Nitrogen Fixation: An Historical Perspective

Abstract

All living things require a source of utilizable nitrogen to survive and grow. Utilizable nitrogen comes in a variety of forms, with ammonia (NH3-) and nitrate (NO3-) the most common. These and other related usable forms of nitrogen are most often the limiting factor for the growth of organisms; a situation that is clearly highlighted in production agriculture. The element nitrogen is not, however, in short supply on this planet, which is blessed with the equivalent of more than 1017 metric tons of nitrogen gas (N2), about 2% of which is free in the atmosphere. Unfortunately, the N2 molecule cannot be directly utilized by the vast majority of living organisms. To become available for use, N2 must first be ``fixed'' (converted to a usable form) by one of several alternative routes (Newton, 1996). The use of the term, fixation, to describe this conversion was instituted early on because it was unclear at that time if the process was oxidative or reductive, but whatever its chemical nature, the nitrogen became trapped (or fixed) in the product and was no longer gaseous.