Summary of soil P levels and stratification GLPF Grant- Team meeting #5 July 23-24, 2013.

Summary of soil P levels and stratification

GLPF Grant- Team meeting #5July 23-24, 2013

Lake Erie eutrophication and dissolved P loads

• Maumee and Sandusky Rivers are the two largest tributaries to Lake Erie 74-78% Agriculture

0

200

400

600

800

1000

Maumee River

1980 1990 2000 2010

Dis

solv

ed R

eact

ive

Pho

spho

rus

(met

ric t

ons)

0

50

100

150

200Sandusky River

Data from: Heidelberg Tributary Loading Program

Conservation practices in the Lake Erie Watershed

• Large-scale conservation practices have been adopted throughout the Lake Erie basin to reduce soil erosion No-till or reduced till Conservation reserve program

• Has successfully reduced sediment loading (Richards et al. 2008, 2009)

Why is dissolved P increasing?

• Typical agronomic soil tests use 0-8” cores• P stratification occurs under no-till practices from the lack of

soil mixing and application of surface fertilizers• Runoff in Maumee and Sandusky Rivers tend to be surficial and

interacts with the top 1-2” of soil

From Sharpley 2003From Vadas et al. 2005

Why is dissolved P increasing?

• Dissolved P in runoff can increase under no-till management

From Kleinman et al. 2011

Research Questions

• How high is soil P and what is the extent of P stratification in the Sandusky River Watershed? Paired with certified crop advisors (CCAs) to collect soil

samples from >1500 fields Most soils were split into 0-2” vs 2-8” samples (n=1405) A subset of soils were split into 0-1, 1-2, 2-5, 5-8” samples

(n=234) Mehlich 3 extractable P measured at a soil test lab

Soil Profile

Research Questions

• Does DRP readily exchange with the typical agricultural soil? Dilute Aqueous Soil Solution (DASS) Extracted DRP from 1 g of soil in 1 L of distilled water

Research Questions

• Does DRP readily exchange with the typical agricultural soil? Dilute Aqueous Soil Solution (DASS) Extracted DRP from 1 g of soil in 1 L of distilled water

• How variable is P stratification within a given field spatially and temporally? Select fields received gridded sampling every ~10 meters

to examine spatial variation (n=78) A subset of fields were sampled in 2009 and again in 2012

to examine temporal variation (n=74)

Soil P levels

• Ranges from 2.8 – 291 ppm• Mean = 41.3 ppm • Median = 35.8 ppm • 90th percentile = 72ppm

90% of the data are <72ppm

Soil test M3P (0-8", ppm)

0 50 100 150 200 250 300

Per

cent

of d

ata

0

5

10

15

20

25

Percentile distribution

0

20

40

60

80

100

Percentile distributionMedian or 50%

Soi

l tes

t M3P

(0-

8",

ppm

)

0

50

100

150

200

250

300

350

50th25th10th

75th90th

The extent of P stratification

• Top: Mean/median = 59/55 ppm, ranged from 4.0 – 319 ppm • Bottom: Mean/median = 35/28 ppm, ranged from 2.0 – 291 ppm• Top 2” are significantly higher than the bottom (paired t-test,

P<0.001, n=1526)

M3P (ppm)

0 25 50 75 100 125 300

Cor

e de

pth

(inch

es)

0-2

2-8

Total M3P (0-8", ppm)

0 50 100 150 200 300 600

Top

M3P

(0-

2", p

pm)

0

50

100

150

200

300

600

1:1 line

3:1 line

Rat

io o

f Top

:Tot

al M

3P

0

1

2

3

4

The magnitude of stratification: ratio

• The ratio of top:total ranged from 0.3 – 3.4 Mean = 1.54 Median = 1.48

• The ratio was highest at lower soil test P Dividing by a smaller # ?

