Paper  bibtex   

@techreport{kramer_mineral_2004,
	type = {Open-{File} {Report}},
	title = {Mineral {Commodity} {Profiles}: {Nitrogen}},
	url = {http://pubs.usgs.gov/of/2004/1290/},
	number = {2004-1290},
	urldate = {2015-06-09TZ},
	institution = {USGS (US Geological Survey)},
	author = {Kramer, D.A.},
	year = {2004}
}