The fertility of soil is reduced by:

Options

A. ammonitying bacteria
B. denitrifying bacteria
C. nitrifying bacteria
D. nitrogen fixing bacteria

Answer

To address the question "The fertility of soil is reduced by:", we will analyze the options provided and identify the correct answer step by step.

### Step-by-Step Solution:

1. **Understanding Soil Fertility**:
- Soil fertility refers to the ability of soil to provide essential nutrients to plants. A fertile soil contains adequate amounts of nitrogen, phosphorus, potassium, and other micronutrients.

2. **Identifying the Role of Bacteria**:
- Different types of bacteria play various roles in soil health. Some bacteria contribute positively to soil fertility by fixing nitrogen or decomposing organic matter, while others can negatively impact fertility.

3. **Focusing on Denitrifying Bacteria**:
- Denitrifying bacteria are microorganisms that convert nitrates (NO3-) present in the soil into nitrogen gas (N2), which is released into the atmosphere. This process is known as denitrification.

4. **Impact of Denitrification on Soil Fertility**:
- The conversion of nitrates to nitrogen gas reduces the amount of available nitrogen in the soil. Since nitrogen is a critical nutrient for plant growth, its depletion leads to a reduction in soil fertility.

5. **Examples of Denitrifying Bacteria**:
- Common examples of denitrifying bacteria include *Thiobacillus denitrificans* and *Micrococcus denitrificans*. These bacteria are known for their role in the denitrification process.

6. **Conclusion**:
- Based on the analysis, denitrifying bacteria are responsible for the reduction of soil fertility due to their ability to convert essential nitrates into nitrogen gas, thereby depleting the soil of vital nutrients.

### Final Answer:
The fertility of soil is reduced by **denitrifying bacteria** (Option B).

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