Soil Organic Matter MCQs Quiz 13

1. ______________ most strongly enhances oxidation of soil organic matter, leading to net carbon loss

 Clay stabilization

 Continuous organic inputs

 Frequent tillage causing aeration and microbial oxidation

 Reduced temperature

2. Formation of stable organic compounds from decomposed matter is called __________

 Immobilization

 Oxidation

 Mineralization

 Humification

3. ______________ is generally considered the most strongly limiting factor for lignin-degrading enzyme activity in soils

 High nitrogen content

 Potassium deficiency

 Soil texture

 Oxygen availability

4. During decomposition of soil organic matter, proteins serve as a major source of _________________

 Energy without nutrient release

 Organic nitrogen that is later mineralized into plant-available forms

 Structural carbon compounds only

 Sulfur exclusively

5. Humus is produced through which process in soil systems?

 Biochemical transformation of decomposed organic residues

 Mechanical weathering of minerals

 Evaporation-driven concentration

 Chemical leaching of nutrients

6. _________________________ pool is the most sensitive soil organic matter to management practices

 Humus

 Labile organic matter

 Passive carbon

 Recalcitrant carbon

7. Which enzyme activity is most sensitive to soil disturbance, such as tillage?

 Urease

 Phosphatase

 Chitinase

 Dehydrogenase

8. An increase in enzyme activity following vermicompost application is primarily due to ___________

 Decreased soil moisture

 Enhanced microbial proliferation and substrate availability

 Reduced microbial biomass

 Chemical oxidation

9. A key limitation of Azospirillum as a biofertilizer is __________

 It is a plant pathogen

 It only fixes nitrogen in association with legumes

 It requires a specific soil pH below 4.0

 Its nitrogen contribution is modest and inconsistent under field conditions

10. A decline in soil enzyme activity generally indicates ___________

 Increased humification

 Soil degradation or stress conditions

 Improved soil fertility

 Enhanced microbial diversity

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