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soil > ch.10 > Flashcards

ch.10 Flashcards

1
Q

Major Elements

A

Carbon, Hydrogen, Oxygen
- Come from air and water and make mostly carbohydrates

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2
Q

Macro-nutrients

A

Nitrogen, Phosphorus, Potassium, Calcium, Magnesium, Sulfur
- Come from special bacteria, decaying organic matter, or weathering minerals in the soil

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3
Q

Micro-nutrients

A

Iron, Zinc, Manganese, Cobalt, Copper, Molybdenum, Sodium, Chlorine, sometimes Silicon, and others

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4
Q

Three Most Important Macro-nutrients

A

Nitrogen (N), Phosphorous (P), and Potassium (K)
- Amounts listed on front of fertilizer bags

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5
Q

Mechanisms of Nutrient Uptake: Nutrient Movement in Soil

A

Mass Flow
Diffusion
Interception

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6
Q

Mass Flow

A

Carried in gravitational water

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7
Q

Diffusion

A

From areas of high to low concentration in soil water

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8
Q

Interceptions

A

Roots grow into areas of nutrient concentration

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9
Q

Mechanism of Nutrient Uptake: Nutrient Absorption by Plant Roots

A
  • Passive Intake
  • Active Intake
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10
Q

Root cells contain membranes that are “semipermeable”; …

A

let certain ions in, keep others out

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11
Q

Passive Intake

A

Water and nitrate flow easily into root cells under normal conditions

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12
Q

Active Intake

A

Phosphorus and Potassium taken into root only by opening and closing special doors in the membrane, which takes energy from the plant

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13
Q

Nitrogen

A
  • Most important agricultural nutrient
  • Protein
  • Locked up in organic matter or soil air as N2 gas
  • “Fixation” : made into usable form
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14
Q

Microbial Nitrogen Fixation

A

Special enzyme called “Nitrogenase”
- Symbiotic
- Free Living

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15
Q

Symbiotic

A

By bacteria inhabiting plant roots
- Mostly Rhizobium, and Alder
- N2 to NH4
- Provides sugar and housing
- 330 lb/A of Nitrogen per year

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16
Q

Free Living

A

By bacteria living in soil rhizosphere
- Azotobacter main
-50 lb/A of Nitrogen per year

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17
Q

Mineralization of Nitrogen

A
  • Soil organic matter contains 5% N
  • Only reusable when released as NH4
  • Natural decompostiton releases about 80 lb/A per year of rich soils. less in the West
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18
Q

Nitrification - NH4 to NO3

A
  • Ammonia (NH4+) is tightly held on the soil exchange
  • NO3 is much more immediately available to plants
  • Several soil microbes (Nitrosomonas, Nitrobacter), can do this within weeks on warm, wet soils, even after heavy NH4 applications
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19
Q

Nitrogen Losses

A
  • Leaching
  • Denitrification
  • Volatilization
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20
Q

Leaching

A

Nitrate is negatively charged = easily leaches
- Can easily pollute groundwater
- 20 lb/A loss per year
- Ammonia (NH4) fert. for slow leaching

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21
Q

Denitrification

A

NO3 can be changed back to N2 gas by certain soil bacteria
- about 15% loss of available Nitrogen per year

22
Q

Volatilization

A

Ammonia can vaporize off as a gas
- Especially in basic soils
- 20% Nitrogen loss

23
Q

Nitrogen Fertalizers

A
  • Anhhydrous Ammonia (NH3)
  • Urea (CO(NH2)2)
  • Ammonium Nitrate (NH4NO3)
  • Ammonium SUlfate (NH4SO4)
24
Q

Nitrogen Others

A
  • Organic Wastes
  • Slow release formulations
25
Q

Anhydrous Ammonia (NH3)

A
  • Most common commercial formulation
  • Relatively cheap
  • App. w/ injection machines under pressure
  • Rel. hazardous, very caustic, must use protective equipment
26
Q

Urea (CO(NH2)2)

A
  • Naturally urine, but also made synthetically
  • Slow release and safe
  • Mod. price
  • Granular or liquid
27
Q

Ammonium Nitrate (NH4NO3)

A
  • Highest analysis for Nitrogen at about 45% by weight
  • very rapid avail. of Nitrate and Ammonium
  • Explosives, not sold anymore
28
Q

