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Soil Science > Final Exam > Flashcards

Final Exam Flashcards

1
Q

What are some examples of organic amendments?

A

*compost–decomposed plant material
*manure–decomposed waste
*non-legume cover crops
*legume cover crops

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2
Q

What are the advantages of organic amendments?

A

-increased aggregation
-increased water holding capacity
-increased CEC
-increased water infiltration
-adds nutrients (nitrogen, phosphorous, potassium, etc.)

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3
Q

Percentage of N, P, and K from organic amendments?

A

percentages vary but are generally below 5%

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4
Q

What are cover crops?

A

*non cash crop grown to amend soil, may be mown or left standing
*increase soil OM, add nutrients (after decomp. OM), tie up nutrients in living plants to prevent nitrate leaching, reduce erosion, suppress weeds

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5
Q

Attributes of legumes

A

-produce nitrogen
-add OM
-some provide nectar sources for pollinators
and beneficial insects

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6
Q

Attributes of Grasses

A

-tie up nitrogen
-add OM
-fibrous roots

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7
Q

Attributes of Brassicas

A

-long tap root
-may have some biofumigant property when incorporated

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8
Q

Attributes of Sunflowers/Buckwheat

A

-add decorative elements for agrotourism
-provide habitat and food source for pollinators and beneficial insects

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9
Q

What factors should you consider when choosing a cover crop?

A
  1. What type of cover crop? (legume, grass, etc.)
  2. Annual or Perennial? Does it self-seed?
  3. When will the cover crop be actively growing?
    -cover crops don’t normally get irrigated, must be grown late fall/winter/early spring
    -most SJV cover crops are chosen to die/go dormant during warm season
    -if not they may need to be killed so they don’t compete with crops for water
    -in either case they should be mown, and may be tilled under
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10
Q

Describe the symbiotic relationship between rhizobia and legumes

A

-are present in legume root nodules
-bacteria are able to harvest nitrogen as N2 from the air and can convert it to ammonium (then converted into nitrate) so it is available to the plant
-in return, bacteria receives carbohydrates from the plant

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11
Q

How can you tell the difference between rhizobia and root nematode nodules?

A

-root nodules that are slightly pink on the inside indicates the presence of healthy rhizobia bacteria

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12
Q

Why should legume seeds be inoculated?

A

-not all strains of rhizobia are naturally present in the soil all the time, or may not be present in high amounts

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13
Q

When does N from legumes become available to a crop?

A

-Nitrogen fixation rates peak just before bloom
-Nitrogen that is fixed is available to the legume when it is actively growing
-Nitrogen will not be available to the crop until the dead legume material begins to decompose

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14
Q

What affects the decomposition rates of cover crops?

A

-temperature
-soil moisture
-whether the material is incorporated in the soil or left on the surface

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15
Q

What is the efficient legume that fixes N?

A

the ‘Lana’ wooly pod vetch (cool season annual that reseeds itself)

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16
Q

Are summer active legume cover crops recommended for our area? Why or why not?

A

-not a standard practice
-growers concerned of costs, whether they will grow without irrigation, and whether it will take water and nutrients from the crop
-compete with crops for water–not recommended for our area

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17
Q

What is the purpose of planting a grass cover crop?

A

-grasses can take up large quantities of nitrogen from soil, reducing nitrate leaching
-to purposefully reduce nitrogen, wheat, oats or barley are often used and harvested as a crop, removing nitrogen from the soil
-can be planted to release N into the soil very slowly–have a high C:N ratio

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18
Q

What is the purpose of planting a Brassica cover crop?

A

-Several species in the mustard family can uptake large amount of nitrogen like grasses do, but decompose more rapidly
-Some brassicas (mustards) produce compounds that are toxic to soil-borne organisms when incorporated–potential for some biofumigant effect
*efficiency of fumigant action is variable

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19
Q

Why is understanding the carbon cycle important?

A

-organisms needs carbon dioxide to survive
-helps us track fuel used by all living organisms
-excess carbon causing global warming

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20
Q

What are the key parts of the carbon cycle?

A

-photosynthesis by plants
-respiration by plants, animals and microorganisms
-decomposition of plants, animals and microorganisms
-combustion of fuel

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21
Q

What is decomposition?

