Water table response to drainage water management in Southeast Iowa

A key component in managing subsurface drainage is controlling water table depth to limit excess drainage off site. The objectives of this work were to evaluate the impact of drainage water management through controlled drainage and shallow drainage on subsurface drainage volumes, water table depths, and crop yields. This research was conducted at the Iowa State University Southeast Research Farm and consisted of four paired management schemes for a total of eight plots. Plots consisted of a corn-soybean rotation with half of the plot planted in corn and half planted in soybeans each year. Preliminary findings for three years show undrained plots had a high occurrence of elevated water tables. Controlled and shallow plots had elevated water tables in the early spring and early fall in accordance with the rainfall and management protocols for controlled drainage. Water table response was quick with drawdown to tile depth within 2 to 3 days after significant rain events. Total annual drainage from the shallow and controlled plots was approximately equal and ranged from 20 to 40% of rainfall, while the conventional plots typically drained greater than 40% of the rainfall. There was no statistically significant difference between drained plots in terms of corn and soybean yield for the study period. Undrained plots, however, had slightly lower yields for both corn and soybeans. Overall, during the period of the study drainage water management through controlled drainage or shallow drainage reduced overall drainage volume while maintaining crop yield.