http://www.lenntech.com/periodic/elements/n.htm
http://en.wikipedia.org/wiki/Haber_process
http://en.wikipedia.org/wiki/Fertilizer
http://dictionary.reference.com/
Complete Chemistry For IGCSE By: RoseMarie Gallagher and Paul Ingram
Biology For IGCSE By: Gareth Williams
nitrogenfertilizers 