A

breakdown of large organic molecules into simpler components

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22
Q

What are the factors controlling rate of decomposition?

A
  1. Moisture
  2. Temperature
  3. Contact of OM with soil
  4. Carbon to Nitrogen ratio
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23
Q

Describe how C:N ratio affects decomposition.

A

*most microorganisms require a certain amount of nitrogen to decompose carbon materials
-Low C:N ratio=they have lots of available nitrogen, will decompose relatively quickly, and plant available nitrogen will be released into the soil
-High C:N Ratio=they will decompose slowly and may tie up all available nitrogen
-microbes scavenge the soil for nitrogen, take all of it up, and none is available to plants to take up

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24
Q

List 3 materials with low C:N ratio

A

-legume cover crops
-grass clippings
-finished compost

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25
Q

List 3 materials with high C:N ratio

A

-bark chips
-mulch
-newspaper

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26
Q

What is humus?

A

-most soil OM decomposes relatively quickly
-Humic substances do not – Humin, Humic acids, Fulvic acids
-Humic substances are highly complex polymers that are extremely resistant to decay

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27
Q

Why is humus important in soil?

A

-play a part in plant health, increase water uptake, stimulate root imitation and elongation and enhance growth of shoots
-has high CEC

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28
Q

What is char?

A

-when a fire occurs, not all of the fuel undergoes total combustion
-some undergoes pyrolysis, where OM is heated to 250-500 degrees C under low oxygen conditions
-leaves behind char (charcoal)

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29
Q

Why is char important and what role does it play in arid climate soils?

A

-in forest ecosystems, 5-10% of soil OM is char
-in grasslands, 40-50% of soil OM is char
-has many of the same properties as humus
-high CEC

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30
Q

What is peat used for?

A

-use for plant “soil” mixes and other horticultural uses, like turfgrass, and is also burned as fuel source in some places
-it is mined from peat bogs in canada, scotland and russia

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31
Q

Why is the use of peat not recommended?

A

-Peat is a huge natural carbon sink, and when we dig it u and let it decompose (burn it), all of the carbon is released into the atmosphere
-if we stop using peat now, it is estimated that it will take 2000 years to sequester the carbon lost in the past 50 years

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32
Q

What can peat be replaced with?

A

-more sustainable alternatives include coco coir and compost

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33
Q

How mobile in zinc in plants?

A

is not as mobile in plants; signs of deficiency appear in the leaves first

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34
Q

Symptoms of Zinc deficiency?

A

-decrease in stem length and rosetting of terminal leaves
-reduced fruit bud formation
-mottled young leaves (interveinal chlorosis)
-dieback of twigs after first year
-striping or banding on corn leaves

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35
Q

How mobile is iron in plants?

A

is not very mobile; deficiency shows in young leaves first

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36
Q

How mobile is manganese in plants?

A

-not very mobile; deficiency begins in young leaves

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37
Q

How mobile is copper

A

-not very mobile; deficiency begins in young leaves

38
Q

How mobile is boron?

A

boron is mobile in some plants and immobile in other; varies

39
Q

Symptoms of Boron deficiency

A

-intensive cropping and irrigation in western soils have caused boron deficiences to become more common
-irrigation water must be checked for B as well, it can be toxic at low levels
symptoms:
-reduced flowering or improper pollination
-death of terminal growth, causing lateral buds to develop, producing a “witch’s broom” effect
-thickened, curled, wilted and chlorotic leaves
-soft or necrotic spots in fruit or tubers

40
Q

How mobile is molybdenum?

A

-is mobile; moves freely from older to younger tissue

41
Q

How is phosphorous used in plants?

A

-phosphorous stimulates seedling development and root formation
-hasten maturity and promotes seed production

42
Q

When is phosphorus required by plants in the greatest amounts?

A

-during cold weather
-with limited root growth
-with rapid vegetative growth
-in high calcerous soils

43
Q

What are the symptoms of phosphorus deficiency?

A

-slow growth; stunted plants
-purplish coloration on foliage of some plants (older leaves first)
-dark green coloration
-delayed maturity
-poor fruit or seed development

44
Q

What forms of phosphorus are taken up by plants?

