Ability of free-living cells ofBradyrhizobium japonicum to denitrify in soils

Summary Experiments to assess the ability of free-living cells of six strains of soybean rhizobia (Bradyrhizobium japonicum USDA 76, 94, 110, 122, 123, and 135) to denitrify nitrate in five soils showed that although some strains ofB. japonicum have the capacity to rapidly denitrify nitrate in soils under anaerobic conditions, it is unlikely that the numbers of soybean rhizobia commonly found under field conditions are sufficient to significantly influence either the extent or the products of denitrification in soil. It is our general conclusion that the advantages, if any, that the ability to denitrify conveys to rhizobia or to the rhizobia-legume symbiosis are not offset by increased losses of plant-available N when denitrifying strains of rhizobia are present as free-living cells in soil.