A Ten Year Study of Nitrate A Ten Year Study of Nitrate Leaching in Vegetable Leaching in Vegetable

Production With Winter Cover Production With Winter Cover CropsCrops

Thesis DefenseThesis Defense

Jeff FeagaJeff Feaga

M.S. M.S. Bioresource EngineeringBioresource Engineering

Part 1 -Part 1 - Methods Common to the Entire Methods Common to the Entire Study.Study.

Part 2 -Part 2 - Ten years of nitrate leaching Ten years of nitrate leaching below vegetable plots with and without below vegetable plots with and without cover crops.cover crops.

Part Part 3 -3 - Spread of conservative, non- Spread of conservative, non-absorbing, and soluble tracers through absorbing, and soluble tracers through field soils.field soils.

Outline of TalkOutline of Talk

Three Key PointsThree Key Points

OneOne Winter cover crops are a successful BMP for Winter cover crops are a successful BMP for

nitrogen management in the Willamette nitrogen management in the Willamette ValleyValley

TwoTwo Variations in rainfall timing and intensity Variations in rainfall timing and intensity

greatly affect the spread of solutes.greatly affect the spread of solutes.

ThreeThree The ADE is limited as a tool for predicting The ADE is limited as a tool for predicting

the spread of chemicals in soil.the spread of chemicals in soil.

MethodsMethods Location/ClimateLocation/Climate – –

North Willamette Research and Extension Center (NWREC) North Willamette Research and Extension Center (NWREC) Aurora, Oregon Aurora, Oregon

Maritime Climate: 104 cm of rainfall/year. Maritime Climate: 104 cm of rainfall/year.

SoilsSoils – Woodburn and Willamette Variant Loam. – Woodburn and Willamette Variant Loam.

ManagementManagement – – Summer VegetablesSummer Vegetables

Cover Cropped (H) Cover Cropped (H) Fallow (C)Fallow (C)

Three Fertilizer Rates (N0, N1, N2)Three Fertilizer Rates (N0, N1, N2)

Winter

Vegetables and Cover CropsVegetables and Cover Crops

Year Spring Crop Winter Crop

1989 Wheat Cereal Rye 1990 Sweet Corn Cereal Rye 1991 Broccoli Cereal Rye 1992 Sweet Corn Cereal Rye 1993 Broccoli Cereal Rye 1994 Sweet Corn Cereal Rye 1995 Broccoli ‘Celia’ Triticale 1996 Sweet Corn ‘Celia’ Triticale 1997 Broccoli ‘Celia’ Triticale 1998 Sweet Corn Cereal Rye 1999 Snap Beans ‘Celia’ Triticale 2000 Sweet Corn Common Vetch / Cereal Rye 2001 Snap Beans Common Vetch / Cereal Rye

Mario

Florian

Jeff

Hudson

Utility Players

Jaechul

Summer Summer VegetablesVegetables

Winter Winter Cover Cover CropsCrops

Separating the cereal rye Separating the cereal rye

from the common vetchfrom the common vetch

Common vetchCommon vetch

Do legumes scavenge nitrate?Do legumes scavenge nitrate?

Block I Block III

1 2 (C) 3 4 (H) 5 21 22 23 (C) 14 25

N2

N0

N2 N1

6 7 8 9 10 26 27 28 29 (H) 30

N0

N1

N2

Block II Block IV

11 12 (C) 13 14 15 31 (C) 32 33 (H) 34 35

N2

N0 N0

N1 N2

N0

N1 N2 N1

16 17 18 19 20 (H) 36 37 38 39 40

N1

N0

N2

OSU North Willamette Research and Extension Center: Cover Crop, Vegetable Rotation Trial

