Preferential flow occurs even when chemicals are applied offset from tiles, indicating preferential flow in both unsaturated and saturated zones. Applications at the same physical distance from tiles take different times to reach tiles depending on overall drain spacing (relative distance from tile to mid-plane). This affects clean-out times between plots. When changing management like fertilizer rates, drainflow immediately reflects some changes but other effects appear later, as drainflow is a time-averaged indicator integrating soil management over time.

1. Purdue Univ.
There is no such thing as a
quick fix: Travel times to
subsurface drains.
Eileen Kladivko and Laura Bowling
Agronomy Dept., Purdue University
West Lafayette, IN, USA
kladivko@purdue.edu

2. Indiana
Southeast Purdue Agricultural Center
(SEPAC)
Clermont silt loam (Typic Glossaqualfs)
0.7% org. C, 65% silt, 12% clay
Fragipan-like horizon at 1.2 m depth

3. Original Goals of SEPAC studies
On the poorly structured, low organic matter,
naturally poorly-drained, Clermont silt
loam soil, to:
• Improve drainage
• Improve soil physical properties
– Reduce crusting and erosion
– Increase infiltration and permeability
• Improve crop growth and yield

4. Added Goals of water quality
• Nitrate-N losses as affected by spacing
and crop management
• Pesticide losses
• Preferential flow
• Travel times to “clean out” plot after
change in management

5. •4 drain spacings (40m as
undrained “control”)
•Border drains between plots
•Measure flow in center
drain (5,10,20m)
•Assume water collected
from midplane to midplane
•Plots 225 m long
•Surface slope <1%
•Drains 0.75m depth
•Restricting layer 1.2m
depth (fragipan)

8. Early observations, context
• Greater drainflow and nitrate loss (per ha)
with closer drain spacing
• Variable nitrate concentrations as yields
varied from year to year
• Pesticides (small amounts) appeared in
first drainage events after application
(preferential flow—still “new” in 80s)
• Sabbatical with Dr. W.Jury brought ideas
on flow paths, chemical transport, drainage
theory, to EJK

9. Purdue Univ.
Day of the Year
135 140 145 150
Concentration
(

g
L
-1
)
0
10
20
30
Drain
Flow
(mm
d
-1
)
0.0
0.5
1.0
1.5
2.0
2.5
3.0
Carbofuran
Atrazine
Cyanazine
Drain Flow
Pesticide loss-- 1991
JEQ 28:997-1004 (1999)

10. Objectives
• Verify that preferential flow, was not just
due to the old installation trench, but
occurred in rest of field.
• Compare travel and cleanout times, at
different application zones, w/ theory and
measurements.
If we change management practices, how
long will it take for drainage water to reflect
the new management?

11. Methods
• Applied KBr tracer, at different distances from
drain, at start of flow season (Nov. 1989)
• Measured Bromide concentrations in
drainflow for next 5+ years
• Calculate Bromide loads from tile, from
measured drainflow volumes

12. Theory
JURY: SOLUTE TRAVEL-TIME ESTIMATES
FOR TILE-DRAINED FIELDS: I. (1975)

13. Theory
JURY: SOLUTE TRAVEL-TIME ESTIMATES
FOR TILE-DRAINED FIELDS: I. (1975)

14. 20m offset vs 10m offset

15. Whole plot, 5m E and W
Offset, West block, 10 and 20m
Centered, East block, 10 and 20m
Offset from tile (test if preferential flow only
occurred in soil of the old trench above tile)
3m wide strip
3m wide strip
Application Zones

16. Unsat’d zone
Estimate 22.5cm H2O to leach to
WT (piston flow; porosity=0.40;
ave vol water content=0.30)
Sat’d zone
Travel times (water
volumes) based on
streamlines
75 cm
depth

17. Results
• Obj- Verify that preferential flow, was not just due to the
old installation trench, but occurred in rest of field
• Bromide arrived at drain as soon as
drainflow started after application, on all
plots.

