Soil Science & Analysis Flashcards

Which USDA soil order is most commonly associated with the shrink-swell behavior caused by high smectite clay content?

Answer: Vertisol

Vertisols are defined by their high shrink-swell clay content (primarily smectite), which causes them to crack deeply when dry and heave when wet, creating diagnostic slickensides and gilgai microrelief.

A soil percolation rate of 60 minutes per inch is generally considered which of the following for conventional septic system design?

Answer: Failing — too slow for any septic application

Most regulatory standards consider percolation rates slower than 60 minutes per inch as too slow for conventional leach fields because effluent cannot move through the soil fast enough to prevent surfacing.

The Universal Soil Loss Equation (USLE) factor 'K' specifically represents which soil characteristic?

Answer: Soil erodibility based on texture, structure, permeability, and organic matter

The K factor in the USLE quantifies the inherent susceptibility of a soil to erosion based on its texture, structure, organic matter content, and permeability.

Which of the following best describes a hydric soil as defined by the USDA NRCS for wetland delineation purposes?

Answer: A soil formed under conditions of saturation, flooding, or ponding long enough to develop anaerobic conditions in the upper part

Hydric soils are defined by the USDA NRCS as soils that formed under conditions of saturation, flooding, or ponding for long enough during the growing season to develop anaerobic conditions in the upper part.

Which soil property is MOST directly used to estimate the plant-available water holding capacity (AWC) of a soil?

Answer: The difference between field capacity and permanent wilting point moisture content

Available water capacity (AWC) is the amount of water held between field capacity (~-0.33 bar) and permanent wilting point (~-15 bars), representing water that plants can actually extract.

When a soil survey report describes a soil as having 'moderate' shrink-swell potential, which clay mineral is MOST likely responsible?

Answer: Illite

Illite has a moderate CEC and intermediate shrink-swell potential compared to low-activity kaolinite and high-activity smectite, making it the most likely candidate for 'moderate' ratings.

In soil contamination remediation planning, 'in situ' treatment methods are preferred over 'ex situ' methods primarily because they:

Answer: Avoid the costs and risks of excavating and transporting contaminated soil

In situ methods treat contamination in place, eliminating the substantial cost, liability, worker exposure, and logistical challenges associated with excavating and transporting large volumes of contaminated material.