Question

The most common biofertilizer for rice crop is
A. Azolla
B. Trifolium
C. Sesbania rostrata
D. Bacillus polymyxa

Answer 1

Hint: A biofertilizer is a living micro-organism, which when applied to the plant's surfaces, or to the soil promotes plant growth. Biofertilizers increase the supply or availability of essential nutrients to the plants. They are the eco-friendly agro product. The most common biofertilizer for rice crop is also known as mosquito fern.

Complete answer: Nitrogen is one of the most essential macro elements required by plants for nucleotide and amino acid synthesis. Nitrogen plays a vital role in the growth of plants. Azolla is rich in nitrogen content which makes it a perfect biofertilizer. Although nitrogen is ample in the earth’s environment, still plants obtain their nitrogen from the soil with the help of nitrogen-fixing bacteria.
Azolla is commonly called mosquito fern or duckweed fern. Sometimes, it is referred to as water fern. Azolla is the genus of aquatic ferns belonging to family Salviniaceae. From one thousand years, Azolla is used in rice paddies as a companion plant. It has nitrogen-fixing cyanobacteria in symbiotic association. It grows widely and forms a dense mat. It does not allow light to pass inside the water body; this prevents the growth of other plants apart from the rice.
So, the correct answer is option A.

Note: Azolla sp. is used to control mosquito larvae in rice fields. The plant grows in a thick mat on the surface of the water, making it more difficult for the larvae to reach the surface to breathe. Nostoc is the cyanobacteria associated with Azolla which helps in nitrogen fixation.