By Brian Hefty

A 70-bushel soybean crop needs approximately 305 pounds of N, and despite what you may have heard, THERE IS ABSOLUTELY NO WAY IT CAN PRODUCE IT ALL!

Now, this is not to say that in all cases you have to apply nitrogen if you want big-time soybean yields.  There is carryover nitrogen in the soil.  There is also approximately 20 to 30 pounds of actual N that will come available each summer PER PERCENT OF ORGANIC MATTER.  For example, a 6% organic matter soil will release 120 to 180 pounds.

As a general guideline, a soybean plant can produce about 70% of the nitrogen it needs through nodulation and nitrogen fixation.  However, your crop won’t produce that much if your soil pH is outside the range of 6.3 to 7.3, if your ground has been flooded recently, or if you have almost any other adverse growing condition for your crop.

So how much should you apply?  Again, you might not need any, and you will likely not need much; unless, of course, this is your first time raising soybeans ever.  In that case, you will probably find 100 pounds of N will pay.  For almost anyone else, 30 to 50 pounds is generally sufficient, but consider the parameters I mentioned above.  Also, use the free Ag PhD Fertilizer Removal app to see how much N YOUR yield goal requires.

Get the Ag PhD Fertilizer Removal App on the iTunes Store.

Get the Ag PhD Fertilizer Removal App on Google Play.

One of the most popular questions we got this winter was, “Is it true that soybeans don’t nodulate if I apply too much N?”  First of all, that’s not true.  However, it is likely that if you apply too much nitrogen, your plant will produce less N though its colonizing rhizobia bacteria.  In other words, you are throwing money away if you overapply.  The only good news there is that there won’t be a whole bunch of excess nitrogen that could potentially leach away.  Soybeans use lots of N, but why would they work hard to draw in bacteria to produce it if it is already available for them in the soil?

In terms of timing, the best time for additional N is likely during flowering or early podset, provided you get moisture soon afterwards.  If you are in a dry area of the country, err on the early side rather than getting the nitrogen on too late.