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Ohio State University Extension

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What’s the Right N Rate for Corn in Ohio?

The first answer is we don’t know. The truth is that our soils, rainfall, temperatures, the year-to-year variation and cropping systems are different enough that any rate we tell you will be wrong.

We formerly used crop yield goal to determine our nitrogen (N) rate. Shown here is Table 9 (Nitrogen recommendations for corn based on yield potential and previous crop) from the 1995 Tri-State Fertilizer Recommendations. With a corn yield of 160 bu/A we would recommend 190 pounds of N per acre in a corn after corn situation, and 160 pounds after soybeans. We gave a credit of 30 pounds nitrogen for soybeans.

Table 9.

 

Yield potential bu/A

 

Previous crop

140

160

180+

Corn

160

190

220

Soybean

130

160

190

Those assumptions of the need for about 1 pound of N/bushel of corn and 30 pounds of N credit after soybean were wrong. Today we know that we have a rotation advantage for corn after soybeans – because the soybean residue breaks down more easily than corn fodder. We also from research know that we can grow a good corn crop in Ohio with about 160 lbs N/A, no matter what the yield. In some years and in some situations we can grow that corn crop with no (as in zero) nitrogen and in some situations 240 lbs N/A is not enough. There is little correlation between N applied and crop yield.

So what is the better answer to arrive at an N rate for corn?

Today the best suggestion we can make is to use an economic model to determine your most economical nitrogen rate. Ohio has worked with a regional group of universities on a Maximum Return To Nitrogen model (MRTN). The regional calculator is based at Iowa State University, on a website dedicated to this on-line calculator:http://extension.agron.iastate.edu/soilfertility/nrate.aspx.

To use the MRTN calculator you need 3-4 pieces of information: location, crop rotation, price of N and corn price.

·        We choose Ohio as the location, soybean as previous crop, $0.50 for a pound of N and $3.57 as the corn price (today’s local January delivery price).

·        The calculator returns an N rate of 158 lbs N/A and that will cost us $79/A.

·        And with this N rate, from research conducted in Ohio in on-farm trials, we should achieve 97% of our maximum yield – and delivers the maximum economic yield.

·        This is the best suggestion we have for a corn crop in Ohio – use your own nitrogen and corn price for your operation to refine this number.

Not satisfied with the MRTN, or the no longer useful yield-goal method to determine your corn nitrogen rate? Then explore some of the calculators that are available – Adapt-N, Encirca, Climate Pro, soil nitrate testing, and many more – all have shown some promise. Use of an in-crop sensor is also being looked at in Ohio – again also showing some promise.

We also want you to consider an N rate trial on your farm, and share the results with us. We shared this trial plan during the winter meetings and encourage wider use.

·         N rate treatments:

o   Treatment #1 = 0 N, as in no nitrogen at all – we allow some flexibility on this one. But you will be surprised at the corn yield.

o   Trt 2 = 50,

o   Trt 3 = 100,

o   Trt 4 = 150,

o   Trt 5 = 200,

o   Trt 6 = 250 pounds of nitrogen.

·         With 3 replications in a trial plan such as this with randomization:

Sample Plot Layout

Rep

1

 

 

 

 

Rep

2

 

 

 

 

Rep

3

 

 

 

 

3

5

2

1

4

6

5

1

4

2

6

3

2

6

1

5

3

4

 

Other information we would request but not required is soil nitrate at V4-V6, an in-crop sensor reading such as from a GreenSeeker, an end-of-season stalk nitrate test and yield. The yield by rate and by replication is the most important information we require. We want to build our database, please help.

Harold Watters, watters.35@osu.edu, office phone 937 599-4227.

Steve Culman, culman.2@osu.edu, office phone 330 263-3787.

Crop Observation and Recommendation Network

C.O.R.N. Newsletter is a summary of crop observations, related information, and appropriate recommendations for Ohio crop producers and industry. C.O.R.N. Newsletter is produced by the Ohio State University Extension Agronomy Team, state specialists at The Ohio State University and the Ohio Agricultural Research and Development Center (OARDC). C.O.R.N. Newsletter questions are directed to Extension and OARDC state specialists and associates at Ohio State.

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