310 KALRA: JOURNAL OF AOAC INTERNATIONAL VOL. 78, No.2, 1995

AGRICULTURAL MATERIALS

Determination of pH of Soils by Different Methods: Collaborative Study

Y ASH P. KALRA

Canadian Forest Service, 5320-122 St, Edmonton, AB, T6H 3S5, Canada

Collaborators: H.P. Agrawal; E. Allen; J. Ashworth; P. Audesse; v.w. Case; D. Collins; S.M. Combs; C. Dawson; J. Denning;

SJ. Donohue; B. Douglas; B.G. Drought; M.A. Flock; J.B. Friedericks; GJ. Gascho; Z. Gerstl; L. Hodgins; B. Hopkins; D.

Horneck; R.A. Isaac; P.M. Kelly; J. Konwicki; J. Kovar; G. Kowalenko; G. Lutwick; R.O. Miller; R. Munter; I. Murchison; A.

Neary; R. Neumann; M. Neville; c.B. Nolan; R. Olive; W. Pask; L. Pastorek; T.R. Peck; T. Peel; J. Ramakers; W.S. Reid; V.

Rodd; R. Schultz; R. Simard; R.S. Singh; J. Sorrels; M. Sullivan; S. Tran; D. Trenholm; J. Trush; M.R. Tucker; E. Turcotte; A.

Van Niekerk; P.N. Vijan; J. Villanueva; C. Wang; D.D. Warncke; M.E. Watson; L. Wikoff; P. Yeung

Fifty-three laboratories (including author's) from Canada, India, Israel, and the United States partici­pated in a collaborative study for the measurement of pH of different types of soils. A method with 2 al­ternative procedures was used for pH measure­ments of mineral soils (alternative I for soils containing less than 17x organic carbon and alter­native II for soils with variable salt content), a sec­ond method was used for saline-sodic soils, and a third method was used for organic soils (soils con­taining at least 17x organic carbon). The pH was measured potentiometrically. The methods were se­lected by the Soil Science Society of America, S889 Committee on Coordination of Official Methods of Soil Analysis. Each laboratory used all 4 proce­dures to analyze 10 blind duplicate samples per procedure. The repeatability relative standard de­viation values (RSDr) were 1.45-7.80% for mineral soils tested by the alternative I, 0.95-6.91 % for min­erai soils tested by the alternative II, 0.74-7.09% for saline-sodic soils, and 0.73-4.66% for organic soils. The corresponding reproducibility relative standard deviation (RSDR) values were 2.67-10.75%,2.03-7.54%,2.45-9.93%, and 2.15-6.32%. Repeatability and reproducibility data indicated that the resuHs are within acceptable levels. The 3 meth­ods for pH measurements of mineral, saline-sodic, and organic soils were adopted first action by AOAC INTERNATIONAL.

Submitted for publication July 12, 1994. The recommendation was approved by the Committee on Feeds,

Fertilizers and Agricultural Related Topics, and was adopted by the Official Methods Board of the Association. See "Official Methods Board Actions" (1994) J. AOAC Int. 77, 203A, and "Official Methods Board Actions" (1994) The Referee 18, October issue.

Before 1990, none of the methods used for soils analyses

had been validated by AOAC INTERNATIONAL. In

1990, the Soil Science Society of America (SSSA) and

AOAC INTERNATIONAL decided to conduct collaborative

studies of soils methods. The first methods chosen for valida­

tion were for pH measurements, since pH is one of the most

important properties of soils.

The pH of mineral soils is normally determined in a 1: 1

soil-to-water mixture (1). Schofield and Taylor (2) suggested

the use of CaCl2 solution for mineral soils to minimize interfer­

ences from suspension effects (due to particles suspended in

the soil-solution mixture) and variable salt content. The recom­

mendations for management of saline-sodic soils are related to

pH values obtained with the saturated paste method (3, 4). The

results by the saturated paste methods were obtained during

over 30 years' work by the U.S. Department of Agriculture Sa­

linity Laboratory and other research laboratories. For organic

soils, a 1:4 soil-to-water mixture is recommended (5).

Collaborative Study

Fifty-three laboratories from Canada, India, Israel, and the

United States participated in this collaborative study. To make

the methods as widely applicable as possible, a broad range of

soils differing in pH, texture, organic matter, and other proper­

ties, was selected. Descriptions of soils used in the study are

presented in the Appendix.

Copies of the protocol including methods and data sheets

were sent to the participants in September 1992. Eighty heat­

sealed plastic bags containing the appropriate amounts of well­

mixed representative soil samples (20 g for the method used for

mineral soils [lOg for each alternative], 50 g for the method for

saline-sodic soils, and 5 g for the method used for organic soils)

were mailed to each of the participants by Fred Kaisaki from

the National Soil Survey Laboratory, U.S. Department of Ag­

riculture, Lincoln, NE, on October 1, 1992.

