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Soil Science Final > Questions > Flashcards

Questions Flashcards

1
Q

A sticky, putty-like feed indicates a high % of which soil separate

A

Clay

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2
Q

For which substance would the particle density equal the bulk density

A

quartz

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3
Q

Soil colours are scientifically described by____ colour designations such as 10YR3/4

A

Munsell

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4
Q

Brown and red colours in subsurface horizons are caused by ___ in the soil

A

iron oxides

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5
Q

Due to greater surface area per unit of soil mass, silt loam generally have a greater capacity than loamy sand to __

A

Absorb water, absorb gas, Release nutrients by weathering

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6
Q

Which soil has more pore space: clay vs sand

A

Clay - micropores + macropores (clay aggregates)

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7
Q

Soil organic matter consist of

A

organisms, dead tissues, polymerized and non-minerals

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8
Q

What is material deposited in lakes called

A

Lacustrine

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9
Q

Which of the following is not a characteristic of soil colloids

A

low water holding capacity

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10
Q

A well-drained soil under a rain forest in brazil contains significant amounts of a clay, which is likely

A

Kaolinite

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11
Q

Which of the silicate clays would likely have the highest of potassium in the crystal structure

A

Fine Grained Mica

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12
Q

Drainage of wetlands can result in extreme soil acidity. Which process, is occurring when the soil is drained

A

Oxidation of sulfur-bearing minerals that produces sulfuric acid

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13
Q

Phosphorous availability in acid soils is constrained by the presence of significant quantities of reactive___

A

Iron

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14
Q

The very high pH levels found in some arid region soils are most likely due to high levels of exchangeable

A

Na+

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15
Q

In various parts of the world, soil phosphorous is associated with which of the following health/environmental problems

A

eutrophication of lakes because of a build-up of soil P in the water sheds

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16
Q

In most soils, mineralization of SOM is an important source of plant available

A

both P + K

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17
Q

You would be most likely to find P deficient plant in which location

A

Sub-Saharan Africa

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18
Q

In what range of soil pH is phosphorous generally most available to plants

A

6-7

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19
Q

The total phosphorous lost from various watersheds is most closely correlated with high soil erosion (T/F)

A

true

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20
Q

The principal form of sulfur taken up by plants is by sulphate ion (T/F)

A

true

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21
Q

Oxidation of sulfides to sulphuric acid in soils developed in marine marshes can become extremely acidic if drained (TF)

A

true

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22
Q

The water contents are different in these soils, but the water potential is the same (TF)

A

True (the width of the film around the soil particles) Water film thickness is the same, so water potential is the same

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23
Q

The great majority of nitrogen in soils can be found in the form of dissolved anions

A

false Nitrogen is in an organic form, only a small amount is available as dissolved ions

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24
Q

Denitrification is NO3- (nitrate) becomes N2(gas) and goes into the atmosphere TF

A

true

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25
Q

What process is this? Biological oxidation of ammonia to NO2 (nitrite) then NO3 (nitrate), usable by plants

A

nitrification

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26
Q

Sodic soils are commonly formed by leaching saline-sodic soils TF

A

true

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27
Q

The mineral nitrogen is required for which part of a plant

A

DNA, enzymes, chlorophyll

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28
Q

The great majority of nitrogen in soils can be found in the form of

A

organic compounds

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29
Q

Secondary minerals are more prominent in the ____ fraction of soils

A

clay

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30
Q

Opposite of mineralization

A

immobolization

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31
Q

what is mineralization

A

process by which chemicals present in organic matter are decomposed or oxidized into easily available forms to plants

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32
Q

all but a few nematodes are pests TF

A

false

33
Q

the osmotic potential is dependent on the presence of salts and other solutes in the soil

A

true

34
Q

CEC of the soil is determined primarily by the amount and type of colloids in the soil, and by the pH

A

true

35
Q

Natural causes of salt in soils

A

Weathering of minerals such as magnesium, calcium, sulphates etc.

Lack of drainage - Arid and semi arid environments have a lack of drainage and this causes low precipitation and minimal leaching

Sea water intrusion - Mediterranean regions

36
Q

Man-made sources of salt in soil

A

Excessive fertilization

Soil amendments such as compost, manure, etc.