FLOODEDFLOODED

FLOODED

6 7

3 2

85

4 1

Sampler # Treatment 1 H2 N0 North 2 H2 N0 South 3 H 2 N 1 South 4 H 2 N 2 North 5 C4 N0 North 6 C4 N0 South 7 C4 N1 South 8 C4 N2 North 9 H4 N0 North 10 H4 N0 South 11 H4 N1 North 12 H4 N2 South 13 H3 N0 North 14 H3 N0 South 15 H3 N1 South 16 H3 N2 North 17 C3 N0 North 18 C3 N0 South 19 C3 N1 North 20 C3 N2 South 21 C1 N0 North 22 C1 N2 North 23 C2 N0 North 24 C2 N0 South 25 C2 N1 North 26 C2 N2 South

= PCAPS C fallow H Winter Cover Crop N0 No Fertilizer N1 Half Recommended N2 OSU Recommended

20

2426

21 22

23

1012

25 11 9

1613

19 17

18

14 15

N

W

S

E

99 m

18 m

9 m

99 m

N0

PCAPSPCAPS

It’s Raining Again!It’s Raining Again!

?

The Flow Weighting ProcessThe Flow Weighting Process

= Mean flow weighted concentration (M/L3) over multiple sampling events = Mean flow weighted concentration measured for multiple samplers as calculated for N sampling events = Average volume of percolation (L3) collected during each sampling event calculated for N sampling events = Number of sampling events

c

ic

iV

n

= Mean flow weighted concentration (M/L3) over multiple sampling events = Mean flow weighted concentration measured for multiple samplers as calculated for N sampling events = Average volume of percolation (L3) collected during each sampling event calculated for N sampling events = Number of sampling events

c

ic

iV

n

Total Mass Solute

Total Volume Water

________________

Soil SamplingSoil Sampling

ExtractionsExtractions

Brandi-Dohrn et al. (1996)Brandi-Dohrn et al. (1996) First two wintersFirst two winters 76% collection Efficiency76% collection Efficiency

Part II – Nitrate Leaching Part II – Nitrate Leaching Results Sampler Collection Results Sampler Collection

EfficiencyEfficiency

-40

-30

-20

-10

0

10

20

30

40

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26

Rank From Sampling Dates #5 - #67

% D

ev

iati

on

Fro

m M

ea

n C

oll

ec

tio

n A

mo

un

t

Sampling dates #5 - #67

Sampling Dates #121 - #172

This AnalysisThis Analysis Winter 1993, 1999, and 2001Winter 1993, 1999, and 2001 Also a 76% collection Also a 76% collection

EfficiencyEfficiency

0

5

10

15

20

25

30

35

40

45

50

Con

cent

ratio

n N

O3- -

N (m

g/L)

0

100

200

300

400

500

600

700

800

900

Cum

ulat

ive

NO

3- -N m

ass

(kg/

ha)

Fallow (C)

Cover Crop (H)

Fallow (C) Cumulative

Cover Crop (H) Cumulative

Flow Weighted Averages: N2 PlotsFlow Weighted Averages: N2 Plots

Equal to 80 kg/ha/year or 71 lbs/acre/year

Average Concentrations:H Plots = 11.4 mg/L

C Plots = 17.1 mg/L

N0 Plots N1 Plots N2 Plots

0.0

0.1

0.2

0.3

0.4

0.5

p - V

alue

N = 10 N = 9N = 10

Concentration

N0 Plots N1 Plots N2 Plots

0.0

0.1

0.2

0.3

0.4

0.5

p - V

alue

N = 9 N = 10N = 9

One Tailed Paired T-tests: P-Value One Tailed Paired T-tests: P-Value DistributionDistribution

Mass

Mass Losses Under Legumes: Mass Losses Under Legumes: Mineralization?Mineralization?

