Twin-Row Corn Production - Nitrogen Rates, Seeding Rates, and Cultivar Selection.

Corn production with twin-row planting on wide rows (96 to 102 cm) has been evaluated on producer fields since 2005 in the Mississippi Delta with significant yield increases from increased seeding rates and higher nitrogen (N) rates.  The original research project (SRxNR) sought to evaluate N rates (202, 246, and 291 kg N ha^-1) and five seeding rates (60,000 to 100,000 seeds ha^-1) with production on 96-cm beds.  A follow-up study was initiated in 2009 to evaluate six hybrids at three seeding rates (74,130, 86,485, and 98,840 seeds ha^-1).  Both studies were established in producer fields with inputs (pesticides, irrigation, fertilizer nutrients, etc.) managed by the producer.  In the initial study with N rates, the preplant or at-planting N was applied by the producer.  Subsequent N was managed by the research team and established the total N applied.  In the SRxNR study, grain yield was significantly increased with increasing seeding rates and N rates.  However, even though the yield advantage from increased N was significant, it was not economically viable.  Maximum yields (17.05 and 16.26 Mg ha^-1) were obtained in 2006 and 2007, respectively, with the highest seeding rates.  In 2008, where corn followed corn (and a different cultivar), there was no significant yield response above 90,000 plants ha^-1.  The follow-up study with cultivars, at a uniform N rate (producer determined) showed differences in yields from the various cultivars planted at the same seeding rates.  The cultivars had different responses to increasing seeding rates in different years.  Even though all cultivars were planted at the same rate (two cultivars at a time) stand counts differed when evaluated at the time of sidedress N application.  These results help to emphasize the need to select cultivars that are adapted to precise plant populations.  Most companies are addressing these issues.