MRTN – An abbreviation for Mister Tennessee or Martin?  Um, no.  It stands for Maximum Return To Nitrogen.  In today’s climate of $1400+ anhydrous ammonia, you really have to scratch your head and wonder what should I do.  Luckily there is a great answer in determining how much nitrogen is worth applying.  Several universities have collaborated in creating a calculator to determine what is financially feasible without leaving money on the table.  These universities include Illinois, Purdue, Ohio State, Iowa State, Wisconsin and Minnesota. 

https://tinyurl.com/2p99d5fp         ß Hopefully this link is easier to type on your smartphone if you’re in the field!  Otherwise you can search for “MRTN Rate Calculator” in the Apple or Google store.

Once you’re on the page (it’s on Iowa State’s website) you can select if you are just applying a single application and price for nitrogen, or perhaps you bought your preplant already and will be buying some side dress nitrogen in-season.  You’ll then select Illinois, South, select form (AA, 28, 32, Urea or Ammonium Sulfate), input the nitrogen price and expected corn price.  After doing so, this is what you’ll see.

A simple breakdown of your information and a calculation of where you should be.  $1450/ton AA is $0.88/pound.  Your MRTN Rate is 179 pounds of nitrogen per acre.  The profitable range is between 167 up to 190 pounds of actual nitrogen.  $1450/ton over 126 sites the past several years says that you’ll achieve 97% of your maximum yield with 179 pounds of nitrogen.  If you’re shooting for 180 bushel corn and maximize yield at 97%, you’ll have a final yield of 174.6 bu/ac. 

I’ve included the graphic below to visually process what that information looks like.

Now, if you’re like me, you’re stuck on the sentence/info above about hitting 97% of your maximum yield and you want 100% of your potential, this tool also provides a nice graphic to show you where we need to be to maximize yield at 100%. 

It appears the “don’t lose any sleep/full rate of nitrogen” number is around 240 pounds/acre.  That number creates a new paradigm of losing sleep at the $0.88/pound level. 
One thing I remember from several years ago in a John McGillicuddy agronomy meeting that I hosted was John saying ‘your goal is to have ample nitrogen 9 out of 10 years.’  At that level, the year you are short, you’re likely going to be a little short with a minimal impact on yield.   Personally, this past year was my 1 in 10 year!