This is a talk about using phosphorus balances as a practical tool for water quality management in agricultural watersheds.

1. Watershed P Balances as a Tool for TMDL
Planning
Lawrence Baker and Heidi Peterson1
1Now at the Minnesota Department of Agriculture
Support:
MPCA/EPA 319 Program

2. Goal: Develop a Watershed P Balance Tool
To Inform Nutrient Reduction Plans
1. Develop watershed-specific P balance with high level
of detail
2. Develop spreadsheet tool to support general use
Albert Lea Lake Watershed
- 164 square miles
- 64% cropland
- City of Albert Lea

3. Fertilizer
Human food
Sewage
Animal
products Crops Lake
Atmospheric
deposition
Deliberate
Exports
Inputs
Retention
(soil P)
Stream P
Animal feed
The Whole Watershed P Balance Concept

4. Relationship between watershed P
balance and stream P
P inputs > Deliberate P export:
Soil test P (STP) increases
Stream P increases
P inputs < Deliberate P export:
STP decreases
Stream P decreases
Is this true?

5. 1. In lab studies, runoff P is predicted from STP
(Vadas et a., 2005, J. Env. Qual.)

6. Stream P, ug/L
Klatt et al., 2003. J. Env. Qual .
2. For watersheds, stream P
concentrations is related to average STP
(Klatt et al., 2003, J. Env. Qual.)

7. How would we use a watershed P balance
approach?
50
40
30
20
10
0
Manure P
0.31 0.39 0.47
% dietary P
Milk production, kg/day
100
80
60
40
20
0
Manure P, g/day
Milk P
1. Move “upstream”: Study of P supplements in dairies
showed overuse of P supplements (Wu et al. 2001, J. Dairy Sci.)

8. % to lake
% exports
% retention
0 25 50 75 100
Hubert
Big Trout
Sibley
Long
Belle Taine
Gilbert
Le Homme Dieu
Fishook
Darling
Lobster
Victoria
% input P
2. Understand fate
of input P
(Schussler et al., 2007,
Ecological Eng.)

9. 50
40
30
20
10
0
No yield reduction below 13 mg/kg
1975
1977
1979
1981
1983
1985
1987
1989
1991
1993
Soil P, mg/kg
40 lb P/acre No P fertilizer
3. Understand temporal watershed P dynamics
(Randall et al., 1997, J. Ag. Production)

10. Approach for Albert Lea Watershed P Balance
Crop cover in 2010
Soybeans (39%)
Corn (56%)
USDA Cropland Data Layer (2010)

11. Albert Lea Lake watershed crop data
Fertilizer
application
per acre
Land area
fertilized
Land
area†
Calculated
total P crop
uptake‡
Calculated
total P
applied
lbs P2O5 lbs % (acre) (tons) (tons)
Alfalfa 11 5 20 687 9 0.3
Corn 66 29 89 33,123 543 426
Corn-
Sweet 62 27 62 1,256 28 10
Soybeans 46 20 5 23,164 223 12
†Area calculated using the USDA, 2010 Cropland data layer.
‡Based on %P dry-matter values from Ketterings and Czymmek (2007).
Crop data were determined from 88 on-farm interviews
(Denton Bruening) + NASS data.

12. Adjusted Number of Animal Units
(Denton Bruening and Colin Whitmer)
Livestock
System Permitted Actual
% of
Permitted
Beef 2,223 829 37%
Dairy 218 218 100%
Horses 245 43 18%
Sheep 398 95 24%
Swine 12,824 6,157 48%
Turkey 445 440 99%
Multi-Animal 434 98 23%
Watershed
16,787 7,880 47%
Total
Visual inspection showed that actual animal counts were
lower than permit values.

13. Swine P Balance
(tons/yr)
Meat = 48.4
Rendered
= 1.5
Manure = 38.5
Piglets = 5.2
Feed = 85.0
Input: 90.2 ton P / yr
Output: 88.4 ton P / yr
We developed P balances for each animal system.

14. Summary of Calculated Livestock Efficiencies
System Input Manure
Product
Export Efficiency
(tons/yr)
Beef 18.1* 14.3 5.0 28%
Pork 90.2 38.5 49.9 55%
Dairy 3.6* 2.4 1.3 37%
Turkey 22.7* 11 12.4 54%
* Includes calves / piglets / poults imported into herd
We developed a spreadsheet calculator for each major
animal system.

15. Average Annual Agricultural Stream P Loads, 2009-
2011 = 24 tons/yr
6.0 tons
High annual variability
5.8 tons
8.7 tons
2.6 tons
0.9 tons
Includes winter adjustment
Tons TP
2009 14
2010 29
2011 26

16. Stream TP flux,
kg/yr
TP yield,
kg/ha-yr
Part. P,
%
Soluble
P, %
Water
yield,
cm/yr
Bancroft Ct. 5411 0.62 26 74 30
Wedge Cr. 7904 0.88 39 61 33
Peter Lund Cr. 5250 0.69 36 64 24
Watersheds are similar with respect to TP yields, dominance
of soluble P, and water yields.

17. Atmospheric Deposition
19
Piglets 5
Holstein
Steer Calves 0.3
Watershed P use efficiency = 824/487 = 1.7
Fertilizer
391
Pork 50
Milk 1.1
Beef 5
Crops
754
Dairy &
beef feed
21
Manure
38
Hog feed
82
Deliberate
exports = 824
Manure
17
Inputs =487
Stream export
24.0 (5% of input)
Units: Tons
Poults 0.02
Manure
11
Turkey Turkey 12
feed
12
Feed Imports
74
Albert Lea Agricultural P balance
Peterson et al., in prep.

18. Atmospheric Deposition
10.5
Fertilizer
80.6
Pork 8.3
Milk 3.7
Beef 3.1
Crops
121
Dairy &
beef feed
25.5
Manure/
Compost
Feed
18.4
9.3
Deliberate
exports: 138
Manure
18.9
Inputs =94
Units: Gg
Chicks 0.004
Turkey 2.1
Manure
4.2
Feed
6.3
Feed Imports
2.9
Manure Chicken 0.2
0.6
Feed
0.9
State-wide P use efficiency = 1.47
Peterson in prep b State-wide Ag P balance

19. Urban P balance (City of Albert Lea)
P x 1000 kg/yr
Industrial effluent 22.7
Household effluent 21.4
Total effluent 43.8
Biosolids P 15.9
Effluent P 28.3
P removal efficiency 36%

21. Part II. Dynamics of P flows through the watershed

22. 3. Identify opportunities to shift current P flow through
system toward a circular P economy (NSF proposal ongoing).
Processing Waste
Food
Food Waste
Sewage Biosolids
Treated
Water
Irrigation
or
Biosolids
Agricultural
Products
Composted/
Animal Feed
Fertilizer