why!) the forms of Fe and N are influenced by poor soil aeration

A

If there’s not enough O2 anaerobic microorganisms are there and they have to use other substances and iron is commonly used. Their use of Fe reduces its presence in the soil. They could possibly use N too. It’s an oxidation-reduction reaction. Nitrogen is the next most easily reduced substance next to water.

153
Q

What are the factors involved in the process of wetland delineation?

A

how water flows in and out of a wetland. In through runoff, groundwater seepage and precipitation. Out by surface and subsurface flows, evaporation and transpiration. Hydroperiod is the pattern that things change, ex. Seasonal, daily, etc. The slower the water moves through the better cause more reactions have time to take place.

154
Q

What are the factors involved in the process of hydric soils?

A

Hydric soils are mostly histosols, in the aquic suborder. Generally have an aquic or peraquic moisture regime. They are subject to periods of saturation that inhibit the diffusion of O2 into the soil, they undergo reduced conditions for substantial periods of time (this means electron acceptors other than O2 are reduced, they also exhibit certain features termed hydric soil indicators.

155
Q

What are the factors involved in the process of hydrophytic vegetation?

A

– plants that have evolved special mechanisms to adapt to life in saturated, anaerobic soils.

156
Q

. Explain how progressively warmer soil temperatures influenced microbial respiration

A

It increased it, the rates more than double for every 10o C rise.

157
Q

). Address items which relate soil temperature to soil depth and month of the year.

A

Temperature is less variable at greater depths, surface soil temp changes with the air temp.

158
Q

Relate intensity of tillage to soil temperature

A

The more intense the tilling the higher the soil temp.

159
Q

What is a defining characteristic of crystallin silicate clays?

A

They are predominately negatively charged

160
Q

What are some defining characteristics of noncrystalline silicate clays?

A

high amounts of both positive and negative charge and high water-holding capacities, extremely high capacities to strongly absorb phosphate and other anions

161
Q

What are some defining characteristics of iron and aluminum oxides?

A

net charge ranges from slightly negative to moderately positive, low in plasticity and stickiness

162
Q

What are some defining characteristics of humus?

A

very high capacities to absorb water, almost no plasticity or stickiness, high amounts of both negative and positive charge but net charge is always negative

163
Q

What is a tetrahedral sheet?

A

an interlocking array of tetrahedra composed of Si surrounded by 5 O each sharing its basal oxygens with its neighbor

164
Q

What is an octahedral sheet?

A

Six oxygen surrounding an aluminum or magnesium atom that form an eight sided geometric solid

165
Q

What is isomorphic substitution?

A

the process by which one element fills a position usually filled by another of simlar size.

166
Q

What is kaolinite?

A

1:1 clay, layers stack vertically, low surface area, low water holding capacity, low negative charge, mostly pH dependent, very little isomorphic substitution, little shrink swell

167
Q

What is smectite/vermiculite?

A

2:1 expanding clay, when wet it expands, high surface area, Mg subs for Al, high water holding and swelling, high surface charge

168
Q

What is fine-grained mica/chlorite?

A

2:1 non-expanding clay, substitution in the tetrahedral sheets, net negative charge, potassium keeps the layers collapsed, moderate surface area, water holding capacity and surface charge, pretty easy to manage

169
Q

What is the history of Kaolinite?

A

Kaolinite has been used for thousands of years to make pottery, roofing tiles, and bricks

170
Q

Contrast non-silicate colloids with silicate clays

A

they rarely have isomophrous substitution, do not ahve a large negative charge, the surfaces of these clays can strongly absorb anions, they are not expansive, quite stable for construction pruposes, and generally exhibit realtively little stickiness, plasticity, and cation adsorption

171
Q

What is the source of a constant negative charge on a silicate clay?

A

isomorphouse substitution of a lower-charged ion for a higher charged ion.

172
Q

What is the source for a constant positive charge on a silicate clay?

A

isomorphouse substitution is lso a source of positive charge if the substituting cation has a higher charge than the ion for which it substitutes

173
Q

What is the source for a pH-dependent negative charge?

A

broken edges of mineral colloids, hydroxyl (OH) groups on the surfaces of inorganic and organic colloids

174
Q

What is the source for pH-dependent positive charges?

A

under moderate to extreme acid soil conditions, some silicate clays and Fe, Al oxides may develop positive charges by protonation

175
Q

What is protonation?

A

the attatchment of H+ ions to the surface of OH groups

176
Q

What is reversibility

A

exchange reactions are rapid and reversible

177
Q

What is charge equivallence?