Deicer from roads

37
Q

Management techniques for salty soils

A

Grow salt tolerant crops - doesn’t solve the problem

Use high quality irrigation water that is not saline

Keep soil moist because water dilutes salt

Avoid over fertilization

Mulching to prevent evapotranspiration (water from leaving soil and plants)

Monitor soil so you prevent soils from becoming too saline

38
Q

Three general rules to reclaiming salty soils

A

Establish internal drainage - add drain tiles

Replace excess exchangeable salt - removable by leaching of excess soluble salts without bringing in further Na+

Leach out most of the soluble salts

39
Q

6 ways roots add organic compounds to rhizosphere

A

getting rid of root cap cells

excretion of mucigel

spilling of cell contents with when epidermal cells are lysed

releasing of specific compounds produced by root hairs

releasing of various compounds by cortical cells

export of symbiotic compounds to fungi

40
Q

What is carbon sequestration

A

Plants take in CO2 from the atmosphere through the process of photosynthesis in order to make glucose to feed themselves. Carbon sequestration is the process of the plants holding on to this CO2 in their roots.

41
Q

3 functional groups of soil fungi

A

Decomposers: breakdown dead tissues and convert it to organic matter

Mutualists: mycorrhizal fungi colonize plant roots and have a symbiotic relationship where they provide a larger surface area for the plants in order to absorb

Pathogens or parasites: colonize roots and other organisms causing them death or reduced production

42
Q

Describe an important role of protozoa

A

Contribution to Mineralization

Protozoa have a low amount of N in their cells in comparison to the bacteria that they eat

When they eat the bacteria they want to get rid of the excess N so they release it in the form of ammonium (NH4)

Bacteria and other organisms rapidly take up the ammonium but some is left for the plant as available nutrients

43
Q

4 important roles of earthworms

A

Increase infiltration: when they move for soil they increase porosity.

This helps with the flow of soil air and water

Provide channels for root growth

Increase water holding capacity

Mix and aggregate soil - their waste helps create aggregates

44
Q

What are the four chemical processes in soil weathering?

A

Hydrolysis
Hydration
Carbonation
Oxidation

45
Q

Define Hydrolysis

A

the chemical process where water is added to a material

46
Q

Define Hydration

A

absorption of water by materials causing swelling

47
Q

Define Carbonation

A

CO2 dissolves causing carbonic acid which acidifies water and increases solvent action

48
Q

Define Oxidation

A

inclusion of oxygen into a mineral

49
Q

4 fates of nitrates in the soil

A

Immobilization by microorganisms:
Ammonium and nitrates are taken up by microorganisms and therefore become unavailable to crops

Removal by plant uptake

Leaching to groundwater:
Nitrates are very volatile and leach easily

Volatilization/Denitrification:
Nitrates to nitrogen gas or ammonia gas which is released into the atmosphere

Ammonification:
Dead OM & waste turns into ammonium in the soil

50
Q

What are 4 of the main functions of SOM?

A

Water storage
Nutrient Storage
Soil aggregation
Carbon sequestration

51
Q

How does OM improve mineral, sandy, and clay soils? (6)

A

Sandy soils - increase water and nutrients content

Clay soils - loosens and improves tilth

Stores organic and inorganic nutrients used by plants and other organisms

Soil aggregates

Improves soil structure

Improves water and air filtration

52
Q

How much water can SOM store?

A

Both humus (stabilized OM) and SOM absorb water like a sponge, humus can store 6 times its own weight

53
Q

Why/how does SOM provide and hold nutrients?

A

Colloids hold water and nutrients

Aggregates help prevent soil erosion which washes away nutrients

Makes several nutrients more available for plant use

54
Q

Describe soil aggregates as a function of SOM

A

Aggregate formation increases water/O2 flow while also preventing erosion and leaching

55
Q

Describe carbon sequestration as a function of SOM

A

Keeps carbon out of the atmosphere
Carbon comes from the atmosphere into the plant and then the plant residues become part of the SOM and the carbon is retained

56
Q

List and describe the groups of nematodes

A

4 groups of free-living nematodes based on their diet

Bacteria feeders
Fungal feeders
Predatory nematodes: eat all types of nematodes and protozoa
Omnivores: eat a variety of organisms or different organisms at different points of their life cycle

Root-feeding nematodes - not free-living

57
Q

What are nematodes functions?

A

Nutrient cycling:
release nutrients in plant available forms

Grazing:
at low nematode densities they stimulate the growth of their prey such as bacteria, plants, and fungus

Dispersal of microbes:
distribute these by carrying them in their digestive systems and then pooping them out

Food source:
nematodes are food for higher predators - including nematode feeding nematodes

Disease suppression and development:
some nematodes consume disease-causing organisms

58
Q

Where are nematodes located in the soil?

