NYS P Index: Source Score

The Source score component considers P in the soil ("Soil Test P"), P applied through manure (Manure P2O5), and P applied through fertilizer (Fertilizer P2O5).

The Source Score is determined by adding the three major components, as follows.

Source Score = Soil Test P + Manure P + Fertilizer P

Now consider each of the Source Score components, below.


Soil Test P Factor

Research continues to demonstrate that P losses increase as soil test P levels increase.

Soil Test P Score = 1.25 x Soil Test P (Morgan, lbs/acre)


Fertilizer and Manure Factors

Fertilizer and Manure Source Score factors are both based on the rate, timing, and method of application, as follows.

Manure Score = 0.75 x Manure P2O5 applied/acre x Timing Factor x Application Method Factor

Fertilizer Score = Fertilizer P2O5 applied/acre x Timing Factor x Application Method Factor


Rate of Application: As more P is applied through manure and fertilizer, more P can be lost from the field.


Timing of Application: More P will be lost from the field if applied during periods of the year with thawing, more rainfall, saturated soils, and/or no growing crops. Consider the graph of average runoff into a NYS stream, below.

As an example, look at the field, pictured below, during two different times of the year.

Higher risks associated with P applications during periods of wetter soil conditions are reflected in the weighting factors applied to the timing categories, below.

Application Timing Weighting Factors
May - August
September - October
November - January
February - April


Method of Application: If manure and fertilizer are applied and left on the soil surface, the P is more likely to move off the field with runoff and/or erosion. If it's tilled it into the soil soon after application, P is less likely to be lost from the field. The following weighting factors are applied to the full range of manure and fertilizer application methods.

Application Method Weighting Factors
Application Method Multiplier
Inject of subsurface band
Broadcast and incorporate within 1-2 days
Broadcast and incorporate in 3-5 days
Surface application or broadcast/incorporated after 5 days
Application on frozen, snow covered or satured ground

Now all of the factors are complete for calculating the Source Score.

Source Score = Soil Test P + Manure P + Fertilizer P

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