A

Exchange takes place on a charge for charge basis, you have to keep the same amount of charge

178
Q

What is ratio law?

A

At equilibrium, ratio of similar cations on exchange sites will be the same as that in the solution

179
Q

What are anion affects on mass action?

A

anions are always present, the type of anion will influence the direction and equilibrium of the reaction. If the anion causes precipitation, volatilization, or strong association then the reaction goes right

180
Q

What is mass action?

A

an exchange reaction will be more likel to proceed to the right of the released ion is prevented from reacting in the reverse direction

181
Q

What is cation exchange capacity (CEC)?

A

the sum total of exchangeable cations that a soil can absorb

182
Q

How do you estimate clay mineralogy from information found on CEC?

A

If you know a soils pH, clay content, and organic matter levels you can estimate clay mineralogy

183
Q

What clays mostly compose Aridisols and what are there CEC’s?

A

Smectice and Fin-grained mica, middle range, low range

184
Q

What clays mostly compose vertisols and what is their CEC?

A

Smectice, middle CEC

185
Q

What clays mostly compose mollisols and what is their CEC?

A

Smectite, middle

186
Q

What clays mostly compose Alfisols and what is their CEC?

A

everything except Fe, AL oxides. low to upper middle range CEC

187
Q

What clays mostly compose Spodosols and what are their CEC?

A

Fe, Al oxides and Kaolinite, very low CEC

188
Q

What clays mostly compose Ultisols and what are their CEC?

A

Fe, Al oxides and Kaolinite, very low

189
Q

What clays mostly compose Oxisols and what are their CEC?

A

Fe, Al oxides and Kaolinite, very low CEC

190
Q

How does pH affect CEC?

A

As pH rises there is more pH dependent charge

191
Q

What is the equation for pH?

A

pH = -log [H+] ex. if [H+] = 10^-5 M log 10^-5 = -5 pH = 5

192
Q

Identify the sources of added hydrogen ions

A

carbonic acid, accumulation of organic matter, oxidation of nitrogen and sulfer, acids in precipitation, and plant uptake of cations

193
Q

Explain how leaching loss of cations can acidify soils over time

A

the H+ ions exchange with the nonacid ions and then they are free to be leached away along with accompanying anions and then the soil become dominated by acid cations such as H+ and Al3+

194
Q

Explain how aluminum is involved in soil acidity

A

When H+ ions are absorbed they attack the structure of the minerals and release Al3+ ions which become adsorbed on the colloid’s cation-exchange sites. The Aluminum is highly toxic to most organisms and it lowers soil pH because it splits water molicules and combines with OH and leaves H in the soil

195
Q

Define active acidity

A

the H+ ion activity in the soil solution

196
Q

Define exchangeable acidity

A

the pool of acidipty that is salt replaceable.

197
Q

Define residual acidity

A

hydrogen and aluminum ions that are bound in nonexchangeable forms by organic matter and clays

198
Q

Why is PhKCL different from Phwater?

A

KCL depends on the ion exchange capacity and type of colloids

199
Q

Describe how humans have influenced soil acidity through nitrogen fertilization and acid rain

A

Excess N fertilization leads to nitrification which acidifies soil. Fossil fuel combustion and burning things leads to acid rain which acidifies soil.

200
Q

Describe toxic effects of Al, Mn, H, and Fe on plants in low pH soils.

A

Aluminum toxicity affects plants by inhibiting root growth and bacteria. Symptoms are stunted root systems and leaves with chlorotic (yellowish) spots. Manganese toxicity affects plants when too much is taken up, symptoms vary but include crinlking or cuppin of leaves and intereinal patches of chlorotic tissue. Hydrogen Toxicity can damage the root membranes and kill beneficial soil bacteria. Iron toxicity is common in acidic rice paddies.

201
Q

What is the optimum range for soil pH for plant growth?

A

6-6.9

202
Q

Describe how liming materials do their job

A

they react with carbon dioxide and water to yield bicarbonate when applied to an acid soil

203
Q

Identify the four key factors influencing the amount of liming material needed to correct acid soil conditions

A
  1. the change required in the pH or exchangeable Al saturation
  2. the buffer capacity of the soil
  3. the amount or depth of soil to ameliorate
  4. the chemical composition of the liming materials to be used
  5. the fineness of the liming material
204
Q

Blueberries, rhododendrons, and azaleas enjoy pH values of 5.0 and below. Describe how to reduce soil pH to accommodate these unusual plants

A

add acid-forming organic and inorganic materials

ogranic-pine needles, sawdust, acid peat moss

inorganic-aluminum sulfate or ferrous sulfate

205
Q

Relate the benefits and downsides of earthworms on soil properties

A

Benefits:

  • burrows allow roots to penetrate
  • enhances aggregate stability of the soil
  • enhance soil fertility and productivity by altering chemical conditions in the soil
  • increase aeration and drainage
  • relieve compaction

Downsides

  • leaves soil surface bare of residues
  • rapidly percolating water can lead to extensive chemical leaching
206
Q

How do earthworms affect nitrogen?

