why are cynobacteria used as biofertilizers? Share with your friends Share 0 Summaiyya Khan answered this Cyanobacteria or blue green algae is used as a biofertiliser because that helps in nitrogen fixation to the soil thus increasing soil fertility and quality. It helps in nitrogen fixation anaerobically. 1 View Full Answer Krishna Priya answered this They are used as biofertilizer because cyanobacterians fix the atmospheric nitrogen in the form of ammonia anaerobically. 2