A

Nematodes are located near their prey groups

They are more common in larger grained soils because of their size

59
Q

How many nematodes are in a tablespoon of soil in the following locations: agricultural soils, grasslands, forests

A

Agricultural soils usually have less than 100 nematodes in each teaspoon

Grasslands have around 50 to 500 nematodes in their soil

Forests have several hundreds of nematodes in their soils

60
Q

What are nematodes useful indicators of? and why?

A

Nematodes are useful indicators of soil quality because of their tremendous diversity and participation in many functions of the soil food web

61
Q

Changes in nematode populations reflect changes in ___ __________

A

soil microenvironments

62
Q

What type of soil will you find nematodes in?

A

Undisturbed & high SOM

63
Q

What are actinomycetes?

A

Type of bacteria

64
Q

Major factors that effect/influence the amount of soil OM present (7)

A 
·       Vegetation
·       Climate
·       Soil texture
·       Drainage
·       Tillage
·       Rotations/residues
·       Policy
65
Q

How to manage SOM and keep it around (7)

A

Conservation tillage

Conserve crop residues

Practice yard recycling

Grow CC, incorporate green manure

Crop rotation

Mulches to manage soil moisture

Cover crops always used – no bare soil

66
Q

Good management of SOM increases: (8)

A 
·       Soil stability
·       Air filtration
·       Water and nutrient holding capacity
·       Infiltration
·       Aggregation
·       Structure
·       Humus
·       CEC
67
Q

define wilting point

A

there is so little water in the soil that the plant cannot overcome adhesion in order to absorb the water

68
Q

What is soil respiration?

A

the amount of CO2 released from the soil

69
Q

What are 3 sources of CO2 in the soil?

A

Respiration of plants through their roots - during the day most plants take in CO2 to perform photosynthesis (create food for themselves in the form of glucose) then during the night they release CO2 (less than they take in during photosynthesis).

Faunal respiration - nematodes, earthworms, protozoa, etc. all breath in oxygen and release CO2

Microbial respiration - aerobic decomposition of SOM to obtain energy for their growth

70
Q

Why does clay have 30% water in it and sand is very well drained?

A

Soils ability to retain water is strongly related to particle size, clay has a larger surface area than sand which means that it has more potential sites for water to attach to (this relationship between water and soil particles is called adhesion).

Clay soils have micropores inside of them as well as macropores on the outside. Sandy soils have very few micro pores compared to clay soils.

CEC

Micro vs macropores

SA

71
Q

Why do clay and sandy soils have a different field capacity and wilting point?

A
72
Q

What is the cation exchange capacity (CEC)?

A

The total number of cations that a soil can hold.

73
Q

How does CEC affect soil fertility?

A

a soil with a high CEC is able to hold more cations - meaning they can hold more nutrients

74
Q

Describe the rhizosphere: where it is, and 3 benefits/purposes of it (4)

A

1-2mm from plant roots

site of nutrient cycling
can act as a significant carbon sink
mineralization: break down nutrient to be part of inorganic pool

75
Q

What are causes of acidity? (6)

A

Industrial fertilizers
Accumulation of OM can produce a lot of Humic acids
Removing crops from land
Soil water - creation of carbonic water
Rain - usually is around 5.5-6.5 when it hits the ground
Nitrification - H+ is released which increased pH

76
Q

Does fungi like more acidic soils than bacteria and actinomycetes?

A

Yes

77
Q

What are colloids? (1) What are some properties of colloids? (5)

A

Groupings of soil (clay and OM) that are the seat for most of the chemical, physical, and biological properties of the soil.

VERY small (less than 2 micro m)
MASSIVE surface area
Can have negative and positive charges
Absorb lots of ions and water molecules
Absorb ions that often are exchanged with plant roots
78
Q

The lower the CEC, the faster the pH will lower over time?

A

yes

79
Q

What are some factors that effect soil fertility? (bad and good) (10)

A

positive vs negative

clay vs sand
humus vs loss of OM
good structure vs compaction
warm vs cold or hot soil
depth - deep vs shallow
moist soil vs dry or wet soil
good drainage vs no drainage
fertilization vs erosion
desirable microbes vs root damaging pests
neutral pH vs pH that is too alkaline or acidic

Soil Science Final (2 decks)

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