11th International Drainage Symposium August 30-September 2, 2022 Des Moines, Iowa

1. Modeling Phosphorus Losses from Tile-Drained
Cropland using RZWQM2-Phosphorus Model
Peng Pan1
Zhiming Qi1
Tiequan Zhang2
Liwang Ma3
1. Department of Bioresource Engineering, McGill University, Sainte-Anne-de-Bellevue, Quebec, Canada.
2. Harrow Research and Development Center, Agriculture and Agri-Food Canada, Harrow, Ontario, Canada.
3. USDA-ARS Rangeland Resources and Systems Research Unit, Fort Collins, Colorado, USA
Presented by
Zhiming Qi
Associate Professor
McGill University
Canada

2. OUTLINE
• Introduction
• RZWQM-P Development
• P Pools
• P model Inputs
• P model parameters
• RZWQM-P Evaluation
DRP & PP in tile drainage and surface runoff in a
corn-soybean field treated with:
• Inorganic Fertilizer
• Liquid Cattle Manure
• Conclusions and Future work
2

3. INTRODUCTION
• Phosphorus pollution
• Nitrate, ammonia and phosphorus (P) are the top 3 substances
released to Canadian water bodies with 55,723.6 tonnes,
51,209.7 tonnes, and 6,053.4 tonnes per year (Environment
Canada, 2010).
• P is the limiting factor of algal bloom in surface water bodies
• Canadian farmers used 1.07 million tonnes phosphate mineral
fertilizers per year, usually with additional 180.96 million tonnes
of livestock manure in which 0.30 million tons of P according to
the 2006 census (Statistics Canada, 2011; 2018).
3

4. INTRODUCTION
• Phosphorus pollution
• Subsurface drainage is a major conduit
for P transported from agricultural soils
(International Joint Commission, 2018).
• In Lake Erie basin, 49% of soluble P and
48% of total P lost via tile drainage
(Smith et al., 2015b). In an Ontario study
this values were 95 to 97% (Tan and
Zhang, 2011)
From Dr. Gary Sands
4

5. INTRODUCTION
• Review of Existing Models
For simulating P loss through tile drainage (adapted from Radcliffe et al., 2015, JEQ)
Models
Drainage Macro-
pore
Phosphorus in tile Maure P
Pools
Manage-
ment
Free Control DP PP
ADAPT Y -- Y Y -- -- Limited
APEX Y Y Y Y -- -- extensive
DRAINMOD Y Y -- -- -- -- extensive
HSPF -- -- -- -- -- -- limited
HYDRUS Y -- Y -- -- -- limited
ICECREAMDB* Y -- Y Y Y Y extensive
P Indexes Y -- Y -- -- -- extensive
PLEASE Y -- -- Y Y -- Limited
SWAT Y -- Simple -- -- -- extensive
RZWQM2 Y Y Y -- -- -- extensive
* Not available yet. As of 2015, DRAINMOD-P was not available either.
5

6. INTRODUCTION
• Using RZWQM2 to develop a new P model
• Excellent management practices: water table management with
free/control tile drainage (by date), macropore, irrigation, manure (19
kinds), tillage (33 kinds), crop residue, N, DSSAT crop models
• Excellent hydrologic subroutine: Green-Ampt for infiltration, Richards
for soil water redistribution, Hooghoudt’s equation for drainage,
Shuttleworth-Wallace ET, freeze-thaw SHAW model, etc.
6
• Justification
• No model available (as of 2015) to simulate P losses via tile drains;
• Existing P models are based Jones et al. (1984) which is obsolete.

7. RZWQM-P Development
• P Pools
Plant
Uptake
Fresh Org P
Active Inorg P
Labile P
Stable Inorg P
Stable Org P
PP
DRP ManwiP
ManwoP
MansiP
MansoP
Manure P
Applied
Fertilizer P
Applied
AvFert P ResFert P
7

8. • Inputs
 Precipitation
 Temperature
 Radiation
 Wind
INPUTS
Weather
 pH
 Soil texture
 Field Capacity
 Saturated Conductivity
 Organic Matter Content
 Soil Porosity
 Wilting Point
 N and P Content
Soil
 Fertilization
 Harvest
 Tillage
 Crops
Agri.
Management
 Location
 Elevation
 Field width
 Field Length
 Field Slope
 Drain Depth
others
RZWQM-P Development
8

9. • Parameters
• Dissolved Reactive P (DRP)
• P Extraction Coefficient.
• Bubbling Pressure.
• Pore size distribution index.
• Particulate P (PP)
• USLE Parameters.
• Soil Replenishment Rate Coefficient
• Soil Detachability Coefficient.
• Soil Filtration Coefficient.
• Macroporosity, Fraction of Dead end pores, Average radius of the
macropore.
• Other Parameters
• Plant P uptake distribution parameter.
• Soil Root growth factor.
RZWQM-P Development
9

10. 10
• Phosphorus mitigation practices
RZWQM-P Development
•Water table control (controlled vs. free)
•Tillage: reduced tillage, no-till etc.
•P fertilizer application rate
•Cropping system

