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It's been a tough winter for wheat. Right now it's looking pretty dreadful and, in spite of the high dollar value for wheat, you have made the decision to cut your losses, abandon your wheat and plant corn. Now you are asking yourself how much of the N you applied to your wheat is still there waiting for those corn roots.
The answer depends on when you topdressed, how much N you applied, and the amount of N you would normally apply to achieve your corn yield goal for the field had you not planted wheat in the first place. The earlier the N was applied to wheat, the greater the opportunity for it to have been lost from the field through denitrification and leaching. A good guess (yes, this is a guess) is that for topdress N applied in February, 50% will be available to corn in June when a supplemental preemergence or sidedress N application can be made. If topdressing was delayed until March, 60% of the N may be available in June, and if topdressing occurred in late March or early April, an estimated 70% or more may still be there for the corn.
How does this translate into supplemental pounds of N per acre required for a corn crop? The worksheet below will help you determine how much N you need to apply. The first step (Step 1) is to calculate the amount of N applied to wheat that remains for the corn crop. Select the row that corresponds to the timing of your wheat N application and, in the first box, enter the amount of N applied. Multiply this amount of N by the proportion factor in the next column and enter the result in the la st box of the row.
In Step 2, enter the amount of preemergence or preplant N recommended for corn in the first box. Enter the value you calculated in Step 1 into the second box in Step 2. By subtraction of box one from box two, an estimate of the amount of supplemental N you need to apply to your corn is calculated.
Worksheet
| Step 1: | Amount of nitrogen remaining from wheat topdress applications | |||||
|---|---|---|---|---|---|---|
| Timing of Wheat N topdressing | Amount of topdress N applied to wheat (lb/acre) | multiplied by | proportion N remaining | = | Amount of N remaining for the corn crop (lb per acre) | |
| Example: | Through February | 90 lbs. | x | 0.5 | = | 45 lbs available |
| March | x | 0.6 | = | |||
| Late March/Early April | x | 0.7 | = | |||
| Step 2: | Amount of additional nitrogen required for corn crop | ||||
|---|---|---|---|---|---|
| Nitrogen rate recommendation for yield goal (lb/acre) | minus | Amount of N remaining from N application to wheat (from Step 1) | = | Amount of additional N required for corn (lb/acre) | |
| Example: | 150 lbs. N recommended | - | 45 lbs. remaining | = | 105 lbs. of additional N required |
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The Corn Growers Guidebook , a WWW resource
for corn management systems in Indiana and the eastern CornBelt.
Purdue University Agronomy Extension WWW
Home Page.
Purdue Agronomy On-Line! , Purdue's Agronomy
Department WWW Home Page.