These facts may help refresh your memory on what it takes to grow high-yielding soybean crops. (They may also help you impress the relatives over the holiday!)
The typical soybean crop needs ~315 lbs N per acre, about 60 percent of which (190 lbs) goes to seed production and 40 percent (125 lbs) goes to stover and roots.
Soybeans fix nitrogen from the atmosphere when nitrogen-fixing rhizobia bacteria are present in the soil. Nitrogen fixation is a result of the symbiotic relationship between rhizobia and the soybean plant and is evident in nodules on soybean plant roots. Most studies show that between 50-60 percent of the nitrogen is from N fixation.
A well-nodulated soybean plant should have five to seven nodules on the primary root.
You can check for nodulation on soybeans as early as two weeks after emergence. When needed, soybeans respond very well to nitrogen applied between flowering and pod fill.
(Sources: AgVenture, Inc., University of Nebraska Lincoln)