Tim Smith from Cropsmith and Fred Below, Ph.D., from the University of Illinois, discuss their research on applying nitrogen on soybeans, when it makes sense to use it, the optimal timing and application rates and what role soil plays in providing additional nitrogen.

  1. Nitrogen Fixation
  • Nodules on the soybean root system
  • Nodules enclose nitrogen-fixing bacteria
  • Active nodules are pink inside
  1. Symbiotic Association
  • Both parties benefit; the bacteria in the nodules receive sugar from the plant and the nodules give the plant nitrogen
  • Temperature, soil acidity, water availability and soil aeration can all have a huge impact on nodule activity and nitrogen fixation
  1. How much of the soybean’s nitrogen comes from the nodules?
    • 50%
  • The rest comes from the soil
  • Soybeans are a huge nitrogen-requiring crop
  1. How much nitrogen do soybean plants need to accumulate per each bushel of grain?
  • 4 – 5 pounds of nitrogen per bushel
  1. Facts about soybeans and nitrogen
  • There is no such thing as a soybean nitrogen credit
  • Soybeans remove about a pound of nitrogen from the soil for each bushel produced
  1. Can supplemental fertilizer nitrogen increase soybean yield?
  • Yes, no negative impact on nodule development and applying 100 lbs. of nitrogen preplant or V3 tended to increase nodule activity
  1. Conclusions
  • Was there a best time to apply nitrogen fertilizer to soybeans?
  • Yes, although yield increases were observed for all application times, preplant applications regularly increased yield over 3 years
  1. Do fertilizer nitrogen applications inhibit nodule formation and activity?
  • No, fertilizer nitrogen applications only had minor effects on nodule number and color

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