soil phosphorus tests in the north-central region
DESCRIPTION
Soil Phosphorus Tests in the North-Central Region. Antonio Mallarino Iowa State University. Basics of Soil Testing. A relative measurement of nutrient sufficiency for plants. Tests measure an amount of nutrient that is proportional to the amount actual available for plants. - PowerPoint PPT PresentationTRANSCRIPT
Soil Phosphorus Tests in the Soil Phosphorus Tests in the North-Central RegionNorth-Central Region
Antonio MallarinoAntonio Mallarino
Iowa State UniversityIowa State University
Basics of Soil Testing
A relative measurement of nutrient sufficiency for plants.
Tests measure an amount of nutrient that is proportional to the amount actual available for plants.
Many P tests are used and measure different amounts of P. The amount measured has no meaning by itself and cannot by used without calibration.
Field Correlation/Calibration
Gives a meaning to a soil test result.
Establish critical concentration ranges for different crops and soils.
Establish probability of response for different test results.
Determine fertilization rates when test is below a critical range: interpretation classes or continuous formulas.
Soil Testing for P
Bray-1 and Olsen have been extensively used across the North-Central region.
Bray-1 underestimates plant-available P in many calcareous soils.
Both tests have been used with a colorimetric determination method, intensity of a blue color.
Colorimetric methods measure orthophosphate P.
Common Extractive Solutions
Bray-1: HCl + NH4F
Olsen or bicarbonate: NaHCO3 (pH 8.5).
Mehlich-3: CH3COOH + HNO3 +
NH4F + EDTA
NH4NO3 + EDTA
Iowa Field Calibrations: Bray & Olsen
Bray-1 Olsen
Bray-1 P (ppm)
0 10 20 30 40 50 60 70
Rel
ativ
e C
orn
Yie
ld (
%)
50
60
70
80
90
100
VL L H VHO
pH > 7.3
Olsen P (ppm)
0 5 10 15 20 25 30 3550
60
70
80
90
100
VL L H VHO
pH > 7.3
(low subsoil P)Classes
(low subsoil P)Classes
The Mehlich-3 Extractant
M3 extractant began to be used in the NC Region for P, K, Ca, Mg, and some micronutrients during the late 1990s.
The NCR-13 committee included the M3 among procedures for P, K, Ca, and Mg.
Iowa published field calibrations for M3-K and the M3-P colorimetric in 1999.
M3- P is similar to Bray-1 P, except in some high-pH soils.
Ols
en P
(p
pm
)
Bray-1 P (ppm)0 20 40 60 80
0
20
40
60
80
Ols
en P
(p
pm
)
Mehlich-3 P (ppm)0 20 40 60 80
0
20
40
60
80
Meh
lich
-3 P
(p
pm
)
Bray-1 P (ppm)0 20 40 60 80
0
20
40
60
80
SOILS OF pH 7.3 OR LOWER
SOILS OF pH 7.4 OR HIGHER
Ols
en P
(p
pm
)
Bray-1 P (ppm)0 20 40 60 80
0
20
40
60
80
Ols
en P
(p
pm
)Mehlich-3 P (ppm)
0 20 40 60 800
20
40
60
80
Meh
lich
-3 P
(p
pm
)
Bray-1 P (ppm)0 20 40 60 80
0
20
40
60
80
Bray-1 Vs M3 and Soil pHM
ehlich-3
P (ppm
)
