On-Farm Twin-Row Corn Production with Varying Nitrogen Management and Cultivar Interactions in the Mid-South.

Multi-year field studies (2011-2012) were established in producer fields to evaluate corn cultivar by nitrogen (N) management interactions.  Each study over the two years has had a similar design. Nitrogen rates were 134, 168, 202, 235, 269, and 302 kg N/ha (120, 150, 180, 210, 240, and 270 lb N/acre) with either 67 or 134 kg N/ha (60 or 120 lb N/acre) applied just after planting and the remaining N applied as a sidedress application at V5 to V7 growth stage (total of 12 treatments).  The N source for all studies was urea-ammonium nitrate solution with ammonium thiosulfate (32-0-0-3).  Each study was replicated six to eight times in a randomized complete block design.  All cultural practices except N application were maintained uniformly by the producer.  Each plot consisted of four rows on 96-cm spacings, 27.4 to 30.5 m in length (90 to 100 ft and 38-in spacing).  The center two rows of each plot was harvested with a commercial combine adapted to plot harvest and a sample taken to determine harvest moisture, bushel test weight and seed weight.  The corn cultivars were selected based on their performance and adaptability to the region and ranged in maturity for 111 to 120 days.  All cultivars were planted with a Monosem twin-row planter at approximate 85,000 seeds/ha.  In 2011, the earliest maturing cultivar had the least response to increasing N yet the highest yield at the lowest N rate.  As the relative maturity of the cultivars increased, the cultivars became more responsive to increasing N but lower yields at the lower N rates.  This effect was not as evident in 2012.  Grain yields were good in both 2011 and 2012 with overall yields greater in 2012.  The 2012 yields ranged as high as 17.6 Mg/ha (280 bu/acre).