Soybean growth and seed yield (SY) are closely related to nitrogen (N) which is provided by soil N sources, fertilizer, and N₂ fixation. In order to achieve yield potential, soybeans must maintain high seed N concentrations while sustaining high photosynthesis rates. We summarized differences in N uptake and N₂ fixation by soybean as affected by environments, genotypes or management, based on data published in scientific journals from 1966 to 2004 and experiments conducted at the University of Nebraska-Lincoln. Most frequent protein content ranged from 37 to 42% and N harvest index averaged 0.8. The slope of the linear regression between SY and N uptake was 11 kg of SY per kg of N uptake (r² = 0.86, N = 412; P<0.01). Most frequent values of N₂ fixation ranged from 61 to 151 kg N ha^-1(36 to 61% of total N uptake), with an overall range of 0 to 337 kg ha^-1. Nitrogen fixation increased as N uptake rose, reaching a maximum at 300-350 kg ha^-1. The strength of the relationship between SY and fixed N decreased when N fertilizer was applied. An inverse non-linear relationship between N fertilizer rate and N fixation was observed if fertilizer was applied at planting in the top layer of soil. However, experiments where N was placed deeper or applied in reproductive stages did not follow this trend. Significative response to N fertilizer was recorded in lower-yielding environments (below 3500 kg ha^-1) in which the crop had constraints for growth, as well as in higher-yielding environments, probably due to a higher N demand. Seed yield above the 75% percentile (3320 kg ha^-1), had 74% and 81% higher N uptake and N fixation. The lack of data above this value, made difficult the prediction of crop behavior and the role of N₂ fixation in high-yielding soybeans.