Bray-1 P (ppm)0 20 40 600 25 50 75 100
0
25
50
75
100pH<6.5
r = 0.96
0 25 50 75 100
pH 6.5-7.3 pH 7.4-8.2
r = 0.95
0 20 40 60
0
25
50
75
100M
ehlich-3
P (ppm
)
0 20 40 60
Mehlich-3
P (ppm
)
Olsen P (ppm)0 20 40 60
r = 0.91 r = 0.82r = 0.91
Bray-1 and M3 in Manured Soils
Bray P (ppm)
0 50 100 150 200 250 300
M3
P c
olo
rim
etri
c (p
pm
)
0
50
100
150
200
250
300
M3 = -1.8 + 1.10BPr 2 = 0.98
Swine manure
Poultry layers manure
Kansas: M3 vs Bray
y = 1.15 x Bray
r2 = 0.91
0
20
40
60
80
100
0 20 40 60 80 100Bray P (ppm)
M3
Co
l P (
pp
m)
Noncalcareous Soils
Calcareous Soils
D. Leikam
Wisconsin: M3 vs Bray
Bray P1, mg P kg-1
0 100 200 300 400
Me
hlic
h I
II,
mg
P k
g-1
0
100
200
300
400
Arlington
Lancaster
Fond du Lac
All sites (1998-2004)
M3 = -8 + 1.51Bray
r 2 = 0.97
L. Bundy
Iowa Field Calibrations: Bray and M3
Bray-1 M3 Colorimetric
Bray-1 P (ppm)
0 10 20 30 40 50 60 70 80
Rel
ativ
e C
orn
Yie
ld (
%)
50
60
70
80
90
100
VL L H VHO (low subsoil P)Classes
pH > 7.3
M3-colorimetric P (ppm)
0 10 20 30 40 50 60 70 80
VL L H VHO (low subsoil P)Classes
pH > 7.3
Now Comes the ICP!
Some labs began using ICP (inductively coupled plasma) for the M3 test.
ICP measures uses a very hot flame that breaks down all compounds.
Great confusion! ICP measures more P than the colorimetric method whatever extractant is used.
But problem with M3 because it is used for several nutrients.
ICP Measures Organic P - MinnesotaS
oil-
Tes
t P
(p
pm
)
0
10
20
30
40
Soil P
Color ICP
Extra P to Extracts
Poly P
Color
ICP ATP
Color
ICP
ICP Measures Organic P - IowaR
eco
vere
d P
(p
pm
)
0
5
10
15
20
25
30
35
40 Ortho P ATP
Color ICP
Color
ICP
M3-ICP vs M3-Colorimetric or Bray
M3-COL (ppm)
0 10 20 30 40 50 60 70 80 90
M3-
ICP
(p
pm
)
0
10
20
30
40
50
60
70
80
90Y = 9.87 + 1.08Xr2 = 0.84P < 0.001
M3-COL (ppm)0 10 20 30 40 50 60 70 80 90
BR
AY
-1 P
(p
pm
)0
10
20
30
40
50
60
70
80
90Y = 1.21 + 0.84Xr2 = 0.97P < 0.001
pH 8.1(excluded)
pH 8.1
pH > 7.3
pH > 7.3
Kansas: M3 ICP vs Colorimetric
M3icp = 6.76 + 1.03M3colr2 = 0.98
0
20
40
60
80
100
0 20 40 60 80 100
M3-Col P (ppm)
M3-
ICP
P (
pp
m)
D. Leikam
Iowa: M3-ICP vs M3-Colorimetric
Relative Absolute
M3-COL (ppm)0 10 20 30 40 50 60 70 80
M3-
CO
L /
M3-
ICP
Rat
io
0.0
0.2
0.4
0.6
0.8
1.0
M3-COL (ppm)0 10 20 30 40 50 60 70 80
M3-
ICP
- M
3-C
OL
(p
pm
)0
5
10
15
20
25
30
Kansas: M3 Colorimetric/ICP Ratio
0.0
0.2
0.4
0.6
0.8
1.0
0 25 50 75 100
Mehlich 3-Col
M3-
Co
l :
M 3
-IC
P R
atio
D. Leikam
MN: M3-ICP vs M3-Colorimetric
ICP-Color Difference vs Mehlich P Colorimetric Value
-10
-5
0
5
10
15
20
0 20 40 60 80 100 120 140 160
Mehlich P Colorimetric (ppm)
M3
P IC
P-C
olo
rim
(p
pm
)
Iowa: M3 ICP & colorimetric and OM
Relative Absolute
But for this data set, high OM sites also had higher pH and lower P by any test.
