Which feature of some species of blue-green algae helps promote them as bio-fertilizers?

Which of the following is/are used as biofertilizers? 1. Azolla 2. Blue-green algae 3. Alfalfa

Blue-green algae are chiefly used as biofertilizer in the crop of -

Which of the following is used as Biofertilizer?

The biofertilizer used as a supplementary food for the cattle, especially for milking bovines is :

Which of the following is not a nitrogen-fixing organism?