Impact of a terminated wheat cover crop in irrigated corn on atrazine rates and water use efficiency

A study was conducted near Garden City, KS with irrigated corn to determine how the integration of a terminated winter wheat cover crop with various atrazine rates would affect Palmer amaranth control and corn water use efficiency (WUE). Without atrazine, the presence of a winter wheat cover crop, killed in the boot stage, resulted in a threefold weed biomass reduction in irrigated corn. The highest rate of atrazine completely masked the weed control effect of the cover crop, producing a greater than 15-fold reduction regardless of the presence or absence of the cover crop. A terminated winter wheat cover crop without atrazine elevated corn yield in only two of nine location-yr, and in one instance, depressed yield. However, a terminated wheat cover crop elevated corn yield in six of nine location-yr combinations when used in conjunction with 1.6 kg ha(-1) atrazine. Although increases in WUE associated with reductions in soil water evaporation produced by the cover crop seemed to be responsible for some of the increase in corn grain yield and stored soil water at the end of the summer growing season, end of season Palmer amaranth biomass had a more profound impact.