Evaluating polymer-coated fertilizer prototypes designed for planting along with maize seed

Side-dress N is a management strategy in maize (Zea Mays L.) production that can increase yield, reduce N leaching, and increase the probability that N remains post-flowering. This management adds cost, is time-sensitive, and can be difficult due to field shape and topography. A plantable, polymer-coated urea N bead of two sizes and two coating thicknesses was developed and field tested across multiple locations during 2015-2017 as a replacement to side-dress application. Locations differed in previous crop history and the initial N rates applied prior to treatments. Bead performance varied among locations but averaged 0.3 Mg ha(-1) compared to an uncoated control or in-season urea-ammonium-nitrate (UAN) application. Bead application increased yield 0.8 Mg ha(-1) when rainfall exceeded 225 mm between planting and R1 (silk appearance) but did not improve yield when rainfall was <125 mm. Nitrogen release from the bead was described by a thermal time function. A common exponential decay function was not adequate to describe the release of N across all locations indicating variation in release of N among locations driven by factors other than soil temperature. Slow-release, polymer-coated fertilizer, placed near the seed at planting, provides the option to apply supplemental N at planting, followed by N release later in the season, eliminating the need for in-season applications. Further research is needed to more closely match coating thickness and N release to crop N demand consistently across locations and development of equipment to enable one-pass seed planting and N application operations.