Soil Organic Matter MCQs Quiz 13

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

 Mechanical weathering of minerals

 Evaporation-driven concentration

 Chemical leaching of nutrients

 Biochemical transformation of decomposed organic residues

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

 Dehydrogenase

 Chitinase

 Phosphatase

 Urease

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

 Continuous organic inputs

 Reduced temperature

 Frequent tillage causing aeration and microbial oxidation

 Clay stabilization

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

 It requires a specific soil pH below 4.0

 It only fixes nitrogen in association with legumes

 Its nitrogen contribution is modest and inconsistent under field conditions

 It is a plant pathogen

5. A decline in soil enzyme activity generally indicates ___________

 Increased humification

 Soil degradation or stress conditions

 Improved soil fertility

 Enhanced microbial diversity

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

 Oxygen availability

 High nitrogen content

 Potassium deficiency

 Soil texture

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

 Sulfur exclusively

 Organic nitrogen that is later mineralized into plant-available forms

 Energy without nutrient release

 Structural carbon compounds only

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

 Passive carbon

 Labile organic matter

 Humus

 Recalcitrant carbon

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

 Humification

 Immobilization

 Oxidation

 Mineralization

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

 Chemical oxidation

 Decreased soil moisture

 Reduced microbial biomass

 Enhanced microbial proliferation and substrate availability

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