Why is Azolla used as a biofertilizer?

Because it has an association with nitrogen-fixing cyanobacteria.

The correct answer is (d) Because it has an association with nitrogen-fixing cyanobacteria.

Azolla is a small aquatic fern that is commonly used as a biofertilizer in agriculture. One of the primary reasons for its use as a biofertilizer is its association with a specific group of nitrogen-fixing cyanobacteria called Anabaena azollae.

Inside the leaf cavities of Azolla, specialized structures called "hairs" provide a favorable environment for the growth and colonization of Anabaena azollae. These cyanobacteria have the ability to fix atmospheric nitrogen into a form that can be utilized by plants. This nitrogen fixation process helps to enrich the soil with available nitrogen, which is a crucial nutrient for plant growth and development.

The association between Azolla and Anabaena azollae is a symbiotic relationship. Azolla provides a suitable habitat and necessary nutrients to support the growth and survival of the cyanobacteria. In return, the cyanobacteria fix nitrogen, making it available for Azolla and surrounding plants.

The ability of Azolla to host nitrogen-fixing cyanobacteria makes it an effective biofertilizer. When Azolla is applied to agricultural fields or water bodies, it can rapidly multiply and form a dense biomass. This biomass can be incorporated into the soil or used as a green manure, providing a natural source of fixed nitrogen to support plant growth and reduce the need for synthetic nitrogen fertilizers.

Therefore, the presence of nitrogen-fixing cyanobacteria in Azolla is the key reason why it is used as a biofertilizer, providing an eco-friendly and sustainable approach to enhance soil fertility and improve crop productivity.