Considerations for late season UAN applications
click image to zoomFigure 2. Corn leaf after foliar application of 28% UAN on July 12, 2011. (Picture taken July 19, 2011). Foliar application of UAN has been identified as the least recommended option for N application (Fernandez, 2010). Early in the growing season, foliar application of UAN may still cause leaf burn, but it will not likely to lead to a yield reduction. Sawyer (2003) recommends no more than 90 lb/ac of N as UAN applied at the V3 stage or younger and no more than 60 lb/ac of N as UAN between the V3 to V7 stage. When the corn is too tall to risk damage during injection, UAN should be applied with drop nozzles between rows. If dry fertilizer is applied over the top of the corn canopy, urea and ammonium nitrate will cause some fertilizer burn if the granule falls in the whorl. It is best to apply dry fertilizer products when the canopy is dry.
In general, planned split-applications of N, even when they include applications made past V7, are preferable to applying all of the N pre-plant and relying on large (30 lb/ac or more of N) foliar applications as a rescue application. Split-applications prevent large amounts of applied N to be subject to environmental losses early in the growing season. If rescue applications are your only option consider the N source and application location. Stick to products like UAN, urea, or ammonium nitrate; slow-release fertilizers are not recommended late in the season. However, inclusion of NBPT (e.g. Agrotain®) would be beneficial for use with urea when surface applied to reduce volatilization (Fernandez, 2011). Further, avoid broadcast or “over the top” applications if possible to avoid risk of leaf burn and the potential decline in yield that would occur. If broadcast application of 28% or 32% UAN is your only option fully consider the potential tradeoffs between potential yield decrease (from leaf burn) and the potential for yield increase.
References (all links last verified on 21 July 2011):
Fernandez, F.G. 2010. Applying nitrogen after planting. http://web.extension.illinois.edu/state/newsdetail.cfm?NewsID=17983
Fernandez, F.G. 2011. Applying nitrogen late in the game. The Bulletin, Univ. Illinois-Extension, 14:3, July 8, 2011. http://bulletin.ipm.illinois.edu/article.php?id=1528
Kelling, K.A., S.M. Combs, and J.B. Peters. 2000. Sampling for plant analysis. (white paper) http://www.soils.wisc.edu/extension/pubs/pa_sampling.pdf
Laboski, C.A.M. 2010. Trouble shooting using plant analysis. Proc. 2010 Wisconsin Crop Management Conference. 49:26-31. http://www.soils.wisc.edu/extension/wcmc/2010/pap/Laboski_analysis.pdf
Laboski, C.A.M. 2011. Assessing the potential for nitrogen loss from heavy rainfall. Wisconsin Crop Manager, 18(6):61-63. http://ipcm.wisc.edu/WCMNews/tabid/53/EntryId/1191/Assessing-the-Potential-for-Nitrogen-Loss-from-Heavy-Rainfalls.aspx
Nelson, K.A., P.C. Sharf, G. Stevens, and B.A. Burdick. 2005. Rescue Nitrogen Applications for Corn. Missouri Soil Fertility and Fertilizers Research Update 2004, Agronomy Miscellaneous Publ. #05-01. http://aes.missouri.edu/pfcs/research/prop403b.pdf
Sawyer, J.E. 2003. Pay attention to management needs of fertilizer products. Iowa State Univ.-Extension. IC-490(4), p. 25-26, April 14. http://www.ipm.iastate.edu/ipm/icm/2003/4-14-2003/fert.html