18. Cumulative load vs. Drainflow
0 25 50 75 100 125 150
Cumulative Drainflow (cm)
0
25
50
75
100
125
150
Cumulative
Load
(kg/ha)
Drain 1, 10 m, centered
Drain 2, 5 m, full width
Drain 3, 20 m, centered
Drain 4, 10 m, offset
Drain 5, 5 m, full width
Drain 6, 20 m offset

19. Results
• Obj- Verify that preferential flow, was not just due to the
old installation trench, but occurred in rest of field
• Bromide arrived at drain as soon as
drainflow started after application, on all
plots.
• The first 10% arrived within 3-5 months
(and first 1.5 mo had no flow)
• Rapid arrival, even when offset from tile, is
evidence of preferential flow. This is
consistent with pesticide results.

20. Results
• Obj- Compare travel and cleanout times, at different
application zones, w/ theory and measurements
Long-term flow behavior:
• Drainflow per area, in order 5m>10m>20m
• Drainflow greater in West block than East

21. Results
• Obj- Compare travel and cleanout times, at different application
zones, w/ theory and measurements
5m plot pair (whole plot)
• East and west had same load vs time during first
2 flow seasons, then diverge
• Suggests some Br lost by seepage from east, at
further distances (outer 20-35%) from drain

22. 5m east vs. west (whole plot)

23. Results
• Obj- Compare travel and cleanout times, at different application
zones, w/ theory and measurements
5m plot pair (whole plot)
• East and west had same load vs time during first
2 flow seasons, then diverge
• Suggests some Br lost by seepage from east, at
further distances (outer 20-35%) from drain
• West had greater flow than east, but same load
for first 2 seasons
• Suggests some “clean water” seeping into plot
from top end

24. Results
• Obj- Compare travel and cleanout times, at different application
zones, w/ theory and measurements
Offset pair (10m, 20m, West block)
• Both start right away—preferential flow
• Both accumulate at slower pace, require more drainflow,
than centered plots
• Similar loads in Yr 1
• Yrs 2, 3, have greater loads in 20m
• Crossover ~Yr 4, w/ ~60cm flow, when 10m accumulates
sl more than 20m
• 10m has further “relative” distances (0.45-0.9) so takes
longer than 20m (0.15-0.45), even though absolute
distance is the same

25. 10m, 20m offset (west)

26. 20m offset vs 10m offset

27. 0 10 20 30 40 50 60 70 80 90 100
Cumulative Drainflow (cm)
0
10
20
30
40
50
60
70
80
90
Cumulative
Load
/
Total
Load
(%)
Drain 4, 10 m, offset
Drain 6, 20 m offset
Drain 4 Theory
Drain 6 Theory
Unsat’d zone
leaching volume
adjusted to match
theory and measured
at 50% cum load
(Drain 4=20cm H2O,
Drain 6=16.3cm H2O)
Adjusted theoretical and measured cum load
vs drainflow (cm) Drains 4 & 6 (offset)

28. Results
• Obj- Compare travel and cleanout times, at different application
zones, w/ theory and measurements
Centered pair (10m, 20m, East block)
• Nearly identical relative mass vs time, since narrow strip
centered on tile

29. 0 5 10 15 20 25
Cumulative Drainflow (cm)
0
10
20
30
40
50
60
70
80
90
Cumulative
Load
/
Total
Load
(%)
Drain 1, 10 m, centered
Drain 3, 20 m, centered
Drain 1 Theory
Drain 3 Theory
Adjusted theoretical and measured cum load
vs drainflow (cm) Drains 1 & 3 (centered)
Unsat’d zone
leaching volume
adjusted to match
theory and measured
at 50% cum load
(Drain 1=5.7cm H2O,
Drain 3=6.7cm H2O)

30. Remember time-averaging effect!
• Drains respond
quickly to mgmt.
or yield changes,
• But, remember lag
or time-averaging
effect. Takes time
for full effect, due
to longer travel
times from closer
to midplane
(further from tile).
Kladivko and Bowling, 2021, JEQ 50:627-638.
NO3-N

31. Summary
• Preferential flow occurs even when chemical is
applied offset from the tile. Suggests preferential
flow in both unsat’d and sat’d zones
• Applications at same physical distance from tile, will
take different amounts of time to reach tile, based on
overall spacing (relative distance between tile and
mid-plane). This affects “clean-out” time for plots.
• When changing field management (fertilizer rate), the
drainflow will reflect some of the change immediately
and some will appear in later years. Drainflow is a
time-averaged indicator of soil management.