SOIL ORGANIC C (%)
1 2 3 4 5
M3-
ICP
/ M
3-C
OL
Rat
io
1.0
1.5
2.0
2.5
3.0
3.5
4.0
SOIL ORGANIC C (%)
1 2 3 4 5M
3-IC
P -
M3-
CO
L (
pp
m)
0
5
10
15
20
25
30
35Y = 2.25 - 0.02Xr² = 0.07P < 0.02
Y = 21.2 - 0.39Xr² = 0.16P < 0.01
MN: M3 ICP & colorimetric and OM
Colorimetric - ICP Difference vs Soil Organic Matter
-10
-8
-6
-4
-2
0
2
4
6
8
10
0 2 4 6 8 10 12
Soil Organic Matter (%)
Me
hli
ch
P I
CP
-Co
lori
m (
pp
m)
Iowa: M3 ICP & colorimetric and pH
Relative Absolute
But for this data set, high pH sites also had higher OM and lower P by any test.
SOIL pH
5.0 5.5 6.0 6.5 7.0 7.5 8.0 8.5
M3-
ICP
/ M
-3C
OL
Rat
io
1.0
1.5
2.0
2.5
3.0
3.5
4.0
SOIL pH
5.0 5.5 6.0 6.5 7.0 7.5 8.0 8.5M
3-IC
P -
M3-
CO
L (
pp
m)
0
5
10
15
20
25
30
35Y = 58.3 - 6.7Xr² = 0.32P < 0.001
Y = 3.96 - 0.34Xr² = 0.14P < 0.01
MN: M3 ICP & colorimetric and pH
Mehlich P ICP-Co lorimetric D ifferencevs So il p H
-1 0
-5
0
5
1 0
1 5
2 0
5 5 .2 5 .4 5 .6 5 .8 6 6 .2 6 .4 6 .6 6 .8 7 7 .2 7 .4 7 .6 7 .8 8 8 .2 8 .4
Soil pH
M3
IC
P -
Co
lor
Dif
fere
nc
e (
pp
m)
NCR-13 M3 ICP-Colorimetric Work
ICP extra P seems to be derived from soluble organic P compounds.
IA, MN, MO: No relationship with soil organic matter or manure history.
Not clear results for pH. Sometimes ICP - Colorimetric difference is smaller for high-pH soils, but often have less P.
Many public and private labs: P from ICP correlates well with colorimetric P but there is no reliable, constant factor.
Iowa M3 ICP Field Calibrations
M3 Soil-Test P (ppm)
0 10 20 30 40 50 60 70 80 90
Rel
ativ
e C
orn
Yie
ld (
%)
50
60
70
80
90
100
110
M3 colorimetric
M3 ICP
Iowa M3 ICP Field Calibrations
M3 Soil-Test P (ppm)
0 10 20 30 40 50 60 70 80 90
Rel
ativ
e C
orn
Yie
ld (
%)
50
60
70
80
90
100
110
M3 colorimetric
M3 ICP
Critical Soil P Concentrations
Model Bray-1 M3-Col M3-ICP
------------------- ppm P ------------------
Cate-Nelson 13 16 20
Lin-Plateau 20 21 32
Quad-Plateau 26 28 43
Iowa M3 ICP & Color Interpretations
M3-colorimetric P (ppm)
0 10 20 30 40 50 60 70 80
Rel
ativ
e C
orn
Yie
ld (
%)
50
60
70
80
90
100
M3-ICP P (ppm)
0 10 20 30 40 50 60 70 80
VL L H VHOVL L H VHO (low subsoil P)Classes
(low subsoil P)Classes
pH > 7.3 pH > 7.3
Colorimetric ICP
Soil-Test CategorySoil Test Method Very low Low Optimum High Very high
-------------------------- ppm P --------------------------
Olsen 0-5 6-10 11-14 15-20 21+
Bray-1 & M3 colorim. 0-8 9-15 16-20 21-30 31+
