Widespread N Loss From Midwestern Corn Fields, 2008-2013: Obstacles To and Opportunities For Improved N Management.

Large areas of the midwestern U.S. have experienced wet springs every year since 2008 except for 2012.  This is historically unusual but agrees with predictions by some climate models that springs in the midwest will become wetter.  Nitrogen is prone to loss from soil under wet conditions.  Aerial photos and windshield surveys documented widespread N deficiency in corn from 2008-2011 in the areas with the most rainfall.  Replicated on-farm experiments documented that in-season N applications can relieve the N deficiency and increase yield.  However, the environmental effects of the lost N can’t be reversed.  Applying a greater proportion of N fertilizer after the corn is planted is the most straightforward opportunity to prevent N loss.  In-season application of all N produced an average yield benefit of 60 bushels/acre/year from 2008-2010 compared to all-preplant N application in an experiment in central Missouri.  Planned in-season application of N fertilizer also allows downward adjustment of rates in a drought year like 2012.  However, there are substantial logistical and social obstacles to widespread adoption of this practice: inadequate fertilizer transport infrastructure, conflicting fieldwork for farmers, concern that yields will be limited by early-season N stress, need for more high-clearance N application equipment to extend the time available to complete the job, quality problems with the dry granular N fertilizers that are fastest to apply, and reluctance to adopt new practices.