A

-primarily taken up as H2PO4- and HPO4=, depending on soil pH
-most of the total soil P is tied up chemically in very slightly soluble compounds–minimizes leaching

45
Q

How available is phosphorus to plants? What factors influence availability?

A

-available soil P may be only 1% or less of the total P present
-the higher the total P in the soil the better the chance of having more P in solution
-cool soil temperatures may induce P deficiency, limited root growth or development in cooler temperature
-maximum availability is between a pH of 6.5-7.5

46
Q

How can you increase P uptake?

A

*when applied with an ammonium form of nitrogen
-increases root growth
-physiological changes making root cells more receptive to P
-increased transfer of phosphorous across the root membranes to the xylem
-lowering of pH

47
Q

How is potassium taken up by plants?

A

-taken up in the form of potassium ions (K+)
-not synthesized into compounds like Nitrogen or Phosphorous

48
Q

How is K used in plants?

A

*essential for the translocation of sugars and for the formation of starch
*required in the opening and closing of stomates by guard cells
Promotes:
-root growth
-increased plant resistance to diseases
-increased size and quality of fruit
-improves winter hardiness

49
Q

How available is K to plants?

A

-soils may take up to 40,000 to 60,000 pounds of K per acre
-90 to 98% of K occurs in primary minerals which are unavailable to plants
-between 1 to 2% is contained in the soil solution and on exchange sites where it is readily available to plants
-large amounts of K are removed from the soil when vegetative, growth is removed–silage, alfalfa

50
Q

What crops require the highest amounts of potassium fertilizer?

A

*plants that produce large amounts of carbohydrates
-potatoes
-grapes
-oranges
-sugar beets

51
Q

What are the symptoms of potassium deficiency?

A

-slow growth
-tip and marginal chlorosis/necrosis starting on more mature leaves
-weak stems and stalks
-small fruit or shriveled seeds

52
Q

How is Ca taken up by plants?

A

taken up as calcium ion Ca++

53
Q

How is Ca used in plants?-Secondary Nutrient

A

-an essential part in cell walls and membranes and must be present for the formation of new cells

54
Q

How mobile is Ca in plant tissue?

A

-once deposited into plant tissue, Ca is not remobilized.

55
Q

What are the symptoms of calcium deficiency?

A

-death of terminal buds, root tips
-abnormal dark green appearance or foliage
-premature shedding of blossoms and buds
-weakened stems
-tip burn of young leaves–celery, lettuce, and cabbage
-water-soaked, discolored areas on fruits–blossom end rot of tomatoes, peppers and melons

56
Q

How is Mg taken up by plants?–Secondary Nutrient

A

-taken up in the form of Mg++

57
Q

How is Mg used in plants?

A

-chlorophyll molecule contains Mg

58
Q

How mobile is Mg in plant tissue?

A

-mobile within plants and readily translocated from older to younger tissue when deficient
-availability is generally higher in western soils
-more often deficient than calcium

59
Q

What are the symptoms of Mg deficiency?

A

-interveinal chlorosis in older leaves
-curling of leaves upward along margins
-marginal yellowing, with green “christmas tree” area along midrib of leaf

60
Q

How is S taken up by plants?–Secondary nutrient

A

-taken up in the form of sulfate ions SO4=
-also can be absorbed as sulfur dioxide SO2 in areas where the atmosphere has been enriched

61
Q

How is S used in plants?

A

-is a constituent of 3 amino acids and is necessary for protein synthesis
-essential for nodule formation of roots
-also responsible for the characteristic odor and taste in garlic and onions

62
Q

How mobile is S in plant tissue?

A

not mobile

63
Q

What are the symptoms of S deficiency?

A

-stunted growth rate and delayed maturity
-Young leaves light green to yellowish color. In some plants older tissue may be affected also
-small and spindly plants

64
Q

Why is nitrogen important to plants?

A

-it is one of the most common deficient nutrients
-plants need relatively large amounts compared to other nutrients
-utilized by plants to synthesize amino acids, the primary components of proteins
-a component of DNA

65
Q

What are the symptoms of nitrogen deficiency?

