Soil Organic Matter MCQs Quiz 5

1. _______ reduces soil organic matter (SOM) stabilization

 Soil aggregation

 High clay content

 Mineral binding

 Sandy soil texture

2. In soil science, humification refers to _______

 Downward movement of dissolved organic matter through the soil profile

 Complete decomposition of organic matter to CO₂

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

 Formation of humic substances

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

 Gravel

 Sand

 Clay

 Quartz

4. A positive priming effect in soil results in _______

 No change in soil carbon dynamics

 Increased decomposition of native soil organic matter (SOM)

 Enhanced carbon sequestration without affecting decomposition

 Reduced microbial activity

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

 Overgrazing of pastures

 Cover cropping

 Burning crop residues

 Intensive conventional plowing

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

 Low temperature

 Warm and moist conditions

 Dry soil

 Frozen soil (permafrost)

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

 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

 Completely mineralize organic carbon to CO₂

 Fix atmospheric CO₂ via autotrophy

8. 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

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

 Months

 Decades to centuries

 Years

 Days

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

 Leaching of dissolved organic carbon to deeper horizons

 Direct plant residue humification

 Microbial processing of plant inputs

 Mineral weathering processes

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Question 1 of 10

Soil Science MCQs