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.
Keywords:
controlled drainage; shallow drainage; modeling; hydrology; drainage water
management.