Interaction of Corn Seeding Rate and Nitrogen Application Rate on Corn Grain Yield.

As seed companies release new corn hybrids to the market place, occasionally increased seeding rates are promoted, and often times these higher seeding rates are accompanied by increased fertilizer nitrogen rates.  The research information that supposedly serves as the basis for these new guidelines are not made available to customers, and thus the validity of the recommendation is often in question.  The goal of this research was to determine if increased corn seeding rates were more responsive to nitrogen and therefore required higher average nitrogen inputs.  Two field experiments were established in the spring of 2006 and 2007 to evaluate corn nitrogen response at two different seeding rates and in two different cropping systems (after soybeans or after corn).  A randomized complete block design was used with 4 replications.  Corn was planted at either 74,100 or 89,000 seeds per acre in 2006 and 74,100 or 98,800 seeds per ha in 2007.  Urea-ammonium nitrate was sidedressed after corn emergence at rates of 0, 67, 133, 201, and 269 kg N per ha.  Based on the first two years of data, there is not a consistent increase in the optimum nitrogen rate for corn planted at higher seeding rates.