71st SWCS International Annual Conference July 24-27, 2016 Louisville, KY

1. F. Ghidey, C. Baffaut, N. Kitchen, K. Sudduth, M. Yost, R, Lerch, and
E. J. Sadler

2. Goodwater Creek Experimental Watershed (GCEW)
GCEW – 7250 ha, located in the claypan soil
region of North-central Missouri
Plots – 18 m wide and 189 m long
(0.374 ha (0.92 ac))

3. Research Plots
 Three Cropping Systems
 CS 1 – Mulch tillage corn-soybean rotation with herbicide
and fertilizers surface applied and incorporated
 CS 2 – No-till corn-soybean rotation herbicide and P
surface applied and not incorporated. N was injected.
 CS 5- No-till corn-soybean-wheat rotation with split
herbicides application, cover crops, and no incorporation.

4. Time Series Data Measured
 Corn, Soybean, and wheat yields were measured from 1992
– 2009.
 Flow and Water Quality were measured during the corn
phase of the rotation from 1997 – 2002.
 Each CS had 3 replications. Only 2 replications were
instrumented to measure the quantity and quality of surface
runoff
 Surface runoff was measured and runoff samples were
collected only from plots that were planted to corn.

5. Corn crops CS1Corn crops CS1
(after Lerch, R.N.)
Research Plots

6. Objectives
 To evaluate Long‐Term effects of the three
cropping systems (CSs) on yield and water
quality
 To calibrate and validate APEX model using
measured data
 To use the model to estimate the long‐term
effects of CSs on yield and water quality

7. Discretization
Plot 20
Distance from The Top (m)
0255075100125150175200
Elevation(m)
261.0
261.5
262.0
262.5
263.0
263.5
264.0
264.5
Elevation
Clay-Elevation
Hillslope segments
based on depth to clay / slope
Foot Backslope Shoulder Summit
23 cm
15 cm
3 cm
EastWest

8. APEX Model Inputs and Outputs
Input data Selected Outputs
 Daily weather
 Measured topography
 Measured soil properties
 Cropping and management
 Crop yields
 Daily runoff
 Atrazine, nitrate, and dissolved
P losses

9. Calibration/Validation Process
 Each cropping system had four plots instrumented for
water quality measurement
 For each CS, data measured from one plot was used for
calibration of APEX model, and the remaining three
plots for validation.
 Performance of the model was evaluated using r2,
Nash and Sutcliffe (Ens), and percent bias (Pbias)
statistical methods

10. APEX calibration and Validation Results
Calibration (1 plot) Validation (3 plots)
r2 Ens Pbias r2 Ens Pbias
CS1
Runoff 0.81 0.72 19.5 0.93 0.84 7.2
Atrazine 0.80 0.74 20.5 0.83 0.87 -3.3
Nitrate 0.66 0.68 20.5 0.61 0.53 -15.9
Phosphorus 0.71 -3.7 -84.0 0.41 0.27 2.7
CS2 Runoff 0.96 0.88 -12.1 0.90 0.85 -5.1
Atrazine 0.95 0.81 15.1 0.80 0.69 -29.7
Nitrate 0.62 0.58 1.6 0.58 0.57 12.1
Phosphorus 0.94 0.62 -56.2 0.74 0.73 5.2
CS5 Runoff 0.90 0.89 1.1 0.87 0.74 6.1
Atrazine 0.84 0.60 51.8 0.64 0.58 35.4
Nitrate 0.35 0.26 41.7 0.79 0.63 49.5
Phosphorus 0.95 0.88 22.1 0.45 0.36 32.4

11. CS1 – Measured and simulated events data (All Plots)
Measured Runoff (mm)
0 20 40 60 80 100 120
SimulatedRunoff(mm)
0
20
40
60
80
100
120
Measured Atrazine (g/ha)
0 20 40 60 80 100
SimulatedAtrazine(g/ha)
0
20
40
60
80
100
Measured Nitrate (kg/ha)
0 5 10 15 20
SimulatedNitrate(kg/ha)
0
5
10
15
20
Measured Phosphorus (g/ha)
0 50 100 150 200
SimulatedPhosphorus(g/ha)
0
50
100
150
200
Y = 0.76 X
R2
= 0.89
Ens = 0.84
Pbias = 9.3%
Y = 1.13 X
R2
= 0.94
Ens = 0.89
Pbias = 0.1%
Y = 0.87 X
R2
= 0.68
Ens = 0.62
Pbias = -7.4%
Y = 0.99 X
R2
= 0.52
Ens = 0.46
Pbias = -15.4%

