What is drainage water management?

Drainage water management is the practice of using a water control structure in the main, submain, (or sometimes lateral) drain to raise the drainage outlet to various depths. This allows farmers to have more control over drainage. The outlet or control structure shown in the figure above is:

• Raised after harvest until early spring to limit drainage outflow and reduce the delivery of nitrate to ditches and streams during the off-season. (Figure 1)
• Lowered so the drain can flow freely before field operations such as planting or harvest. (Figure 2)
• Raised again after planting and spring field operations to create a potential to store water that could be used by the crop in midsummer. (Figure 3)

Potential Yield Benefits: With proper management of the structures and timely rainfall, the potential exists to improve crop yields beyond the typical crop response to drainage. However, results from field research on the agronomic benefits of the practice are very limited and inconclusive.

Demonstrated Water Quality Benefits: Published studies have found reductions in annual nitrate load in drain flow ranging from about 15% to 75%, depending on location, climate, soil type, and cropping practice. Nitrate load is reduced by about the same percentage as drain flow is reduced, since most studies have found little change in the nitrate concentration in the drain flow.

"Golden Rule of Drainage": Only drain the amount of water necessary to insure trafficable conditions for field operations and to provide an aerated crop root zone. Any drainage in excess of this likely carries away nitrate and water that is no longer available for crop uptake. --- Attributed to Dr. W. Skaggs