KALRA: JOURNAL OF AOAC INTERNATIONAL VOL. 78, No.2, 1995 311

Table 1. Soils used in the collaborative study for pH measurementsB

Sample No. Soil Sample No. Soil Sample No. Soil Sample No. Soil

1-1 Malbis HI Laurentides 1-111 Houston 21-IV Peck 90-9

2-1 Peck 90-9 2-11 Peck 90-11 2-111 Houston 22-IV Peck 90-10

3-1 Peck 90-12 3-11 Houston 3-111 Peck 90-12 23-IV Peck 90-11

4-1 Saline soil 4-11 Peck 90-12 4-111 Halii 24-IV Peck 90-9

5-1 Peck 90-11 5-11 Peck 90-11 5-111 Peck 90-11 25-IV Houghton Oa3

6-1 Halii 6-11 Peck 90-12 6-111 Peck 90-10 26-IV Houghton Oa4

7-1 Peck 90-10 7-11 Myakka 7-111 Myakka 27-IV Peck 90-12

8-1 . Myakka 8-11 Malbis 8-111 Peck 90-12 28-IV Houghton Oa3

9-1 Halii 9-11 Peck 90-10 9-111 Peck 90-11 29-IV Houghton Oa5

10-1 Laurentides 10-11 Halii 10-111 Peck 90-9 30-IV Houghton Oa2

11-1 Peck 90-10 1HI Peck 90-10 11-111 Saline Soil 31-IV Peck 90-12

12-1 Saline Soil 12-11 Myakka 12-111 Peck 90-10 32-IV Houghton Oa5

13-1 Peck 90-11 13-11 Halii 13-111 Saline soil 33-IV Laurentides LFH

14-1 Peck 90-9 14-11 Peck 90-9 14-111 Laurentides 34-IV Peck 90-11

15-1 Myakka 15-11 Malbis 15-111 Peck 90-9 35-IV Houghton Oa 1

16-1 Houston 16-11 Peck 90-9 16-111 Laurentides 36-IV Laurentides LFH

17-1 Malbis 17-11 Saline Soil 17-111 Myakka 37-IV Houghton Oa4

18-1 Laurentides 18-11 Houston 18-111 Halii 38-IV Houghton Oa2

19-1 Peck 90-12 19-11 Laurentides 19-111 Malbis 39-IV Peck 90-10

20-1 Houston 20-11 Saline Soil 20-111 Malbis 40-IV Houghton Oal

a Roman numbers indicate the method used for the analysis: I = method 994.16-Altemative I; II = method 994.16-Altemative II; III = method 994.17; and IV = method 994.18.

The soil samples conformed to all known regulations of the United States concerning biological pest abatement. The soil samples did not require special handling or disposal measures, nor did the participating laboratory need to be licensed or in­spected to receive, handle, or dispose of these samples. The "blind duplicate" design was used. A number was assigned to each soil sample as follows: duplicate 1 x 2 in. cards containing numbers from 1 to 20 were placed in a large kraft paper bag and mixed for 1 min by vigorous shaking. The cards were then removed (blind selection) one at a time and samples received

the numbers in the order they were removed from the bag. This procedure was repeated for every set of samples prepared for each procedure. Numbers assigned to all samples are presented in Table 1.

994.16 pH Measurement of Mineral Soils

First Action 1994

Alternative I

(Applicable to pH measurement of mineral soils [soils con­

taining <17% organic carbon].)

Method Performance:

See Table 994.16A for method performance data.

A. Principle

Air-dried soil sample is mixed with H20 (1 + 1). pH is

measured potentiometrically.

B. Apparatus

(a) pH meter.-Equipped with glass electrodes (indicating and reference), or combination electrode.

(b) Automatic pipet.-Capable of accurately delivering 10 mL.

(c) Stirrer.--Glass rod or portable mechanical stirrer, capa­ble of stirring at 1550 rpm. Small stirrer motor mounted on handle with short, slightly bent plastic or glass rod agitator is acceptable.

(d) Glassware.-Paper cups holding 28 g; or glass beak-

ers, 50 mL.

C. Reagents

(a) H20.-Distilled or deionized.

(b) Standard buffers.-pH 4.00, 7.00, and 10.00. Use pH 4.00 and 7.00 for acid soils, and pH 7.00 and 10.00 for al­

kaline soils.

D. Calibration

Calibrate pH meter to appropriate setting using 2 standard buffers, C(b), depending on type of test sample. If reading of

second standard buffer is not within 0.05 pH unit after adjust­

ing to first standard buffer, follow manufacturer's instructions.

E. Preparation of Standard Soils

Use 3 different standard soils (air-dried) of known pH, cov­

ering pH range of test samples. Weigh 10 g air-dried soil into paper cup. (Note: Calibrated volume measurement of soil may

be substituted for weighing.) Add 10 mL H20, C(a), to soil with automatic pipet. (Note: For fine-textured soils containing

312 KALRA: JOURNAL OF AOAC INTERNATIONAL VOL. 78, No.2, 1995

Table 994.16A. Method performance for pH measurements of mineral soils using alternative I

Overall mean of Repeatability laboratorY values standard

Soil (x) deviation (s,) Repeatability (r)

Malbis 5.62 0.30 0.86

Peck 90-9 6.13 0.19 0.54

Peck 90-12 4.88 0.18 0.51

Saline soil 9.74 0.16 0.46

Peck 90-11 7.86 0.39 1.11

Halii 4.55 0.18 0.51

Peck 90-10 5.87 0.18 0.51

Myakka 5.94 0.29 0.83

Laurentides 4.28 0.33 0.94

Houston 7.73 0.11 0.31

high level of organic matter it may be necessary to add addi­tional 1O mL H20 to make suspension.) Mix thoroughly 5 sec with glass rod or mechanical stirrer. Let soil-H20 suspension stand for 30 min. Measure pH of each standard as in G. pH values are acceptable within ± 0.1 pH unit of known values. If

pH values fall outside this range, recalibrate instrument with standard buffers and check pH of standard soils again. Follow manufacturer's instructions for recalibration. Replace elec­trodes if they cannot be calibrated within acceptable limits.

