Summary of soil P levels and
stratification
GLPF Grant- Team meeting #5
July 23-24, 2013
Lake Erie eutrophication and dissolved P loads
Dissolved Reactive Phosphorus (metric tons)
1000
800
Maumee River
600
400
200
0
Sandusky River
200
• Maumee and Sandusky
Rivers are the two
largest tributaries to
Lake Erie
150
100
50
0
1980
1990
2000
2010
Data from: Heidelberg Tributary Loading Program
 74-78% Agriculture
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?
From Vadas et al. 2005
From Sharpley 2003
• 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
Why is dissolved P increasing?
From Kleinman et al. 2011
• Dissolved P in runoff can increase under no-till management
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
100
80
15
60
10
40
5
20
Percentile distribution
20
Percent of data
Soil test M3P (0-8", ppm)
25
350
300
250
200
150
100
50
0
0
0
0
50
100
150
200
250
300
Soil test M3P (0-8", ppm)
Percentile distribution
Median or 50%
•
•
•
•
90th
75th
50th
25th
10th
Ranges from 2.8 – 291 ppm
Mean = 41.3 ppm
Median = 35.8 ppm
90th percentile = 72ppm
 90% of the data are <72ppm
The extent of P stratification
600
0
0-2
2-8
25
50
75
100
300
125
300
Top M3P (0-2", ppm)
Core depth (inches)
M3P (ppm)
3:1 line
200
1:1 line
150
100
50
0
0
50
100
150
200 300 600
Total M3P (0-8", ppm)
• 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)
The magnitude of stratification: ratio
4
3
2
1
Top > Total
Top = Total
Ratio of Top:Total M3P
Ratio of Top:Total M3P
4
Top < Total
3
2
1
0
0
0
50
100 150 200 250 300 350
Total M3P (ppm)
• The ratio of top:total ranged from 0.3 – 3.4 *Using a correction
 Mean = 1.54
Median = 1.48
• The ratio was highest at lower soil test P
 Dividing by a smaller # ?
factor not possible
The magnitude of stratification: ratio
4
2
1
0.8
0.6
Ratio of Top:Total M3P
Ratio of Top:Total M3P
4
2
1
0.8
0.6
0.4
0.4
0.2
0.2
0
50
100 150 200 250 300 350
Total M3P (ppm)
• 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)
The magnitude of stratification: difference
200
150
100
50
Top > Total
0
Top = Total
-50
Top < Total
M3P difference (top - total)
M3P difference (top - total)
200
150
100
50
0
-50
-100
0
-100
50
100
150
Total M3P (ppm)
• 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
300
4-part stratification
M3P (ppm)
0
25
50
75
100
M3P (ppm)
125 300
0
Median
1-2
2-5
5-8
60
54.5
49
34
26
40
60
80 100 120 140 160
1
Depth into soil (inches)
Core depth (inches)
0-1
20
0
2
3
4
5
6
7
8
• Stratification evident even in the top 1” of soil
(ANOVA, P<0.001, n=232)
• Although the degree of stratification varied some…
4-part stratification
M3P (ppm)
0
25
50
75
100
M3P (ppm)
125 300
0
Median
1-2
2-5
5-8
60
54.5
49
34
26
40
60
80 100 120 140 160
1
Depth into soil (inches)
Core depth (inches)
0-1
20
0
2
3
4
5
6
7
8
• 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
4-part stratification
M3P (ppm)
0
25
50
75
100
M3P (ppm)
125 300
0
Median
1-2
2-5
5-8
60
54.5
49
34
26
40
60
80 100 120 140 160
1
Depth into soil (inches)
Core depth (inches)
0-1
20
0
2
3
4
5
6
7
8
• 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
