Soil Science & Analysis Flashcards

Which soil horizon is characterized by the accumulation of leached materials such as clay, iron oxides, and organic matter?

Answer: B horizon

The B horizon (subsoil) is the illuvial zone where materials leached from upper horizons accumulate.

What does a soil pH of 4.5 indicate about a forest soil's nutrient availability?

Answer: Likely deficiency of phosphorus and molybdenum with possible aluminum toxicity

At pH 4.5, phosphorus and molybdenum become unavailable while aluminum and manganese reach toxic levels.

In a forest soil with a bulk density of 1.6 g/cm³, which condition is most likely indicated?

Answer: Compaction or lack of structure

Bulk density above 1.4-1.5 g/cm³ typically indicates compaction, which restricts root growth and water infiltration.

What is the primary function of mycorrhizal fungi in forest soils?

Answer: Extending effective root surface area for water and nutrient uptake

Mycorrhizal fungi form symbiotic associations with tree roots, dramatically increasing the absorptive surface area for phosphorus, water, and other nutrients.

Which soil texture class has the highest water-holding capacity per unit volume?

Answer: Silty clay loam

Fine-textured soils like silty clay loam have abundant small pores that retain water against gravity, giving them the highest water-holding capacity.

What is cation exchange capacity (CEC) and why is it important for forest management?

Answer: The soil's ability to hold positively charged nutrient ions; indicates nutrient retention potential

CEC measures how many cations a soil can hold and exchange with plant roots, directly indicating its fertility and resistance to nutrient leaching.

Which diagnostic horizon defines a Spodosol in USDA soil taxonomy?

Answer: Spodic horizon with accumulated organic matter and aluminum/iron oxides

Spodosols are defined by the presence of a spodic horizon — a subsurface zone of illuvial organic matter and sesquioxides, common under coniferous forests.