If pH values of all standard soils are >0.1 pH unit lower or higher than known pH of soil, recheck reference electrode.

Repeat pH measurements of standard soils just before analysis of test sample.

F. Preparation of Test Sample

Air dry soil at 20° -4Q°C for 1-4 days depending on the rela­tive humidity and soil properties. Grind air-dried soil to pass 2 mm sieve and mix well. Prepare soil sample-H20 suspension as in E, beginning "Weigh 10 g air-dried soil into paper cup ... ".

Repeatability Reproducibility Reproducibility relative standard relative standard

standard Reproducibility deviation (RSD,), deviation deviation (SR) (R) 0/0 (RSDR),%

0.40 1.14 5.28 7.20

0.23 0.66 3.04 3.69

0.28 0.80 3.60 5.73

0.26 0.74 1.67 2.67

0.44 1.25 4.92 5.54

0.29 0.83 3.94 6.35

0.24 0.68 3.14 4.00

0.34 0.97 4.80 5.80

0.46 1.31 7.80 10.75

0.22 0.63 1.45 2.81

G. Determination

Perform pH measurement at 20°-25°C. Before analysis stir test sample from F with glass rod or mechanical stirrer. Insert electrode(s) of calibrated pH meter from D into container and swirl soil-H20 suspension slightly. (Note: Position of reference electrode with respect to glass electrode and flow rate from reference electrode may affect pH determination; follow manufacturer's instructions for electrode[s].) Read pH imme­diately (after 30-60 s) to the nearest 0.1 pH unit. After remov­ing electrode(s) from soil-H20 suspension rinse them with H20; blot off excess H20 with filter paper.

Follow manufacturer's instructions for storing and main­taining pH electrodes.

Alternative II

(Applicable to pH measurement of mineral soils with vari­able salt content.)

Method Performance:

See Table 994.16B for method performance data.

Table 994.168. Method performance for pH measurements of mineral soils using alternative II

Repeatability Reproducibility Overall mean of Repeatability Reproducibility relative standard relative standard

laboratorY values standard standard Reproducibility deviation (RSD,), deviation Soil (x) deviation (s,) Repeatability (r) deviation (SR) (R) % (RSDR), %

Malbis 5.09 0.07 0.20 0.13 0.37 1.40 2.47 Peck 90-9 5.53 0.12 0.34 0.17 0.48 2.21 3.13 Peck 90-12 4.39 0.14 0.40 0.20 0.57 3.09 4.51

Saline soil 9.25 0.09 0.26 0.19 0.54 0.95 2.03

Peck 90-11 7.36 0.18 0.51 0.33 0.94 2.41 4.47 Halii 4.34 0.08 0.23 0.18 0.51 1.75 4.16

Peck 90-10 5.40 0.06 0.17 0.13 0.37 1.13 2.41

Myakka 4.31 0.04 0.11 0.12 0.34 0.99 2.86

Laurentides 3.69 0.25 0.71 0.28 0.80 6.91 7.54

Houston 7.48 0.15 0.43 0.16 0.46 2.02 2.17

KALRA: JOURNAL OF AOAC INTERNATIONAL VOL. 78, No.2, 1995 313

H. Principle

Salt content in soil influences ionic activity, which affects pH value of soil-water suspension. W anions are displaced by cations. Exchangeable AI is displaced, which increases con­centration of H+ in solution. pH is decreased by ca 0.5 pH unit if CaCh is used instead of H20.

I. Apparatus

Same as in B.

J. Reagents

See C(a)-(b). (c) CaCl2 solution.-O.01M. Dissolve 14.7 g CaCl2 2H20

in 10 L H20. pH of solution should be 5.0--6.5. If required, adjust pH with Ca(OHh or HCl. Specific conductivity should be 2.32 ± 0.08 mS/cm at 25°C.

K. Calibration

Perform as in D.

L. Preparation of Standard Soils

Use 3 different standard soils (air-dried) of known pH, cov­ering pH range of test samples. Weigh 10 g air-dried soil into paper cup. (Note: Calibrated volume measurement of soil may be substituted for weighing.) Add 10 mLO.01M CaCI2> J(c), to soil with automatic pipet. (Note: For fine-textured soils con­taining high level of organic matter it may be necessary to add additional 10 mLO.01M CaCl2 to make suspension.) Mix thor­oughly 5 s with glass rod or mechanical stirrer. Let soil-CaCl2 suspension stand for 30 min. Measure pH of each standard as in G. pH values are acceptable within ± 0.1 pH unit of known values. If pH values fall outside this range, recalibrate instru­ment and check pH of standard soils again. Follow manufac­turer's instructions for recalibration. Replace electrodes if they cannot be calibrated within acceptable limits.

If pH values of all standard soils are 0.1 pH unit lower or higher than known pH of soil, recheck reference electrode.

Repeat pH measurements just before analysis of test sample.

M. Preparation of Test Sample

Air dry soil at 20° -40°C for 1-4 days, depending on relative humidity and soil properties. Grind air-dried soil to pass 2 mm

sieve and mix well. Prepare soil sample-CaCl2 suspension as in L, beginning "Weigh 10 g air-dried soil into paper cup .... "

N. Determination

Proceed as in G. Ref.: J. AOAC Int. 78, 310 (1995).

