NYS P Index: Particulate P Transport Score

The next step in assessing a field with the P Index is to determine the potential for particulate P loss, shown in the diagram, below.

Particulate P Transport score = Soil Erosion Factor + Flooding Frequency Factor + Flow Distance to Stream Factor + Concentrated Flow Factor

Note: The Particulate P Transport score is a value between 0 and 1, so all raw scores greater than 1 are rounded back to 1.

Soil Erosion Factor

Phosphorus is also transported from fields to watercourses in particulate form, bound to soil during erosion. Erosion often occurs due to high intensity, short duration rainfall events. Particulate P is also less available for algal growth than dissolved P, because it is bound to soil particles.

The assessment is partially based on the measurement for soil erosion developed by the Natural Resources Conservation Service known as the Revised Universal Soil Loss Equation (RUSLE). RUSLE estimates average annual soil loss over the crop rotation due to sheet and rill erosion from a field. This includes all erosion short of gullies that cannot be erased with tillage. Such gullies are considered concentrated flows (more on that, later). More information on RUSLE can be found at http://msa.ars.usda.gov/ms/oxford/nsl/rusle/overview.html

The Soil Erosion Factor within the Particulate P Transport Score is calculated as follows.

Soil Erosion Factor = 0.1 x Erosion Rate from RUSLE (tons/acre)

Flooding Frequency Factor

The flooding frequency factor is determined with the same method as for the Dissolved P Transport Score.

Flooding Frequency Flooding Factor
Rare to Never ( > 100 years)
0
Occasional (10 - 100 years)
0.2
Frequent ( < 10 years)
1.0

Flow Distance to Stream Factor

The flow distance factor is also handled with the same method as for the Dissolved P Transport score.

If intermitent stream (dashed blue line)
 > 200 feet
0
25-200 feet
1 - ((Distance - 25) / 175)
 < 25 feet
1
If perennial stream (solid blue line)
> 300 feet
0
50-300 feet
1 - ((Distance-50) / 250)
< 50 feet
1

Concentrated Flow Factor

Because RUSLE doesn’t measure erosion from larger gullies, the influence of gullies that cannot be erased by tillage should be included in the Particulate P Transport Score. Such gullies are called concentrated flows.

Concentrated Flow Factor: If present, add 0.2. If absent, 0.

Now all the factors are complete for the Dissolved P Transport score.

Particulate P Transport score = Soil Erosion Factor + Flooding Frequency Factor + Flow Distance to Stream Factor + Concentrated Flow Factor

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