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    Web-sites:

    http://www.biotecharticles.com/Agriculture-Article/Biofertilizers-Types-Benefits-and Applications-172.html

    http://www.peoi.org/Courses/Coursesen/bot/bot10.html

    http://archive.bio.ed.ac.uk/jdeacon/microbes/nitrogen.htm

    http://www.mrrse.com/biofertilizers-market

    https://www.britannica.com/science/nitrogen-fixing-bacteria

    https://ecofriendlycoffee.org/azolla-as-a-biofertilizer-in-coffee-plantations/

    http://www.ecochem.com/t_compost_faq2.html