DRP in dilute aqueous soil solution (mg P/L)
Dilute aqueous soil suspension (DASS)
• DRP from 1 g of soil extracted
with 1 L of distilled water over
16h
0.14
0.12
• DRP readily exchanges with
water
0.10
0.08
0.06
 Mean DRP = 0.037 mg P/L
0.04
 Ranged from 0.003 – 0.115
mg P/L
0.02
0.00
0
20 40 60 80 100 120 140 160 180
Total M3P (ppm)
• Mean DRP = 0.026 mg P/L
• Ranged from 0.009 – 0.047
mg P/L
• DASS was positively related to
soil test P (log-transformed,
r2=0.73, p<0.001)
2012 Total M3P (ppm)
160
Total M3P
1:1 line
140
120
100
80
60
40
20
0
Ratio
5
2012 Ratio of Top:Total M3P
180
1:1 line
4
3
2
1
0
0 20 40 60 80 100 120 140 160 180
2009 Total M3P (ppm)
0
1
2
3
4
2009 Ratio of Top:Total M3P
5
2012 M3P difference (top - total, ppm)
Temporal variation in P stratification
Difference
150
1:1 line
100
50
0
-50
-50
0
50
100
150
2009 M3P difference (top - total, ppm)
• Sampled 74 fields in 2009 and again in 2012
• No distinct trends in how fields changed from 2009-2012
Temporal variation in P stratification
120
M3P difference (top - total, ppm)
200
Ratio of Top:Total M3P
Total M3P (0-8", ppm)
4
150
100
50
0
2
1
0.8
0.6
0.4
0.2
2009
2012
100
80
60
40
20
0
-20
-40
-60
-80
2009
2012
2009
2012
• 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)
120
M3P (2012 - 2009, ppm)
100
80
2012 > 2009
60
40
20
2012 = 2009
0
-20
Temporal
variation in P
stratification
2012 < 2009
-40
-60
-80
-100
Top
Bottom
Total
• 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
Spatial variation in P stratification
• Gridded sampling in 3 fields
Grid Acres
n
Sample
distance
1
72
30
9.6 m
2
47
20
9.7 m
3
70
28
9.1 m
Tillage
Rot. no
till (till
for corn)
Drainage
Somewhat poor,
tiled
Well-drained, tiled
Well-drained, tiled
Spatial variation in P stratification:
Total M3P (ppm)
Grid 2
Grid 1
80
Grid 3
70
70
60
60
60
Meters
50
Mean M3P:
• Grid 1 = 50.5 ppm
• Grid 2 = 54.1 ppm
• Grid 3 = 58.4 ppm
50
40
40
40
30
30
20
20
20
10
10
5 10 15 20 25 30 35
0
50
100
150
200
250
300
6 8 10 12 14
Meters
5
10 15 20 25 30 35
Spatial variation in P stratification:
Ratio top:total
0.6
Grid 2
Grid 1
80
Grid 3
70
70
60
60
60
Meters
50
Mean Ratio:
• Grid 1 = 1.4
• Grid 2 = 1.3
0.6
• Grid 3 = 1.2
0.8
50
40
40
40
30
30
20
20
1.0
1.2
1.4
1.6
1.8
2.0
20
10
10
5 10 15 20 25 30 35
0.8
1.0
1.2
1.4
1.6
1.8
2.0
6 8 10 12 14
Meters
5
10 15 20 25 30 35
Spatial variation in P stratification:
Difference top-bottom (ppm)
Grid 2
Grid 1
80
Grid 3
70
70
60
60
60
Meters
50
Mean difference:
• Grid 1 = 18.1 ppm
• Grid 2 = 10.9 ppm
• Grid 3 = 7.3 ppm
50
40
40
40
30
30
20
20
20
10
10
5 10 15 20 25 30 35
-60
-40
-20
0
20
40
6 8 10 12 14
Meters
5
10 15 20 25 30 35
Spatial variation in P stratification:
Coefficient of Variation
1.8
Coefficient of Variation
1.6
1.4
1.2
• CV= standard deviation
mean
All data
Grid 1
Grid 2
Grid 3
• As much variation by field
as across 1400 fields for
total M3P and the
difference
1.0
0.8
0.6
0.4
0.2
0.0
Total M3P
Ratio
Difference
• Variation in the ratio lower
by field
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?