Crop Yield and Nitrate Losses From Sidedressing N at Canopy Closure.

There is growing interest in applying N to corn in response to remotely sensed plant N status.  Remote sensing of N status appears to be most successful after canopy closure (V10), but needs to be before reproduction starts (R1) for optimal N use and lowest NO₃ leaching under natural rainfall (Jaynes and Colvin, 2006).  While the yield benefits of sidedressing N at V10 are well documented, little information is available on the impacts to water quality.  We compared grain yields and NO₃ losses in drainage water as a result of applying N either once after plant emergence or equally split between just after emergence (V1) and early crop growth (V6 or V10).  Nitrogen treatments consisted of 138 kg ha^-1 applied post-emergence (V1), and 69 kg ha^-1 applied post-emergence and again at either V6 or V10.  Grain yield for corn and soybean, grown in a 2-yr rotation, and drainage water NO₃ concentrations and flow were measured on replicated tile-drained plots in a producer’s field from 2006 through 2009.  Results from yield and water quality measurements will be reported.