A

-slow growth; stunted plants
-yellow/green in color (chlorosis)
-death (necrosis) of tips and margins of leaves beginning with more mature leaves

66
Q

What forms of nitrogen are taken up by plants? Which aren’t?

A

-nitrogen is take up by plants primarily as nitrate (NO3) or ammonium (NH4+) ions
-nitrate is mobile in the soil and moves with soil water to plant roots
-Ammonium is bound to the surfaces of soil particles and is not mobile

67
Q

How is nitrogen gas fixed and made available to plants?

A

-Nitrogen makes up about 78% of the earth’s atmosphere, but N2 is not readily available to plants
-N2 can be converted to a plant available form bu rhizobia bacteria fixation, fixation by other soil bacteria, lightening, or recycled from decomposing plant and animal matter–only around 2% of nitrogen in OM becomes available to plants each year

68
Q

Why are rhizobium bacteria important? Describe their attributes.

A

*form a symbiotic relationship with legumes
-they convert atmospheric nitrogen to NO3-, which is absorbed by the plant
-they are located in root nodules
-can fix several hundred lbs of nitrogen per year in cropping ecosystems
-can fix 25-75 lbs of nitrogen per year in natural ecosystems

69
Q

Runoff

A

-applying nitrate fertilizer and irrigating
-afterwards, runoff can go back into canals or other bodies of water

70
Q

Leaching

A

-nitrates move through the soil–still goes back into plant consumption or dentrification

71
Q

Nitrification

A

-comes from OM or fertilizers–can go back into plant consumption or dentrification

72
Q

Mineralization

A

-comes from OM–goes through nitrification and either plant consumption or dentrification

73
Q

Denitrification

A

Nitrates (NO3)–gaseous losses of N2 and N2O

74
Q

How is nitrogen fertilizer made?

A

*Nitrogen based fertilizers are primarily manufactured through the Haber-Bosch process
-100 year old method of heating and pressurizing nitrogen from the air over a hydrogen source (typically from natural gas)

75
Q

What are the causes of erosion?

A

*Geologic Erosion
-wind/water movement over soil
*Soil degradation by humans
-overgrazing
-deforestation
-fuel wood over exploitation
-inappropriate agricultural applications
-urbanization

76
Q

Soil desertification

A

-feedback loop–when land is overgrazed it becomes exposed to wind and water
-it dries out and erodes; water, OM, and nutrients are lost
-this leads to fewer plants, and the cycle spirals

77
Q

Factors that effect erosion

A

*Soil type
-smaller particles are more prone to erosion
*Topography
*Plant Vegetative Cover

78
Q

Methods to reduce erosion in Agriculture

A

-terrace hilly areas
-conservation tillage
-allow weeds and grasses to grow in ditches and waterways

79
Q

T/F: The soils in the SJV are made primarily from colluvial debris

A

False

80
Q

T/F: Soil Texture is the relative percentage of minerals, water and air in soil

A

False

81
Q

T/F:Among sand, silt, and clay, clay has the largest particle size

A

False–Sand

82
Q

How do soils regulate water supplies?

A

act as a filter to clean water

83
Q

What are the soils in dry climates called?

A

Aridosols

84
Q

What are the soils with an accumulation of silicate clay that are moderately leached called?

A

Alfisols

85
Q

What is a loam soil?

A

the properties of the soil are relatively even or moderate

86
Q

What do dendrometers measure?

A

Trunk diameter

87
Q

List 3 issues with providing too much water to plants

A

-wilting
-excess succulent tissue growth, leading to insect pest issues (aphids)
-root rotting diseases

88
Q

How does CEC change the way farmers should apply cationic plant fertilizers?

A

high CEC=high doses of fertilizer at one time
low CEC=divided application into smaller doses to prevent leaching

89
Q

List 4 symptoms of water stress in plants

A

-yellowing (necrosis) of leaves
-dead leaves
-reduced yield
-plant stunting
-wilting

90
Q

How to calculate crop evapotranspiration to determine how much water to apply

A

ETo x Kc(convert to decimal) / DU (convert to decimal)

Soil Science (3 decks)

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