Top > Total

Total M3P (ppm)

0 50 100 150 200 250 300 350

Ra

tio o

f To

p:T

ota

l M3

P

0

1

2

3

4

Top = Total

Top < Total

*Using a correction factor not possible

The magnitude of stratification: ratio

• Ratios need to be on a log-scale Ratio 2:1=2 ; ratio 1:2=0.5

• The ratio is significantly higher than 1 (one-sample t-test, P<0.001)

Rat

io o

f Top

:Tot

al M

3P

0.2

0.4

0.6

0.8

2

4

1

Total M3P (ppm)

0 50 100 150 200 250 300 350R

atio

of T

op:T

otal

M3P

0.2

0.4

0.6

0.8

2

4

1

M3P

diff

ere

nce

(top

- to

tal)

-100

-50

0

50

100

150

200

• The difference (top–total) ranged from -78 – 176 ppm Mean = 18 ppm Median = 15.8 ppm The difference is significantly greater than zero

(one-sample t-test, P<0.001)• The difference was highest at higher soil test P

Top > Total

Top = Total

Top < Total

Total M3P (ppm)

0 50 100 150 300

M3

P d

iffer

ence

(to

p -

tota

l)

-100

-50

0

50

100

150

200

The magnitude of stratification: difference

4-part stratification

• Stratification evident even in the top 1” of soil (ANOVA, P<0.001, n=232)

• Although the degree of stratification varied some…

M3P (ppm)

0 25 50 75 100 125 300

Cor

e de

pth

(inch

es)

0-1

1-2

2-5

5-8

Median

60

49

34

26

54.5

M3P (ppm)

0 20 40 60 80 100 120 140 160

Dep

th in

to s

oil (

inch

es)

0

1

2

3

4

5

6

7

8

4-part stratification

• Stratification evident even in the top 1” of soil (ANOVA, P<0.001, n=232)

• Although the degree of stratification varied some… • 85% of the samples had some degree of stratification

M3P (ppm)

0 25 50 75 100 125 300

Cor

e de

pth

(inch

es)

0-1

1-2

2-5

5-8

Median

60

49

34

26

54.5

M3P (ppm)

0 20 40 60 80 100 120 140 160

Dep

th in

to s

oil (

inch

es)

0

1

2

3

4

5

6

7

8

4-part stratification

• Stratification evident even in the top 1” of soil (ANOVA, P<0.001, n=232)

• Although the degree of stratification varied some… • 85% of the samples had some degree of stratification

M3P (ppm)

0 20 40 60 80 100 120 140 160

Dep

th in

to s

oil (

inch

es)

0

1

2

3

4

5

6

7

8

M3P (ppm)

0 25 50 75 100 125 300

Cor

e de

pth

(inch

es)

0-1

1-2

2-5

5-8

Median

60

49

34

26

54.5

Total M3P (ppm)

0 20 40 60 80 100 120 140 160 180

DR

P in

dilu

te a

queo

us s

oil s

olut

ion

(mg

P/L

)

0.00

0.02

0.04

0.06

0.08

0.10

0.12

0.14

Dilute aqueous soil suspension (DASS)

• DRP from 1 g of soil extracted with 1 L of distilled water over 16h

• DRP readily exchanges with water Mean DRP = 0.037 mg P/L

Ranged from 0.003 – 0.115 mg P/L

• DASS was positively related to soil test P (log-transformed, r2=0.73, p<0.001)• Mean DRP = 0.026 mg P/L

• Ranged from 0.009 – 0.047 mg P/L

2009 Total M3P (ppm)

0 20 40 60 80 100 120140 160 180

2012

Tot

al M

3P (

ppm

)

0

20

40

60

80

100

120

140

160

180

2009 Ratio of Top:Total M3P

0 1 2 3 4 5

2012

Rat

io o

f T

op:T

otal

M3P

0

1

2

3

4

5

2009 M3P difference (top - total, ppm)

-50 0 50 100 150

2012

M3P

diff

eren

ce (

top

- to

tal,

ppm

)

-50

0

50

100

1501:1 line 1:1 line 1:1 line

Temporal variation in P stratification

• Sampled 74 fields in 2009 and again in 2012• No distinct trends in how fields changed from 2009-2012

