2.Soil organic matter

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1. What are the remains of plants and animals found in soil called?
   A) Soil minerals  |  B) Soil Organic Matter  |  C) Soil water  |  D) Soil air
2. What is the general percentage of organic matter found in mineral soils?
   A) 0.1 to 5 percent  |  B) 10 to 15 percent  |  C) 20 to 25 percent  |  D) 50 percent
3. What is the dark brown or black colloidal substance formed after complete decomposition of organic matter?
   A) Bacteria  |  B) Mineral  |  C) Humus  |  D) Soil
4. Which elements constitute more than 90 percent of soil organic matter?
   A) Nitrogen and Phosphorus  |  B) Carbon, Hydrogen, and Oxygen  |  C) Iron and Zinc  |  D) Calcium and Magnesium
5. Which of the following substances decomposes most rapidly?
   A) Lignin  |  B) Cellulose  |  C) Sugars and Starch  |  D) Fats
6. What is the correct chemical formula for Glucose?
   A) CO2  |  B) H2O  |  C) C6H12O6  |  D) C12H22O11
7. Into how many main groups are soil microorganisms classified?
   A) Two  |  B) Three  |  C) Five (Bacteria, Fungi, Algae, etc.)  |  D) Eight
8. What is the approximate volume of Nitrogen in the atmosphere?
   A) 21 percent  |  B) 0.03 percent  |  C) 78 percent  |  D) 50 percent
9. Which bacterium lives as a symbiont in the root nodules of legumes?
   A) Azotobacter  |  B) Rhizobium  |  C) Clostridium  |  D) Nitrosomonas
10. Which gas is primarily released during the decomposition of organic matter?
    A) Oxygen  |  B) Nitrogen  |  C) Carbon Dioxide (CO2)  |  D) Hydrogen
11. What is the primary 'Plant Source' of soil organic matter?
    A) Animal manure  |  B) Green Manure  |  C) Insects  |  D) Microbes
12. What is the suitable temperature for the decomposition process?
    A) Below 5°C  |  B) 10-20°C  |  C) 30-40°C  |  D) Above 50°C
13. What is the average Carbon-Nitrogen (C:N) ratio of soil?
    A) 4-9:1  |  B) 10-12:1  |  C) 20-30:1  |  D) 100:1
14. The process in which ammonium nitrogen is converted into Nitrate is called:
    A) Aminization  |  B) Nitrification  |  C) Denitrification  |  D) Immobilization
15. Which is an example of Anaerobic Bacteria?
    A) Azotobacter  |  B) Rhizobium  |  C) Clostridium  |  D) Beijerinckia
16. What kind of electrical charge does Humus carry?
    A) Positive  |  B) Negative  |  C) Neutral  |  D) None
17. What should be the ideal soil moisture for organic matter decomposition?
    A) 10-20%  |  B) 60-80% of water holding capacity  |  C) 100%  |  D) Zero moisture
18. The conversion of proteins and complex nitrogen compounds into Amino acids is called:
    A) Aminization  |  B) Ammonification  |  C) Nitrification  |  D) Denitrification
19. What is the function of 'Nitrosomonas' bacteria in the nitrogen cycle?
    A) Convert nitrate to nitrogen  |  B) Convert ammonia to Nitrite (NO2)  |  C) Nitrogen fixation  |  D) Making humus
20. What is the effect of adding organic matter on the Cation Exchange Capacity (CEC) of soil?
    A) Decreases  |  B) Increases  |  C) No effect  |  D) Becomes zero
21. Why does Lignin decompose very slowly?
    A) Because it is water-soluble  |  B) Due to its complex structure (Benzene ring)  |  C) Because it is not found in soil  |  D) None
22. What is the average Carbon-Nitrogen ratio (C:N ratio) of Humus?
    A) 5:1  |  B) 10:1  |  C) 50:1  |  D) 100:1
23. The process of converting organic nitrogen into inorganic forms (Ammonium/Nitrate) is:
    A) Immobilization  |  B) Mineralization  |  C) Volatilization  |  D) Denitrification
24. Which 'weak acid' is formed by the decomposition of organic matter in soil?
    A) Sulphuric acid  |  B) Hydrochloric acid  |  C) Carbonic acid (H2CO3)  |  D) Nitric acid
25. What is the typical C:N ratio of the bodies of microorganisms?
    A) 4-9:1  |  B) 20-30:1  |  C) 50-80:1  |  D) 10-12:1
26. Which enzyme hydrolyzes Starch into 'Maltose'?
    A) Maltase  |  B) Diastase  |  C) Cellulase  |  D) Pepsin
27. What is the average Cation Exchange Capacity (CEC) of Humus?
    A) 10-20 cmol/kg  |  B) 50-80 cmol/kg  |  C) 200 cmol/kg  |  D) 15 cmol/kg
28. The loss of nitrate in soil by converting it into gaseous nitrogen (N2) or nitrous oxide is:
    A) Nitrification  |  B) Denitrification  |  C) Ammonification  |  D) Aminization
29. What causes the 'earthy fragrance' from soil after the first rain in summer?
    A) Bacteria  |  B) Fungi  |  C) Actinomycetes  |  D) Algae
30. During humus formation, resistant lignin and protein combine to form:
    A) Sugar  |  B) Lignoproteinate  |  C) Vitamin  |  D) Fat
31. Approximately what percentage of soil organic matter is Lignin?
    A) 1-5%  |  B) 10-30%  |  C) 50-80%  |  D) 90%
32. What is the ideal pH range for the growth of Fungi?
    A) 4.0 to 5.0 (Acidic)  |  B) 7.0 to 8.0  |  C) Above 9.0  |  D) Exactly 7.0
33. Bacteria that fix atmospheric nitrogen in the soil without the help of any plant are:
    A) Symbiotic  |  B) Non-symbiotic  |  C) Parasitic  |  D) Pathogenic
34. What is the effect of organic matter decomposition on the Buffering Capacity of soil?
    A) Decreases  |  B) Increases  |  C) Becomes zero  |  D) No effect
35. The fraction of humus that is soluble only in alkali is called:
    A) Fulvic acid  |  B) Humic acid  |  C) Humin  |  D) Amino acid
36. At which pH does the process of Nitrification occur most efficiently?
    A) Highly acidic  |  B) Neutral (pH 7.0)  |  C) Highly alkaline  |  D) Zero pH
37. Why do microorganisms synthesize 'polyuronides' during organic matter decomposition?
    A) For energy storage  |  B) For synthesis of microbial tissues  |  C) To kill plants  |  D) None
38. What is the specific function of 'Nitrobacter' bacteria?
    A) Forming ammonia  |  B) Converting nitrite to Nitrate (NO3)  |  C) Forming nitrogen gas  |  D) Digestion of starch
39. What will be the rate of decomposition if the detritus is rich in lignin and chitin?
    A) Very fast  |  B) Slow  |  C) Unchanged  |  D) Zero
40. What is the effect of a wide Carbon-Nitrogen ratio in soil?
    A) Nitrogen becomes more available to plants  |  B) Competition for nitrogen between microbes and plants increases  |  C) Decomposition stops  |  D) Salt increases