12. Measured and Simulated CS1 Corn Yields
CS1-Corn
Year
1996 1998 2000 2002 2004 2006 2008 2010
CornYield(T/ha)
0
2
4
6
8
10
12
Measured
Simulated
Low measured yields
are over‐estimated

13. Comparing CS1, CS2, and CS5 Measured and Simulated
Average Yields (1997-2009)
Measured Simulated
CornYield(T/ha)
0
2
4
6
8
CS1
CS2
CS5
CORN
a a
a
a
c
b
Measured Simulated
SoybeanYield(T/ha)
0.0
0.5
1.0
1.5
2.0
2.5
3.0
CS1
CS2
CS5
Soybean
b
a
a a
c
b

14. Simulated Average Annual Runoff (1997-2009)
CS1 CS2 CS5AverageAnnualRunoff(mm)
0
100
200
300
400
500
Soybean Years
a
a
a
CS1 CS2 CS5
AverageAnnualRunoff(mm)
0
100
200
300
400
500
Corn Years
a
a a

15. Percent Atrazine Applied (1997-2009) lost to Runoff
CS1 CS2 CS5
AtrazineAppliedLosttoRunoff(%)
0
2
4
6
8
10
a
b
c
CS2 - 2.1 times higher than CS1
CS5 - 3.4 times higher than CS1

16. Nitrate Losses to Runoff (1997 – 2009)
Applied N (corn years) Lost to
Runoff (%)
Average Annual N losses during
Corn and Soybean Years
CS1 CS2 CS5
NitrogenAppliedLosttoRunoff(%)
0
5
10
15
20
25
30
a
a
a
CS1 CS2 CS5
AverageAnnualN-Losses(kg/ha)
0
2
4
6
8
10
12
14
16
18
Corn-Years
Soybean-Years
26% 27%
34%

17. Dissolved Phosphorus Losses to Runoff (1997 – 2009)
Applied P (corn years)Lost to
Runoff (%)
Average Annual P losses during Corn
and Soybean Years
CS1 CS2 CS5
AverageAnnualP-Losses(g/ha)
0
200
400
600
800
1000
1200
1400
1600
Corn-Years
Soybean-Years
86%
94%
105%
CS1 CS2 CS5
PhosphorusAppliedLosttoRunoff(%)
0
1
2
3
4
5
6
c
a
b
CS2 - 3.9 times higher than CS1
CS5 - 2.7 times higher than CS1

18. Pathways for Nitrate Losses
SURQ PERC DNIT VOL HARV
%NitrogenLoss
0
10
20
30
40
50
CS1
CS2
CS5

19. Pathways for Dissolved Phosphorus Losses
SURQ PERC HARV
%DissolvedPhosphorusLoss
0
20
40
60
80
100
CS1
CS2
CS5

20. Summary and Conclusion
 The performance of APEX model in estimating
atrazine, nitrate, and dissolved P losses to runoff was
satisfactory.
 APEX overestimated crop yield, particularly corn
yield, for the dry seasons.
 Average atrazine losses from CS2 and CS5 (no-till)
were 2 and 3 times higher than from CS1 (mulch-
tillage). Split atrazine application in no-till (CS5)
further increased atrazine loss in surface runoff.
 Average dissolved P losses from CS2 and CS5(no-till)
were 4 and 3 times higher than CS1(mulch-tillage).

21. Summary and Conclusion
 Dissolved P losses during the soybean years were more
the same as those lost during the corn years.
 Approx. 45 and 90% of N and P applied was harvested
with crop.
 N and P losses to runoff were less than 10 and 5%.
 N and P percolation were higher for no-till systems
because of higher Ksat.
 Denitrification and volatilization represented ~25% of
applied N.

22. Thank you!