Total M3P Ratio Difference

Temporal variation in P stratification

• Significant, but slight increase in total M3P from 2009-2012 (means: 2009 = 43ppm, 2012 = 47ppm; paired t-test P=0.007)

• No significant change in the ratio (means: 2009 = 1.83, 2012 = 1.81) or the difference (means: 2009 = 30ppm, 2012 = 32ppm)

2009 2012

Tot

al M

3P (

0-8"

, ppm

)

0

50

100

150

200

2009 2012

Rat

io o

f Top

:Tot

al M

3P

0.2

0.4

0.6

0.8

2

4

1

2009 2012

M3P

diff

eren

ce (

top

- to

tal,

ppm

)

-80

-60

-40

-20

0

20

40

60

80

100

120

Temporal variation in P stratification

• D M3P is the difference between 2012 and 2009• Means:

Top= 5.9 ppm ± 3.0 SE *(significantly >0, one-tailed t-test, P=0.05) Bottom = 4.1 ppm ± 2.1 SE Total = 4.5 ppm ± 1.6 SE *(significantly >0, one-tailed t-test, P=0.05)

• Top is more variable than bottom

Top Bottom Total

M

3P (

2012

- 2

009,

ppm

)

-100

-80

-60

-40

-20

0

20

40

60

80

100

120

2012 > 2009

2012 = 2009

2012 < 2009

Spatial variation in P stratification

• Gridded sampling in 3 fields

Grid Acres n Sample distance Tillage Drainage

1 72 30 9.6 mRot. no till (till

for corn)

Somewhat poor, tiled

2 47 20 9.7 m Well-drained, tiled

3 70 28 9.1 m Well-drained, tiled

5 10 15 20 25 30 35

Met

ers

10

20

30

40

50

60

70

5 10 15 20 25 30 35

10

20

30

40

50

60

70

Meters

6 8 101214

20

40

60

80

Spatial variation in P stratification: Total M3P (ppm)

Mean M3P:• Grid 1 = 50.5 ppm• Grid 2 = 54.1 ppm• Grid 3 = 58.4 ppm

0 50 100 150 200 250 300

Grid 1

Grid 2

Grid 3

5 10 15 20 25 30 35

10

20

30

40

50

60

70

Meters

6 8 101214

20

40

60

80

5 10 15 20 25 30 35

Met

ers

10

20

30

40

50

60

70

0.6 0.8 1.0 1.2 1.4 1.6 1.8 2.0

Spatial variation in P stratification: Ratio top:total

Mean Ratio:• Grid 1 = 1.4• Grid 2 = 1.3• Grid 3 = 1.2

Grid 1

Grid 2

Grid 3

0.6 0.8 1.0 1.2 1.4 1.6 1.8 2.0

Meters

6 8 101214

20

40

60

80

5 10 15 20 25 30 35

10

20

30

40

50

60

70

5 10 15 20 25 30 35

Met

ers

10

20

30

40

50

60

70

Spatial variation in P stratification: Difference top-bottom (ppm)

Mean difference:• Grid 1 = 18.1 ppm• Grid 2 = 10.9 ppm• Grid 3 = 7.3 ppm

Grid 1

Grid 2

Grid 3

-60 -40 -20 0 20 40

• CV= standard deviation mean

• As much variation by field as across 1400 fields for total M3P and the difference

• Variation in the ratio lower by field

Spatial variation in P stratification: Coefficient of Variation

Total M3P Ratio Difference

Coe

ffici

ent o

f Var

iatio

n

0.0

0.2

0.4

0.6

0.8

1.0

1.2

1.4

1.6

1.8

All data Grid 1 Grid 2 Grid 3

Summary

• Most (90%) total soil test P levels are <72ppm

• Soil P stratification is prevalent in the Sandusky River Watershed

• P in soil readily exchanges with water and this exchange is predicted by M3P

• Fields tend to accumulate P over time and this accumulation appears to be higher in the top 2” of soil

• Variation in P levels and stratification can be as high within a field as across 1400 fields

Questions?