This document discusses the challenges of reducing phosphorus runoff from agricultural fields in a large region. The challenges include the large spatial scale involved, fields generally contributing small amounts of phosphorus, and the high costs of implementing conservation practices to reduce phosphorus on a per-pound basis. Edge-of-field monitoring provides data on phosphorus losses through surface runoff and tile drainage. Models can estimate phosphorus losses and the potential impact of different conservation practices, but costs vary significantly depending on existing phosphorus losses and the practices used.

1. Nutrient Management
Challenge of Reducing Field P
Contribution
Greg LaBarge,
Field Specialist Agronomic Systems
Great Lakes Big Rivers Conference-December 2018

2. The Challenge
• Scale
• Spatial – Landscape extent of small parcels
• Field Level P Contribution
• Economics
• Implementation cost per pound P reduction

3. Units
Category Value
Parcel count
(number)
126,919
Acres 5,513,628
Average
Parcel size
(Acres)
43.4
Acres

4. Units
Category Value
Parcel count
(number)
126,919
Acres 5,513,628
Average
Parcel size
(Acres)
43.4
Acres
P Type Target
Total P 860 MT
DRP portion 186 MT
DRP 0.05 PPM

5. What Determines Loss
Potential in a Field?
Source + Transport = Loss
• Soil Test
Level (P)
• Nutrient
additions
• Soil Type
• Drainage
• Management
• Cover
• Distance to
water
• Pounds of
loss per acre
Tools
• For P, P Risk Index
• For soil erosion, RUSLE 2

6. Edge of Field-EOF
20 sites with paired fields total
of 40 fields being sampled for
edge of field losses of nutrient
Monitoring both:
• Surface
• Subsurface water (Tile)
USDA-ARS-Dr Kevin King

7. Water Flow on Acre
of Ground in WLEB
Surface
Discharge
8%
Tile
Discharge
25%
Soil
Retained
68%
Annual Water Flows
Average of 6 Silty Clay Loam field sites
in NW Ohio
2015-2017 Water Years
Average Rainfall 35.1 inches
Source Inches Percentage
Surface Discharge 2.8 8%
Tile Discharge 8.6 25%
Total Discharge 11.4 32%
Soil Retained 23.7 68%
Total 35.1 100%
Source: USDA-ARS
Silty Clay Loam
Soil Water Holding Capacity (NRCS)
6.9 inches
to 60 inches deep

9. Discharge from a 40 Acre Field
Source Inches
Annual ft3
from 40
Acre
Equivalent
Olympic Size
Swimming
Pools
Surface
Discharge 2.8 8% 406,583 5
Tile Discharge 8.6 25% 1,248,793 14
Total
Discharge 11.4 32% 1,655,376 19

10. Water Flows in Maumee River
River Flow Minutes
out of year
1,000 CFS 28
10,000 CFS 3
Time period for annual
discharge from 40 acre field
to flow past gauge station

11. Field Level
DRP Concentrations <
DRP Concentration: Subsurface < Surface
Filtering through results
in lower P concentrations
Source: USDA-ARS

12. Field Level
DRP Loading >
3 times Water Volume
Subsurface vs Subsurface
DRP Loading: Subsurface > Surface
Source: USDA-ARS

13. Annual P Loading from a 40 Acre Field at
(0.25 pound/Acre loss)
Source Water (ft3) DRP Load (lbs)
Surface
Discharge 405,977 2.1
Tile Discharge 1,251,487 7.8
Total
Discharge 1,657,464 9.9

14. Soil Test?

15. Influence of Soil Test P on Field P Losses
King et al., 2018
Duncan et al., 2017

16. Influence of Soil Test P on Field P Losses
Soil Test P above
agronomic rates
increases
environmental risk
King et al., 2018
Duncan et al., 2017

17. Influence of Soil Test P on Field P Losses
Soil Test P above
agronomic rates
increases
environmental risk
BUT Soil Test P
does not equal
environmental risk
King et al., 2018
Duncan et al., 2017

