1. Soil pH and SMP Buffer pH methodologies

a. Time for SMP buffer to set in soil-water slurry

b. Conditions on LabFit for soil pH and Sikora buffer pH

2. Laboratory survey on pH and lime recommendations

prepared for SERA-6 conferenceJune 4-5, 2007

F.J. SikoraUniversity of Kentucky

Soil pH and buffer pH methodology:water and SMP/Sikora buffer reaction time

with soil and a laboratory survey

Variations in methods for determining 1:1 soil:water pH

Reference pub

Quantity of soil

Stirring (or mixing) time after adding

water

Standing time before determining

pH

Stirring during/before pH measurement

SPAC, Inc. 4.25 cm3, 5 g, or 10 cm3

Stir for 5 sec 10 min stir during pH measurement

Southern 10 cm3 Mix for 5 sec 30 min stir soil suspension by swirling the cup slightly just

prior to reading pH

Northeastern Scoop 5 cm3 or weigh 5 g

Stir vigorously for 15 sec

30 min place electrodes in the slurry, swirl carefully and

read pH immediately

North Central

4.25 cm3

(5 g scoop)Stir

vigorously for 5 sec

10 min place electrodes in the slurry, swirl carefully and

read pH immediately

Western 5 0.1 g Stir thoroughly for 5 sec

15 min place electrodes in the slurry, swirl carefully and

read pH immediately

Variations in SMP methods for determining buffer pH

Reference pub

Quantity of soilVolume of buffer added to soil pH

slurry and shaking time

Oscillations/minStanding time

before determining

pH

SPAC, Inc. 4.25 cm3 or 5 g 10 mL buffer, shake for 10 min

(or 15 min)

>180 30 min (or 15 min)

Southern

Northeastern Scoop 5 cm3 or weigh 5 g

10 mL buffer, shake for 10 min

(or 15 min)

250 30 min (or 15 min)

North Central 4.25 cm3

(5 g scoop)10 mL buffer, shake

for 10 min (or 15 min)

250 30 min (or 15 min)

Western 5 0.1 g 10 mL buffer, stir every 5 minutes for

20 min

20 min

Mclean, Eckert, Reddy, and Trierweiler. 1978. An improved SMP soil lime requirement method incorporating double-buffer and quick-test features. SSSAJ 42:311-316.

excerpt from

1975 North Central publicationon soil test methods.

Table in the current North Central region publication on soil test methods.

SMP Buffer pH

Lexington Quality Control Sample 4108

6.3

6.4

6.5

6.6

6.7

6.8

6.9

7.0

0 50 100 150 200 250 300 350 400 450 500 550

Days after Jan 1, 2005

Bu

ffer

pH

- 2 s

- 3 s

+ 3 s

+ 2 s

SMP buffer

mean

Sikora buffer

LEXINGTON LAB

PRINCETON LAB

buf

buf

stirring time for buffer in soil

time buffer set in soil prior to measurement

LabFit method with Sikora buffer

0.33 min.±0.11

37 min.±4

1.5 hrsfor 3 trays(n=120)

Method for adding water to soil

Each sample stirred with stir rod and let set for 30 min.

y = 0.9613x + 0.1576

R2 = 0.9763

4

5

6

7

8

9

10

4 5 6 7 8 9 10

water pH, old way

water

pH,

new

inst

r

5,10

y = 1.0486x - 0.4033

R2 = 0.9607

5

5.5

6

6.5

7

7.5

8

5 5.5 6 6.5 7 7.5 8

SMP buffer pH, old way

KY b

uffer

pH,

new

inst

r

5,10

Sik

ora

Buf

fer

pH,

LabF

it in

stru

men

t

Soi

l pH

, La

bFit

inst

rum

ent

Soil pH, NAPT median SMP Buffer pH, NAPT median

Soil pH Buffer pH

1:1 line

regression line

y = 0.8927x + 0.6065

R2 = 0.9647

4

5

6

7

8

9

10

4 5 6 7 8 9 10

water pH, old way

water

pH,

new

instr

5,10 tray swilred

y = 0.9613x + 0.1576

R2 = 0.9763

4

5

6

7

8

9

10

4 5 6 7 8 9 10

water pH, old way

water

pH,

new

inst

r

5,10

Soi

l pH

, La

bFit

inst

rum

ent

Soi

l pH

, La

bFit

inst

rum

ent

Soil pH, NAPT median Soil pH, NAPT median

Each sample stirred with stir rod for 5 sec and let set for 30 min.

Tray swirled for 5 sec. and let set for 30 min.

1:1 line

regression line

Soil pH

A Mid-Atlantic Soil Testing and Plant Analysis Work Group survey on methods for

soil pH, buffer pH and lime recommendations

Objectives are to assess:

1. variation in lab methods being used.

2. effect of method variation on intra- and interlaboratory error.

3. variation in how lime recommendations are made.

& SERA6

0

0.05

0.1

0.15

0.2

0.25

9811

3

9812

3

9910

9

9911

9

_001

09

_001

19

_011

09

_011

19

2002

109

2002

119

2003

109

2003

119

2004

109

2004

119

2005

009

2005

019

2006

009

2006

019

Soil pH MAD values in the NAPT program

SMP Buffer pH MAD values in the NAPT program

0

0.05

0.1

0.15

0.2

0.25

9811

3

9812

3

9910

9

9911

9

_001

09

_001

19

_011

09

_011

19

2002

109

2002

119

2003

109

2003

119

2004

109

2004

119

2005

009

2005

019

2006

009

2006

019

extra slides

y = -0.837 x + 7.00

r 2 = 0.658

y = -0.803x + 6.347

R2 = 0.691

0.0

0.5

1.0

1.5

2.0

2.5

3.0

3.5

5 5.5 6 6.5 7 7.5 8

SMP buffer pH

Co

eff

icie

nt

of

Va

ria

tio

n (

%)

y = -0.1749x + 2.6093

R2 = 0.1805

0.0

0.5

1.0

1.5

2.0

2.5

3.0

3.5

4 5 6 7 8 9 10

water pH

Co

eff

icie

nt

of

Va

ria

tio

n (

%)

Variations in methods for Mehlich III extractable nutrients

Reference pub

Quantity of soil Volume of Mehlich III Mixing time and method

SPAC, Inc. 5 cm3 50 mL 5 min on reciprocating shaker

Southern 2.5 cm3 25 mL 5 min on reciprocating shaker

Northeastern Scoop 2.5 cm3

or 2.5 g(references orig. method on 10:1

ratio based on vol.)

25 mL 5 min on reciprocating shaker

at 200 epm

North Central

1.7 cm3

(2 g scoop)20 mL 5 min on shaker at

200 or more epm between 24 to 27oC

Western 2 0.05 g 20 mL 5 min on reciprocating shaker