A

They make it available for biological processes

207
Q

explain how earthworms can be a very unwelcome addition to forest ecosystems in northern Minnesota

A

The soil there developed without earthworms and therefore the species need a thick forest floor and when the earthworms mix it up the stuff that lives there no longer can

208
Q

Explain how mycorrhizal fungi help higher plants

A

they improve P availabilty and water uptake

209
Q

Describe the prevalence and activities of soil algae, fungi, bacteria, and actinomycetes

A

Soil Algae- produce organic atter and have favorable effects on soil aggregation

Fungi - there are tons, humus formation and aggregate stabilization and decomposition

Bacteria - participate in virtually all of the ogranic transactions that characterize a healthy soil

actinomycetes - the most abundant prokaryote, decompose stuff

210
Q

List six major beneficial effects of soil organisms

A

Organic Material Decomposition, Breakdown of Toxic Compounds, Inorganic Transfomations, Nitrogen Fixation, Rhizobacteria, and Plant Protection

211
Q

Explain what is known about how Pseudomonas bacteria inhibit the take-all fungus of wheat.

A

the buildup of the pathogen over the first few years is eventually overshadowed by a subsequent buildup of specific organisms antagonistic to the pathogn

212
Q

Describe how the various classes of microbes “get along” with each other

A
  • microbiotic crusts of arid rangelands are intricate living systems that greatly benefit the associated natural vegation communities and consis of mutualistic associations with algea, fungi, mosses, bacteria, and liverworts
  • changes in environment affect both the number and kinds of soil organisms
  • the communities of plants and animals aboveground is greatly influence by the belowground communities
213
Q

Evaluate the influence of no-till compared to plowed conditions in Georgia

A

fungi are higher in no-till but bacteria and protozoa are higher in plowed

214
Q

Categorize organic compounds in the soil as to their rate of decomposition

A
  1. Sugars, starches, and simple proteins
  2. crude proteins
  3. hemicellulose
  4. cellulose
  5. fats and waxes
  6. lignins and phenolic compounds

Rapid-slow

215
Q

Compare and contrast degradation of organic matter under aerobic and anaerobic conditions

A

Aerobic- decomposition, breakdown of cellulose and starch, breakdown of proteins, breakdown of lignin, organic decay

Anaerobic- bacteria and archaea in wet soils, it releases relatively little energy for the organisms involved

216
Q
A
217
Q

Compare the C/N ratio of various organic materials

A

high- sawdust, newspaper, spodosol O horizon

low - hairy vetch, broccoli residue

218
Q

If the C/N ratio of an organic material exceeds 25:1, two negative consequences result. List those two consequences, and describe why they occur

A

it will deplete the soil’s supply of soluble nitrogen and cause plants to suffer from nitrogen deficiency. Secondly, the decay of organic materials can be delayed. the plants have to take N from other places because it’s not readily available

219
Q

Categorize the types of soil organic matter and the transformations among them

A

Biomass:living organisms

Detritus:identifiable dead tissue

Humus: (Humic and Nonhumic) nonliving nontissue

220
Q

List 5 positives for the environment which can result from increasing soil organic matter

A

less flooding, less pesticides are needed, greater groundwater recharge, less water polution, less land degradation

221
Q

List and defend five general guidelines for managing soil organic carbon

A

A continuous suply of plant residues must be addd to the soil to maintain an appropriate level of soil organic matter

There is no ideal amount of soil organic matter. Do not try to maintain a higher SOM level than needed

Adequate nitrogen is requisite for adequate OM because of the relationship between nitrogen and carbon in humus and because of the positive effect of nitrogen on plant productivity

Tillage should be elimnated or limited.

Perennial vegetation should be encouraged to leave land relatively undisturbed

222
Q

gravimetric water content (Mass water content)

A

mass of water / mass of soil

223
Q

For the macronutrient nitrogen, describe its role in the plant, plant deficiency symptoms, response to oversupply, and forms taken up by plants

A

A major part of amino acids, nucleic acids, and is essential for carbohydrate use within plants. if deficient plants tend to exhivit chlorosis (yellowish or pale green leaf colors). If too much is applied excessive vegetative growth occurs, the cells of the plant stems become enlarged but relatively weak and plants become top heavy and fall over. It is taken up by plants as dissolved nitrate (NO3-) and ammonium (NH4+)

224
Q

What are the five possible fates of ammonium and four possible fates of nitrate.

