Soil Organic Matter MCQs Quiz 5

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

 Direct plant residue humification

 Leaching of dissolved organic carbon to deeper horizons

 Microbial processing of plant inputs

 Mineral weathering processes

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

 Cover cropping

 Burning crop residues

 Intensive conventional plowing

 Overgrazing of pastures

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

 Clay

 Sand

 Quartz

 Gravel

4. _______ reduces soil organic matter (SOM) stabilization

 Sandy soil texture

 High clay content

 Soil aggregation

 Mineral binding

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

 Leach dissolved organic carbon (DOC) to deeper soil layers

 Completely mineralize organic carbon to CO₂

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

 Fix atmospheric CO₂ via autotrophy

6. A positive priming effect in soil results in _______

 No change in soil carbon dynamics

 Enhanced carbon sequestration without affecting decomposition

 Reduced microbial activity

 Increased decomposition of native soil organic matter (SOM)

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

 Frozen soil (permafrost)

 Low temperature

 Dry soil

 Warm and moist conditions

8. Mineralization in soil nutrient cycling is _______

 Formation of stable humus

 Conversion of inorganic forms to organic forms

 Conversion of organic forms to inorganic forms

 Fixation of atmospheric carbon

9. In soil science, humification refers to _______

 Formation of humic substances

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

 Complete decomposition of organic matter to CO₂

 Downward movement of dissolved organic matter through the soil profile

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

 Decades to centuries

 Days

 Months

 Years

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Soil Science MCQs