Hydrological modification of subsurface drainage systems
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Controlled Drainage (CD), a subsurface drainage management system, has been researched in many regions. Previous research has reported CD to reduce subsurface drainage and as a result reduce nitrate loading. CD has been reported to have little effect on nitrate concentrations, so exploring alternative treatments to reduce these concentrations would be constructive. This research was intended to measure the effect of CD on surface runoff, crop yield, water table depth, and to document a biofilter's effect on nitrate concentrations. CD increased surface runoff ranging from 53% to 130%, increased corn yield by 14% over two years, and decreased nitrate loading with a range of 47% to 93%. The use of a biofilter decreased nitrate concentrations and loading by 35%. Water table measurements were also taken every five minutes on average over a two-year period and showed potential long-term water retention in a CD system.