994.17 pH Measurement of Saline-Sodie Soils

First Action 1994

(Applicable to pH measurement of saline-sodic soils [i.e., containing large amounts of soluble salts and sufficient ex­changeable sodium to interfere with growth of most crop plants].)

Method Performance: See Table 994.17 for method performance data.

A. Principle

H20 is added to air-dried soil until saturated paste is ob­tained and then pH is measured. For determination of sodium adsorption ratio, salt analysis is performed on saturation extract from paste.

B. Apparatus

(a) pH meter.-Equipped with glass electrodes (indicating and reference), or combination electrode.

(b) Glassware.-Paper cups holding 25-250 g; or glass beakers, 50-400 mL.

(c) Spatula.

C. Reagents

(a) H20.-Distilled or deionized. (b) Standard buffers.-pH 4.00, 7.00, and 10.00. Use pH

4.00 and 7.00 for acid soils, and pH 7.00 and 10.00 for alkaline soils.

Table 994.17. Method performance for pH measurements in soil paste

Repeatability Reproducibility Overall mean of Repeatability Reproducibility relative standard relative standard

laboratorY values standard standard Reproducibility deviation (RSD,), deviation Soil type (x) deviation (s,) Repeatability (r) deviation (SR) (R) % (RSDR), %

Malbis 5.47 0.05 0.14 0.18 0.51 1.00 3.27

Peck 90-9 5.99 0.22 0.63 0.25 0.71 3.59 4.14

Peck 90-12 4.82 0.21 0.60 0.28 0.80 4.43 5.78

Saline soil 9.48 0.07 0.20 0.26 0.74 0.74 2.76

Peck 90-11 7.64 0.12 0.34 0.22 0.63 1.58 2.94

Halii 4.35 0.09 0.26 0.17 0.48 2.02 3.95

Peck 90-10 5.83 0.17 0.48 0.22 0.63 2.84 3.82

Myakka 5.42 0.10 0.29 0.17 0.48 1.80 3.22

Laurentides 4.18 0.30 0.86 0.42 1.20 7.09 9.93

Houston 7.51 0.11 0.31 0.18 0.51 1.46 2.45

314 KALRA: JOURNAL OF AOAC INTERNATIONAL VOL. 78, NO.2, 1995

D. Calibration

Calibrate pH meter to appropriate setting using 2 standard

buffers, C(b), depending on type of test sample. If reading of

second standard buffer is not within 0.05 pH unit after adjust­

ing to fIrst standard buffer, follow manufacturer's instructions for recalibration.

E. Preparation of Standard Soils

Use 3 different standard soils (air-dried) of known pH, cov­

ering pH range of test samples. Weigh 50-250 g air-dried soil

into paper cup or glass beaker. (Note: Use smaller amounts of

soil for pH measurement only; use larger amounts to obtain

sufficient volume of saturation extract for other measure­

ments.) Wet soil with H20, C(a), while stirring with spatula.

(Note: Calibrated volume of soils may be substituted for

weighing. Alternatively, add sufficient amount of soil to known

volume of H20 to obtain saturated paste. Moisture content in

soil may vary [25-100%] depending on soil texture, clay min­

eralogy, and content of organic matter.)

Tap container gently against workbench to settle soil paste.

At saturation, surface of paste should glisten but no supernatant

H20 should be present. (Note: Saturated soil paste also slides

freely and cleanly from spatula when blade is turned vertically.

At saturation, soil will slowly flow together after it has been

parted by spatula.) Add more H20 if needed to obtain saturated

paste. If excess H20 is present, add small amount of soil, stir,

and tap container again. Add H20 or soil until proper moisture

content is obtained.

Cover container with watch glass and let stand for 1-4 h.

After 60 min some high clay soils may require addition of more

H20, as interstitial spaces in some clays become saturated with

H20. After further saturation let soil paste stand longer.

Measure pH of each standard as in G. pH values are accept­

able within ± 0.1 pH unit of known values. If pH values fall

outside this range, recalibrate instrument and check pH of

standard soils again. Follow manufacturer's instructions for re­

calibration. Replace electrodes if they cannot be calibrated

within acceptable limits.

Repeat pH measurements of standard soils just before

analysis of test sample.

F. Preparation of Test Sample

Air dry soil at 20° -40°C for 1-4 days, depending on relative

humidity and soil properties. Grind air-dried soil to pass 2 mm sieve and mix well. Prepare soil paste as in E, beginning

"Weigh 50-250 air-dried soil. ... "

G. Determination

Perform pH measurement at 20°-25°C. Insert electrode(s)

of standardized pH meter from D almost to the bottom of con­

tainer containing soil paste. Gently rotate container to remove

air bubbles and provide good contact between electrode(s) and

soil paste. Remove hands from container while measuring pH

of soil paste.

Read pH immediately (after 30-60 s) to the nearest 0.1 pH

unit. After removing electrode(s) from soil paste, rinse them with H20; blot off excess H20 with fIlter paper.

Follow manufacturer's instructions for storing and main­

taining pH electrodes.

Ref.: 1. AOAC Int. 78, 310 (1995).

994.18 pH Measurement of Organic Soils

First Action 1994

(Applicable to pH measurement of organic soils [soils con-

taining �17% organic carbon].)

Method Performance:

See Table 994.18 for method performance data.

A. Principle

Dried soil sample is mixed with H20 (1 + 4). pH is meas­

ured potentiometrically.

