Pre-Tassel Nitrogen Applications for Improving Corn Yields in Mississippi- Fact or Fiction?.

Traditionally, nitrogen (N) applications for corn in the Midsouth has involved either a single or split application just prior to planting or after crop emergence followed by a sidedressed application at the 5-6 true leaf growth stage (PP-SD). Producers have been interested in later N application, up to tasseling.  A field evaluation of corn response to tassel nitrogen (TN) was initiated in 2009.  The standard (PP-SD) N treatments ranged from 134 to 314 kg N ha^-1 with 134 kg N ha^-1 applied at planting and 0, 45, 90, 134, and 179 kg N ha^-1applied at the 5-6 leaf stage.  Pre-tassel N was applied at rates of 0, 22, 45, and 67 kg N ha^-1 as urea.  The N was hand-applied to simulate an aerial application.  The treatments were a factorial arrangement of PP-SD N (5 levels) and TN (4 levels) in a randomized complete block design with four replications.  Cultural practices were maintained uniformly across the study.  Grain yields, harvest moisture, bushel test weight, and 100-seed weights were determined from each plot.  Grain yields have been significantly increased with TN especially at the lower PP-SD N rates.  Although yields have been quite different across years, the response to TN has been evident in each year.  In 2009, corn yields ranged from 3.78 to 11.06 Mg ha^-1 with the highest yields were measured where the highest N rates were applied.  The TN applications increased grain yields by 1.60 to 2.16 Mg ha^-1 when averaged across the PP-SD N rates.  In 2010, the highest yield was obtained with 269 kg N ha^-1 when average across the TN rates.  Actual yields ranged from 8.58 to 14.18 Mg ha^-1.  When averaged across all N rates, adding 22 to 45 kg N ha^-1 significantly increased grain yields by 0.75 to 1.13 Mg ha^-1.  In 2011, optimum yields (11.32 to 11.85 Mg ha^-1) were obtained with 269 kg N ha^-1 averaged across TN rates. Adding TN increased yields from 12.1 to 18.0% when averaged across the PP-SD treatments.