Ammonium Sulfate (NH4SO4)

A
  • 21% Nitrogen by weight
  • Also supplies needed Sulfur
  • Most used Granular, non-commerical
  • Strong acid former
29
Q

Organic Wastes

A

Composts, Manures, Sludge
- Only 1-8% Nitrogen
- Very expensive for large areas
- Not economical, mostly organic amendments

30
Q

Slow release formulations

A

Special mixed formulations that release over extended periods
- Polyform UF, Ureaform, Osmocote, Sulfocote, etc.
- Very expensive
- Used exclusively for ornamentals

31
Q

Phosphorus

A
  • Second most important
  • All energy reactions (ATP)
  • Most imp. for legumes (pea fam)
  • Plenty is western soils
  • Very slowly released from soils to plants
32
Q

Minerals 1

A

“Apatite” or rock phosphate (CaS(PO4)3)F

33
Q

Minerals 2

A
  • Most common soil minerals cont. phosphorous
  • Slowly hydrolyzes to phosphoric acid via several insoluble intermediates
    • Fast @ pH 6.5
    • Mycorrhizal fungi
      break down
      materials much
      faster
    • Moves in soil sol.
      rapidly once
      hydrolized
34
Q

Organic Matter

A

Up to 80% of soil P from OM
- Supplies half needed P in crops in MidWest
- Broken off from soil OM by phosphatase enzyme from plant roots and soil microbes
- Phosphates also major enzyme found in Mycorrhizal fungi

35
Q

Phosphorus Fertilizers

A
  • Pure Rock Phosphate
  • Phosphoric Acid
  • Superphosphate
  • Concentrated or Triple Superphosphate
36
Q

Pure Rock Phosphate

A

Ground up Apatite
- About 32% P, almost none quickly to plant
- Cheap, further refining

37
Q

Phosphoric Acid

A

Byproduct of refining process, often sold as fertalizer
- about 40% P, much immediately available to plant
- many times liquid form., need special applic.

38
Q

Superphosphate

A

Hydrated Ca phosphate
- Very common fert.
- About 20% usable P, very safe

39
Q

Concentrated or Triple Superphosphate

A

Less hydrated and more concentrated calcium phosphate
- Very common, home use
- Abt 45% usable P
- Very safe
- Fairly expensive

40
Q

Potassium

A
  • Total soil is huge, esp in West, but most tied up in minerals, not soluble
  • Very slow weathering from mice and feldspar
  • Abt 150% ib/A avail. in most soils, high production crops need more
  • Needed for plant cell membrane function including water Uptake and disease resistance
  • Very non soluble in acid soils, needed east more than out west
41
Q

Potassium Losses

A
  • Luxury consumption
  • Soil microbes
  • Clay particles
  • Leaching
42
Q

Luxury Consumption

A

Many plants store Potassium in Amounts higher than needed
- Store much per acre, released after death

43
Q

Soil Microbes

A

Can also concentrate Potassium up to thousands ibs/A
- Released upon microbe death

44
Q

Clay Particles

A

Held tightly to ion exchange, many times too tightly to be released to plant roots
- Overcome by shear amounts in most soils

45
Q

Leaching

A

Only in sandy soils

46
Q

Potassium Gains

A
  • Mineral weathering
  • OM breakdown
  • Released from exchange
47
Q

Minerals Weathering

A

Especially of Mica and Feldspar
- Main release method in low OM western soils

48
Q

OM Breakdown

A

Especially important in eastern soils where it is the main supply mechanism

49
Q

Released from Exchange

A

Depends on Clay type
- 2:1 clays exchange better than 1:1
- Very slow

50
Q

Potassium Fertalizers

A

-Potash (KCI)
- Potassium Sulfate (K2SO4)

51
Q

Potash - Potassium Chloride (KCI)

A

1 Potassium fertalizer in US

  • Mined in western US, Utah and Mexico
  • Salt brine in salt lakes, Searl’s Lake by Trona
  • Add. of CI ion = prob
  • 50% usable potassium
52
Q

Potassium Sulfate (K2SO4)

A
  • Much like potash, no CI ion and good source of sulfur
  • Much more expensive than potash

soil (1 decks)

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