ESA ESA Soil Science & Biogeochemistry

Question 1

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

Accepted Answer

B horizon

Answer

The B horizon (subsoil) is the zone of illuviation where materials translocated from upper horizons accumulate.

Question 2

The primary driver of nitrogen fixation in terrestrial ecosystems is:

Accepted Answer

Biological N2 fixation by diazotrophic microorganisms

Answer

Biological nitrogen fixation by diazotrophs (e.g., Rhizobium, free-living cyanobacteria) is the dominant pathway converting atmospheric N2 to bioavailable forms.

Question 3

Cation exchange capacity (CEC) of a soil is primarily determined by:

Accepted Answer

Clay content, clay mineralogy, and organic matter content

Answer

CEC reflects the abundance of negatively charged sites on clay particles and organic matter surfaces that retain exchangeable cations.

Question 4

Which process converts ammonium (NH4+) to nitrate (NO3−) in soils?

Accepted Answer

Nitrification

Answer

Nitrification is a two-step aerobic microbial process: ammonia-oxidizing bacteria convert NH4+ to NO2−, which nitrite-oxidizing bacteria then convert to NO3−.

Question 5

Soil organic matter decomposition is primarily regulated by which set of factors?

Accepted Answer

Temperature, moisture, and substrate quality (C:N ratio)

Answer

Decomposition rates are controlled by temperature and moisture availability, which govern microbial activity, and by litter chemistry (C:N ratio, lignin content).

ESA - Ecological Society of America Certified Ecologist Practice Test

ESA - Ecological Society of America Certified Ecologist Practice Test

ESA ESA Soil Science & Biogeochemistry