Soil Organic Matter MCQs Quiz 5

1. In current soil science models, soil organic matter (SOM) formation is primarily driven by _______

 Microbial processing of plant inputs

 Leaching of dissolved organic carbon to deeper horizons

 Direct plant residue humification

 Mineral weathering processes

2. _______ reduces soil organic matter (SOM) stabilization

 Mineral binding

 Sandy soil texture

 Soil aggregation

 High clay content

3. Turnover of the passive soil organic carbon (SOC) pool typically occurs over _______

 Decades to centuries

 Years

 Months

 Days

4. _______ mineral fraction stabilizes soil organic matter (SOM) most effectively through chemical binding and physical protection

 Sand

 Gravel

 Clay

 Quartz

5. In soil biogeochemistry, the “microbial carbon pump” refers to the process by which microorganisms _______

 Fix atmospheric CO₂ via autotrophy

 Completely mineralize organic carbon to CO₂

 Leach dissolved organic carbon (DOC) to deeper soil layers

 Convert labile plant-derived carbon into stable soil organic matter (SOM) through microbial necromass and metabolites

6. Which of the following conditions most accelerates soil organic matter (SOM) decomposition?

 Dry soil

 Frozen soil (permafrost)

 Low temperature

 Warm and moist conditions

7. Mineralization in soil nutrient cycling is _______

 Formation of stable humus

 Fixation of atmospheric carbon

 Conversion of inorganic forms to organic forms

 Conversion of organic forms to inorganic forms

8. Which agricultural practice is most effective at increasing soil organic matter (SOM) over time?

 Intensive conventional plowing

 Burning crop residues

 Overgrazing of pastures

 Cover cropping

9. In soil science, humification refers to _______

 Downward movement of dissolved organic matter through the soil profile

 Release of inorganic nutrients (e.g., NH₄⁺, NO₃⁻) from organic matter

 Complete decomposition of organic matter to CO₂

 Formation of humic substances

10. A positive priming effect in soil results in _______

 Increased decomposition of native soil organic matter (SOM)

 No change in soil carbon dynamics

 Enhanced carbon sequestration without affecting decomposition

 Reduced microbial activity

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