With Ohioans nearing completion of the harvest season for grain crops, producers throughout the state are also working to finish post-harvest field operations such as fertilization, herbicide and manure applications, and fall tillage. Once these operations are completed fields will receive little traffic in the coming months, until preparation for planting begins in early spring.
Because of this reduced need for trafficability, subsurface drainage systems do not necessarily need to be free-flowing (figure 3) until field operations are close to resumption. Therefore, the time frame following harvest and post-harvest field operations is one of the points when producers who utilize controlled drainage structures will go back and raise the water tables in their fields (figure 1). A higher water table allows for water that would otherwise be transported off the field via tile, to be largely retained in the field. The water table is raised in controlled drainage systems by adding boards on top of each other within the control structure.
Drainage Control Structure Images credit to Dr. Jane Frankenberger, Purdue University
Drainage Control Structures must be managed to maximize efficacy. Though raising the water table during the growing season is often of interest due to its potential for water storage (figure 2), raising the water table during the non-growing season is important for reducing the risk of subsurface nutrient loss, particularly nitrate leaching. In fact, if producers implement this practice through a cost share program, effective management of the structure is sometimes a requirement for participation and/or payment.
To view more general information on this practice and its measured efficacy, see https://agbmps.osu.edu/bmp/controlled-drainagedrainage-water-management-nrcs-554 . Further research on this practice in Ohio field conditions is currently being conducted.
To see more detailed guidance about utilizing this practice, see previous CORN article from 2015 by Dr. Larry Brown and Dr. Norman Fausey: https://agcrops.osu.edu/newsletter/corn-newsletter/2015-39/setting-outlet-water-level-drainage-water-management-structures .