As of October 25, 2004, confinement producers who are required to submit manure management plans (MMP) must include the phosphorus (P) index when developing an original MMP. Producers who submitted an original MMP prior to October 25, 2004, will need to use the P index when preparing their MMP updates as indicated in the table below:

Left: Phosphorus tends to bond to soil particles, so soil erodibility and the potential for soil to leave the field are major factors determining results from the P index. Photo courtesy of USDA-NRCS.

The P index was developed by scientists from Iowa State University, the National Soil Tilth Laboratory and the Natural Resources Conservation Service to determine the risk of P loss from a field. The index is based on erosion, soil test, location of the field, P applications and other factors.

Once a P index-based MMP is required, producers will need to run the P index on each field in their plan. The P index assesses a field as having Very Low, Low, Medium, High, or Very High risk of P loss to surface waters. The results of the P index will be used to determine manure application rates in the MMP.

Changes to Iowa law in 2002 required using the P index to determine manure application rates in MMPs.

• For more information about the P index, see the DNR P index fact sheet (*.pdf file)
  
  
• The DNR's MMP rule with P index (*.pdf file) is available