Managing Risks

If a field’s rotational average P Index value is too high, planners can change management to:

  • reduce sources (amount of phosphorus available to runoff in the field), or
  • reduce transport (potential for runoff and erosion from the field). 

Different combinations of management activities can be used to achieve reductions in phosphorus losses through addressing sources or transport or both. An appropriate strategy will depend on the soil and landscape conditions as well as the farm’s existing management system and production goals.

Strategies to reduce phosphorus available to runoff can include:

  • Reducing manure and fertilizer phosphorus application rates to less than crop removal.
  • Reducing manure and fertilizer P on the surface when the field is vulnerable to runoff.

Strategies to reduce P transport from the field can include:

  • Reducing tillage
  • Reducing residue removal
  • Cover crops
  • Working fields on the contour
  • Contour strips and countour buffers
  • Grass filter strips

Some of the strategies that will reduce rainfall runoff and erosion can increase runoff from frozen soil. This is because fall tillage, especially fall tillage on the contour, leaves depressions in the field surface that can capture runoff from melting snow.  This is can be important to understand when identifying fields for late fall and winter manure applications.