Active Sensor Strategies for Inseason Application of Urea in Corn.

Addition of N fertilizer during the mid-vegetative growth stage is being used in Iowa to protect corn yield potential. The objectives were to compare pre-plant, split, and rescue N strategies, and evaluate N use efficiency and grain yield of variable rate sensor N. In 2012 and 2013, the N strategies were pre-plant (168 kg N ha^-1 prior to planting), split (84 kg N ha^-1 pre-plant + 84 kg N ha^-1 at V10 + sensor N at V10), and rescue (168 kg N ha^-1 pre-plant + sensor N at V10). Six fertilizer N rates were applied pre-plant (0 - 280 kg N ha^-1) with and without sensor applied N. Additionally, published sensor N trial results in Iowa from 2009 (normal year), 2010 (wet year), and 2012-13 (dry years) were evaluated.  There were no differences in corn NUE or grain yield between N strategies at the 168 kg N ha^-1 pre-plant rate. Sensor applied N with reduced pre-plant N rates (100 kg N ha^-1 + sensor N) successfully maintained yield potential in 2012 and 2013. Comparison of normal, wet, and dry years showed that sensor N applied with 50 - 100 kg N ha^-1 pre-plant N maintained relative yields greater than 95%, with greater response to sensor applied N during wet years.