Soil Organic Matter MCQs Quiz 4

1. In soils, iron (Fe) and aluminum (Al) oxides stabilize soil organic matter (SOM) primarily via _______

 Indirect stimulation of microbial activity

 Weak van der Waals bonding

 Ligand exchange

 Physical trapping only within large pores

2. Soil organic matter (SOM) improves soil structure by _______

 Promoting aggregate formation and stability

 Reducing water infiltration

 Increasing soil compaction

 Reducing soil porosity

3. In soil science, the “priming effect” refers to _______

 Conversion of inorganic carbon (e.g., CO₂) into organic carbon via microbial fixation

 Complete inhibition of microbial activity due to toxic compounds

 Stabilization of soil organic matter (SOM) against decomposition

 A change in the decomposition rate of native Soil Organic Matter following the addition of fresh organic inputs

4. The mechanism underlying the priming effect is primarily associated with _______

 Enhanced microbial activity and extracellular enzyme production

 Chemical weathering only

 Leaching of nutrients

 Physical breakdown of soil aggregates

5. ______________ is considered as the largest terrestrial carbon pool

 Atmosphere

 Vegetation

 Soil

 Oceans

6. In soil science and biogeochemistry, the acronym DOC stands for _______

 Dynamic organic carbon

 Dissolved organic carbon

 Decomposed organic carbon

 Dry organic carbon

7. The cation exchange capacity (CEC) of soil increases with Soil Organic Matter primarily because of _______

 Mineral particle size only

 Positive surface charges

 Negative functional groups

 Soil water content

8. Which of the following practices is a primary cause of soil organic matter (SOM) depletion?

 Crop residue retention

 Application of organic amendments

 Cover cropping

 Intensive tillage

9. Root-derived carbon in soils is generally _______

 Inorganic in nature

 More stable due to stronger interactions with soil minerals

 Rapidly lost through leaching

 Less stable than surface litter inputs

10. In soil biogeochemistry, the Q₁₀ coefficient represents _______

 Temperature sensitivity of a biological process e.g., SOM decomposition

 Gravimetric moisture content of soil

 Rate of carbon input from plant litter

 Change in soil pH per 10°C increase

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Soil Science MCQs