0

50

100

150

200

N m

ass

(kg

/ha)

Fallow Cover Crop Fallow Cover Crop Fallow Cover Crop

Cereal Years (1992-1999) 1st Legume Year (2000) 2nd legume year (2001)

N0

N1

N2

Fertilizer Treatment

Mass N03-N

May 2001May 2001 Soil Sampling: Chemical Soil Sampling: Chemical Profiles Profiles

0

20

40

60

80

100

120

0 20 40 60 80

NO3--N Concentration (ppm)

Dep

th (c

m)

Cover

Fallow

0

20

40

60

80

100

120

0 20 40 60 80

Br- Concentration (ppm)

De

pth

(c

m)

Cover

Fallow

Residual Nitrate From Summer 2000

Br- from Dec 2000 Application

Crop Treatment and Br- Tracer Crop Treatment and Br- Tracer RecoveryRecovery

0

400

800

1200

1600

2000

Br-

Mas

s (m

g)

C Cumulative massH Cumulative mass

0

5

10

15

20

25

0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6 1.8 2.0Pore Volumes

Br-

Con

cent

ratio

n (m

g/L)

C average concentration

H average concentration

C fitted concentration

H fitted concentration

C Plots 42% H Plots 32%

385 days

Cover Crops Are Effective Nitrate Cover Crops Are Effective Nitrate ScavengersScavengers

Concentration Concentration - 34% lower under N2 cover cropped plots than fallow - 34% lower under N2 cover cropped plots than fallow

plots during cereal years , (p = 0.05)plots during cereal years , (p = 0.05)

Mass losses Mass losses - 43% lower under N2 cover cropped plots than fallow - 43% lower under N2 cover cropped plots than fallow

plots during cereal years , (p = 0.05)plots during cereal years , (p = 0.05)

Rainfall timing and amount Rainfall timing and amount - influence concentrations, especially on the following - influence concentrations, especially on the following

year’s results.year’s results.

Legumes assimilated NOLegumes assimilated NO33 and Br and Br - More data needed to test ability for long-term - More data needed to test ability for long-term

scavengingscavenging

Switching FocusSwitching Focus

Part 3 –Part 3 – Transport of conservative, non-absorbing, Transport of conservative, non-absorbing,

and soluble tracers through field soils.and soluble tracers through field soils. Three applicationsThree applications

How is this study different?How is this study different? Structured field soilsStructured field soils Natural rainfallNatural rainfall Sampling methods – PCAPS enable measurement Sampling methods – PCAPS enable measurement

of flux concentrations, don’t require positive or of flux concentrations, don’t require positive or applied pressure for sampling.applied pressure for sampling.

ADEADE

RtD

RtVz

RtD

RtVz

RtDAR

MtzC

hd

w

hd

w

hd/4

/exp

/4

/exp

/4,

22

Which Parameters to Focus On?

C (z, t) = Concentration (mg/L)

Dhd = Hydrodynamic Dispersion: Molecular Diffusion + Mechanical Dispersion (Both in cm2/s)

Vw = Pore Water Velocity

The Three D’sThe Three D’s

mhd DDD 0

wm VD

whd VDD 0

Dhd = Hydrodynamic dispersion (cm2/s) D0 = Molecular diffusion of bromide (cm2/s) Dm = Mechanical dispersion (cm2/s) = Dispersivity (cm) Vw = Pore water velocity (cm/s)

Note*D0 is a

constant

Solving for the real dispersivitySolving for the real dispersivity

w

hd

V

DD 0

D0* = Diffusion coefficient for bromide with tortuosity constant (cm2/s)

k = 0.4, Tortuosity coefficient

whd VDD 0

3 Average Breakthrough 3 Average Breakthrough CurvesCurves

1992 Br -

1995 Cl-

2000 Br-

0

4

8

12

16

20

0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6 1.8

Co

nc

en

tra

tio

n B

r- (m

g/L

)MeasuredFitted

0

2

4

6

8

10

12

0.0 0.4 0.8 1.2 1.6 2.0 2.4

Co

nc

en

tra

tio

n C

l- (

mg

/L)

MeasuredFitted

0

4

8

12

16

20

0.0 0.4 0.8 1.2 1.6 2.0

Time (relative pore volumes)

Co

nc

en

tra

tio

n B

r- (

mg

/L)

MeasuredFitted

0

4

8

12

16

20

0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6 1.8

Co

nc

en

tra

tio

n B

r- (m

g/L

)

