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WorksheetsSoil Science Multiple Choice Worksheet
Total questions: 37
Worksheet time: 19mins
What is the main source of phosphorus in soils?
apatite
phosphorite
apacline
biotite
hematite
Which nutrient does not lead to eutrophication?
K⁺
All these lead to eutrophication
NH₄⁺
NO₃⁻
HPO₄²⁻
What is the estimated CEC (cmolc/kg) of a soil with: • 1000 mg/kg Ca²⁺ (atomic weight 40 mg/mmol) • 80 mg/kg Mg²⁺ (atomic weight 24 mg/mmol) Remember: 1 cmol = 10 mmol. Don’t forget charge.
0.67 cmolc/kg
5 cmolc/kg
0.163 cmolc/kg
1.23 cmolc/kg
2.83 cmolc/kg
Two labs gave different lime recommendations (Texas lab says 4000 lb lime, Iowa lab says 1000 lb lime). Why?
These are close enough to be the same
Recommendations may be for different crops
One lab is obviously wrong
Two different lime requirement tests based on regional buffering capacity
A soil with 1000 mg/kg exchangeable Ca²⁺ has ______ cmolc/kg satisfied by Ca²⁺. (Ca atomic weight = 40 mg/mmol; 1 mmol = 0.1 cmol)
100
5
50
2.5
Base saturation (%) of a soil with: 10 cmolc/kg Ca, 15 cmolc/kg Mg, 1 cmolc/kg H, 2 cmolc/kg K, 1 cmolc/kg Al
93%
29%
100%
27%
97%
Which soil/scenario leads to more P uptake?
soils dominated by Al and Fe oxides
amending soil with potash
adding pyrite to the soil
using crops that form symbiotic mycorrhizae / fostering symbiosis
In alkaline soils, P is often fixed/unavailable due to:
sodium
Fe and Al oxides
Ca carbonates
Fe and Al in solution
What steps are needed to reclaim a sodic soil?
First step is to reduce exchangeable Na⁺ by applying gypsum
First step is to leach out the Na⁺ from soil
After reclamation, monitor soil Na⁺ levels (ESP)
After Ca²⁺ replaces Na⁺, irrigate to flush and leach Na₂SO₄ from soil
Which answer best describes ammonification?
Volatilization of ammonia from ammonium under high pH during drying
Microbial conversion of organic N to ammonium under aerobic conditions
Conversion of ammonium to nitrate under aerobic conditions
Conversion of nitrate to gaseous N under low/no oxygen
Fixation of ammonium in soil minerals (esp. vermiculite)
Best management practices (check all that apply)
Cover crops
Urban greenspaces
Selective Forestry
Riparian Buffers
Conservation Tillage
What happens to pH when neutral salts (CaCl2 or KCl) are added to soil solution? (Example: soil pH 5.5 + CaCl2 pH 7)
Ca2+ replaces acid cations on colloids → soil pH decreases
pH stays the same due to carbonate buffering at pH 5.5
Cl- forms HCl and makes soil extremely acidic
The higher pH salt increases soil pH slightly
Sodic soil reclamation
First irrigate to remove Na+, ensure drainage, then monitor ESP
Give up
First apply gypsum, then irrigate to leach Na2SO4, then monitor ESP
First apply lime, then irrigate to leach Na2SO4, then monitor EC
Identify three of the four colloid groups and arrange by CEC (lowest → highest):
Lowest CEC: Fe and Al oxides 2. Amorphous colloids 3. Phyllosilicate clays 4. Highest: Organic matter
Lowest CEC: Montmorillonite 2. Amorphous colloids 3. Kaolinite 4. Highest: Illite
Lowest CEC: Illite 2. Kaolinite 3. Amorphous colloids 4. Highest: Montmorillonite
Lowest CEC: Amorphous colloids 2. Kaolinite 3. Illite 4. Highest: Montmorillonite
Octahedral layer atomic makeup is:
Si atom surrounded by 8 Al
Si surrounded by 4 O
Si surrounded by 4 O and 2 OH
Al or Mg surrounded by 4 O and 2 OH
18) Hydroponics hemp P experiment: manure highest yield; low vs high phosphate same yield. Best explanation?
Manure provides nutrients other than phosphate that enhance yield.
High phosphate inhibits hemp growth in hydroponics.
Manure increases water retention in hydroponics.
Low phosphate is more effective than high phosphate for hemp.
Which is not an essential plant nutrient?
K⁺
Al³⁺
Ca²⁺
SO₄²⁻
Zn
When hydrolyzed, which cation produces the most H⁺ in soil?
HCl
Al³⁺
H₂S
H⁺
Ca²⁺
3. lbs of P in 100 lb bag of 4-5-1 = _____
5 lbs
4 lbs
1 lb
2 lbs
Which cations involved in CEC are more common on colloid surfaces at pH 7.5?
