Which one of the following statements is cor- rect

Options

A. Both Azotobacter and Rhizobium fix atmospheric nitrogen in root nodules of plants.
B. Cyanobacteria such as Anabaeena and Nostoc are important mobilizers of phos- phates and for plant nutrition in soil.
C. At present it is not possible to grow maize without chemical fertilizers
D. Extensive use of chemical fertilizers may tead to eutrophication of nearby water bodies.

Answer

To determine which statement is correct, let's analyze each option step by step:

### Step 1: Analyze the first statement
**Statement**: Both Azofactor and Rhizobium fix atmospheric nitrogen in root nodules of plants.

- **Explanation**: Azofactor (more commonly referred to as Azotobacter) and Rhizobium are both nitrogen-fixing bacteria. However, Rhizobium specifically forms symbiotic relationships with leguminous plants, where it fixes nitrogen in root nodules. Azotobacter, on the other hand, is free-living and does not form nodules; it can fix nitrogen in the soil but not in root nodules. Therefore, this statement is incorrect.

### Step 2: Analyze the second statement
**Statement**: Cyanobacteria Anabena and Nostoc are mobilizers of phosphate and plant nutrients in soil.

- **Explanation**: Cyanobacteria, including Anabena and Nostoc, are known for their ability to fix atmospheric nitrogen, not for mobilizing phosphate. They can contribute to soil fertility primarily through nitrogen fixation. Thus, this statement is also incorrect.

### Step 3: Analyze the third statement
**Statement**: At present, it is not possible to grow maize without fertilizers.

- **Explanation**: While fertilizers can enhance maize growth, it is indeed possible to grow maize without them, particularly with the use of organic manures or through sustainable agricultural practices. Therefore, this statement is incorrect.

### Step 4: Analyze the fourth statement
**Statement**: Excess use of chemical fertilizers leads to eutrophication of nearby water bodies.

- **Explanation**: This statement is correct. The excessive use of chemical fertilizers can lead to nutrient runoff into nearby water bodies, causing an increase in nutrient levels (particularly nitrates and phosphates). This nutrient overload can result in eutrophication, which is characterized by excessive growth of algae and depletion of oxygen in the water, harming aquatic life.

### Conclusion
The correct statement is: **Excess use of chemical fertilizers leads to eutrophication of nearby water bodies.**

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