Varying Nitrogen Rates and Application Timing for Optimizing Corn Production In Mississippi.

As nitrogen (N) prices increase and environmental concerns grow, the need for efficient N use continues to grow.  In order to effectively use N,   the most appropriate rate, applied at the most appropriate time, is the key to economically optimum yields with the least impact top the environment.  The actual rates of application and timing of application may not be the same for different soil types, irrigated vs non-irrigated systems, or for different areas of the state.  Studies were established at the Delta Research and Extension Center (DREC, Stoneville) and North Mississippi Research and Extension Center (NMREC, Verona) to evaluate N rates and application timing in an effort to optimize grain yields keeping in mind that multiple systems could be equally effective at each location.  A series of N rates selected for each region and evaluated with five application scenarios.  These included 100% preplant (100PP), 75% PP + 25% as a sidedress (75PP-25SD), 50% PP + 50% SD (50PP-50SD), 25% PP + 75% SD (25PP-75SD), and 100% sidedress (100SD).  At each location urea-ammonium nitrate solution was the source used in the study.  Yield summaries from the NMREC location showed that in most years, the   ratio of PP N to SD N had little effect on yield when averaged across N rates.  There has been an N response each year but the level of response depends on the year.  In 2008 and 2010, grain yield was optimized with 269 kg N ha^-1 while in 2009 there was no significant response above 179 kg N ha^-1.  At the DREC location, under irrigated conditions, there was no difference between the systems in 2008.  In 2009, the higher yields occurred as more N was applied as a sidedress.  The N response has also varied with optimum N rates varying depending on the year.