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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
List 3 materials with high C:N ratio
-bark chips -mulch -newspaper
26
What is humus?
-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
27
Why is humus important in soil?
-play a part in plant health, increase water uptake, stimulate root imitation and elongation and enhance growth of shoots -has high CEC
28
What is char?
-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)
29
Why is char important and what role does it play in arid climate soils?
-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
30
What is peat used for?
-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
31
Why is the use of peat not recommended?
-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
32
What can peat be replaced with?
-more sustainable alternatives include coco coir and compost
33
How mobile in zinc in plants?
is not as mobile in plants; signs of deficiency appear in the leaves first
34
Symptoms of Zinc deficiency?
-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
35
How mobile is iron in plants?
is not very mobile; deficiency shows in young leaves first
36
How mobile is manganese in plants?
-not very mobile; deficiency begins in young leaves
37
How mobile is copper
-not very mobile; deficiency begins in young leaves
38
How mobile is boron?
boron is mobile in some plants and immobile in other; varies
39
Symptoms of Boron deficiency
-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
How mobile is molybdenum?
-is mobile; moves freely from older to younger tissue
41
How is phosphorous used in plants?
-phosphorous stimulates seedling development and root formation -hasten maturity and promotes seed production
42
When is phosphorus required by plants in the greatest amounts?
-during cold weather -with limited root growth -with rapid vegetative growth -in high calcerous soils
43
What are the symptoms of phosphorus deficiency?
-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
What forms of phosphorus are taken up by plants?
-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
How available is phosphorus to plants? What factors influence availability?
-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
How can you increase P uptake?
*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
How is potassium taken up by plants?
-taken up in the form of potassium ions (K+) -not synthesized into compounds like Nitrogen or Phosphorous
48
How is K used in plants?
*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
How available is K to plants?
-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
What crops require the highest amounts of potassium fertilizer?
*plants that produce large amounts of carbohydrates -potatoes -grapes -oranges -sugar beets
51
What are the symptoms of potassium deficiency?
-slow growth -tip and marginal chlorosis/necrosis starting on more mature leaves -weak stems and stalks -small fruit or shriveled seeds
52
How is Ca taken up by plants?
taken up as calcium ion Ca++
53
How is Ca used in plants?-Secondary Nutrient
-an essential part in cell walls and membranes and must be present for the formation of new cells
54
How mobile is Ca in plant tissue?
-once deposited into plant tissue, Ca is not remobilized.
55
What are the symptoms of calcium deficiency?
-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
How is Mg taken up by plants?--Secondary Nutrient
-taken up in the form of Mg++
57
How is Mg used in plants?
-chlorophyll molecule contains Mg
58
How mobile is Mg in plant tissue?
-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
What are the symptoms of Mg deficiency?
-interveinal chlorosis in older leaves -curling of leaves upward along margins -marginal yellowing, with green "christmas tree" area along midrib of leaf
60
How is S taken up by plants?--Secondary nutrient
-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
How is S used in plants?
-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
How mobile is S in plant tissue?
not mobile
63
What are the symptoms of S deficiency?
-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
Why is nitrogen important to plants?
-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
What are the symptoms of nitrogen deficiency?
-slow growth; stunted plants -yellow/green in color (chlorosis) -death (necrosis) of tips and margins of leaves beginning with more mature leaves
66
What forms of nitrogen are taken up by plants? Which aren’t?
-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
How is nitrogen gas fixed and made available to plants?
-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
Why are rhizobium bacteria important? Describe their attributes.
*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
Runoff
-applying nitrate fertilizer and irrigating -afterwards, runoff can go back into canals or other bodies of water
70
Leaching
-nitrates move through the soil--still goes back into plant consumption or dentrification
71
Nitrification
-comes from OM or fertilizers--can go back into plant consumption or dentrification
72
Mineralization
-comes from OM--goes through nitrification and either plant consumption or dentrification
73
Denitrification
Nitrates (NO3)--gaseous losses of N2 and N2O
74
How is nitrogen fertilizer made?
*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
What are the causes of erosion?
*Geologic Erosion -wind/water movement over soil *Soil degradation by humans -overgrazing -deforestation -fuel wood over exploitation -inappropriate agricultural applications -urbanization
76
Soil desertification
-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
Factors that effect erosion
*Soil type -smaller particles are more prone to erosion *Topography *Plant Vegetative Cover
78
Methods to reduce erosion in Agriculture
-terrace hilly areas -conservation tillage -allow weeds and grasses to grow in ditches and waterways
79
T/F: The soils in the SJV are made primarily from colluvial debris
False
80
T/F: Soil Texture is the relative percentage of minerals, water and air in soil
False
81
T/F:Among sand, silt, and clay, clay has the largest particle size
False--Sand
82
How do soils regulate water supplies?
act as a filter to clean water
83
What are the soils in dry climates called?
Aridosols
84
What are the soils with an accumulation of silicate clay that are moderately leached called?
Alfisols
85
What is a loam soil?
the properties of the soil are relatively even or moderate
86
What do dendrometers measure?
Trunk diameter
87
List 3 issues with providing too much water to plants
-wilting -excess succulent tissue growth, leading to insect pest issues (aphids) -root rotting diseases
88
How does CEC change the way farmers should apply cationic plant fertilizers?
high CEC=high doses of fertilizer at one time low CEC=divided application into smaller doses to prevent leaching
89
List 4 symptoms of water stress in plants
-yellowing (necrosis) of leaves -dead leaves -reduced yield -plant stunting -wilting
90
How to calculate crop evapotranspiration to determine how much water to apply
ETo x Kc(convert to decimal) / DU (convert to decimal)

Soil Science (3 decks)

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