Research studies have shown that from 40 to 80 percent of the nitrogen required for a soybean crop comes from nitrogen fixed in the nodules, depending on the degree of nodulation and the level of soil nitrogen. Hence, it is important that soybean plants be well-nodulated for most efficient soybean production.
Sims, J. L.; Lacefield, E. C.; and Murdock, Lloyd W., "Soybean Inoculant Quality" (1979). Agronomy Notes. 94.