M3-ICP 0-15 16-25 26-35 36-45 46+
Crop P Fertilizer Recommendation----------------------- lb P2O5/acre ----------------------
Corn 100 75 55 0 0
Soybean 80 60 40 0 0
Soil-Test CategorySoil Test Method Very low Low Optimum High Very high
-------------------------- ppm P --------------------------
Olsen 0-5 6-10 11-14 15-20 21+
Bray-1 & M3 colorim. 0-8 9-15 16-20 21-30 31+
M3-ICP 0-15 16-25 26-35 36-45 46+
Crop P Fertilizer Recommendation----------------------- lb P2O5/acre ----------------------
Corn 100 75 55 0 0
Soybean 80 60 40 0 0Maintenanceadjust basedon removal
Iowa Soil-Test P Interpretations
Four States Bray-1 P Classes
Class IA IL MN NE WI
- --------------------------- ppm ------------------------------
VL 0-8 na 0-5 0-5 0-7
L 9-15 na 6-11 6-15 8-12
O, M 16-20 22-32 12-15 16-24 13-18
H 21-30 32+ 16-20 25-30 19-28
NE, 8-inch sampling depth; others 6 to 7 inchesOptimum, Medium: IA, IL, WI apply maintenance
MN, NE starter or < maintenance
EnvironmentalEnvironmentalSoil Phosphorus TestsSoil Phosphorus Tests
Mehlich-3 P (ppm)0 20 40 60 80 100 120 140
Bray-1 P (ppm)0 20 40 60 80 100 120
To
tal D
isso
lved
P in
Ru
rno
ff (
mg
/L)
0.0
0.2
0.4
0.6
0.8
1.0
Olsen P (ppm)0 10 20 30 40 50 60 70 80 90
Iron-oxide P (ppm)0 10 20 30 40 50 60 70 80
0.0
0.2
0.4
0.6
0.8
1.0
FeO 0-6" vs FeO 0-2" H20 0-6" vs FeO 0-2"
Water extractable P (ppm)0 5 10 15 20 25 30 35
P saturation index (%)0 2 4 6 8 10 12 14 16
Y = 0.065 + 0.0047XR2 = 0.72
Y = 0.063 + 0.0043XR2 = 0.73
Y = 0.081 + 0.0073XR2 = 0.77
Y = 0.050 + 0.0076XR2 = 0.77
Y = 0.107 + 0.015XR2 = 0.75
Y = 0.046 + 0.038XR2 = 0.73
Dissolved P in Runoff
Bray-1 P (ppm)0 20 40 60 80 100 120
Dis
solv
ed P
(p
pm
)
0.00
0.02
0.04
0.06
0.08
0.10
0.12
0.14
Olsen P (ppm)0 10 20 30 40 50 60
Iron-Oxide P (ppm)0 10 20 30 40 50 60 70 80 90
Dis
solv
ed P
(p
pm
)
0.00
0.02
0.04
0.06
0.08
0.10
0.12
0.14
Soil P Saturation Index (%)0 5 10 15 20 25
Mehlich-3 P (ppm)0 20 40 60 80 100 120 140
Water Extractable P (ppm)0 5 10 15 20 25 30 35
P in Tile Drainage
Soil P Testing in the NC Region
No problem with Bray and Olsen tests in the NC Region. Known high pH issue.
M3-COL is similar to Bray in acid or neutral soils, better in IA high-pH soils. Some different results in WI.
M3-COL and M3-ICP are different soil tests!! Getting M3-COL or Bray from M3-ICP is a very risky business.
Base interpretations on calibrations! Used in P indices for NMPs or MMPs.