Palmer amaranth influences selection of crop production practices such asirrigation, nitrogen (N) application, and weed control. The objectives ofthis research were to determine if Palmer amaranth was more responsive toapplied N than corn and if this differed under dryland and irrigatedconditions in Kansas. Field experiments were conducted near Manhattan, KS,in 2005 and 2006 to evaluate the influence of N rate and Palmer amaranthdensities when grown with corn in two soil moisture environments. A verydrought-stressed environment and a well-watered environment occurred in2006, while both environments in 2005 were intermediate. Dryland weed-freecorn yields were 46.5% of irrigated corn yields at the high N rate acrossyears. Irrigated corn yields responded to increasing N rates. In thepresence of Palmer amaranth, parameter estimates I and A for the yield lossrelationship were not different across N rates for each environment and yearexcept 2006 where 100% yield loss was estimated in dryland compared to 62.5%loss in irrigated environment at high N rates. In three of fourenvironment-years, N rate did not affect the corn yield loss relationshipwith weed density. In 2006 irrigated environment, greater N rates had lesscorn yield loss caused by Palmer amaranth. By corn anthesis, weed-free cornbiomass was 167.5% greater in irrigated than dryland environments in 2006.Palmer amaranth with no corn increased its biomass by 373 and 361% as N rateincreased in 2005 and 2006, respectively. Nitrogen concentrations in planttissues of corn or weed increased similarly as N rates increased from 0 to224 kg N ha−1, thus highlighting that both corn and Palmeramaranth responded similarly to increasing N. In general, soil moistureenvironment was most critical when determining potential corn yield,followed by Palmer amaranth density and N rate.
