Using Active Canopy Sensing to Adjust Nitrogen Application Rate in Corn

Remote sensing that uses active sensors continue to be tested as an N stress detection method and provide in‐season rate adjustments to corn ( Zea mays L.). The objectives of the study were to use active canopy sensing to vary in‐season N application at the V10 corn growth stage and compare applied N rate, grain yield, and nitrogen use efficiency (NUE) with N applied before planting. A fertilizer N rate study was conducted in 2009 and 2010 near Ames, IA. Pre‐plant N rates were 0 to 270 kg N ha −1 and then sensor‐based rates were applied in‐season at the V10 corn growth stage. Rainfall events occurred 3 to 5 d after N application each year, providing corn response to the in‐season applied N and increasing relative corn canopy biomass by the V13 growth stage. The pre‐plant applied nitrogen (PP‐N) 270 kg N ha −1 rate used as the N‐reference did not result in the highest green normalized difference vegetative index (GNDVI) or produce the highest grain yields. The pre‐plant plus sensor applied nitrogen (PP+S‐N) recovered corn yield from plant N stress at V10. The best yield recovery with deficit pre‐plant N and sensor‐directed N application rate occurred each year when no pre‐plant N had been applied. Overall, economic optimum nitrogen rate (EONR) and NUE in PP‐N and PP+S‐N were the same. The PP+S‐N application does give corn growers options for addressing in‐season N deficiency and protect yield potential when corn N need is uncertain or when soil N losses are unavoidable.