BMPs for southwestern and west central MN (corn)

Key points

Best management practices for nitrogen vary region by region. This is because Minnesota has a wide diversity of soils and climatic conditions. As a result, region-specific recommendations have been developed based on the combination of these factors and years of University research.

The southwestern and west central areas of Minnesota are typically warmer and drier than other parts of the state. Glacial till and loess soils are predominant in this region. The soils formed from glacial till generally have clay loam to silty clay loam textures and poor internal drainage. They account for the majority of the soils in this area.

In the far southwestern corner of the state (Pipestone and Rock counties), the soils formed from loess deposits. They generally have a silt loam texture and because they were deposited on old glacial till, are also poorly drained.

The typically drier climate of these regions reduces the risk of nitrogen losses. As a result, there are more options available for managing nitrogen.

Recommended nitrogen management practices

Some practices are recommended throughout the state:

• Take credit for nitrogen supplied by previous legume crops, sugarbeet tops and manure.
• Include all sources of fertilizer N.
  • Starter
  • Weed and feed programs
  • Phosphorus sources such as MAP and DAP.

Recommendations specific for corn in these regions (northwest, west central, and southwest) for fine and medium-textured soils:

Select the optimum N rate for corn:

• Use the University of Minnesota guidelines, which take current fertilizer and corn prices, soil productivity, and economic risk into account.
• Use the soil nitrate test, when appropriate, and adjust the nitrogen rate accordingly.

Recommended N application methods

• Fall application of anhydrous ammonia (AA) when soil temperatures have stabilized below 50 degrees F at a 6-inch soil depth.
• Fall application of urea when soil temperatures have stabilized below 50 degrees F at 0 to 6-inch soil depth. Urea should be incorporated to a depth of 3 inches.
• Spring applied urea. Incorporate to a depth of at least 3 inches within 3 days
• Spring applied UAN. Incorporate to a depth of at least 3 inches within 3 days.
• Apply sidedress N before corn is 12 inches tall (V7) under rainfed conditions.
• Split apply nitrogen if soils have a high leaching potential.

Acceptable nitrogen management practices with risk

Some nitrogen management practices carry greater risk. These may be either economic or environmental. Economic risk can occur when added inputs don't result in additional yield. Environmental risks are primarily related to potential nitrogen loss to ground or surface waters.

Acceptable practices with risk include:

• Late fall application of ESN (incorporated).
• Spring preplant application of ESN (incorporated).
• Fall application of anhydrous ammonia with a nitrification inhibitor.
• Fall application of urea with either a urease or nitrification inhibitor.
• Nitrogen management practices that are not recommended.

Nitrogen management practices that are NOT recommended

Some management practices are not recommended because the economic and environmental risks are too great.

Practices that are NOT recommended:

• Fall application of UAN (28-0-0) or any fertilizer containing nitrate-nitrogen.
• Shallow or no incorporation of fall-applied urea.
• Application of nitrogen containing fertilizers to frozen ground, including MAP and DAP.
• Surface application of ESN without incorporation.