B. Apparatus

(a) pH meter.-Equipped with glass electrodes (indicating

and reference), or combination electrode.

Table 994.18. Method performance for pH measurements of organic soils

Repeatability Reproducibility Overall mean of Repeatability Reproducibility relative standard relative standard

laboratoIY values standard standard Reproducibility deviation (RSDr), deviation Soil (x) deviation (sr) Repeatability (r) deviation (SR) (R) % (RSDR), %

Houghton Oa3 7.43 0.05 0.14 0.06 0.17 0.73 3.16

Peck 90-9 6.24 0.22 0.63 0.30 0.86 3.57 4.74

Peck 90-12 5.08 0.24 0.68 0.32 0.91 4.66 6.32

Houghton Oa4 7.07 0.06 0.17 0.18 0.51 0.87 2.51

Peck 90-11 7.96 0.21 0.60 0.38 1.08 2.62 4.82

Houghton Oa5 6.85 0.17 0.48 0.23 0.66 2.50 3.43

Peck 90-10 6.07 0.18 0.51 0.27 0.77 2.94 4.49

Houghton Oa2 7.73 0.26 0.74 0.34 0.97 3.32 4.36

Laurentides LFH 6.62 0.10 0.29 0.15 0.43 1.55 2.33

Houghton Oa 1 7.37 0.06 0.17 0.16 0.46 0.77 2.15

KALRA: JOURNAL OF AOAC INTERNATIONAL VOL 78, No.2, 1995 315

(b) Automatic pipet.-Capable of accurately delivering 20 mL.

(c) Stirrer.-Glass rod or portable mechanical stirrer, capa­ble of stirring at 1550 rpm. Small stirrer motor mounted on handle with short, slightly bent plastic or glass rod agitator is acceptable.

(d) Glassware.-Paper cups holding 28 g; or glass beak-ers,50mL.

C. Reagents

(a) H20.-Distilled or deionized. (b) Standard buffers.-pH 4.00, 7.00, and 10.00. Use pH

4.00 and 7.00 for acid soils, and pH 7.00 and 10.00 for alkaline soils.

D. Calibration

Calibrate pH meter to appropriate setting using 2 standard buffers, C(b), depending on type of test sample. If reading of second standard buffer is not within 0.05 pH unit after adjust­ing to fIrst standard buffer, follow manufacturer's instructions.

E. Preparation of Standard Soils

Use 3 different air-dried standard organic soils of known pH, covering pH range of test samples. Weigh 5 g air-dried soil into paper cup. (Note: Calibrated volume measurement of soil . may be substituted for weighing.) Add 20 mL H20, C(a), to soil with automatic pipet. Mix thoroughly 5 sec with glass rod or mechanical stirrer. Let soil-H20 suspension stand for 30 min. Measure pH of each standard as in G. pH values are acceptable within ± 0.1 pH unit of known values. If pH values fall outside this range, recalibrate instrument and check pH of standard soils again. Follow manufacturer's instructions for re­calibration. Replace electrod:!s if they cannot be calibrated within acceptable limits.

If pH values of all standard soils are >0.1 pH unit lower or higher than known pH of soil, recheck reference electrode.

Repeat pH measurements of standard soils just before analysis of test sample.

F. Preparation of Test Sample

Pass dried soils (at 30°C) through 2 mm sieve and mix well. (Note: Many organic soils become hydrophobic when they are dried and may require longer time to wet.) Weigh 5 g dried soil sample into paper cup. (Note: Calibrated volume measurement of soil may be substituted for weighing.) Add 20 mL H20, C(a), to soil with automatic pipet. Mix thoroughly 5 sec with portable mechanical stirrer. Let soil-H20 suspension stand for 30 min before pH measurements.

G. Determination

Perform pH measurement at 20°-25°C. Before analysis stir test sample from F with glass rod or mechanical stirrer. Insert electrode(s) of calibrated pH meter from D into container and swirl soil-H20 suspension slightly. (Note: Position of reference electrode with respect to glass electrode and flow rate from reference electrode may affect pH determination; follow manufacturer's instructions for placement of electrode[s].)

Read pH immediately (after 30--60 s) to the nearest 0.1 pH unit. After removing electrode(s) from soil-H20 suspension rinse them with H20; blot off excess H20 with ftlter paper.

Follow manufacturer's instructions for storing and main­taining pH electrodes.

Ref.: 1. AOAC Int. 78, 310 (1995).

Results and Discussion

The results of analyses were received from 53 collaborators by February 5, 1993, and are presented in Tables 2-5. Results were analyzed using statistics software and worksheets devel­oped by the Statistics Committee, AOAC INTERNATIONAL (6--8). Results of statistical analyses are presented in Tables 994.16A-B, 994.17, and 994.18.

All 53 participants provided results obtained by the meth­ods for mineral and organic soils, while 51 laboratories pro­vided data from the method for saline-sodic soils. In general, the more diluted the soil suspension, the higher pH of the soil. The alternative I for mineral soils and the method for saline-so­dic soils use a mixture of soil and water. In alternative I for mineral soils the amount of water is fIxed (100%). However, for saline-sodic soils the amount of water needed to prepare a saturated paste depends on soil properties such as texture and organic matter. For soils that require 100% water for saturated paste, the pH will be the same as when using alternative I for mineral soils; it will be lower if less water is needed. Halii soil uses less water to make a paste (method for saline-sodic soils) than in the alternative I for mineral soils; therefore, the pH would be lower by 0.2 unit. For Mykka soil, the pH differences are large because this type of soil is a fIne sand and, therefore, much less water is required to prepare a paste.

