BMPs for south central Minnesota

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 soils in the south central region were formed in glacial till. This material was deposited as the last glacier was melting and receding. Soils that form in till generally have clay loam to silty clay loam textures and poor internal drainage. They also have a variety of rock sizes scattered throughout the root zone (but we probably don't need to tell you that).

In this region, increased rainfall combined with poor internal drainage increases the risk of N loss through drainage tile or denitrification.

Recommended nitrogen management practices

Some practices are recommended throughout the state:

• Take credit for nitrogen supplied by previous legume crops 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 this region:

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.

Recommended N application methods

• Spring preplant applications of anhydrous ammonia and urea are highly recommended.
• Incorporate broadcast urea to a depth of at least 3 inches within 3 days.
• Split applications of ammonia, urea and UAN are highly recommended.
• Inject or incorporate sidedress applications or urea or UAN into moist soil to a depth of at least 3 inches within 3 days.
• Apply sidedress N before corn is 12 inches tall (V7) under rainfed conditions.

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 greater risk include:

• Fall application of anhydrous ammonia with a nitrification inhibitor after soil temperatures at a 6-inch depth are stabilized below 50 degrees F.
• Spring preplant application of UAN. The UAN should be incorporated.
• Late fall or spring preplant applications of ESN.

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 applications of urea and anhydrous ammonia without a nitrification inhibitor.
• Sidedressing all nitrogen when corn follows corn.
• Fall application of UAN (28-0-0).
• Application of any N fertilizers, including MAP and DAP, to frozen soils.