ABSTRACT
Without microbial nitrogen fixation there would be no plants, no cattle, and eventually no life , a s all nitrogen would be released into the atmosphere. This is well known, as is the major role of the Rhizobia (root-dwelling) bacteria in recapturing atmospheric nitrogen. An acre of alfalfa may fix 400 lb of nitrogen in a single season.32 It is estimated that root nodule bacteria of leguminous plants restore 5 to 6 million tons of nitrogen to U .S . soil yearly.34 The subsequent utilization of nitrogen by herbivorous, then carnivorous , animals makes initial assimi lation by soil bacteria a vital step in basic nutrition of higher life forms .