All valid data were included in the statistical analyses. The tests used for determination of outliers were: (I) Cochran test for removal of laboratories showing signifIcantly greater within-laboratory variability than the other laboratories, and (2) Grubbs (Single and Double Grubbs) test for removal of laboratories with extreme values. The repeatability relative standard deviation (RSDr) values were 1.45-7.80% by the al­ternative I of the method for mineral soils, 0.95�.91 % by the alternative II of the method for mineral soils, 0.74-7.09% from the method for saline-sodic soils, and 0.73-4.66% from the method for organic soils. The corresponding reproducibility relative standard deviation (RSD0 values were 2.67-10.75%,

2.03-7.54%, 2.45-9.93%, and 2.15�.32%. There were out­liers indicated but repeatability and reproducibility standard deviations show that these values are well within acceptable limits for pH measurement in soil (9). Therefore, no laborato­ries were deleted from statistical analysis. It is interesting to note that one sample (Laurentides) gave the highest RSDr and RSDR values by the methods for mineral and saline-sodic soils; this sample was not analyzed by the method for organic soils.

Collaborators' Comments

The participants were asked to indicate any questions, prob­lems, and suggestions regarding their work with these methods.

316 KALRA: JOURNAL OF AOAC INTERNATIONAL VOL. 78, No.2, 1995

Table 2. Collaborative study results for pH measurements of mineral soils using alternative I

Lab. 2 3 4 5 6 7 8 9

Sample

10 11 12 13 14 15 16 17 18 19 20

1 5.90 6.35 5.13 9.61 8.04 4.50 6.12 6.08 4.51 4.37 6.13 9.62 8.08 6.49 6.10 7.83 5.95 4.38 5.15 7.83

2 5.48 6.01 4.82 9.77 7.98 4.43 6.14 5.90 4.48 4.25 5.84 9.77 7.88 6.11 5.91 7.71 5.69 4.28 4.85 7.65

3 5.50 6.10 4.80 9.65 7.80 4.20 5.90 5.80 4.20 4.05 5.80 9.60 7.85 6.00 5.80 7.80 5.50 4.05 4.80 7.70

4 5.45 6.04 4.84 9.97 7.93 4.38 5.90 5.91 4.33 4.26 5.85 9.99 7.87 6.04 5.85 7.91 5.52 4.30 4.87 8.04

5 5.37 6.19 5.13 9.33 7.52 4.76 5.92 5.67 4.44 4.20 5.89 9.44 7.73 6.19 5.70 7.68 5.59 4.24 4.87 7.42

6 5.18 5.80 4.59 9.67 7.85 4.38 5.74 5.75 4.30 4.03 5.70 9.65 7.89 6.10 5.75 7.65 5.57 4.06 4.68 7.58

7 5.46 6.13 4.88 9.70 7.95 4.38 5.95 5.86 4.38 4.16 5.93 9.65 7.97 6.14 5.85 7.82 5.53 4.17 4.91 7.82

8 5.64 6.21 4.98 9.89 8.06 4.62 6.08 6.07 4.52 4.22 5.85 9.80 8.08 6.47 6.19 7.86 5.84 4.28 4.95 7.91

9 5.30 5.70 4.50 9.90 7.80 4.20 5.70 5.50 4.30 4.60 5.80 10.00 8.40 6.00 5.60 7.70 5.20 3.90 4.50 7.60

10 5.86 6.12 4.91 9.54 7.91 4.98 5.93 5.93 4.58 4.24 5.85 9.50 7.87 6.12 5.82 7.65 6.14 4.42 5.03 7.57

11 4.92 5.65 4.42 9.67 7.78 4.66 5.57 5.77 4.05 3.82 5.32 9.65 7.51 6.73 6.75 7.25 5.46 3.93 4.36 6.97

12 5.40 5.89 4.80 9.89 7.94 4.22 5.83 5.70 4.34 4.04 5.92 9.84 8.00 6.12 5.79 8.06 5.49 4.17 4.89 7.80

13 6.29 6.51 5.48 9.36 7.80 5.48 6.54 6.27 4.86 4.49 5.99 9.05 7.95 6.29 5.02 7.60 6.54 4.78 5.06 7.63

14 5.65 6.24 5.04 9.79 8.05 4.54 6.04 6.05 4.49 4.39 5.99 9.77 8.03 6.31 6.07 7.82 5.73 4.42 5.01 7.76

15 5.45 6.05 6.05 10.15 8.15 4.55 5.85 6.25 4.65 5.09 6.14 11.69 9.31 6.35 7.03 7.96 7.10 4.61 5.61 7.67

16 5.55 6.05 4.84 9.76 7.70 4.44 5.82 5.98 4.40 4.25 5.81 9.86 7.90 6.12 6.09 7.77 5.82 4.39 4.88 7.76

17 5.42 6.81 4.78 9.73 7.76 5.14 6.11 5.83 4.23 6.10 5.81 9.90 7.85 5.92 7.27 7.30 5.33 4.15 4.91 7.51

18 5.46 6.10 4.73 9.47 7.85 4.32 5.90 5.78 4.30 4.11 5.91 9.56 7.76 6.13 5.81 7.58 5.57 4.16 4.80 7.51

19 4.95 5.68 4.37 9.85 4.13 4.12 5.54 5.33 3.78 3.75 5.66 9.95 7.70 5.75 5.66 7.56 5.18 3.81 4.55 7.21

