Agricultural subsurface drainage changes the field hydrology and potentially the amount of water available to the crop by altering the flow path and the rate and timing of water removal. Evapotranspiration (ET) is normally among the largest components of the field water budget, and the changes in ET from the introduction of subsurface drainage are likely to have a greater influence on the overall water yield (surface runoff plus subsurface drainage) from subsurface drained (TD) fields compared to fields without subsurface drainage (UD). To test this hypothesis, we examined the impact of subsurface drainage on ET at two sites located in the Upper Midwest (North Dakota-Site 1 and South Dakota-Site 2) using the Landsat imagery-based METRIC (Mapping Evapotranspiration at high Resolution with Internalized Calibration) model. Site 1 was planted with corn (Zea mays L.) and soybean (Glycine max L.) during the 2009 and 2010 growing seasons, respectively. Site 2 was planted with corn for the 2013 growing season. During the corn growing seasons (2009 and 2013), differences between the total ET from TD and UD fields were less than 5 mm. For the soybean year (2010), ET from the UD field was 10% (53 mm) greater than that from the TD field. During the peak ET period from June to September for all study years, ET differences from TD and UD fields were within 15 mm ( 0.05) and showed no consistent relationship.

Drainage water recycling, storing subsurface drainage water for reuse as irrigation water, is a practice that is gaining interest to meet both production and environmental goals. There is limited research on the feasibility of this practice in Iowa and the rest of the U.S. Corn Belt. The objectives of this study were to quantify net irrigation requirements at multiple locations in Iowa, the potential supply of subsurface drainage water that could be stored for reuse, and the frequency that stored drainage water would be adequate to meet crop water demands. The growing season net irrigation requirement ranged from 114 mm to 269 mm for maize and 103 mm to 259 mm for soybean. The mean annual subsurface drainage depth was 226 mm. In 50% of years that irrigation was required, subsurface drainage water was adequate to fully meet crop water demands. These results are the first step towards understanding the feasibility and design requirements of drainage water recycling systems in Iowa.