69th SWCS International Annual Conference July 27-30, 2014 Lombard, IL

1. Evaluating N export
from a tile drained
headwater watershed
in central Ohio
Mark Williams
Kevin King
Norm Fausey
Soil Drainage Research Unit
Columbus, OH
69th SWCS International Annual Conference
July 27-30, 2014

2. < 1
1 to 10
10 to 100
100 to 500
500 to 1000
> 1000
Yield (kg km-2 yr-1)
(USGS NAWQA Program; water.usgs.gov)
Nitrogen processing in headwater watersheds
controls downstream water quality
Strahler stream order
(Adapted from Alexander et al., 2007)
%ofstreamNloadfrom
headwaterstreams

3. Drainage is required for agricultural production
but can facilitate increased nitrogen transport
Land benefiting from improved drainage
2 to 5
5 to 10
10 to 20
20 to 40
40 to 60
> 60
Percent

4. Above: University of Minnesota research plots
Right: USDA-ARS field-scale research in Ohio
Majority of subsurface drainage research has
been conducted at plot and field scales
Some examples:
Logan et al. (1994) – annual N loads up to 86 kg ha-1 from tile drained plots
Jaynes et al. (2001) – annual N load between 13 and 61 kg ha-1 from a 22 ha field

5. Nested watershed design
(e.g., Tomer et al., 2003)
Watersheds with different
drainage intensity
(e.g., Kennedy et al., 2012)
Extrapolate plot and
field scale results
(e.g., David et al., 1997)
Common methods to infer the effect of tile
drainage on watershed nitrogen export

6. B1
B2
B4
B3
B8
B6
B5
0 150 300 600 1,200
m
Long-term tile and watershed
monitoring in central Ohio

7. 1. Summarize discharge and water quality data from
long-term monitoring in watershed B
2. Quantify the relationship between discharge and
nitrogen concentration
3. Determine the contributions of tile drainage to
watershed nitrogen loads
Study objectives:

8. Watershed characteristics
Area: 389 ha
Slope: 0.009 m m-1
Soil types:
Bennington silt loam (53%)
Pewamo clay loam (46%)
Drained area:
319 ha (82%)
7 to 201 ha
Tile depth: 0.9 to 1.0 m
Tile spacing: 15 m
Precipitation: 985 mm yr-1
Management:
Corn-soybean rotation with
rotational tillage

9. Discharge & water quality monitoring
Watershed outlet Tile drain
Tile drain Isco equipment

10. Tile & watershed hydrology
0
30
60
90
120
150
J F M A M J J A S O N D
Averagedischarge&
rainfall(mm)
Month
Precipitation Tile flow Watershed discharge
King et al. 2014. J. Environ. Qual. (in progress)

11. Storage/evaporation
Annual rainfall
(1,004 mm)
Summed tile discharge
(283 mm)
Runoff/
seepage
Watershed discharge (508 mm)
49%
28%23%
Water balance
773 to 1,239 mm
Variability
310 to 767 mm (39-62%)
187 to 564 mm (18-45%)

12. 0
10
20
30
40
50
60
Wtrshd B OH IA MN IL
%ofrainfallrecoveredasdischarge
3.9 km2
1.2 km2
481 km2
16000 km2
Logan et al. (1980) Algoazany et
al. (2007)
Watershed Tile
Comparing precipitation to discharge ratios
across studies show similar relationships

13. Total N concentration (mg L-1)
NO3-Nconcentration(mgL-1)Nitrate (NO3-N) was the predominant form of
nitrogen in stream and tile water

14. NO3-Nconc.(mgL-1)
0.0
15.0
30.0
45.0
60.0
0 0.25 0.5 0.75 1
Edge-of-
field tile
(7-28 ha)
Tile main
(22-49 ha)
County
main
(201 ha)
Watershed
outlet
(389 ha)
Percent of time NO3-N conc.
was equaled or exceeded
47%14%
4%
Nitrate concentrations were variable and often
exceeded 10 mg L-1

15. NO3-Nconcentration(mgL-1)
10010-310-510-7
Discharge (mm h-1)
Field tile (B2, B4, B8) Tile main (B5, B6)
County main (B3) Watershed outlet (B1)
0
2
4
6
8
10
12
Winter Spring Summer Fall
Summed tile
Watershed
Season
a
b b
b
b b
a
c
Nitrate concentrations increased with
increasing discharge and varied seasonally

16. 0
5
10
15
20
25
30
0 5
NO3-N
J F M A M J J A S O N D
NO3-Nconc.(mgL-1)
Month
Corn
Soybean
Nitrate concentrations in edge-of-field tiles were
typically greater when corn was planted
B2, B4, and B8

17. Watershed outlet
Summed tile
NO3-Nload(kgha-1)
Month
J F M A M J J A S O N D
Year
Monthly and annual nitrate loads

18. TileNO3-Nload(kgha-1)
Watershed NO3-N load (kg ha-1)
Tile drainage accounted for 56% of monthly
watershed discharge and 73% of nitrate export

19. Tile drainage contributes significantly to nitrogen
export from systematically drained headwater
watersheds
Discharge NO3-N load
56% 73%

20. Keeping nitrogen in fields and out of streams
Nitrogen leaching
In-stream
processing??

21. Practices with potential
Drainage water
management
Cover crops
4R nutrient stewardship

22. Questions??
Contact Information:
Mark Williams
USDA-ARS
590 Woody Hayes Dr.
Columbus, OH 43210
mark.williams2@ars.usda.gov