Evaluating N export from a tile drained headwater watershed in central Ohio

Mark WilliamsKevin KingNorm Fausey

Soil Drainage Research Unit Columbus, OH

69th SWCS International Annual ConferenceJuly 27-30, 2014

< 11 to 1010 to 100100 to 500500 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)

% o

f str

eam

N lo

ad fr

om

head

wat

er s

trea

ms

Drainage is required for agricultural production but can facilitate increased nitrogen transport

Land benefiting from improved drainage

2 to 55 to 1010 to 20

20 to 4040 to 60> 60

Percent

Above: University of Minnesota research plotsRight: 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

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

B1

B2 B4

B3

B8

B6

B5

0 150 300 600 1,200m

Long-term tile and watershed monitoring in central Ohio

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:

Watershed characteristicsArea: 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

Discharge & water quality monitoring

Watershed outlet Tile drain

Tile drain Isco equipment

Tile & watershed hydrology

0

30

60

90

120

150

J F M A M J J A S O N D

Aver

age

disc

harg

e &

ra

infa

ll (m

m)

MonthPrecipitation Tile flow Watershed discharge

King et al. 2014. J. Environ. Qual. (in progress)

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%)

0

10

20

30

40

50

60

Wtrshd B OH IA MN IL

% o

f rai

nfal

l rec

over

ed a

s di

scha

rge

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

Total N concentration (mg L-1)

NO

3-N

con

cent

ratio

n (m

g L-

1 )Nitrate (NO3-N) was the predominant form of nitrogen in stream and tile water

NO

3-N

con

c. (m

g L-

1 )

0.0

15.0

30.0

45.0

60.0

0 0.25 0.5 0.75 1Edge-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

NO

3-N

con

cent

ratio

n (m

g L-

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 tileWatershed

Season

a

b bb

b b

a

c

Nitrate concentrations increased with increasing discharge and varied seasonally

0

5

10

15

20

25

30

0 5

NO3-N

J F M A M J J A S O N D

NO

3-N

con

c. (m

g L-

1 )

Month

CornSoybean

Nitrate concentrations in edge-of-field tiles were typically greater when corn was planted

B2, B4, and B8

Watershed outletSummed tile

NO

3-N

load

(kg

ha-1

)

Month

J F M A M J J A S O N D

Year

Monthly and annual nitrate loads

Tile

NO

3-N

load

(kg

ha-1

)

Watershed NO3-N load (kg ha-1)

Tile drainage accounted for 56% of monthly watershed discharge and 73% of nitrate export

Tile drainage contributes significantly to nitrogen export from systematically drained headwater watersheds

Discharge NO3-N load

56% 73%

Keeping nitrogen in fields and out of streams

Nitrogen leaching

In-stream processing??

Practices with potential

Drainage water management

Cover crops

4R nutrient stewardship

Questions??

Contact Information:Mark WilliamsUSDA-ARS590 Woody Hayes Dr.Columbus, OH 43210mark.williams2@ars.usda.gov