Blue green algae used in rice fields to increase fertility is

Options

A. Rivularia
B. Nostoc
C. Aulosira
D. Anabaena.

Answer

To answer the question about which blue-green algae is used in rice fields to increase fertility, we can follow these steps:

### Step 1: Understand the Role of Blue-Green Algae
Blue-green algae, also known as cyanobacteria, play a significant role in agriculture, particularly in rice fields. They are known for their ability to fix atmospheric nitrogen, which is essential for plant growth.

**Hint:** Remember that blue-green algae can enhance soil fertility by converting atmospheric nitrogen into a form that plants can use.

### Step 2: Identify the Options
The options given are:
- Rebularia
- Nostoc
- Olocera
- Anabena

**Hint:** Look for the specific blue-green algae that are commonly recognized for their use in agriculture.

### Step 3: Research the Algae
Among the options, we need to identify which one is specifically known for its use in rice fields.
- **Nostoc** and **Anabena** are also known for nitrogen fixation, but they are not primarily associated with rice cultivation.
- **Rebularia** is not a commonly recognized blue-green algae in this context.

**Hint:** Focus on the algae that has been widely studied and used in rice cultivation.

### Step 4: Identify the Correct Answer
The correct answer is **Olocera**, which is a type of blue-green algae (cyanobacteria) that is specifically used to enhance the fertility of rice fields by fixing nitrogen.

**Hint:** Remember that Olocera is particularly beneficial in rice cultivation due to its nitrogen-fixing capabilities.

### Final Answer
The blue-green algae used in rice fields to increase fertility is **Olocera**.