Which comes first, the corn planting or nitrogen application?

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While some parts of the Corn Belt made planting progress in the past week, not everyone did.  And many farmers who are concerned about planting corn after the optimum planting dates may also wonder about changing their routine of field work. For example, should corn planting or nitrogen application be first? The answer is easy, and we have some tips to make it easier.

Although many farmers may be surprised about how far behind others are, keep in mind that soils have been wet in some parts of the Corn Belt since late February, and there has not been any fieldwork, including nitrogen application and pre-plant herbicide application. So, the legitimate question becomes, what are the priorities for field work, since you are still at square one? Iowa State University agronomist John Sawyer says the easy answer is getting your corn planted first. But he quickly says if you were debating which to do first, create a plan to get it all done. And that may require some creativity with labor and equipment.

Put on fertilizer, only if it does not delay planting, says Sawyer. And he suggests doubling up on the field work, if you don’t already do that. Such as broadcasting urea or UAN solution and incorporating it will normal tillage before planting. He warns against allowing them to remain on the top of the soil very long and be lost to volatility. Since rains have been frequent, he suggests using a rain to a positive advantage: A rain (at least 0.25 to 0.50 inch within approximately two days after application) will eliminate volatile loss concern.

Anhydrous ammonia may have been your first choice for nitrogen, but it has not been applied. What would happen if a window opens and a corn planter follows the anhydrous knives? Sawyer says there is not a waiting period, but seedlings will not grow in the ammonia channel because of injury. He says a deep application will avoid that problem, as well as the use of GPS, which would allow corn to be planted between the ammonia knife tracks.

A post-plant sidedress application may be the wisest choice, but that will require the proper equipment. Sawyer ranks the choices as follows:

  1. injected anhydrous ammonia, UAN or urea,
  2. broadcast dry ammonium nitrate, ammonium sulfate or urease treated urea,
  3. surface dribbling UAN solution between rows,
  4. broadcast UAN, and
  5. broadcast urea.

He says sidedressing can begin as soon as the corn rows are visible, and since roots will reach the row middle at an early stage, applying the nitrogen every other row should be an option. If you are planting corn within the row from a prior crop of soybeans, he says there should be adequate nitrogen from the soybeans to get the corn plant started. But use starter fertilizer if planting after corn.

Broadcast urea or ammonium sulfate will burn a corn plant if the granules fall within the corn whorl. Broadcast UAN has less volatile loss than dry urea, but a urease inhibitor will help prevent that. However the best cure is for rain to move the nitrogen into the root zone. But broadcasting UAN will also cause leaf burn and impede early growth. He says research has shown cosmetic plant damage if the corn is at the V3 growth sage and the application exceeds 60 pounds of N per acre. However, higher rates will begin to depress yields if the growth stage exceeds V3.

Sawyer suggests using the late spring soil nitrate test if nitrogen is going to be sidedressed. That collects soil from the top 12 inches of soil when the corn is 6-12 inches tall and the rates of nitrogen application can be adjusted.

But what if the corn becomes too tall for sidedressing, based on continued wet conditions? High clearance equipment can be used, says Sawyer if normal sidedress knives cannot be used. But that will change your nitrogen choice away from anhydrous ammonia. You would be using UAN solution either dribbled between the rows or shallow injection with a coulter. He says, “Research in Iowa has shown corn can respond to mid- to late-vegetative growth stage N application when there is deficient N supply, but there can be loss in yield potential. Reduced yield occurs more frequently when soils are dry at and after application (applied N not getting into the root zone) and with severe N stress. Best responses occur with sufficient rainfall shortly after application to move N into the active root zone.”


Corn should be planted first, and then nitrogen applied, if it has not already been applied. If it does not delay planting, fertilize first. Sidedressing nitrogen can occur after corn is visible, but choices should be carefully selected and broadcast forms of nitrogen could end up burning the corn to the point of yield loss. Before planning to sidedress, ensure the appropriate equipment is available, along with the necessary nitrogen products.

Source: FarmGate blog

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