0

2

4

6

8

10

12

0.0 0.4 0.8 1.2 1.6 2.0 2.4

Co

nc

en

trati

on

Cl- (

mg

/L)

0

4

8

12

16

20

0.0 0.4 0.8 1.2 1.6 2.0

Time (relative pore volumes)

Co

nc

en

tra

tio

n B

r- (m

g/L

)

= 3.74 cm

= 20.6 cm

= 15.8 cm

1992 Br- 1995 Cl- 2000 Br-

0

20

40

60

80

Disp

ersiv

ity (c

m)

Distribution of Values

They definitelydo not appear to be constant!

Dispersion is a function of Dispersion is a function of scalescale

Blue = Bromide 2000 Red = Chloride 1995 Green = Bromide 1992

Rainfall VariedRainfall Varied

0

5

10

15

201992 Bromide

0

5

10

15

20

25

30

35

40

1995 Chloride

0

5

10

15

20

25

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24

2000 Bromide

Months Passed Since Tracer Application

Rai

nfa

ll (c

m)

November1992

November1995

December2000

1992 Br-: = 0.02 cmSampler # 17

1995 Cl- = 49.9 cmSampler #6

0

8

16

24

32

40

0.0 0.5 1.0 1.5Time (relative pore volumes)

Co

nce

ntr

atio

n B

r- (m

g/L

)

MeasuredFitted

0

2

4

6

8

10

0.0 0.4 0.8 1.2 1.6 2.0 2.4 2.8

Time (relative pore volumes)

Co

nce

ntra

tion

Cl

- (m

g/L

)

MeasuredFitted

131 days

440 days

0

5

10

15

20 1992 Bromide

0

5

10

15

20

25

30

35

40

1995 Chloride

Months Passed Since Tracer ApplicationR

ainf

all (

cm)

1 Pore Volume

1 Pore Volume

How Important is Molecular Diffusion? How Important is Molecular Diffusion? Peclet Number Analysis Peclet Number Analysis

Typically, DTypically, D00 is not considered: True? is not considered: True?

0D

dV

diffusion

dispersionPe

w d = characteristic length controlling transport

Characteristic LengthCharacteristic Length Peclet Number**Peclet Number**Silt Grain Size (0.001 cm)Silt Grain Size (0.001 cm) 6.9 x 106.9 x 10-4-4

Ped Size of 1 cmPed Size of 1 cm 0.690.69

Ped Size of 5 cmPed Size of 5 cm 3.473.47

**Using Average Velocity Calculated From PCAPS Flux

Distribution of Experimental

Peclet #’s

Characteristic lengthIS at Ped Scale!

0D

DPe hd Bear (1972)

1992 Br- 1995 Cl- 2000 Br-

100

101

102

2

34568

2

34567

2

34568

Pec

let N

umbe

r

1 cm Ped Controlled

5 cm Ped Controlled

10 cm Ped Controlled

Can PCAPS Can PCAPS Values Predict the Values Predict the Spatial Concentration Profile?Spatial Concentration Profile?

0

20

40

60

80

100

120

0 10 20 30 40 50

Concentration Br- (mg/L)

Dep

th

Spatially f it ADE

Field Measured

PCAPS Parameters

0

4

8

12

16

20

Dec-00

Feb-01

Apr-01

Jun-01

Aug-01

Oct-01

Dec-01

Feb-02

Apr-02

Mo

nth

ly R

ain

fall

(cm

)0

30

60

90

120

150

Cu

mu

lati

ve

Ra

infa

ll (c

m)Monthly Rainfall (cm)

Cumulative Rainfall (cm)

Soil Sampling Event

Sampler #20

PCAPS PCAPS Values Were Much Higher Values Were Much Higher Than Spatial Than Spatial Values Values

-5

0

5

10

15

20

25

30

5 7 8 17 19 20 23 25 26Sampler Number (Fallow Plots Only)

Dis

per

sivi

ty (

cm)

PCAPS Parameters

May 2001 Soil Sampling

Sep 2001 Soil Sampling

48 cm

Temporal Correlation of Temporal Correlation of

Do Samplers Consistently Fit Do Samplers Consistently Fit Values Above or Values Above or Below the Mean?Below the Mean?

