Soil Organic Matter MCQs Quiz 3

1. Recalcitrant carbon in soils is characterized as _______

 Short-lived

 Highly soluble

 Resistant to microbial breakdown

 Easily decomposable

2. The C:N ratio of stable SOM is approximately _______

 20-25:1

 10–12:1

 2-5:1

 40-50:1

3. Soil organic matter (SOM) enhances soil water retention by _______

 Blocking soil pores

 Increasing soil water holding capacity

 Reducing water infiltration

 Increasing surface runoff

4. In soil microbiology, carbon use efficiency (CUE) refers to the fraction of assimilated carbon that is ______

 Converted into microbial biomass

 Fixed from inorganic carbon via photosynthesis

 Lost as CO₂ via respiration

 Lost through leaching of dissolved organic carbon

5. In soil organic matter (SOM) models (e.g., the three-pool model), the intermediate pool with a turnover time of several years to decades is most commonly referred to as _______

 Dissolved organic carbon (DOC)

 Mineral-associated organic matter (MAOM)

 Particulate organic matter (POM)

 Soil organic carbon (SOC)

6. In soil science, biochar is best classified as _______

 Labile carbon

 Recalcitrant carbon

 Dissolved organic carbon

 Microbial biomass

7. Immobilization in soil nutrient cycling is _______

 Fixation of atmospheric carbon

 Loss of nutrients through leaching

 Microbial uptake and assimilation of inorganic nutrients

 Release of nutrients into the soil solution

8. Soil respiration primarily measures _______

 Water loss through evaporation

 Carbon dioxide (CO₂) release from soil organisms

 Nitrogen fixation rates

 Oxygen uptake by roots

9. In standard soil organic matter (SOM) models (e.g., the three-pool model), the most stable pool with the slowest turnover rate is referred to as the _______

 Active pool

 Dissolved organic carbon

 Intermediate pool

 Passive pool

10. Microbial biomass contributes to soil organic matter (SOM) primarily by _______

 Forming microbial necromass that stabilizes organic matter

 Eliminating essential nutrients

 Reducing soil aggregation

 Reducing soil carbon content

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Soil Science MCQs