20 5.51 6.12 4.84 9.67 8.07 4.45 6.16 6.07 4.54 4.40 6.11 9.75 8.10 6.42 6.20 8.04 5.89 4.60 5.28 8.09

21 5.40 6.01 4.70 10.23 7.84 4.75 5.75 5.78 4.25 4.06 5.74 9.95 7.75 6.60 6.90 7.69 7.45 4.27 4.68 7.14

22 5.40 6.00 4.80 9.74 7.82 4.40 5.80 5.70 4.40 4.06 5.83 9.76 7.86 6.06 5.70 7.91 5.40 4.06 4.78 8.01

23 5.78 6.30 5.03 9.88 8.18 4.46 6.10 6.05 4.48 4.30 6.00 9.89 8.00 6.23 6.33 8.05 5.70 4.33 4.94 7.75

24 5.11 5.74 4.32 9.57 7.52 4.21 5.39 5.08 4.24 3.65 5.44 9.63 7.60 5.86 5.45 7.57 5.58 3.79 4.50 7.53

25 5.47 5.97 4.73 9.72 7.84 4.31 5.83 5.76 4.32 4.15 5.88 9.65 7.85 6.02 5.78 7.85 5.51 4.18 4.77 7.88

26 5.59 5.96 5.03 9.62 7.95 4.55 5.74 6.25 4.47 4.19 5.65 9.53 8.00 5.92 5.62 7.99 5.46 4.10 4.79 7.90

27 5.46 6.11 4.91 9.66 7.84 4.57 5.95 5.88 4.39 4.21 5.96 9.76 7.90 6.13 5.96 7.67 5.51 4.24 4.88 7.70

28 6.25 6.45 5.20 C).55 7.90 4.65 6.15 6.20 4.65 4.60 6.10 9.65 7.95 6.45 6.15 7.85 5.80 4.50 5.50 7.85

29 5.25 5.85 4.66 9.91 7.78 4.44 5.75 5.62 4.37 4.02 5.67 9.89 7.82 5.85 5.80 7.86 5.30 4.01 4.65 7.86

30 5.45 6.05 4.81 9.79 7.97 4.82 5.91 5.94 4.79 4.16 5.90 9.78 7.98 6.07 5.92 7.82 5.48 4.16 4.84 7.89

31 5.46 5.98 4.81 9.69 7.88 4.63 5.95 6.00 4.41 4.24 5.88 9.66 7.87 6.17 6.08 7.69 6.00 4.29 4.84 7.60

32 5.42 6.02 4.78 9.71 7.95 4.74 5.84 5.81 4.72 4.10 5.86 9.68 7.95 6.06 5.81 7.77 5.40 4.06 4.79 7.74

33 5.45 5.96 4.69 9.52 7.75 4.36 4.33 5.77 4.27 4.12 5.75 9.54 7.80 6.00 5.80 7.68 5.50 4.15 4.61 7.65

34 5.44 6.02 4.78 9.60 7.99 5.25 5.82 6.54 4.69 4.32 5.73 9.57 7.83 6.17 6.57 7.62 5.63 4.55 4.94 7.91

35 5.52 6.07 4.90 9.69 8.05 4.42 5.93 5.90 4.41 4.21 5.88 9.67 8.03 6.12 5.91 7.91 5.52 4.22 4.86 7.91

36 5.54 6.02 6.25 9.92 7.99 5.05 5.99 6.00 4.90 4.12 4.87 9.91 7.94 6.28 6.06 7.80 5.70 4.15 4.80 7.61

37 5.42 6.11 4.82 9.65 7.97 4.69 6.10 5.78 4.62 4.06 5.97 9.75 7.94 6.13 5.81 7.74 5.51 4.09 4.90 7.77

38 5.50 6.10 4.90 9.70 7.90 4.80 5.90 5.90 4.80 4.20 5.90 9.70 7.90 6.10 5.90 7.90 5.50 4.20 4.90 7.90

39 5.63 6.14 4.94 9.76 8.02 4.39 5.91 6.01 4.40 4.22 5.94 9.69 7.93 6.05 5.97 7.83 5.56 4.22 4.84 7.90

40 5.40 6.06 4.83 9.60 7.89 4.51 5.90 5.71 4.36 4.06 5.87 9.68 7.95 5.98 5.69 7.84 5.46 4.06 4.78 7.88

41 5.16 5.96 4.73 9.68 7.88 4.73 5.79 5.55 4.69 3.91 5.78 9.66 7.86 5.97 5.50 7.73 5.19 3.95 4.75 7.72

42 5.58 6.07 4.82 9.93 8.01 4.42 5.84 5.97 4.33 4.17 5.77 9.78 7.96 6.20 5.97 7.76 5.78 4.28 4.80 7.78

43 5.50 6.10 4.90 10.00 8.00 4.70 5.90 5.80 4.70 4.10 5.90 10.00 8.00 6.00 5.80 8.00 5.50 4.10 4.80 8.00

44 5.45 5.96 4.81 9.72 7.92 4.39 5.83 5.95 4.29 4.19 5.81 9.74 7.85 6.11 6.07 7.79 5.52 4.15 4.75 7.76

45 7.08 6.60 5.18 10.14 7.44 5.73 6.13 6.20 5.18 4.63 5.42 9.97 6.90 6.98 6.96 7.13 7.07 4.90 5.11 6.83

