en-USes-ES

USDA www.usda.gov
Current U.S. Department of Agriculture information, programs and resources.

NATIONAL ORGANIC PROGRAM www.ams.usda.gov/nop
USDA's National Organic Program.

OMRI www.omri.org
Organic Materials Review institute.

IFOAM www.ifoam.org
International Federation of Organic Agriculture Movements.

OTA www.ota.com
Organic Trade Association.

NATURAL NITROGEN NITROGENOUS ROCK, www.naturalnitrogen.com
Book published in 2003 by H. Opdebeeck Arg.Ing,M.Sc., H.Tejeda Arg.Ing.,Ph.D., E.De Marez Arg.Ing, M.Sc.