Null Hypothesis: Three normalized Null Hypothesis: Three normalized Values Values came from a population with a mean of 1.came from a population with a mean of 1.

Only six samplers fit the alternative hypothesis.Only six samplers fit the alternative hypothesis.

Result: The group of Result: The group of Values Have No Correlation Values Have No Correlation in Timein Time

Exceptions: Samplers measuring the lowest and Exceptions: Samplers measuring the lowest and highest highest valuesvalues

Spatial Spatial DistributionDistribution

Filliben test:Filliben test: Significant Log-Normal Distribution of Values in Space

0

2

4

6

8

10

12

14

16

-1 to -0.9

-0.8 to -0.7

-0.6 to -0.5

-0.4 to -0.3

-0.2 to -0.1

0 to 0.10.2 to 0.3

0.4 to 0.5

Range of Log10 Dispersivity Values (normalized)

Fre

qu

en

cy

Tracer Transport ConclusionsTracer Transport Conclusions

Variation in Variation in not explained by velocity: rainfall cycles and not explained by velocity: rainfall cycles and

periods between diffusion and dispersion periods between diffusion and dispersion dominated transport.dominated transport.

Soil StructureSoil Structure Transport processes reflect the soil ped Transport processes reflect the soil ped

structure, not grain size.structure, not grain size.

Prediction of tracer spreadPrediction of tracer spread The main parameter of the ADE controlling The main parameter of the ADE controlling

solute spread is not constant in time and solute spread is not constant in time and space. As we implement it, the ADE is not space. As we implement it, the ADE is not capable of accurate transport predictions in capable of accurate transport predictions in natural conditions.natural conditions.

The Scientific Value of Long The Scientific Value of Long Term Experiments:Term Experiments:

10 Years of NWREC experiments were the 10 Years of NWREC experiments were the minimum to understand this soil system.minimum to understand this soil system.

Nature is highly variable, so cover crop Nature is highly variable, so cover crop experiments of a couple of years may not experiments of a couple of years may not lead to the true conclusions.lead to the true conclusions.

Laboratory and fast breakthrough tracer Laboratory and fast breakthrough tracer experiments rarely represent field experiments rarely represent field conditions.conditions.

How can we measure temporal aspects of How can we measure temporal aspects of model parameters if long-term studies are model parameters if long-term studies are not funded?not funded?

Thanks!Thanks!My major professor John Selker for his devotion to his students, his My major professor John Selker for his devotion to his students, his

intense interest in hydrology, and his love of practical solutions.intense interest in hydrology, and his love of practical solutions.

My committee: Richard Dick, Marshal English and Mike GamrothMy committee: Richard Dick, Marshal English and Mike Gamroth

USDA, USGS, EPA and the ODA for funding contributionsUSDA, USGS, EPA and the ODA for funding contributions

The ODA for funding this particular analysis.The ODA for funding this particular analysis.

All of the former students and Bob Christ that worked collecting All of the former students and Bob Christ that worked collecting datadata

Joan Sandeno for all the chromatographic analysis and organizing Joan Sandeno for all the chromatographic analysis and organizing the harveststhe harvests

Del Hemphill for doing all the farmin’ and welcoming new members Del Hemphill for doing all the farmin’ and welcoming new members into the PCAPS club at the NWREC.into the PCAPS club at the NWREC.

Yutaka Hagimoto for his help FINDING the PCAPS and soil samplingYutaka Hagimoto for his help FINDING the PCAPS and soil sampling..

All of the folks in Gilmore hall, especially Dave and Kristy, who All of the folks in Gilmore hall, especially Dave and Kristy, who make work far better than bearable.make work far better than bearable.

Surface FloodingSurface Flooding