Question

In paddy fields, blue-green algae are grown
(A) For medicinal uses
(B) To increase fertility
(C) To serve as food for fishes
(D) To conserve water

Answer 1

Hint: In paddy fields, blue-green algae are grown to increase the ability of the soil to increase the yield of the crop. This will help the farmers to increase their stock and will in return get more money from the buyers.

Complete answer:
In paddy fields, blue-green algae are grown to increase fertility. Soil fertility means the ability of soil to sustain agricultural plant growth, i.e. to provide plant habitat and lead to sustained and consistent yields of top quality. Fertile soil has subsequent properties: The absence of toxic substances which can inhibit plant growth.

Additional Information: Blue-green algae form a self-sufficient system that is capable of fixing atmospheric nitrogen in organic forms and which grows upon a free water surface. It is thus ideally suited for propagation in the field of rice crops. The development and use of blue-green algae require special techniques. As early as 1939, P.K. De suggested that the fertility of tropical rice fields was due largely to the activity of the nitrogen-fixing blue-green algae and his suggestion has been validated by subsequent work. supported long-term field trials, a progressive increase within the yield of rice was observed in Japan and therefore the effect of the algal application was found to be like that of 60 kg/ha of ammonium sulfate (Watanabe 1965).
So, the correct answer is ‘(b) To increase fertility’.

Note: The success of algal technology depends on the ability of the introduced algal forms to survive, establish, and colonize the soil quickly. It's therefore important to pick fast-growing strains as seeding material.