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Managing corn stover with Fall nitrogen applicationsPosted Friday, September 16, 2011, at 12:41 PM
Management of corn stover has become more of a concern as new hybrids produce stronger stalks, relatively larger amounts of biomass, more corn-on-corn acres are planted and less tillage is done. Stronger stalks are desirable to help with the standability of the crop. This same trait however makes it harder for the stalk to break down. This in turn results in larger amounts of residue the following year and can also delay planting or seed emergence by keeping soils cool and wet longer into the spring.
One practice that is being promoted is the application of nitrogen, typically urea-ammonium nitrate (UAN) or ammonium sulfate (AMS), to increase microbial activity and induce microbial activity. According to Fabian Fernandez, University of Illinois Extension soil and plant fertility specialist, microbial decomposition of corn stover is typically slow because the material has a high C:N ratio. The application of nitrogen (N) would theoretically reduce the C:N ratio and allow microbes to act on or start eating the material quicker.
Research conducted at the University of Wisconsin showed no benefit for fall application of nitrogen. They observed no change in the C:N ratio. Also they observed no differences in soil temperature the following spring due to nitrogen treatment. In summary, they concluded that applying nitrogen in the fall to aid the breakdown of corn stover was not justified because it did not contribute to residue breakdown and resulted in nitrogen loss. Fernandez said that the reason for this lack of response is that low temperatures, and not nitrogen levels, are the limiting factor for microbial decomposition of residue. Also dry falls such as 2010 and so far 2011, reduce microbial activity because of the progressive decline in temperature that occurs during the fall and the lack of moisture.
Because of improved hybrids and more intense management (fungicide applications), infection, stalk rot, or other problems to the cornstalk are less frequent. A healthier plant would provide less opportunity for pathogens to enter plants and begin the decomposition process. In turn this would indicate that fields with lower pathogen levels would lower the chance to see greater stover decomposition with the addition of nitrogen.
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As our local University of Missouri Agronomy Extension Specialist, Crook has been writing a column for the print edition Agriculture page for the past three years and we will now be sharing it on our web version. Crook has a bachelor and masters degree in agronomy from University of Missouri and received his doctorate in Agronomy from Kansas State University. He was in soybean variety development research for 22 years for various seed companies and has been Saline County's agronomy specialist for 10 years.