11. 11
Objectives
• To evaluate the performance of RZWQM2-
P in simulating P losses through tile
drainage water
• To assess long-term impacts of tillage on P
losses through tile drainage flow

12. • Field Experiment (compost & tillage)
• AAFC experimental site, Ontario (42° 12′ 15″ N, 82° 44′ 50″W)
• Drainage design: spacing 8.7 m; depth 0.6 m; 5 pipes per plot
• Factorial experimental design (compost x tillage)
Compost rate (CMP0 and CMP75):
0 and 70 Mg dry weight ha-1
Tillage (NT and CT) :
no till and
conventional tillage
RZWQM-P Evaluation Methods
12
Treatments:
NT-CMP0, NT-CMP75
CT-CMP0, CT-CMP75

13. 13
2018 site visit

14. 14

15. • Field Experiment: Field Management
15
Year Crop
Tillage date Compost （leaf）
disk
Mold-
board
Date Rate
Organic
matter
N (g kg-1) P (g kg-1) C: N
(Mg ha-1) (g kg-1) Total NH4-N Total
Water
extracta
ble
1998 soybean 10-May 5-Nov 10-Dec 75 196 17.4 0.471 2.96 0.067 6.53
1999 soybean 2-May 15-Oct 21-Oct 75 480 16.0 0.033 2.08 0.082
17.4
0
2000* maize 10-May 15-Nov 8-Dec 75 338 16.7 0.25 2.51 0.075
11.9
7
2001 soybean 2-May 20-Oct No compost application
Table 1. Details on tillage and compost application at both experiment farms.
* Additional commercial fertilizers at the
rates recommended locally (200 kg N ha-1
and around 17 kg P ha-1) were surface-
applied around 30 April each year.

16. • Field Experiment: Drainage Water Sampling
16
• ISCO model 2900 (Lincoln, Nebraska, USA)
• One sample every 10,000 L in Conventional Tillage
one sample every 25,000 L in the No Till plots
• Water sample composition
24 samples (max.) per period
• P analysis: Dissolved and total P
Year Collection Period Year Collection Period Year Collection Period
Start Date End Date Start Date End Date Start Date End Date
1998 9/15/1998 2/3/1999 2000 4/25/2000 5/23/2000 2001 2/1/2001 2/14/2001
1999 2/3/1999 3/8/1999 5/23/2000 6/26/2000 2/14/2001 3/19/2001
3/8/1999 4/1/1999 6/26/2000 7/31/2000 3/19/2001 4/4/2001
4/1/1999 4/14/1999 7/31/2000 8/9/2000 4/4/2001 4/18/2001
4/14/1999 4/20/1999 8/9/2000 9/25/2000 4/18/2001 5/15/2001
4/20/1999 4/27/1999 9/25/2000 10/12/2000 5/15/2001 5/30/2001
4/27/1999 8/6/1999 10/12/2000 11/14/2000 5/30/2001 8/21/2001
8/6/1999 4/25/2000 11/14/2000 12/20/2000 8/21/2001 10/16/2001
12/20/2000 2/1/2001 10/16/2001 11/14/2001
Table 2. Aggregated periods for water samples
From Dr. Gary Sands

17. • Model Initialization
17
Soil layer Initial Soil P Calibrated soil hydraulic parameters
Labile Total Pb λ ksat klat
(m) g kg-1 g kg-1 (cm) (mm h-1) (mm h-1)
0-0.01 0.023 0.90 -20.00 0.22 4.5 2.5
0.01-0.20 0.021 0.90 -21.00 0.20 5.0 5.0
0.20-0.40 0.011 0.65 -21.50 0.20 5.0 5.0
0.40-0.60 0.005 0.50 -21.50 0.20 5.0 5.0
0.60-1.10 0.005 0.40 -16.64 0.20 1.9 1.9
1.10-3.00 0.001 0.10 -16.64 0.19 1.9 1.9
3.00-3.09 0.001 0.10 -16.16 0.19 0.1 0.1
Table 3. Initial soil P concentration and Calibrated soil hydraulic
parameters used in model

18. • Model Calibration & Validation
18
Table 4. Calibrated parameters for soil, tillage, and phosphorus cycle
• Parameters were calibrated manually against tile flow and P losses data
• Calibration treatment (CT-CMP75); validation (NT-CMP75 CT-CMP0 NT-CMP0)
Parameters
Calibrated
values
Parameters
Calibrated
values
Albedo Soil replenishment coefficient 1
Dry soil 0.5 Initial DRP in ground water reservoir (kg ha-1
) 14
Wet soil 0.7 Initial PP in ground water reservoir (kg ha-1
) 13
Crop at maturity 0.8 Plant P parameters
Fresh residue 0.22 Maize
Tillage Biomass P Fraction at Emergence 0.002
Moldboard -intensity 1 Biomass P Fraction at 50% Maturity 0.001
Moldboard -mix efficiency 0.25 Biomass P Fraction at Maturity 0.0008
Disk-intensity 0.4 P uptake distribution parameter 5
Disk-mix efficiency 0.5 Soybean
Macroporosity (m3
m-3
) 0.009 Biomass P Fraction at Emergence 0.004
P extraction coefficient 1 Biomass P Fraction at 50% Maturity 0.002
Soil filtration coefficient 0.1 Biomass P Fraction at Maturity 0.001
Soil detachability coefficient 0.4 P uptake distribution parameter 5

