Jharkhand PSC Prelim Exam 2006 Solved Paper

(2) A Bio fertilizer (also biofertilizer) is a substance which contains living microorganisms which, when applied to seeds, plant surfaces,or soil, colonize the rhizosphere or the interior of the plant and promotes growth by increasing the supply or availability of primary nutrients to the host plant.
Anabaena in association with water fern Azolla contributes nitrogen up to 60 kg/ha/season and also enriches soils with organic matter.
In recent years, blue-green algae, a group of soil microorganisms have been shown to be agriculturally important, particularly in tropical rice field soils. This is because of capacity of some of the algae to synthesize organic substances and also to fix atmospheric nitrogen.