The phosphorus index and manure management plans for confinements
by Jeremy Klatt, Iowa Department of Natural Resources
The Iowa Environmental Protection Commission (EPC) adopted rules that include using the phosphorus (P) index to determine application rates for manure management plans (MMPs) at their June 21 meeting. The P index was developed by scientists from Iowa State University, the National Soil Tilth Laboratory and the Natural Resources Conservation Service (NRCS) 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.
The Department of Natural Resources (DNR) developed rules for using the P index to determine manure application rates as required by state law. The rules apply to confinement feeding operations that are required to use MMPs and will be phased in over the next four years.
Depending on the P index results, manure application rates can be based on phosphorus or nitrogen (N). The EPC adopted the following application rates based on results of the P index.
Very Low (0-1). Nitrogen-based manure management.
Low (>1-2). Nitrogen-based manure management.
Medium (>2-5). Nitrogen-based manure management if practices will not raise the field to the “high” risk category. Manure applications must not result in application of P in excess of two times the P removal of the crop rotation.
High (>5-15). Until Dec. 31, 2008, fields with a P index rating between 5 and 10 may receive manure at a P-based rate if practices will be adopted to reduce the P index of the field to the “medium” risk category. After Dec. 31, 2008, no manure may be applied until practices are adopted that reduce the P index to the “medium” risk category.
Very High (>15). No manure application.
Here are some important points to consider about the P index and MMPs.
For more information about the P index, including the P index calculator go to the Iowa NRCS Web site at http://www.ia.nrcs.usda.gov/.
Additional changes to manure management plans that were adopted by the EPC:
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Page last updated October 5, 2004
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