“…Literature reports for the amount of N2 fixed by alfalfa range from 56 to 463 kg ha ^ yr ^ (Nutman, 1976;Burns and Hardy, 1975). The percentage of total N accumulated annually in alfalfa that is derived by symbiotic fixation is also quite variable, ranging from less than 40% (Heichel et al, 1981) to greater than 90% (West, 1981).…”