CORN AND WEED INTERACTIONS WITH NITROGEN IN DRYLAND AND IRRIGATED ENVIRONMENTS

Corn yield potential is limited by water deficit stress and limited soil nitrogen. Field and greenhouse experiments were conducted near Manhattan, KS in 2005 and 2006. The field experiment evaluated the influence of nitrogen (N) rate and increasing Palmer amaranth (PA) density grown alone and in competition with corn in two moisture environments. In 2006 the dryland environment was very drought stressed, while 2005 had more intermediate conditions. Weed-free corn yields were approximately half in dryland environments compared to the irrigated environment across years. Increasing PA density increased corn yield loss similarly in both 2005 environments and in 2006 dryland environment across all N rates. In the 2006 irrigated environment corn yield loss was increased by decreasing N rate and increasing PA density. Maximum predicted yield loss at high PA densities in both 2005 environments was 20-54 % while in 2006 dryland environment, maximum yield loss was 95 % and in the irrigated environment was 62%. In general, soil moisture environment was more critical than N rate or PA density when determining potential corn yield. In the greenhouse study a factorial arrangement of two irrigation methods and five crop-weed combinations (corn, PA, GF