CLARB Soils and Geology

Question 1

What USDA soil texture classification contains a balanced mixture of sand, silt, and clay in roughly equal proportions?

Accepted Answer

Loam

Answer

Loam is the USDA texture class that contains approximately 25-50% sand, 25-50% silt, and 10-25% clay, making it ideal for most plant growth.

Question 2

Which soil horizon is commonly referred to as 'topsoil' and contains the highest concentration of organic matter?

Accepted Answer

A horizon

Answer

The A horizon (topsoil) is the uppermost mineral soil layer and contains the greatest accumulation of organic matter and biological activity.

Question 3

What term describes the maximum amount of water a soil can hold after excess gravitational water has drained away?

Accepted Answer

Field capacity

Answer

Field capacity is the soil moisture content remaining after gravitational drainage has ceased, typically reached 24-48 hours after saturation.

Question 4

Which pH range is considered slightly acidic and generally optimal for most landscape plants?

Accepted Answer

5.5–6.5

Answer

A pH of 5.5–6.5 allows maximum nutrient availability for most plants, as key nutrients like nitrogen, phosphorus, and potassium are most soluble in this range.

Question 5

Which soil property describes the soil's ability to resist pH changes when acids or bases are added?

Accepted Answer

Buffer capacity

Answer

Buffer capacity measures how resistant soil is to pH change; soils high in organic matter or clay tend to have greater buffering ability.

CLARB - Council of Landscape Architectural Registration Boards Practice Test

CLARB - Council of Landscape Architectural Registration Boards Practice Test

CLARB Soils and Geology