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Late getting your N on? Here are a couple solutions

Agriculture.com Staff 07/02/2009 @ 9:02am

In some parts of the countryside this year, the rains have come frequently and heavily enough to cause the fieldwork to pile up. Applying fertilizer is no exception.

Rain delays mean a lot of farmers who may have applied nitrogen at planting are now turning to sidedress applications to get those nutrients on the ground before it's too late. When doing so, it's important to keep a few things in mind, says University of Illinois soil fertility specialist Fabian Fernandez. First, make sure you're sidedressing at the right time.

"Corn takes up large amounts of N during approximately the V8 to the tassel stage," he says. "Nitrogen uptake is mostly done shortly after pollination, so applying N before the V8 development stage is probably the best time." More specifically, Fernandez says the V6 stage is the best time to sidedress; after that point is when yield loss potential can begin.

"The earlier the better" is a good plan for other applications. If you're broadcast-applying UAN, for example, Fernandez says the smaller the plant, the less potential exists for foliar damage. This type of damage is usually only "an aesthetic concern and rarely translates into yield reductions" if applications are made early.

"For over-the-top applications, urea granules will have the least impact on leaf burn compared to UAN or dry products such as ammonium nitrate or ammonium sulfate. To minimize adhesion of dry products to the leaves, it is best to apply when the foliage is dry," he said. "One way to reduce damage from UAN is to apply in advance of rain. If rain falls within a few hours after application, it will wash the fertilizer off the foliage. It will also reduce the potential for volatilization of urea.

"If a broadcast application of UAN is the only option available, try to do it as soon as possible, because the smaller the plant, the less the potential for foliar damage. However, if the plant is bigger and more N is needed, the yield benefit from the additional N will likely outweigh the leaf burn caused by the application."

But, if you're even too late for this to work, you can still get N on without causing too much damage past the V8 stage, Fernandez says. Doing so requires changing what you're applying and how you're applying it.

"When N applications are needed later than V8, to avoid extensive foliage damage it is very important to fit the high-clearance equipment with drop hoses so that UAN is applied directly to the soil surface without touching the crop canopy," he says. "If you plan to include herbicide with your UAN application, make sure you read the herbicide label to make sure such an application is allowed. Also, be aware that including herbicide with the UAN solution can intensify leaf burning."

According to a University of Illinois report, in Minnesota, adding 2 pounds atrazine per acre at a rate of more than 90 pounds N per acre at V3 development stage, for example, caused severe leaf burning. Applying 2 pounds atrazine per acre at 60 pounds N per acre causes similar leaf burning as applying 120 pounds N per acre with UAN alone.

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