P Index Fundamentals of Nutrient Management Training Course December 15, 2005 Isaac Wolford, West Virginia NRCS State Agronomist

WHAT IS THE P (PHOSPHORUS) INDEX ? The P index quantitatively determines the relative risk of P movement from a given field by considering most of the factors that govern P losses.

WHAT IS THE P (PHOSPHORUS) INDEX ? The Phosphorus Index (P Index) is a tool that can identify farm fields that are a potential source of phosphorus (P) pollution of surface waters. Using the P Index can help a farmer identify fields and management practices that have the greatest potential to pollute bodies of water with phosphorus.

What does Phosphorus Index Do? PHOSPHORUS INDEX COMBINES THE EFFECT OF SOURCE FACTORS TRANSPORT FACTORS

SOURCE FACTORS What does Phosphorus Index Do? TRANSPORT FACTORS Soil Test P Source, Method, Rate, Timing of P Soil Erosion

Site Vulnerability Site vulnerability to P-loss as a function of Total P Index rating values Site vulnerability ratingTotal P Index rating value Low<8 Low<8 Medium8 to 14 Medium8 to 14 High15 to 32 Very High>32

Site Vulnerability Low to medium site vulnerability ratings indicate that current management practices are adequate for protection of surface waters from phosphorus pollution. High and very high site vulnerability ratings indicate a need for improved management practices.

Phosphorus Concerns Leading To The Index Use Annual application of phosphorus exceeding its removal by crops. Phosphorus accumulation in soils leads to high soil test values for phosphorus. Movement of phosphorus from crop fields into bodies of water may lead to excessive growth of algae (algal bloom).

Phosphorus Concerns Leading To The Index Use Thus, algal bloom caused by phosphorus movement to a body of water leads to reduction of oxygen in water. However, most P initially added to land through fertilizer or manure reacts with soil components, converting to an insoluble form or attaching to soil particles. Thus, most P loss in agriculture is associated with loss of soil particles. Thus, most P loss in agriculture is associated with loss of soil particles.

The West Virginia Situation Currently in West Virginia, there are no state nutrient management regulations. This presentation focuses on requirements as they relate to USDA NRCS Nutrient Management Standard (590). Recent CAFO Management rules have referenced the use of the 590 Standard.

The West Virginia Situation Use of the 590 Standard is limited to USDA programs and CAFO management plans (As outlined in the CAFO permit rules). Surrounding states have adopted a phosphorus index. Each state has a different type of phosphorus index. There is discussion on standardizing the P Index in the East.

NEW FOR 2005  The latest version of RUSLE2 contains a Nitrogen Leaching Index.  The Index number can be applied to the existing scale.

RUSLE2 N LEACHING INDEX N Leaching Index

LEACHING INDEX NUMBER INDEX NUMBER BY SOIL TYPE

National Phosphorus Management Options

Phosphorus Application Option 1 The Phosphorus Index P INDEX RATING P APPLICATION Low Risk Medium Risk High Risk Very High Risk Nitrogen Based Phosphorus Based CROP REMOVAL Phosphorus Based NO APPLICATION

Phosphorus Application Option 2 The Phosphorus Threshold Soil P Threshold Level P APPLICATION < ¾ TH = > ¾ TH, ¾ TH, < 1 ½ TH = > 1 ½ TH, 1 ½ TH, < 2 TH = > 2 TH Nitrogen Based Phosphorus Based CROP REMOVAL Phosphorus Based ½ CROP REMOVAL Phosphorus Based NO APPLICATION

Phosphorus Application Option 3 Soil Test Phosphorus Soil Test Phosphorus Level P APPLICATION LOWMEDIUMHIGH VERY HIGH EXCESSIVE Nitrogen Based Phosphorus Based 1½ TIMES CROP REMOVAL Phosphorus Based CROP REMOVAL Phosphorus Based NO APPLICATION

Status of the P Index in West Virginia West Virginia has utilized a P Index within the 590 standard since the mid-1990s. The P Index has remained unchanged since its inception.

The Current P Index in West Virginia The current P Index is only utilized in a five county area in the Potomac Valley of West Virginia.

Statewide Standard  Manure or litter may be applied at the nitrogen based application rate when soil test phosphorus levels are low to medium.  If the current soil test indicates the soil phosphorus level is high, a phosphorus based application rate of up to 1.5 times the crop removal rate will be used.  If the phosphorus level is very high, greater than 80lbs/ac, manure or litter may be applied at the crops estimated phosphorus removal rate.

Statewide Standard  If the phosphorus level is less than 120 lbs., a single application of phosphorus applied as manure may be made at a rate equal to the recommended phosphorus application or estimated phosphorus removal in harvested plant biomass for a maximum period of 3 years. When such application is made the nitrogen application rate will not exceed crop needs during the year of organic fertilizer application.

Phosphorus Field Risk Assessment (Potomac Valley SCD)  When animal manures or other organic by- products are applied and the current soil test indicates the soil phosphorus level is very high, greater than 80lbs/ac, a field-specific assessment of the potential for phosphorus transport from the field shall be completed.

Phosphorus Field Risk Assessment (Potomac Valley SCD)  For fields with high or very high potential losses, appropriate conservation practices identified in the Phosphorus Index must be installed to reduce the vulnerability to off- site phosphorus transport.  A record of the assessment rating for each field or sub-field, and information about conservation practices and management activities that can reduce the potential for phosphorus movement from the site, will be included in the plan.

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