ABSTRACT A water management study for corn and soybeans was conducted on a claypan soil in south central Illinois to determine yield response to irrigation and drainage. The study investigated all possible combinations of four drainage methods under both sprinkler irrigation and nonirrigated conditions. Over the seven year period of the experiment, average annual corn yield increases were 3.9 t/ha for irrigation and up to 1.8 t/ha for drainage. A synergistic yield increase of up to 5.0 t/ha for corn was present. Soybeans were less responsive to either irrigation or drainage over a 4-yr period with average annual yield increases of 0.4 t/ha for both practices. A synergistic yield increase of up to 0.7 t/ha for soybean was produced over the 4-yr period.