Effects of Seeding Rates and Nitrogen Rates on Corn Production in Twin-row Planting Systems for the Mississippi Delta.

A multiple-year research project was established in 2005 on a production field to evaluate the interaction of nitrogen (N) rates (202, 246, and 291 kg N ha^-1) and  seeding rates (60,000 to 100,000 seeds ha^-1) for twin-row (20-25 cm apart) corn production (96-cm beds).  The study was planted each year on Bosket very fine sandy loam, following cotton (2005-2007) or corn (2008), with a MonosemJ twin-row vacuum planter.  Seeding rates were based on calibration tables supplied by the manufacturer and modified prior to the 2008 season.  Stand counts at the time of sidedress N application indicated that stands were equal to or greater than expected.   No yields could be measured in 2005 due to adverse effects of Hurricane Katrina.  The 2006 and 2007 growing seasons produced some of the highest yields reported in the Midsouth for irrigated corn.   There was a significant response to increasing N rates and seeding rates in both 2006 and 2007 where corn followed cotton.  Grain yields in 2006 averaged 15.60, 15.77, and 15.97 Mg ha^-1 for the increasing N rates when adjusted to 15.5 % moisture and averaged across seeding rates.  In 2007, the yields were 15.35, 15.45, and 15.60 Mg ha^-1 for the same N rates.  Grain yields in 2006 ranged from 13.93 to 17.05 Mg ha^-1 for increasing seeding rates and 14.33 to 16.26 Mg ha^-1 in 2007.  Each increase in seeding rate resulted in a subsequent significant increase in grain yield both years.  While the response to increasing N rates was significant, the cost of the fertilizer N could not be recovered.  In 2008 following corn, there was no significant N response above 246 kg N ha^-1 and no increase in yield with seeding rates above 90,000 seeds ha^-1.  A cultivar shift in 2008 could also have contributed to lower yields.