Estimating Nitrogen Use Efficiency (NUE) with the Ramp Calibration Strip Fertilization Strategy and an Update of Oklahoma's Extension Program.

The nitrogen (N) ramp calibration strip (RCS) fertilization strategy has been established for winter wheat (Triticum aestivum).  The RCS method is used to determine mid-season, top-dress N application rates.  Visual and/or sensor based (i.e. GreenSeeker™) analysis of the RCS can be used to determine the appropriate mid-season, top-dress N rate.  RCS applicators for winter wheat systems have been developed to apply N rates at a minimum of 0 kg ha^-1, stepping up by a pre-selected rate through 16 steps to a desired maximum N rate.  Oklahoma State University promoted an extensive extension effort of the RCS method for the 2007 wheat crop; likewise, the effort was continued for the 2008 wheat crop.  Multiple locations throughout Oklahoma were used.  Additionally, 21 locations throughout Oklahoma were used to further evaluate the impact of the RCS approach over the producer’s normal N fertilization practices.  Furthermore, three research station locations were used to evaluate the estimation of nitrogen use efficiency (NUE) using the RCS.  The RCS approach is a viable tool for determining sufficient mid-season N needs of the crop to produce maximum yields, improving NUE, lowering the environmental impact of N pollution, and reducing economic inputs.