Phosphorus Index for Oregon and Washington Steve Campbell USDA - Natural Resources Conservation Service Portland, Oregon Dan Sullivan Oregon State University Corvallis, Oregon

Purpose and Concept of the Phosphorus Index l The Phosphorus Index is a tool to assess the potential for phosphorus transport from a field to surface waters. l The index is based on soil properties, field characteristics, and management practices.

NUTRIENT ENRICHMENT CAN LEAD TO EXCESS ALGAE GROWTH Why is there a concern about phosphorus transport to surface waters?

Some Water Quality Impacts of Eutrophication l Impaired water quality for fisheries, recreation, industry, and drinking. l Some blue-green algae form compounds that are toxic to livestock and humans. l Oxygen depletion during decay of aquatic plants. l Increases in pH can cause an increase in ammonia concentrations, which can be harmful to fish.

P Management: Then and Now Then PROBLEM: Soils “fix” P in insoluble forms, limiting crop yields Now PROBLEM: Soils have a finite P sorption capacity. As we load a site with P, soluble P concentrations increase in runoff.

P Management: Then and Now Then FACT: We can control P loss from agricultural sites by reducing soil erosion losses Now FACT: Enough P to cause eutrophication can occur because dissolved P can move in runoff, without soil erosion

P Management: Then and Now Then FACT: Phosphorus does not move through the soil Now FACT: P can move through soil and reach surface water via tile drains

Phosphorus Transport Processes In: Sharpley et al., 1999; ARS-149

History of the Phosphorus Index l Developed by Lemunyon and Gilbert, USDA-SCS in 1993 (Journal of Production Agriculture 6:4) l Adopted by NRCS - Oregon in 1994 using the national model l Revision to the 1994 version in 2000 to reflect Pacific Northwest conditions.

Oregon and Washington P Index Revision Process l Developed by a committee composed of members from: –Natural Resources Conservation Service –Oregon State University –Washington State University –Agricultural industry

Factors in the Oregon and Washington Phosphorus Index l TRANSPORT FACTORS –Soil erosion potential –Runoff class –Flooding hazard –Distance to perennial surface water / buffer width –Subsurface drainage

Factors in the Oregon and Washington Phosphorus Index l SOURCE FACTORS –Soil Test P concentration –P application rate - commercial and organic forms –P application method and timing

Each P Index factor is assigned a weight based on its relative effect on P transport

Each P Index factor is assigned a P Loss Rating with corresponding points Each P Index factor is assigned a P Loss Rating with corresponding points

Soil erosion can transport sediment- bound P to surface waters.

Soil Erosion Factor (sheet and rill) predicted by the Revised Universal Soil Loss Equation (RUSLE) Soil Erosion Factor (sheet and rill) predicted by the Revised Universal Soil Loss Equation (RUSLE)

P Index Runoff Class Factor l This factor is based on: –Soil Hydrologic Group - considers water infiltration rate, depth to seasonal high water table, and depth to impermeable layers. –Field slope - the steeper the slope, the higher the potential for P transport.

Runoff Class Factor

Flooding can carry both soluble and sediment-bound P into surface waters

Flooding Hazard Factor - from soil surveys or local information Flooding Hazard Factor - from soil surveys or local information

Vegetated buffers can be effective in trapping P in runoff Filter StripRiparian Forest Buffer

Distance to Water / Buffer Width Factor Distance to Water / Buffer Width Factor

Soil sampling to determine Soil Test P levels is essential for using the P Index

Soil Test P: Agronomic & Environmental Interpretations In: Sharpley et al., 1999; ARS-149

Soil Test P Factor P Index Points = (Soil Test P - 40) / 10

Nutrient Balance: Grass Hay Biosolids fertilization, agronomic rate to supply 160 lb available N per acre Nutrient Balance: Grass Hay Biosolids fertilization, agronomic rate to supply 160 lb available N per acre Applied Nutrients Removed Nutrients

P Application Rate Factor P Application Rate Factor P Index Points = (lb/ac P 2 O 5 ) / 50

P Application Method Factor l Based on how and when phosphorus is applied to the soil l Is the P source injected, incorporated with tillage, or surface applied ? l What time of year is the P source applied ?

Application methods that inject P sources or incorporate with tillage reduce the risk of P transport.

Phosphorus sources that are surface applied have a higher risk of transport to surface waters.

Surface applied manure solids on a perennial forage crop

P Application Method Factor

Potential for P Transport Source Factors Soil Erosion Runoff Surface & Subsurface Soil Test P Rate of P applied fertilizer or manure Method & timing of P application P Index Class low, medium, high, very high Phosphorus Index Adapted from SERA-IEG 17, No. 389

In Sharpley et al., 1999; ARS-149 The P Index identifies area with high potential for P transport Phosphorus Index

P Index Site Vulnerability Classes

Evaluate current management Implement management or conservation practices that will reduce risk of P transport P Index: I’ve got a “high”or “very high” class rating, now what?

Phosphorus Index Summary l The Phosphorus Index is a planning tool to assess the potential for phosphorus transport from a field to surface waters. l Users of the P Index may include conservation planners, extension specialists, other agricultural professionals, and land managers.