Nitrogen and corn

By Harold Watters, CCA, Ohio State University Extension agronomist

We had some very good speakers again at the Conservation Tillage Conference in March. This year I led what I called the Crop College. We in the past had Corn University and Soybean College but there was a request to broaden those to more than just corn and soybean, so this year we did at least add wheat to the mix along with presentations on tillage and nutrient management.

Day two this year I had Jim Camberato from Purdue come to speak about nitrogen. He pointed out work that he participated in to re-evaluate the Maximum Return To Nitrogen (MRTN) economic model. While there are a lot of reasons why it shouldn’t work, it actually does pretty well to give us an N rate for corn. Ohio uses this economic model, housed at Iowa State University: http://cnrc.agron.iastate.edu. We are part of a group of seven states who developed the model and house our Ohio nitrogen rate yield data there to help in making recommendations. Here is my 2019 trial at South Charleston, Ohio in Table 1. As in the work Jim did, you see that the MRTN is the in the group of highest yield.

 

Table 1. Corn yield at South Charleston Ohio, 2019 in OSU corn N rate trial.

TreatmentYield bu/ATotal NRemarks
7225.8175MRTN pre-plant
6223.1250N-rich strip
12220.1200w/ 20 lb. S broadcast at plant
11199.2200 
10192.5150 
5189.3100All pre-plant N
9188.210050 band planter, 50 sidedress
3157.350Pre-plant N
4140.750Sidedress N
2139.870Sensor rec.
8131.050Row band planter N
198.60 
LSD17.8 
C.V.12.2 
Prob > F2.313E-23Significant 

We currently have over 200 trials in the model for Ohio use, more than any area for either of our neighboring state. It uses location, rotation, corn price and nitrogen price to generate a MRTN rate in the Corn Nitrogen Rate Calculator. What’s our number? It is about 175 to 180 units of N per acre. Run the model to get your number or see Table 2. For me, I prepaid for N last fall at a 170 N rate, but am slipping toward 160 I fear.

 

 Table 2. Ohio CNRC 

Price of Nitrogen Fertilizer ($/ lb)

Price/ bushel corn$0.30$0.35$0.40$0.45$0.50
$3.25185176168162155
$3.50187180173166160
$3.75191184176170164
$4.00195186180174168
$4.25199190184177171
$4.50200193185180175

 

Something else to think about — we lose about 30 to 40 pounds of N each year to leaching and probably about the same amount to denitrification. So that’s 60 to 80 pounds of N we pay for that doesn’t get to our crop. If we delay the application of our N for corn until closer to the time we need it, we may reduce the risk of loss.

You can use an in-season “crop monitor”— think NDVI sensor, a drone with a camera, satellite, or even the calculator between your ears — to set our N rate. To try an NDVI sensor for variable rate applications check this website: http://soiltesting.okstate.edu/sensor-based-n-rate-calculator/ with some experience with these tools you can adjust your nitrogen rate, save a few bucks, and reduce the impact on the environment. My goal would be to determine crop-N needs at about 800 GDDs into the season. That is about V8 corn. Over the recent past few years when we had excessive moisture early the V10 to V12 applications have been too late to allow the plant to recover lost yield. Another wise move is to have a bit more than 25 to 40 units of N at planting — 60 to 100 makes for a faster recovery from these really wet springs. And I keep asking you all to do this because it would be a great learning exercise, but maybe put a strip or at least a patch in your field with no N at all.

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