H⁺ and Al³⁺
Ca²⁺, Mg²⁺, K⁺
Colloid charges dependent on soil pH are due to:
soil moisture content
organic matter amount
broken edges/functional groups protonated or deprotonated
isomorphic substitution
What factors affect soil CEC?
Soil texture
Type of colloid
Amount of soil organic matter
Soil pH
All of the above
When are you most likely to observe micronutrient deficiency?
intensively cropped or NPK-only fertilized soils
very alkaline soils
highly leached, acidic soils
sandy soils
all of the above
Why did it take ~180 kg/ha fertilizer N for continuous corn to reach the yield of corn rotated with soybean with no fertilizer?
Soybeans provide lots of P; law of minimum improves corn N uptake
Corn rotated with soybean is fertilized more than continuous corn
Corn uptake from soil+fertilizer N was the same in both systems
Soybeans fix N via symbiosis; residues/exudates supply N for following corn
Under what conditions can soil colloids have a net positive charge?
More likely in alkaline arid saline/sodic soils
Only occurs in 2:1 silicates due to isomorphic substitution
Never; soils always net negative
Low pH soils: high H+ binds to edge oxygen at broken edges of pH-dependent colloids
Occurs in OM-rich saturated Histosols due to hydrated cation interactions
Saline and sodic soils more likely in which soil order?
aridisol
spodosol
andisol
ultisol
salicisol
Applying ______ can reduce soil pH, whereas applying ______ can increase soil pH.
Applying ammonium-based fertilizers
can reduce soil pH, whereas applying lime can increase soil pH.
Applying lime can reduce soil pH, whereas applying sulfur can increase soil pH.
Applying nitrogen can reduce soil pH, whereas applying phosphorus can increase soil pH.
Applying compost can reduce soil pH, whereas applying sand can increase soil pH.
Order cations by retention strength (lowest → highest): Cations: K+, Ca2+, Al3+
Lowest: K+ Ca2+ Highest: Al3+
Lowest: Ca2+ K+ Highest: Al3+
Lowest: Al3+ Ca2+ Highest: K+
Lowest: Ca2+ Al3+ Highest: K+
Which processes contribute to soil acidification over time?
denitrification
continuous crop production (fertilizers + crop removal)
weathering of minerals rich in Ca, K, etc. releasing base cations
leaching of cations
What happens when calcitic lime is added to soil with pH < 6?
Ca²⁺ dissociates; replaces Al³⁺/H⁺; H⁺ reacts with CO₃²⁻ → H₂CO₃ → CO₂ + H₂O; acidity neutralized; pH increases
Ca²⁺ replaces Al³⁺/H⁺; Al³⁺ hydrolyzes producing H⁺; pH decreases
Buffering from CO₃²⁻ prevents any pH change
None of these
I have no idea
Which statements about saline/sodic soils are true?
Saline soils have high salts (EC > 4 dS/m), usually Mg and Ca salts
Sodic soils: high pH, generally not saline (low EC), but ESP > 15% (high Na)
Saline soils generally have pH under 8.5
All of these answers are true
Best description of biological N fixation:
NO₃⁻ → NH₄⁺ under low O₂ by symbiotic microbes
N₂ → organic N by microbes in symbiosis with plant host
Organic N → inorganic N by Nitrosomonas/Nitrobacter
N₂ → organic N by mycorrhizae symbiosis
Plant–mycorrhizae symbiosis
Rice field: ammonium nitrate applied, then flooded until harvest; rice appears N-deficient. Why?
N leached easily; lost with floodwater
Other nutrients were limiting (law of minimum)
Fertilizer form not plant-available; needed mineralization
Fertilizer volatilized as N₂, N₂O, or NO due to denitrification
N mineralization can’t occur under flooded conditions
Ammonia volatilization is more likely:
in water-saturated anaerobic soils
in alkaline soils that are drying
during lightning strikes
Why is soil pH important?
affects plant and microbial growth
affects nutrient availability and toxicity
affects CEC
all of the above
Permanent charge in 2:1 phyllosilicate clays is due to:
isomorphic substitution (crystal imperfections)
amount of organic matter
broken edges/functional groups protonated/deprotonated
soil moisture content
Calculate the total estimated CEC for the soil sample.10% Smectite [CEC = 150 cmolc/kg]
5% Mica [CEC = 30 cmolc/kg]
2% Kaolinite [CEC = 10 cmolc/kg]
1% Organic Matter [CEC = 200 cmolc/kg]
hint: don't forget that % need to be divided by 100
10 meq/100g
18.7 cmolc/kg
5 meq/100g
40 meq/100g
