MCE Agricultural Nutrient Management Program

Phosphorus Site Index

The Phosphorus Site Index, or PSI, is an integral part of a nutrient management plan. If a producer intends to add phosphorus in commercial or organic forms (including starter fertilizer) to a field and the soil test indicates a phosphorus fertility index value (FIV-P) of 150 or more for that particular field, then the PSI should be calculated.

The PSI takes into consideration phosphorus loss potential due to site and transport characteristics and management and source characteristics.

Site and Transport Characteristics
soil erosion, as determined by the Revised Universal Soil Loss Equation (RUSLE) soil runoff class subsurface drainage leaching potential (See Leaching Index Values for MD counties) distance from the edge of the field to surface water priority of receiving water

Management and Source Characteristics
soil test FIV-P method and rate of phosphorus fertilizer application method and rate of organic phosphorus application

Nutrient Management Regional Specialist Lief Eriksen (pictured right) uses a clinometer to measure the slope of a field, which is one part of the PSI calculation.

Nutrient management advisors in the county Maryland Cooperative Extension offices and private consultants can calculate the PSI for any agricultural field.

Want more information on the PSI?
Download the following free publications:

Nutrient Manager Newsletter - "Focus on Phosphorus Site Index"

Soil Fertility Guide (P-3) - "Phosphorus Site Index"

Soil Fertility Management (SFM-6) - "The Maryland Phosphorus Site Index - An Overview"

Soil Fertility Management (SFM-7) - "The Maryland Phosphorus Site Index Technical Users Guide"

Questions and/or comments should be sent to jsalak@umd.edu
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Page last modified November 15, 2007 | © 2005 University of Maryland

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