FM FM Soil Science & Hydrology 1 — Questions and Answers
Question 1: Which soil property most directly determines water infiltration rates in forest soils?
- Soil color
- Soil texture (Correct answer)
- Depth to bedrock
- Organic matter color
Correct answer: Soil texture
Soil texture (the ratio of sand, silt, and clay) controls pore size distribution, which determines how quickly water can move into and through the soil.
Question 2: Which soil horizon typically contains the highest concentration of organic matter in a forest soil profile?
- B horizon
- C horizon
- A horizon (Correct answer)
- R horizon
Correct answer: A horizon
The A horizon (topsoil) accumulates organic matter from decomposing plant material above and supports the highest biological activity.
Question 3: What is 'field capacity' in the context of forest soil hydrology?
- The maximum water a soil holds when fully saturated
- The minimum water available to plants before wilting
- The amount of water soil retains after gravitational drainage (Correct answer)
- The rate at which water moves through the soil profile
Correct answer: The amount of water soil retains after gravitational drainage
Field capacity is the water content remaining in soil after excess gravitational water has drained away, representing the upper limit of plant-available water.
Question 4: Which process describes the downward movement of water through soil layers toward groundwater?
- Evapotranspiration
- Interception
- Percolation (Correct answer)
- Overland flow
Correct answer: Percolation
Percolation refers to the gravitational movement of water downward through soil pores and fractures toward deeper layers and the water table.
Question 5: In a mature, undisturbed forest watershed, what approximate percentage of annual precipitation typically becomes streamflow?
- 70–80%
- 50–60%
- 10–30% (Correct answer)
- 40–50%
Correct answer: 10–30%
Mature forests intercept, evaporate, and transpire the majority of precipitation, so only 10–30% typically reaches streams as streamflow under normal conditions.
Question 6: What is the primary hydrological function of riparian buffer zones in forest management?
- Increase timber production near streams
- Filter sediment and nutrients from runoff before it enters streams (Correct answer)
- Reduce wildlife movement corridors
- Raise stream water temperatures in winter
Correct answer: Filter sediment and nutrients from runoff before it enters streams
Riparian buffers trap suspended sediments and absorb nutrients from upslope runoff, protecting stream water quality and aquatic habitat.
Question 7: Which soil classification system is the standard used in US forest soil surveys and management?
- World Reference Base (WRB)
- Canadian System of Soil Classification
- FAO Soil Classification
- USDA Soil Taxonomy (Correct answer)
Correct answer: USDA Soil Taxonomy
The USDA Soil Taxonomy is the official classification system used by the NRCS and US Forest Service for describing and mapping forest soils across the country.
FM FM Soil Science & Hydrology 1
Which soil property most directly determines water infiltration rates in forest soils?