Environmental Research Foundation . . P.O. Box 5036, Annapolis, MD 21403 . .
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To subscribe, E-mail the words . . ESA is the nation's professional organization for ecologists. Ecology is the branch of biological science that deals with the relationships between organisms and their environment. As every farmer knows, planting legumes adds nitrogen to the soil because microorganisms on the plants' roots fix nitrogen from the atmosphere. Until 1940, human industrial activities fixed almost zero nitrogen.