18. Fertilizer Application?

19. Fertilizer
Application?
Source: Mullen, 2013

20. Fertilizer
and Manure
Application?
Source: Mullen, 2013

21. P Index
(and Other Tools)
Category Value
Parcel count
(number)
126,919

22. P Index Calculations
for 77 Farms (38,186 Acres) in WLEB
Estimated P loss
(lbs. per acre) *
Loss with nutrient
applications
Percent Acres
0-0.5 20%
>0.5-1.5 52%
>1.5-2.5 20%
>2.5-5.0 8%
>5.0-10.0 0%
*Calculated through Annual Phosphorus Loss Estimator (APLE) Tool

23. P Index Calculations
for 77 Farms (38,186 Acres) in WLEB
Estimated P loss
(lbs. per acre) *
Sediment P Loss
Percent Acres
Dissolved P Loss
Percent Acres
Loss with nutrient
applications
Percent Acres
0-0.5 51% 74% 20%
>0.5-1.5 38% 25% 52%
>1.5-2.5 7% 1% 20%
>2.5-5.0 2% 0% 8%
>5.0-10.0 2% 0% 0%

24. Cost per Pound of P Reduction
on 40 Acre Field (0.25 pound/Acre loss)
BMP Practice
Predicated
Reduction
Effectiveness
Original
DRP Load
(lbs)
Reduction
(lbs)
Total Cost to
Implement
Cost per lb of
P reduction
BMP 1 40% 9.9 4.0 $1120 $281

25. Cost per Pound of P Reduction
on 40 Acre Field (0.25 pound/Acre loss)
BMP Practice
Predicated
Reduction
Effectiveness
Original
DRP Load
(lbs)
Reduction
(lbs)
Total Cost to
Implement
Cost per lb of
P reduction
BMP 1 40% 9.9 4.0 $1120 $281
BMP 2 58% 9.9 5.7 $1120 $196

26. Cost per Pound of P Reduction
on 40 Acre Field (0.25 pound/Acre loss)
BMP Practice
Predicated
Reduction
Effectiveness
Original
DRP Load
(lbs)
Reduction
(lbs)
Total Cost to
Implement
Cost per lb of
P reduction
BMP 1 40% 9.9 4.0 $1120 $281
BMP 2 58% 9.9 5.7 $1120 $196
BMP 3 95% 9.9 9.4 $6500 $691

27. Cost per Pound of P Reduction
on 40 Acre Field (1.5 pound/Acre loss)
BMP Practice
Predicated
Reduction
Effectiveness
Original
DRP Load
(lbs)
Reduction
(lbs)
Total Cost to
Implement
Cost per lb of
P reduction
BMP 1 40% 60 24.0 $1120 $47

28. Cost per Pound of P Reduction
on 40 Acre Field (1.5 pound/Acre loss)
BMP Practice
Predicated
Reduction
Effectiveness
Original
DRP Load
(lbs)
Reduction
(lbs)
Total Cost to
Implement
Cost per lb of
P reduction
BMP 1 40% 60 24.0 $1120 $47
BMP 2 58% 60 34.8 $1120 $32

29. Cost per Pound of P Reduction
on 40 Acre Field (1.5 pound/Acre loss)
BMP Practice
Predicated
Reduction
Effectiveness
Original
DRP Load
(lbs)
Reduction
(lbs)
Total Cost to
Implement
Cost per lb of
P reduction
BMP 1 40% 60 24.0 $1120 $47
BMP 2 58% 60 34.8 $1120 $32
BMP 3 95% 60 57.0 $6500 $114

30. Cost per Pound of P Reduction
on 40 Acre Field
BMP Practice
Predicated
Reduction
Effectiveness
Total Cost to
Implement
0.25 lb/A loss
Cost per lb of P
reduction
1.5 lb/A loss
Cost per lb of P
reduction
BMP 1 40% $1120 $281 $47
BMP 2 58% $1120 $196 $32
BMP 3 95% $6500 $691 $114

31. The Challenge-Summary
• Scale
• Spatial-large geographic region
• Field Level P Contribution-Generally small Contributions
• Economics
• Implementation cost per pound P reduction-Need to
target conservation practices to improve ROI