Shallow and controlled drainage systems in Iowa's tile landscapes

Large parts of the Upper Midwest, relatively flat and poorly drained soils, are artificially drained through subsurface(tile) drainage systems for improved crop production. While subsurface drainage removes excess water and improves crop production, it carries nitrate (NO3) from the soil profile contributing to the pollution of surface water bodies. This negative environmental impact of subsurface drainage is needed to limit through in-field management, drainage management, or edge of field practices. This study presents the results of hydrological modeling showing how different drainage design and its management would impact subsurface drainage, surface runoff and crop production in Iowa's tile landscapes. WEBster soil cultivated with Continuous Corn (WEBS_CC) was simulated using DRAINMOD with two drain depths 0.75 and 1.20 m at different spacing from 10 to 50 m over a weather record of 60 (1945-2004) years. Further subsurface drainage was controlled to maintain water table at 0.60 m below surface level during the winter (November to March) and summer (June to August) months. The results showed that there is a tradeoff between maximizing crop production while minimizing subsurface drainage. Further, there seems a choice between subsurface drainage or surface runoff as a pathway to remove excess water from the system. Both shallow and controlled drainage might reduce subsurface drainage but increase surface runoff. Controlled drainage showed slightly higher potential than shallow drainage in reducing subsurface drainage associated with less increase in surface runoff.