Impact of agricultural drainage in Minnesota

Glacial processes in the Upper Midwest created an abundance of highly productive but poorly drained soils (Figure 1). While it’s improved agricultural production, drainage also affects hydrology, water quality and wetland habitats.

Agricultural land benefiting from improved drainage
Figure 1: Agricultural land benefiting from improved drainage. Source: D. Jaynes, Department of Agriculture Agricultural Research Service (ARS).

Improved agricultural production

Poorly drained soils increase risks to agricultural production from excess water and high water tables. Proper soil drainage improves agricultural production by:

  • Ensuring timely planting and field operations.

  • Minimizing soil compaction and salt buildup.

  • Promoting conditions for good seedbed establishment and germination.

  • Minimizing high water table stresses to growing crops.

  • Outyielding poorly drained soils

  • Offering less year-to-year yield variability.

  • Improving the opportunity to employ other conservation practices such as minimum tillage.

Other effects

Both artificial drainage and land-use change (prairie to agriculture) affect hydrology, water quality and habitat. It’s difficult to separate the individual effects of drainage and land-use change.

Hydrology

Surface and subsurface drainage have very different hydrologic impacts.

  • Surface drainage: Speeds flow from landscape and increases peak flows.

  • Tile drainage: Promotes more infiltration, slowing water delivery from the landscape (compared to surface drainage). However, studies indicate potential for overall water yield increases from 5 to 10 percent.

Local hydrologic effects are dampened at larger watershed scales.

Water quality

Surface and subsurface drainage affect water quality differently:

  • Surface drainage: May increase losses from surface runoff (primarily sediment and phosphorus).

  • Tile drainage: May reduce surface runoff pollutants, but may increase dissolved nutrients such as nitrate.

Wetland reductions

Drainage activities have reduced the number and extent of wetlands. In some areas, they’ve reduced by as much as 90 percent.

However, wetlands are now protected by federal and state laws. In some areas, wetlands are actually being restored, usually on land that once was cultivated.

Drainage usage

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Conservation drainage practices

It’s important to meet water quality goals, while addressing drainage needs for agriculture. Consider incorporating one or more of these conservation practices:

  • Nutrient best management practices.

  • Controlled drainage or drainage water management (Figure 5).

  • Two-stage ditches.

  • Shallow drainage.

  • Reduce drainage intensity.

  • Woodchip bioreactors.

  • Improved surface inlets.

  • Improved side inlets.

  • Winter cover crops.

  • Wetland restoration.

  • Nutrient retention basins.

Read more about these practices

Installation of drainage
Figure 5: Installation of drainage water management system with control structures. Photo: Brad Carlson
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Gary R. Sands, Extension engineer

Reviewed in 2018

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