CCA Soil Management 3 — Questions and Answers
Question 1: Which factor most directly controls the rate of organic matter decomposition in soil?
- Soil color
- Soil temperature and moisture (Correct answer)
- Parent material
- Soil slope
Correct answer: Soil temperature and moisture
Microbial activity driving decomposition is strongly regulated by temperature and moisture, with optimal rates occurring at warm, moist (but not saturated) conditions.
Question 2: A soil test reveals high phosphorus but low pH. Which condition most likely explains the reduced P availability?
- P is leaching below the root zone
- P is being fixed by Al and Fe oxides at low pH (Correct answer)
- P is volatilizing as phosphine gas
- P is immobilized by soil bacteria
Correct answer: P is being fixed by Al and Fe oxides at low pH
At low pH, aluminum and iron oxides become highly reactive and fix phosphorus into insoluble compounds, reducing plant availability.
Question 3: Which soil texture class has the largest total surface area per unit weight and the highest water-holding capacity?
- Sandy loam
- Silt loam
- Clay (Correct answer)
- Loamy sand
Correct answer: Clay
Clay particles have the smallest size and therefore the greatest surface area per unit weight, giving clay soils high water-holding and cation exchange capacity.
Question 4: What is the term for the process where fine clay particles move downward through the soil profile and accumulate in a lower horizon?
- Eluviation
- Illuviation (Correct answer)
- Gleization
- Podzolization
Correct answer: Illuviation
Illuviation is the process of deposition or accumulation of materials transported from upper horizons into a lower horizon, such as clay forming an argillic horizon.
Question 5: Which cover crop is most effective at scavenging residual soil nitrate and preventing winter leaching losses?
- Hairy vetch
- Cereal rye (Correct answer)
- Crimson clover
- Sunn hemp
Correct answer: Cereal rye
Cereal rye is a non-legume with extensive fibrous roots that rapidly takes up residual nitrate in fall and winter, preventing leaching losses.
Question 6: Which soil characteristic is most commonly used to identify the boundary between the A and E horizons in a podzolized soil profile?
- Increase in organic matter
- Loss of clay, iron, and aluminum (Correct answer)
- Accumulation of carbonates
- Higher bulk density
Correct answer: Loss of clay, iron, and aluminum
The E (eluvial) horizon is defined by the loss of silicate clay, iron, and aluminum, leaving a lighter-colored, coarser-textured layer below the A horizon.
Question 7: A field shows wheel-track compaction restricting root growth to the top 6 inches. Which management practice most directly addresses subsoil compaction?
- Surface application of compost
- Chisel plowing to 10 inches
- Subsoiling or deep ripping below the compacted layer (Correct answer)
- Increasing nitrogen fertilizer rate
Correct answer: Subsoiling or deep ripping below the compacted layer
Subsoiling or deep ripping mechanically fractures compacted layers below normal tillage depth, restoring root channels and water infiltration.
CCA Soil Management 3
Which factor most directly controls the rate of organic matter decomposition in soil?