Example: Estimating Manure Phosphorus Application Rates

Example: Estimating Manure Phosphorus Application Rates

(pdf version of Example)


P-Based Application Rate = Corn Phosphorus Need (2); Manure P Content (11)

  • Corn Phosphorus Need was calculated previously in equation 2.
  • Manure P Content is representative concentration of manure P from manure analysis.

P-Index Interpretation:

The Nebraska P-Index developed by the University of Nebraska (2006) will be used for analysis. The P Index risk value is the sum of the erosion and runoff components. The interpretation of risk and recommended manure application risk fall into one of four levels:

Low (0-2). Current practices keep water quality impairment low due to agricultural P pollution. Manure can be applied at rates sufficient to meet crop P needs.

Medium (2-5). Delivery of agricultural P many cause some water quality impairment and consideration should be given to alternative conservation and P management practices. Manure can be applied at rates sufficient to meet crop N needs.

High (5-15). Phosphorus loss from the field causes much water quality impairment. Remedial action, such as alternative conservation measures or P management practices, is required. Manure can be applied, but applied P should not exceed crop P removal. Crop P removal can be the sum of single year crop P removal over 5 years with no manure application during the next four years to this same field.

Very High (> 15). Impairment of water quality is extreme and remedial action is urgently required. Phosphorus application should be discontinued. Improved conservation measures should be implemented.

Requirements for application of a phosphorus-based manure rate to a field include:

  • No single manure application shall exceed the nitrogen-based rate of the planned crop receiving the particular manure application.
  • Phosphorus in manure should be considered 100 percent available unless soil phosphorus concentrations are below optimum levels for crop production. In that case, 70% availability for first year will be assumed.
  • If the actual crop schedule differs from the planned crop schedule, then any surplus or deficit of phosphorus shall be accounted for in the subsequent manure application.

Nebraska P-Index Results (Assessment completed in 2007)

Field P-Index Value Application Rate
Field 1-Pivot 0.7 N-based Rate
Field 2-Feedlot Quarter 1.2 N-based Rate
Field 3-Dry Quarter (West) 10.3 P-based Rate; 4-year P supply for single application
Field 3-Dry Quarter (East) 6.6 P-based Rate; 4-year P supply for single application


Nebraska P Index table

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