Mississippi Delta growers are hoping to boost their corn yields  by planting in twin-row systems on raised beds. Their success will depend on, among other things, seeding rates and nitrogen (N) fertilization.
Mississippi State University research at the Delta Research and Extension Center is evaluating these key components of twin-row production. Researchers are also comparing twin-row vs. single-row planting systems on highly productive irrigated soils in the Delta.
Twin-row planters and drills are already being used to optimize soybean production with conventional row spacings of 38-40 in. on raised beds, which facilitate drainage and irrigation. Now, growers want to use these same planters for other crops to increase yields and profitability and make better use of their equipment.
The idea behind the twin-row planting system is that corn yields can be significantly increased by boosting the seeding rates and adjusting in-row plant spacing. This was examined in a three-year, on-farm study at Stoneville, MS, partly funded by the Mississippi Corn Promotion Board.
Five seeding rates ranging from 25,000 to 40,000 seeds/acre and three N rates — 180, 220 and 260 lbs./acre — were evaluated in a combination of treatments, which were replicated four times in a grower's field. N was applied as urea-ammonium nitrate solution plus sulfur (30-0-0-2) with 60-90 lbs./acre N applied at planting and the remaining N sidedressed.
In 2007, DeKalb DKC 66-23 corn was planted into a fine, sandy loam soil with a Monosem twin-row planter on 38-in. rolled beds. Stand counts just prior to the sidedressed N application ranged from 4.5% to 12% higher than expected based on the planter book settings; the greatest variation was found at the lowest seeding rate.
GRAIN YIELDS IN the 2007 study ranged from 228 to 263 bu./acre when adjusted to 15.5% moisture. High temperatures and low humidity during the field-drying period resulted in lower harvest moisture, decreasing bushels per acre sold due to the excess shrinkage.
Each increase in seeding rate led to a significant increase in grain yield with the highest yield at 259 bu./acre from a stand of 42,350 plants/acre. When averaged across all five seeding rates, grain yields were 244.7, 246.4 and 248.8 bu./per acre for N rates of 180, 220 and 260 lbs./acre, respectively.
Though statistically significant, the increased N rates were not economical. The cost of the additional fertilizer could not be covered by the value of the increased yield.
These results were very similar to the results from 2006 when grain yields were even higher than in 2007. In 2006 there was a significant response to both increased seeding rates and increased N rates. However, the yield increase due to the higher N rates did not offset the cost of the additional fertilizer.