Question:

Given the relative costs between AMS and Urea, what's the downside to trying to correct a nitrogen deficiency using granular urea.  All the extension literature harps on the use of AMS, but at this stage in the game we've got a grower who can get Urea for about half the price of AMS (per lb of actual N) to correct an actual deficiency and inoculation failure.

Jordan:

I’ve not looked at urea. I don’t know of a downside but I have not looked at urea. Years ago we looked at granular UAN (I can’t seem to find the old data, this is the fertilizer historically used in tobacco) and AMS was more effective. I just found a citation that showed UAN, AMS and urea increased peanut yields when a nitrogen deficiency was present.

https://scisoc.confex.com/crops/2017am/webprogram/Paper107962.html

Follow Up:

The only thing I could think of off-hand was the nitrification of urea being slightly slower than that of ammonium, but the reality is that's a process that is still quick (relatively speaking).

Jordan:

Ammonium nitrate was the fertilizer I could not remember. We did not increase yield as well at higher rates with this fertilizer compared with AMS. The higher concentration of ammonium nitrate may have something to do with it. And some nitrogen loss.  That is a concern with urea and nitrogen loss. But the article in the link shows urea and liquid UAN increased yield. The abstract does not have all the details, but I have concerns about high rates of foliar applied nitrogen. These are reasons why I have stuck with AMS as our recommendation. Of course, a lot of this work was done a decade or so ago.