Predicting Pre-Plant Nitrogen Applications to Corn Using Indicator Crop N-Rich Reference Strips.

The use of active optical reflectance sensors in corn (Zea mays L.) has proven to accurately determine optimum nitrogen (N) fertilizer requirements and direct in-season N fertilizer applications.  However, corn producer adoption of this technology has been slow due to an array of agronomic, economic, and technical reasons.  Agronomically, the narrow timeframe to identify and correct N deficiencies using sensor-based N fertilizer application strategies with traditional sidedress application equipment is the most notable reason for corn producer’s reluctance.  Thus, it is important to investigate alternative strategies to widen the window for applying N fertilizer to corn.  The objective of this research was to evaluate the response of winter wheat (Triticum aestivum L.) and spring barley (Hordeum vulgare L.) indicator crops to applied N over winter and early spring to estimate optimal early season N fertilizer application rates of the subsequent corn crop.  Winter wheat was planted in the fall of 2012 at two locations in north-central Oklahoma as two strips along the outside of the eventual corn trial.  Two strips of spring barley were planted in the spring of 2013 adjacent to the winter wheat strips.  Each strip was split and a sufficient rate (150 kg ha^-1) and zero rate of N fertilizer was applied at planting.  In the spring of 2013, corn was planted between the indicator crop strips and a randomized complete block design was used to evaluate six at planting N fertilizer treatments ranging from 0 to 225 kg ha^-1 in 45 kg ha^-1 increments.  Estimates of biomass and N deficiencies of each crop were determined using an active optical reflectance sensor, denoted as normalized difference vegetation index (NDVI), throughout the growing season.  Agronomic optimum N rate (AONR) will be determined for the corn at grain harvest.  Using the indicator crop’s NDVI response to applied N coupled with pre-existing algorithms, our hypothesis is that the AONR for the corn crop can be determined.  However, Oklahoma experienced an unseasonably cool and moist 2013 growing season that delayed corn harvest; therefore the results and conclusions are forthcoming.