CCA Soil Management 2 — Questions and Answers
Question 1: Which soil property best describes the ability of a soil to resist changes in pH when acids or bases are added?
- Soil plasticity
- Buffer capacity (Correct answer)
- Cation exchange capacity
- Base saturation
Correct answer: Buffer capacity
Buffer capacity refers to a soil's ability to resist pH change when acids or bases are added, which is largely determined by organic matter and clay content.
Question 2: A soil has a bulk density of 1.35 g/cm³ and a particle density of 2.65 g/cm³. What is its total porosity?
- 49% (Correct answer)
- 51%
- 35%
- 65%
Correct answer: 49%
Total porosity = (1 - bulk density/particle density) × 100 = (1 - 1.35/2.65) × 100 ≈ 49%.
Question 3: Which tillage practice involves cutting and mixing residue into the top few inches of soil without full inversion?
- Moldboard plowing
- Subsoiling
- Vertical tillage (Correct answer)
- Deep ripping
Correct answer: Vertical tillage
Vertical tillage uses straight or slightly angled blades to cut and minimally mix residue in the surface layer without inverting the soil profile.
Question 4: Which soil order is characterized by an argillic or natric horizon and is commonly found in semi-arid grasslands?
- Mollisols
- Alfisols (Correct answer)
- Aridisols
- Ultisols
Correct answer: Alfisols
Alfisols have an argillic horizon with moderate-to-high base saturation and are typically found under temperate forests or semi-arid grasslands.
Question 5: What is the primary mechanism by which nitrogen is lost from waterlogged soils?
- Volatilization
- Leaching
- Denitrification (Correct answer)
- Immobilization
Correct answer: Denitrification
Denitrification occurs when anaerobic bacteria convert nitrate (NO₃⁻) to nitrogen gases (N₂, N₂O) under waterlogged, oxygen-depleted conditions.
Question 6: Which aggregate stability test is most commonly used to evaluate a soil's susceptibility to surface sealing and crusting?
- Wet sieve analysis
- Penetrometer reading
- Slake test (Correct answer)
- Atterberg limit test
Correct answer: Slake test
The slake test measures how quickly aggregates break apart when submerged in water, indicating susceptibility to surface sealing and crusting.
Question 7: When managing saline-sodic soils, which amendment is typically applied first to displace sodium before leaching?
- Lime (CaCO₃)
- Gypsum (CaSO₄) (Correct answer)
- Sulfur (S)
- Potassium chloride (KCl)
Correct answer: Gypsum (CaSO₄)
Gypsum supplies calcium that displaces sodium from cation exchange sites, making sodium available for leaching from the root zone.
CCA Soil Management 2
Which soil property best describes the ability of a soil to resist changes in pH when acids or bases are added?