Which one is a biofertilizer

Why are blue green algae not popular as biofertilisers ?

The main sources of biofertilisers are

Organic farming includes

$I.$ use of biofertilisers and biopesticides

$II.$ crop rotation

$III.$ locally developed pest resistant varieties

Choose the correct option

Give scientific reasons : The pressure on use of organic farming and biotic fertiliser has been increased.

Relation between bacteria and legume having nodulated roots is that of