Drainage Water Management: Fate of Water and Nitrate.

Drainage water management (DWM) has been proposed as an alternative water management technique on agricultural fields to reduce nitrate losses via subsurface drainage and to improve water quality of local and downstream freshwater rivers and streams. To date, studies have focused on the efficiency of DWM in reducing tile flow and nitrate from the fields. What is still unknown is the fate of the water and nitrate that is held back. The objective of this project was to determine the pathways that nitrate and water follow when DWM was applied. We hypothesized that the water and nitrate that is held back in the field would increase the water table as well as denitrification rates to remove nitrate, or that water was move to deeper groundwater. To test this, two no-till corn and soybean rotation fields were each instrumented with Agridrain structures to measure outflow and, deep and shallow monitoring wells to determine water table levels and nitrate concentrations. Water samples were collected weekly to daily for both outlets, and weekly for wells to determine the nitrate concentrations. In 2012 we determined that water held back in the north tile during Feb. and March flowed out the south tile. We found that tile outflow had a rapid response to rain events, and there was a strong relationship between the outlet water level and the water table level on the wells located in the field. An aquiclude in limited any deep seepage. In 2013, both tile systems were raised to various water table heights and lowered to further determine the flow paths from Jan. through April. When both were raised, water table heights indicated movement of water around the control structures and across the road to a nearby tile system. We conclude that lateral movement was the main flow path followed by water under saturated conditions, and that little nitrate removal occurred along these flow paths.