Hi folks! I'm Kolby Grint and I'm the northwest regional specialist with the Nutrient and Pest
Management Program. And today I'm going to be talking about the economic nitrogen rate in corn.
In Wisconsin to determine the economic nitrogen rate for corn, we recommend using
the maximum return to nitrogen rate or the MRTN. So the MRTN is just a ratio that demonstrates
the cost per pound of nitrogen and the cost per bushel in corn. When the difference is greater
between these two, we're going to have a lower valued MRTN factor. When the difference is closer,
we're going to end up with a higher factor. With the maximum being 0.20.
So this is kind of demonstrated in this figure. When we have a really small difference and we're
spending either more for nitrogen, or our commodity prices are lower, the return that
we're going to get per dollar of nitrogen spent is going to be lower. So our recommended end rate
is also going to be lower. When the difference is great, we're going to see more return for
spending money on nitrogen and therefore the recommended rate is going to be higher.
So how do we determine the MRTN rate? There are several ways that we can do this and
I'm going to show you them all! The first way that I'm going to show you is if you're using
a SnapPlus nutrient management plan it's really easy to go back in and adjust the rate depending
on changes in commodity prices or changes in fertilizer prices as you get closer to planting.
So in SnapPlus on the cropping screen system,
where within a single field and that cropping year, there is a little box for the MRTN info
and you can click that box. Then here you can calculate your N price and dollars per
pound and input it, as well as the current corn price. Then it's going to calculate that factor
and adjust your MRTN ratio as well as the rate that is recommended within SnapPlus.
If you're doing this by hand or without SnapPlus we have a resource in NPM, a chart
which will be linked in the description, that you can use for most years. In some years though,
such as in the winter of 2021-2022, the price of nitrogen might exceed what is on this chart
or in some years we've had prices of corn that are higher. So it's always a good idea if you can't
find the MRTN ratio that you should be using on this chart,
you can also just calculate the MRTN ratio by hand and round it up. So
for an example of this, I'm in December of 2021 and I did a quick calculation calculating
the dollar per pound of urea. Currently the price is really high at $900 for one ton of urea
and then we divided that by 2,000 pounds to get the dollar per pound of urea fertilizer.
Then we know that there are 0.46 pounds or it's 46% nitrogen per pound of urea so we divided
the value from the last division by 0.46 and that gave us a value of 0.98
or 98 cents per pound of nitrogen.
Then calculating our MRTN ratio, we had
98 cents per pound of nitrogen with our current corn price of $5.25 per bushel of
corn and that gives us an MRTN ratio of 0.19, which we would then round up to 0.20
After we've calculated our MRTN ratio, we can look at the University of Wisconsin
nitrogen guidelines for corn or look at A2809, which will both be linked in the description,
to then determine the actual rate that we should be supplying to our crop depending on what our
previous crop and rotation was, our soil type, and the productivity level of our soil. Getting
that actual rate that you should be using if you're calculating it by hand. For example, let's
say that we were using a loamy high productivity yield potential soil, our previous crop was corn,
and we calculated our ratio of 0.20 so the rate that we would want to apply is 135 pounds of N.
It's kind of interesting to look at this table. Just seeing how much
the nitrogen rate fluctuates depending on that ratio.
So it's a great decision to go ahead and calculate your MRTN rate you know just before you're
deciding to purchase fertilizer and make the best decision that you can to remain profitable.
The third way to calculate your MRTN rate is to just use our corn rate calculator app,
available with npm, which will be linked in the description. This app allows you
to really quickly calculate your MRTN by just filling out the information that we would have
used in SnapPlus or if you were calculating by hand into the app and then you can just email
yourself the results or record them in an excel spreadsheet.
From there you could really easily just calculate the rates for your different fields, make the
manure credit or legume credit deductions that you need, and get yourself some really great economic
nitrogen rates. Thanks for watching my video on determining the economic N rate in corn!
If you have any questions feel free to email me or give me a call.