A
  1. plant uptake
  2. volatilization
  3. immobilization/mineralization
  4. adsorption or fixation
  5. nitrification
  6. Leaching loss
  7. dentrification
  8. immobilization
  9. plant uptake
225
Q

What is volatilization?

A

it’s when NH4 turns into NH3 (therefore solid turning into a gas)

226
Q

What is dentrification?

A

an anaerobic process by which heterotrophic bacteria reduce nitrate to such gases as NO, N2O and N2

227
Q

Explain how mineralization and immobilization counteract each other

A

they are the same equation going in opposite directions

228
Q

Give the reason why ammonium fixation, on a percentage basis, is higher in subsoil than in topsoil

A

due to the higher clay content of subsoils

229
Q

Describe the mechanisms of ammonia volatilization

A

NH4 dissolves with OH to form water and NH3 (gas)

230
Q

Reproduce the equations for the two steps of nitrification, including the energy production, and discuss the soil conditions influencing this important process

A

Step 1:

NH4+ + 1.5 O2 –> NO2 + 2H + H20 + 275 kJ energy

Step 2:

NO2 + 0.5O2 –> NO3 + 76 kJ energy

needs to be an abundance of exchangeable Ca and Mg, high smectite or allophane clays are bad. need well-drained soils

231
Q

Leaching of nitrates costs crop productivity and adversely impacts the environment. Explain why this is so

A

negatively charged nitrate ions are not adsorbed by the negatively charged colloids that dominate most soils and therefore the nitrate ions move downward freely with drainage water and are readily leached from the soil

232
Q

Why is soil nitrate lower when plants are grown?

A

because much of the nitrate formed is removed by plant uptake

233
Q

Identify the causes of hypoxia in the Gulf of Mexico

A

the nitrogen stimulates more growth of algea which sinks to the bottom when it dies and the microorganisms deplete the oxygen in the water when they decompose this tissue. This leads to hypoxia which is a state of low oxygen in water.

234
Q

Describe the conditions under which denitrification can cause gaseous losses of soil nitrate

A

lack of free O2

available organic C

warm soils best

available NO3

saturation for only a few hours

235
Q

Write out the general reaction for biological nitrogen fixation

A

NH3 + organic acids amino acids Proteins (plant or bacterial)

236
Q

Describe the symbiotic relationship between leguminous plants and either Rhizobium or Bradyrhizobium bacteria

A

Rhizobium forms nodules on the roots

237
Q

For the macronutrient phosphorus, describe its role in plants, along with its plant deficiency symptoms

A

a limiting nutrient, P deficient symptoms include stunting and purpling, enhances photosynthesis, important for structural tissues, root growth, seed production, and flowering

238
Q

Three aspects of the phosphorous problem

A

total P is generally low, mostly unavailable, added H2PO4 is fixed

239
Q

Describe how (and why!) applications of P fertility in the US, developed, and developing regions have changed over the past decades.

A

it has remained pretty steady in the US, is leveling off in developed countries, and is continuing to increase in developing countries

240
Q

Sequentially describe the process of P-induced eutrophication

A

algae and plants cover the surface of the water

they die and sink to the bottom

microogranisms use up the oxygen dissolve in the water to decompose them

the decrease in oxygen severely limits the growth of many aquatic organisms

241
Q

Why do P pools differ so much between forest and agricultural watersheds

A

because the addition of fertilizer results in inorganic P accumulating in the soil

242
Q

List five of the seven approaches for practical management of soil P

A
  1. adjust application to soil status
  2. localized placement
  3. combine ammonium with posphorus
  4. cycling of OM
  5. control of soil pH
  6. enhance mycorrhizal symbiosis
  7. choose P-efficient plants
243
Q

Describe 4 steps to keep P from getting into water.

A
  1. avoid excess accumulation
  2. minimize loss in funof and sediment
  3. capture P from runoff
  4. tie up P with inorganic amendments
244
Q

For the macronutrient potassium, describe its role in plants and its plant deficiency symptoms

A

third most limiting nutrient in crops, important for osmotic regulation, photosynthesis, starch formation and sugar translocation, helps adapt to environmental stress, deficiency symptom - necrotic leaf edges

245
Q

Compare K with N and P for its environmental impacts.

