Soil Organic Matter MCQs Quiz 5

1. _______ reduces soil organic matter (SOM) stabilization

 Soil aggregation

 Mineral binding

 High clay content

 Sandy soil texture

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

 Low temperature

 Dry soil

 Frozen soil (permafrost)

 Warm and moist conditions

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

 Cover cropping

 Intensive conventional plowing

 Burning crop residues

 Overgrazing of pastures

4. Mineralization in soil nutrient cycling is _______

 Fixation of atmospheric carbon

 Conversion of inorganic forms to organic forms

 Conversion of organic forms to inorganic forms

 Formation of stable humus

5. In soil science, humification refers to _______

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

 Formation of humic substances

 Downward movement of dissolved organic matter through the soil profile

 Complete decomposition of organic matter to CO₂

6. 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

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

 Days

 Months

 Decades to centuries

 Years

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

 Quartz

 Gravel

 Clay

 Sand

9. 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

 Mineral weathering processes

 Direct plant residue humification

10. A positive priming effect in soil results in _______

 Reduced microbial activity

 Enhanced carbon sequestration without affecting decomposition

 Increased decomposition of native soil organic matter (SOM)

 No change in soil carbon dynamics

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