Managing Nitrogen in Flood and Drought.

Climate models predict wetter springs and greater annual fluctuation in precip for the midwestern U.S. Springs were extremely wet from 2008 to 2011, while 2012 was extremely dry across most of this region. Fertilizer and soil nitrogen are vulnerable to loss when subject to excessive rainfall. Such loss resulted in widespread N deficiency in corn from 2008 to 2011, which I estimate cost corn producers 2 billion bushels of lost yield during these years. N lost from corn fields contributed to Gulf hypoxia and atmospheric nitrous oxide & radiative forcing. When N deficiency occurs, supplemental N applications can produce large yield responses until at least the tasseling stage. If supplemental N is broadcast, yield loss due to leaf burn is minimal with urea, intermediate with ammonium nitrate, and high with UAN solution. Aerial photographs provide a tool to quickly and quantitatively assess the severity of N deficiency and gauge how much N to apply. In wet years, planned in-season N applications are usually much more successful than preplant applications at delivering N to the crop. Planned in-season N applications also offer the opportunity to reduce N rate in a drought year like 2012.