A

it doesn’t really have any

246
Q

Describe why liming acid soils can reduce leaching losses of K

A

the complementary ion effect, the K easily replaces Ca

247
Q

Explain the potassium-related concept of luxury consumption

A

plants can take up far more than they need

248
Q

Compare the plant availabilities of soil K sources

A

K in primary mineral structure- unavailable

non exchangeable K in secondary mineral - slowly available

exchangeable K on soil colloids and K soluble in water - readily available

249
Q

sort out four practical recommendations for effective

potassium management.

A
  • apply less K at a time but more often
  • apply lime to acid soils
  • capitalize on k supplying power of soils
  • whole plant removal depletes K more rapidly thus return of plant residues is very important
250
Q

List and describe each of the four goals of nutrient management

A
  • cost effective plant production
  • efficient use/conservation of nutrients
  • enhance soil quality
  • protect the environment
251
Q

Explain how nutrient management plans work

A

they attempt to balance the inputs of N and P with their desirable outputs to prevent undesirable outputs. it specifies practices for how nutrients will be used in plant production

252
Q

Of the many available best management practices, our text discusses four: buffer strips, cover crops, conservation tillage, and forest stand management. Prepare a schematic diagram of a “multi-species riparian buffer strip”

A
253
Q

Explain why Figure 16.8 shows rye is a better cover crop than vetch.

A

rye adsorbs more left over stuff

254
Q

Identify the amount of the soil surface which must be covered with plant residue under conservation tillage.

A

at least 30%

255
Q

Sort through pages 688-691 to find ways in which clear-cutting affects nutrient losses from forested lands

A

leaching and runoff, erosion of litter, and volatilization in fire

256
Q

Most forests are not fertilized. Describe how these ecosystems conserve nutrients

A

recycling stuff ( OM mineralization) and surface soil enrichment (by acting as nutrient pumps or fixing nitrogen)

257
Q

Describe the best ways to make use of animal manures for crop production

A

spread daily

liquid vs. dry storage

composting

pelletizing

258
Q

Identify limitations in using sewage sludge as a nutrient resource

A

heavy metals

259
Q

Convert %P2O5 to %P

A

Multiply by .44

260
Q

Conver %K2O to %K

A

Multiply by .83

261
Q

A soil fertility “diagnostician” must be a bit like a detective to be effective. List the text’s five guidelines for success

A
  1. organize a record of your observations
  2. interview landowner or manager
  3. look for spatial patterns
  4. examine plants, especially leaves, for nutrient dificiency symptoms
  5. measure shoot and root growth, check for symbiotic associations
262
Q

Soil analysis requires three successive steps; list each one

A
  1. Sampling the soil
  2. chemical analysis of the sample
  3. interpretation of the results
263
Q

Advise a rookie on how to take representative soil samples from his field

A

take samples from obviously different areas, take 12-15 samples per area, sample at the same time of the year

264
Q

Describe how the site-index approach to phosphorus management works

A

researchers have integrated phosphorous source, transport, and management charateristics of a site into an index of phosphorus polution risk.

265
Q

Contrast geological and accelerated soil erosion

A

geological is always occuring w/o the influence of humans, human disturbance accelerates soil erosion

266
Q

Identify the three main types of water erosion

A

Sheet erosion, rill erosion, gully erosion

267
Q

Differentiate among the five conservation tillage systems

A

no till- soil undisturbed prior to planting in a narrow seedbed

ridge till- soil undisturbed prior to planting which is done on ridges higher than row middles. residues are moved aside of incorporated on about 1/2 of soil surface

strip till- soil undisturbed prior to planting, narrow and shallow tillage in row using rotary tiller, in row chisel, etc.

mulch till - surface disturbed by tillage prior to planting but at least 30% of resue left on or near surface tools such as chisels, field cultivators, disks, ect are used

reduced till - any other tillage and planting system that keeps at least 30% of residues on surface

268
Q

Identify the factors that are involved in the RUSLE and describe how they influence soil loss

A

R-Rainfall factor - driving force for sheet and rill erosion

K-soils susceptibility for erosion - amount of soil lost per unit of erosive energy

LS- topographic factor - as slope length increases and steepness increases erosion increases

C- cover or management - depends on the amount of tillage and the amount of surface residue left

P- support practices aimed at guiding and slowing runoff

269
Q

Describe how conservation tillage affects soil physical, chemical, and biological properties

A

OM levels increase

Earthworms numbers are elevated

Macroporosity increases

Aggregation goes up

Infiltration and percolation both improve

Soil water holding capacity is enhanced

Soils cooler, wetter (can be negative in spring)

May have more immobilization and denitrification

Surface pH may drop

270
Q
A

PLS 366 (11 decks)

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