Increasing Corn Yields with Increased Seeding Rates and Nitrogen Management in a Twin-Row Production System.

A corn research project was initiated in 2005 on a production field to evaluate the interaction of seeding rates (60,000 to 100,000 seeds ha^-1) for twin-row (20-25 cm apart) corn production (96-cm beds) and nitrogen (N) rates (202, 246, and 291 kg N ha^-1).  The study was planted each year on Bosket very fine sandy loam, following cotton (2005-2007) or corn (2008), with a Monosem™ twin-row vacuum planter.  Seeding rates were based on calibration tables supplied by the manufacturer and adjusted prior to the 2008 season.  Stand counts just prior to sidedress N application indicated that plant stands were equal to or greater than anticipated.  No grain yields were measured in 2005 due to adverse effects from Hurricane Katrina.  The 2006 and 2007 growing seasons produced some of the highest yields reported in the Midsouth for irrigated corn.  In each of those years where corn followed cotton, there was a significant response to increasing N rates and seeding rates.  Grain yields in 2006 averaged 15.60, 15.77, and 15.97 Mg ha^-1 (adjusted to 15.5% moisture) for the increasing N rates 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. In 2006 and 2007, each increase in seeding rate resulted in a subsequent increase in grain yield.  While the response to increasing N rates was significant, the cost of the fertilizer N could not be recovered.  In 2008 with corn 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.