Assess the risk for each field before an application
These maps are based on a NWS flood forecast model. Cropped fields are smaller than the grids and can vary considerably within a grid. Local characteristics can significantly affect the model’s applicability to a given field. Always apply your own knowledge of the landscape when assessing the risk of runoff for your fields. Considerations include:
Risk increases with soil moisture
The system assumes grid-wide average conditions for soil moisture. If you know that your fields are particularly wet (for example, you experienced a recent rainfall event that was greater than in other parts of the grid) you should know that the risk of runoff from your fields will be higher than what is shown on the risk map. The opposite may hold true if you estimate that your soil moisture values are lower than the grid-wide average.
Even if the map shows low risk of runoff, your fields may not be dry enough to spread
Applying liquid manure (typically equivalent to 1/3 to 1 inch or more of rainfall) to wet fields can lead to direct manure runoff, even if the field is otherwise a low risk site due to low slope or low P-index. Make sure your fields are dry enough to accept additional moisture. If liquid manure should runoff or pond in a field or discharge into tile lines, application must stop until the runoff can be checked. Additionally, operating field equipment on wet fields can lead to soil compaction which can greatly reduce crop yields.
Liquid manure applications increase soil moisture
An application of 27,000 gallons per acre of liquid manure is the equivalent of adding approximately 1 inch of water to your fields. A liquid manure application effectively increases your soil moisture, and therefore the risk of runoff from fields receiving liquid manure will be higher than what is shown on the risk map.
Some fields are always higher risk areas
These are areas of concern on your farm and might include fields with higher slopes, tighter soils, poor drainage, or fields that are closer to sensitive features such as ponds, streams, lakes, wetlands, sinkholes, etc. Many of these areas may be identified in your nutrient management plan. You should use caution when applying manure or any agrichemical products in these areas, regardless of what the risk map indicates.
If you must haul manure during high runoff risk times:
Avoid field spreading manure by:
- Using neighboring or other available manure storage facilities
- Creating in-field stacking in areas that pose the least environmental runoff risk.
For manure storing guidelines, see Natural Resources Conservation Service’s “Conservation Practice Standard Waste Storage Facility, Code 313.”
If field spreading of manure is necessary:
Identify lower-risk fields for spreading or stacking manure:
- Apply to your driest fields
- Avoid sensitive areas of your fields. For information on what options you have, see the MPCA Manure Management Plan
- Use your Manure Management Plan or Nutrient Management Plan to find fields with:
- low slope
- low erosion, and
- low delivery potential (low P-Index)
- Apply to flatter fields without channelized flow, gullies
- Apply to fields farthest from surface water, conduits to groundwater, and areas of concentrated flow
- Apply to fields that do not drain to Outstanding, Exceptional, or nutrient impaired water bodies
In winter, follow these additional restrictions, from MPCA Manure Management Plan:
- No nutrient spreading in the winter within 300 feet of lakes, streams, intermittent streams, public waters wetlands, drainage ditches without berms, and open tile intakes.
- Do not spread during snowmelt that creates runoff or when rainfall over ¼ inch is expected within 24 hours.
- Only spread liquid manure to slopes less than 2 percent and soild manure to slopes less than 6 percent.
- Only spread manure where tillage is on the contour (if slopes are greater than 2 percent).
- Make sure to apply liquids at rates that prevent runoff during the application process.
- Find alternative fields or management where MPCA determines that water will be polluted if you do spread.