19. • Model Evaluation Criteria
19
Table 5. Statistical model performance evaluation criteria
Rating
Model accuracy evaluation statistics
|PBIAS| R2 IoA
Drainage Water flow
Satisfactory 10 - 15% 0.6 - 0.7 0.75 - 0.85
Good 3 - 10% 0.7 - 0.75 0.85 - 0.9
Very Good < 3% > 0.75 > 0.9
Phosphorus Loss
Satisfactory 15 - 30% 0.4 - 0.65 0.75 - 0.85
Good 10 - 15% 0.65 - 0.80 0.85 - 0.9
Very Good < 10% > 0.80 > 0.9
PBIAS: percent bias of the mean
R2: coefficient of determination
IoA: index of agreement

20. 20
RZWQM-P Evaluation Results
• Model Performance
Statistics
Calibration Validation
CT-CMP75 NT-CMP75 CT-CMP0 NT-CMP0
Drainage (mm)
Obs. mean 112.37 99.02 75.84 104.51
Sim. mean 102.71 107.07 86.21 96.49
Rating good good satisfactory good
DRP (g ha-1)
Obs. mean 181.62 361.83 45.89 57.38
Sim. mean 219.95 262.42 164.57 195.59
Rating satisfactory satisfactory unsatisfactory unsatisfactory
PP (g ha-1)
Obs. mean 347.11 323.32 274.1 361.73
Sim. mean 277.43 338.79 209.29 253.45
Rating satisfactory good satisfactory unsatisfactory
TP (g ha-1)
Obs. mean 555.32 760.92 331.38 433.60
Sim. mean 570.70 688.68 428.72 514.24
Rating very good good satisfactory unsatisfactory
Table 6. Model performance on simulating annual drainage
flow and P losses

21. 21
Statistics
Calibration Validation
CT-CMP75 NT-CMP75 CT-CMP0 NT-CMP0
Manure P 567 567 0 0
Fertilizer P 54 54 54 54
Residue P 23.11 22.30 23.09 22.38
Plant uptake P 51.30 47.41 51.30 47.36
DRP loss
Runoff 21.60 43.76 1.95 3.95
Drainage 0.84 1.02 0.62 0.78
PP loss
Runoff 3.17 5.82 0.97 1.93
Drainage 1.00 1.24 0.75 0.98
• Simulated P Balance
Table 6. P input and simulated output (P uptake and losses through tile flow and
surface runoff). Unit kg P/ha

22. 22
• Long-term impacts of tillage on P loss
Table 7. Tillage practices applied in RZWQM-P long-term simulation
Implement name Tillage intensity Mix efficiency
No till 0.00 0.00
Paraplow 0.20 0.05
Row cultivator
（Standard treatment）
0.25 0.10
Moldboard 0.93 0.30
One-way disk 0.40 0.40
Tandem disk 0.50 0.50

23. 23
a)
Tillage Intensity
0.0 0.2 0.4 0.6 0.8 1.0
Minimum
Bulk
Density
(g
cm
-3
)
1.00
1.05
1.10
1.15
1.20
1.25
1.30
1.35
c)
Tillage Intensity
0.0 0.2 0.4 0.6 0.8 1.0
Average
Actual
ET
(mm
day
-1
)
1.06
1.08
1.10
1.12
1.14
1.16
1.18
1.20
1.22
d)
Tillage Intensity
0.0 0.2 0.4 0.6 0.8 1.0
Average
Surface
Residue
Mass
(kg
ha
-1
)
3000
4000
5000
6000
7000
8000
b)
Tillage Intensity
0.0 0.2 0.4 0.6 0.8 1.0
Average
Infiltration
(mm
day
-1
)
1.64
1.66
1.68
1.70
1.72
1.74
1.76
y=0.3995x2
-0.6644x+1.337
R2
=0.9912
y=-0.0585x2
+0.1450x+1.6601
R2
=0.9972
y=--0.0943x2
+0.2230x+1.0759
R2
=0.9900
y=1804x2
-5734x+7075
R2
=0.9994
• Long-term impacts of tillage on P loss

24. 24
Conclusion
• RZWQM2-P model performed well in simulating annual
PP and TP loss through tile drainage compared with
observed data
• Simulation on DRP loss through tile drainage was
unsatisfactory for the no compost plots as it may
overestimated DRP loss from soil matrix
• model application showed that tillage could reduce tile
drainage and P loss in tile drainage compared with no-
till management.
• DRP loss simulation should be improved by adjusting
the manure P mineralization parameters and winter
drainage.
• Effects of tillage or other management practices on P
losses in RZWQM2-P model still need to be further
tested using more data.

25. 25
Presented by
Zhiming Qi
Brace Associate Professor
Department of Bioresource Engineering
McGill University
Montreal Area, Canada
zhiming.qi@mcgill.ca