(a) Phosphate containing fertilizers enhances algae
growth. This process in which nutrient enriched water
body support a dense plant population, which kills animal
life by depriving it of oxygen and results in subsequent
loss of biodiversity is known as Eutrophication.
(b) Azotobacter fix molecular nitrogen from the
atmosphere without symbiotic relations with plants.
Whereas Rhizobium fix atmospheric nitrogen in root
nodules of plants by converting it to ammonia.
(c) Cyanobacteria are important for photosynthesis and
nitrogen fixation.
(d) There are few varities of maize that do not require
chemical fertilizers and are able to fix the atmospheric
nitrogen.