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Appendix C: Phosphorus Index

Author: OMAFRA Staff
Creation Date: 01 March 2002
Last Reviewed: 01 March 2002
Agronomy Guide > Pub 811: Appendices > Phosphorus Index
Excerpt from Agronomy Guide for Field Crops (Appendices)
Order OMAFRA Publication 811: Agronomy Guide for Field Crops

Table of Contents

  1. Introduction
  2. Phosphorus Index to Assess Risk of Surface Water Contamination
  3. Example Calculation
  4. Soil Erosion Value1 - Table A
  5. Water Run-off Value - Table B
  6. P Soil Test Value - Table C
  7. P2O5 Fertilizer Value - Table D
  8. P2O5 Manure Value - Table E
  9. Application Restrictions at Various Phosphorus Index Values - Table F
  10. Updates on Appendix C: Phosphorus Index
  11. Related links...

Introduction

The Phosphorus Index evaluates erosion potential as well as application rate and placement of all phosphorus sources. This indicates the risk of off-site movement, while the proximity to a watercourse dictates the risk of off-site movement actually causing contamination of surface water. The final result of the phosphorus index calculation is a set of application rate restrictions at various distances from a watercourse. Tables A through E, below, provide the values needed to determine the Phosphorus Index.

Phosphorus Index to Assess Risk of Surface Water Contamination

Value From
Table A
(     ) 

+

Value From
Table B
(    )  

+

 Value From
Table C
(    ) 

+

 Value From
Table D
(    ) 

+

 Value From
Table E
(    ) 

=

 

Phosphorous
Index
(    ) 

Example Calculation

Value From
Table A:
corn no-till planted on a 3% slope
( 2  ) 

+

Value From
Table B:
clay loam soil on a 3% slope
( 4    )  

+

 Value From
Table C:
P soil test of 35 ppm
( 8    ) 

+

 Value From
Table D:
10 kg/ha (9 lb/ac), placed with planter
( 2.5    ) 

+

 Value From
Table E:
143 kg/ha (128 lb/ac) of P2O5 applied in manure, incorporated 3 days
( 7    ) 

=

 

Phosphorous
Index
(23.5   ) 

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Table A. Soil Erosion Value1
Slope within 150 m
(500 ft)
of watercourse		 Length of Slope m (ft) Hay Other Crops
Up & Down Slope Cross Slope
Plow No-Till Plow No-Till
Flat (< 0.5%) All 2 4 2 4 2
Gentle
(0.5%-2%)		 Short: 60 m (200 ft) 2 4 2 4 2
Gentle
(0.5%-2%)		 Long: 480 m (1,600 ft) 2 16 4 16 2
Moderate
(2%-5%)		 Short: 60 m (200 ft) 2 16 2 8 2
Moderate
(2%-5%)		 Long: 480 m (1,600 ft) 2 16 8 16 4
Steep (>5%) Short: 60 m (200 ft) 2 16 4 16 4
Steep (>5%) Long: 480 m (1,600 ft) 2 16 16 16 16

1Note: These values simulate a worst case scenario of soybeans on very fine sand in a high rainfall area. To obtain more accurate results using the universal soil loss equation refer to the nutrient management computer program (NMAN).

Table B. Water Run-off Value
Slope Soil Texture
Sand Loam Clay Loam Clay
Flat (1%) 1 1 2 4
Gentle (3%) 1 2 4 8
Moderate (5%) 1 2 4 8
Steep (8%) 2 4 8 8

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Table C. P Soil Test Value
P Soil Test Factor
< 15 ppm 2
15-30 ppm 4
31-60 ppm 8
61-100 ppm 16
> 100 ppm 32

Table D. P2O5 Fertilizer Value
Rate (Line K)
kg/ha (lb/ac)		 Method
Placed with
Planter		 Incorporated <2 weeks Incorporated
>2 weeks		 Not
Incorporated
None 0 0 0 0
<50 (<45) 2.5 4 7 13
50-75 (45-67) 3.5 5 8 14
>75 (>67) 5.5 7 10 16

Table E. P2O5 Manure Value
Rate (Line C)
kg/ha (lb/ac)		 Method
Injected Incorporated
<5 days		 Not
Incorporated
Crop Cover		 Not
Incorporated
Bare Soil
None 0 0 0 0
<37 (<33) 2.5 4 7 13
37-57 (33-54) 3.5 5 8 14
>57 (>54) 5.5 7 10 16

Once the Phosphorus Index is calculated, it is possible to outline restrictions to application rates and locations. Because the main risk from phosphorus pollution is to surface water, higher Phosphorous Index values will mean that a greater separation distance is required from surface waters for manure or broadcast fertilizer applications. The zone where application rates are restricted to crop removal is also increased. Application restrictions are outlined in Table F. Application Restrictions at Various Phosphorus Index Values.

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Table F. Application Restrictions at Various Phosphorus Index Values
P. Index Separation Distance
<3 m
(<10 ft)		 3-30 m
(10-100 ft) 		30-60 m
(100-200 ft)		 >60m
(>200 ft)
< 30 STOP! No application Caution!
Only apply P2O5 up to crop removal
(Line M # 0)		 No additional restriction due to
Phosphorous Index 		No additional restriction due to
Phosphorous Index
30-50 STOP! No application Caution!
Only apply P2O5 up to crop removal
(Line M # 0) 		Caution!
Only apply P2O5 up to crop removal
(Line M # 0) 		No additional restriction due to
Phosphorous Index
>50 STOP! No application STOP! No application Caution!
Only apply P2O5 up to crop removal
(Line M # 0) 		Caution!
Only apply P2O5 up to crop removal
(Line M # 0)

Source: Nutrient Management Practices BMP

Note: For a more detailed analysis of the Phosphorus Index, refer to the Nutrient Management Computer Program (NMAN) or the Determining the Phosphorus Index for a Field, factsheet order no. 05-067.

Updates on Appendix C: Phosphorus Index

No updates available at this time.

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Related links...

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