To accommodate the world's expanding population, which is projected to double by 2050, an ever-increasing production of food crops will be necessary. This must be achieved primarily by increasing productivity of currently farmed area, since suitable new land is very limited. Concomitantly, total usage of fertilizer nitrogen and application rates per unit area will increase, with accompanying environmental deterioration, unless alternative technologies are developed. An obvious good of biological nitrogen fixation research is to find ways to enable the major cereal crops to utilize biological...