Conservation Drainage for Improved Water Quality in Missouri.

Controlled or managed subsurface drainage systems reduce tile drainage flow which can reduce nitrate-N and ortho-P loss in crop production systems.  In the past, Missouri has not been extensively tile drained, but the need to remove excess water in the soil during the spring and autumn has increased the number of patterned drainage systems installed in the region.  Research has focused on the effects of managed drainage for different soil types and crop production systems, and the impact of polymer-coated urea on fertilizer loss through the subsurface drainage system.   Managed drainage has reduced nitrate-N loss in tile drainage water up to 85% while ortho-P loss has been reduced up to 80% in a poorly-drained claypan soil.  In a silty clay river bottom soil, nitrate-N loss was reduced 29%.  Grain yield responses were affected by the drainage system and enhanced efficiency N fertilizer selection.  In an annual pasture system, forage yields increased with a subsurface drainage system, but were not affected by controlled drainage.  Managed drainage has worked effectively in reducing nutrient loss through subsurface drainage water flow in Missouri.