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Drainage innovations help protect water quality

There is a growing emphasis on managing agricultural drainage water to improve both yields and water quality, says Gary Sands, a University of Minnesota Extension biosystems engineer. New techniques can help cut pollutants in drainage water without lowering drainage efficiency. Some examples:

•Two-stage ditches have gradual side slopes that mimic a natural flood plain, keeping sediment from being carried downstream.

•Shallow drainage involves placing tile lines about 3 ft. beneath the soil surface, rather than the more conventional four feet. Shallow drainage systems cut drainage water volume by up to about 40%, according to Iowa State University (ISU) research.

•Controlled-drainage water management uses an outlet structure with stacked risers or stop logs, installed in tile mains to raise and lower the field’s water table. Water can be conserved in the soil during the winter and the growing season, and then released before planting and harvesting. In the summer, the water table can be adjusted up or down according to rainfall and crop needs. The practice can reduce drainage water flow 25-35%, according to ISU research.