More nitrogen fertilizer is applied to corn than to all other U.S. crops combined, contributing to atmospheric heat trapping when nitrous oxide is produced.  Higher nitrogen rate is well known to increase nitrous oxide emissions, and earlier N application time may increase the window during which nitrous oxide can form.  An experiment was initiated in 2012 comparing nitrogen management and drainage effects on corn yield and nitrous oxide emissions.  Two nitrogen treatments were used:  140 lb N/acre applied before planting, and N applied variably when corn was knee-high with N rate guided by canopy sensors.  Little nitrous oxide was released in 2012, a drought year.  In 2013, in-season N application reduced nitrous oxide emissions by 75% compared to pre-plant N application; in 2014 the reduction was 40%.  In both years, in-season N application increased corn yield by nearly 20 bushels/acre relative to pre-plant application.  Nitrate concentration in drainage water was also reduced.