B.S.F. or B.Sc.F. Bachelor of Science in Forestry Bachelor of Science in Forestry: Soil Science and Forest Health 3 — Questions and Answers
Question 1: Which soil property most directly controls the rate at which water enters the soil surface during a rainfall event?
- Soil texture
- Hydraulic conductivity and infiltration rate (Correct answer)
- Soil color
- Base saturation percentage
Correct answer: Hydraulic conductivity and infiltration rate
Hydraulic conductivity and infiltration rate determine how quickly water moves into and through the soil, controlling runoff potential during rain events.
Question 2: Armillaria root disease in conifers spreads primarily through the soil via:
- Airborne basidiospores landing on root wounds
- Rhizomorphs growing through soil and contacting healthy roots (Correct answer)
- Nematode vectors carrying fungal propagules
- Waterborne mycelium in saturated soils
Correct answer: Rhizomorphs growing through soil and contacting healthy roots
Armillaria species produce string-like rhizomorphs (bootlaces) that grow through soil and infect healthy roots through direct contact with colonized stumps or roots.
Question 3: In a forest soil profile, a dense, brittle subsurface layer that restricts root penetration and water movement is called a:
- Fragipan (Correct answer)
- Duripan
- Argillic horizon
- Albic horizon
Correct answer: Fragipan
A fragipan is a dense, brittle subsurface horizon that appears cemented when dry but slakes when moist, restricting root and water penetration in forest soils.
Question 4: Foliar nitrogen content in forest trees is a useful indicator of soil nitrogen availability primarily because:
- Nitrogen is immobile in the phloem and accumulates in older leaves
- Leaf N concentration reflects long-term soil N supply integrated over the growing season (Correct answer)
- Atmospheric nitrogen deposition is measured directly in foliage
- Trees store excess nitrogen in leaves as a reserve for future use
Correct answer: Leaf N concentration reflects long-term soil N supply integrated over the growing season
Foliar N concentration integrates soil nitrogen availability over the growing season since trees allocate nitrogen proportionally to photosynthetic demand relative to supply.
Question 5: Which process is primarily responsible for converting organic nitrogen in forest floor litter to plant-available ammonium?
- Nitrification
- Denitrification
- Ammonification (mineralization) (Correct answer)
- Nitrogen fixation
Correct answer: Ammonification (mineralization)
Ammonification is the microbial decomposition of organic nitrogen compounds (amino acids, proteins) into ammonium (NH4+), the first step making N plant-available.
Question 6: Sulfur dioxide emissions from coal combustion contribute to forest decline by causing:
- Soil alkalinization reducing micronutrient availability
- Acid deposition that leaches base cations and increases aluminum toxicity in roots (Correct answer)
- Nitrogen saturation in forest ecosystems
- Ozone formation that damages leaf cuticles
Correct answer: Acid deposition that leaches base cations and increases aluminum toxicity in roots
SO2 dissolves in precipitation to form sulfuric acid, which acidifies soil, displaces calcium and magnesium from exchange sites, and releases toxic aluminum ions harmful to tree roots.
Question 7: The USDA Soil Taxonomy classification for a soil with a spodic horizon (accumulation of illuviated organic matter and aluminum/iron) is:
- Ultisol
- Spodosol (Correct answer)
- Inceptisol
- Alfisol
Correct answer: Spodosol
Spodosols are defined by the presence of a spodic horizon, where organic matter chelated with aluminum and iron is deposited below an eluviated E horizon, common under coniferous forests.
B.S.F. or B.Sc.F. Bachelor of Science in Forestry Bachelor of Science in Forestry: Soil Science and Forest Health 3
Which soil property most directly controls the rate at which water enters the soil surface during a rainfall event?