B.S.F. or B.Sc.F. Bachelor of Science in Forestry Bachelor of Science in Forestry: Soil Science and Forest Health 2 — Questions and Answers
Question 1: Which soil horizon is typically referred to as the 'zone of leaching' where minerals and organic matter are washed downward?
- A horizon
- E horizon (Correct answer)
- B horizon
- C horizon
Correct answer: E horizon
The E horizon is the eluviation layer where clay, iron, aluminum, and organic matter are leached downward by percolating water.
Question 2: A forester observes that trees in a stand are exhibiting interveinal chlorosis on young leaves. Which micronutrient deficiency is most likely responsible?
- Calcium
- Iron (Correct answer)
- Manganese
- Zinc
Correct answer: Iron
Iron deficiency causes interveinal chlorosis specifically in young leaves because iron is immobile in plants and new growth shows symptoms first.
Question 3: Cation exchange capacity (CEC) is highest in soils dominated by which clay mineral?
- Kaolinite
- Illite
- Smectite (montmorillonite) (Correct answer)
- Chlorite
Correct answer: Smectite (montmorillonite)
Smectite clays have an expandable lattice structure with very high surface area, giving them the highest CEC of common clay minerals.
Question 4: In forest soils of the southeastern US, Phytophthora cinnamomi causes a root rot disease that is most severe under which soil condition?
- Well-drained sandy soils
- Poorly drained, waterlogged soils (Correct answer)
- Highly acidic peat soils
- Calcareous limestone soils
Correct answer: Poorly drained, waterlogged soils
Phytophthora cinnamomi thrives and spreads its zoospores most effectively in poorly drained, saturated soils where anaerobic conditions develop.
Question 5: Which of the following best describes the role of ectomycorrhizal fungi in forest nutrient cycling?
- They fix atmospheric nitrogen directly into soil
- They extend the effective root surface area and enhance mineral nutrient uptake (Correct answer)
- They decompose lignin in woody debris
- They convert ammonium to nitrate for plant uptake
Correct answer: They extend the effective root surface area and enhance mineral nutrient uptake
Ectomycorrhizal fungi form a sheath around tree roots and extend hyphae far into the soil, dramatically increasing the volume of soil explored for water and nutrients like phosphorus.
Question 6: Bulk density of forest soils is typically lower than agricultural soils because of:
- Higher clay content in forest soils
- Greater organic matter accumulation and reduced compaction (Correct answer)
- Lower annual precipitation in forested regions
- Higher proportion of coarse rock fragments
Correct answer: Greater organic matter accumulation and reduced compaction
Forest soils accumulate organic matter from leaf litter and have little mechanical disturbance, resulting in more pore space and lower bulk density than tilled agricultural soils.
Question 7: The Humus-Carbonate soil type common in high-elevation spruce-fir forests is characterized by a thick accumulation of which organic layer?
- Mull humus integrated with mineral soil
- Mor humus with a distinct Oi/Oe/Oa horizon sequence (Correct answer)
- Moder humus with partial mixing by earthworms
- Anmoor humus in seasonally flooded soils
Correct answer: Mor humus with a distinct Oi/Oe/Oa horizon sequence
Mor humus forms under cool, moist conditions with acidic litter where decomposition is slow, producing distinct organic layers that remain separate from the mineral soil.
B.S.F. or B.Sc.F. Bachelor of Science in Forestry Bachelor of Science in Forestry: Soil Science and Forest Health 2
Which soil horizon is typically referred to as the 'zone of leaching' where minerals and organic matter are washed downward?