Soil Organic Matter MCQs Quiz 2

1. Modern soil organic matter (SOM) theory emphasizes _______

 Humification as the only pathway of SOM formation

 Lignin stability as the key factor

 Chemical recalcitrance as the sole determinant of stability

 Mineral protection mechanisms and microbial processing

2. Which mechanism provides physical protection to soil organic matter (SOM)? _______

 Chelation

 Mineral dissolution

 Oxidation

 Aggregation

3. Humic substances in soil organic matter are generally _______

 Composed only of microbial proteins

 Low molecular weight and highly unstable compounds

 Pure carbohydrates derived from plant residues

 High molecular weight and relatively stable organic complexes

4. Humin in soil organic matter is characterized as _______

 Soluble in alkali

 Highly volatile

 Soluble in acid

 Insoluble in both acid and alkali

5. The largest input to soil organic matter (SOM) in most agroecosystems is derived from _______

 Plant residues

 Atmospheric deposition

 Animal manure

 Microbial biomass

6. Non-humic substances in Soil Organic Matter include _______

 Proteins and carbohydrates

 Fulvic acid

 Humic acid

 Humin

7. Turnover of labile carbon in soil organic matter typically occurs over _______

 Days to years

 Centuries

 Thousands of years

 Millennia

8. ________is the fraction of soil organic matter that remains soluble across all pH levels (acidic, neutral, and alkaline)

 Fulvic acid

 Humic acid

 Humin

 Lignin

9. Soil Organic Carbon (SOC) represents _______

 Humus fraction of soil

 Microbial biomass carbon

 Carbon fraction of soil organic matter

 Total soil organic matter

10. ________________ of soil organic matter contributes most to rapid nutrient cycling

 Recalcitrant pool

 Humin fraction

 Labile pool

 Passive pool

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Question 1 of 10

Soil Science MCQs