Released June 30, 2009
URBANA, Ill. -- The season's prolonged wet conditions are leaving corn growers with no other alternative than to sidedress applications for nitrogen (N), so they've been asking University of Illinois Assistant Professor of Soil Fertility, Fabián Fernández questions about when and how to apply N.
"Corn takes up large amounts of N during approximately the V8 to the tassel stage. Nitrogen uptake is mostly done shortly after pollination, so applying N before the V8 development stage is probably the best time," Fernández said.
He says research has shown that, if applications are done around V6, yield loss due to N stress is rare. In cases where no N was applied or the N supply is very low, make it a priority to apply N early, preferably before V6, to avoid loss of yield potential.
Nitrogen can be applied as a liquid or as a dry product.
"Injection into the soil and dribbling between rows are the best ways to sidedress N because these applications can reduce volatilization of urea and protect the crop from foliar damage," Fernández said.
He cautions that, if ammonia is used for the application, it is important to wait until soil conditions will allow the knife track to close properly. Applying dry products, such as ammonium nitrate and urea, over the top of the crop can result in foliar damage as the granules fall into the whorl or leaf axil of the corn plant. Also, as the leaf emerges from the whorl, the margin might be white due to excess N in the leaf.
"Typically this damage is merely an aesthetic concern and rarely translates into yield reduction," said Fernández. Also, urea is subject to volatilization if rain does not fall within 3 to 4 days after application. As much as 30% of the urea can volatilize if there is no rainfall within approximately 10 days after the application.
"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.
UAN solution can cause foliage damage, too. If the application is done when plants are small -- about 6 inches -- the damage will not likely result in yield loss. Even when plants are bigger -- V4 -- the foliage damage caused by a rate as high as 90 to 100 pounds N per acre typically does not cause significant yield reduction.
"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," Fernández said.
"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," he said.
Research from Minnesota has shown yield reduction when a rate of more than 60 pounds N per acre was applied at V8. "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," said Fernández.
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.
In Minnesota, adding 2 pounds atrazine per acre at a rate of more than 90 pounds N per acre at V3 development stage 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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http://www.aces.uiuc.edu/news/stories/news4831.html
Source: Fabian Fernandez, 217-333-4426, fernande@illinois.edu
Writer: Gary Beaumont, 217-333-9440, beaumont@uiuc.edu