46 5.57 6.55 4.87 9.72 7.38 4.78 5.95 6.34 7.80 4.14 5.88 9.67 7.91 6.06 5.56 7.74 5.44 4.19 4.84 7.73

47 5.59 6.22 5.05 9.79 8.07 4.55 6.08 5.82 4.44 4.25 5.95 9.69 8.08 6.45 6.11 7.78 5.76 4.36 4.98 7.91

48 5.55 6.09 4.90 9.66 7.98 4.50 5.96 5.95 4.44 4.22 5.89 9.66 7.99 6.22 6.02 7.84 5.99 4.41 4.99 7.76

49 5.51 6.04 4.80 9.60 7.91 4.80 5.92 5.72 4.78 4.01 5.82 9.61 7.87 6.19 5.70 7.67 5.62 4.10 4.84 7.68

50 5.22 5.81 4.60 9.64 7.70 4.68 5.68 5.60 4.67 4.00 5.68 9.65 7.76 5.91 5.65 7.80 5.33 4.04 4.66 7.80

51 5.70 6.22 5.03 9.63 8.04 4.51 6.05 6.09 4.50 4.81 6.04 9.65 8.01 6.29 6.16 7.92 5.77 4.90 5.11 7.81

52 5.62 6.17 4.98 9.69 7.96 4.42 5.98 5.90 4.43 4.22 5.95 9.66 7.98 6.15 5.91 7.74 5.61 4.25 4.96 7.76

53 5.83 6.17 4.90 9.32 7.19 5.26 5.93 6.29 4.70 5.13 6.38 9.50 7.90 6.42 6.36 7.74 6.29 7.73 4.86 7.40

KALRA: JOURNAL OF AOAC INTERNATIONAL VOL. 78, No.2, 1995 317

Table 3. Collaborative study results for pH measurements of mineral soils using alternative II

Lab. 2 3 4 5 6 7 8 9

Sample

10 11 12 13 14 15 16 17 18 19 20

1 3.76 7.49 7.47 4.49 7.48 4.53 4.36 5.32 5.64 4.48 5.64 4.44 4.44 5.77 5.33 5.80 9.08 7.56 3.75 9.10

2 3.59 7.41 7.50 4.41 7.45 4.30 4.28 5.07 5.44 4.52 5.40 4.28 4.20 5.46 5.10 5.52 9.35 7.48 3.64 9.35

3 3.50 7.60 7.60 4.25 7.60 4.25 4.25 5.15 5.45 4.20 5.45 4.25 4.20 5.60 5.15 5.60 9.35 7.60 3.50 9.35

4 3.61 7.44 7.42 4.34 7.45 4.32 4.37 5.03 5.29 4.24 5.36 4.35 4.25 5.51 5.06 5.51 9.53 7.44 3.59 9.46

5 3.73 7.13 7.25 4.85 7.33 4.43 4.35 4.91 5.35 4.44 5.40 4.37 4.22 5.48 5.01 5.58 8.76 7.28 3.93 8.74

6 3.38 7.26 7.41 4.49 7.25 4.29 4.26 5.05 5.35 4.22 5.38 4.32 4.26 5.51 5.13 5.54 9.09 7.56 3.70 9.05

7 3.62 7.58 7.55 4.33 7.56 4.33 4.28 5.09 5.41 4.30 5.43 4.28 4.27 5.57 5.13 5.58 9.26 7.53 3.68 9.24

8 3.58 7.33 7.37 4.34 7.34 4.28 4.31 4.98 5.26 4.22 5.36 4.32 4.28 5.36 4.99 5.36 9.29 7.53 3.52 9.27

9 3.50 7.40 7.50 4.30 7.10 4.20 3.80 4.80 5.10 4.00 5.40 3.80 3.80 5.20 4.80 5.30 7.00 7.40 3.60 9.71

10 3.73 7.28 7.39 4.83 7.39 4.42 4.34 5.11 5.40 4.39 5.44 4.33 4.34 5.60 5.20 5.69 9.09 7.47 3.78 9.03

11 3.66 6.82 7.22 4.39 6.70 4.41 4.43 5.02 5.36 4.34 5.38 4.32 4.23 5.48 5.10 5.48 8.61 7.67 3.69 9.24

12 3.34 7.15 7.36 4.15 7.41 4.16 4.18 4.84 4.99 3.93 5.09 4.20 3.97 5.26 4.89 5.40 9.44 7.43 3.65 9.43

13 3.59 7.35 7.49 4.52 7.42 4.35 4.24 4.91 5.49 4.72 5.44 4.26 4.26 5.49 5.12 5.53 9.14 7.45 3.96 9.19

14 3.78 7.62 7.59 4.46 7.71 4.42 4.42 5.26 5.60 4.40 5.54 4.46 4.49 5.67 5.26 5.68 9.41 7.64 3.78 9.42

15 4.66 7.59 7.88 4.74 7.78 4.50 4.55 5.20 5.62 4.37 5.64 4.63 4.70 6.05 5.47 5.74 9.47 7.70 3.70 9.39

16 3.98 7.49 7.60 4.63 7.57 4.60 4.59 5.32 5.59 4.56 5.59 4.57 4.51 5.71 5.34 5.74 9.32 7.66 4.08 9.37

17 3.34 6.92 7.09 4.59 6.98 4.31 4.17 4.95 5.31 4.18 5.29 4.17 4.16 5.42 4.99 5.44 9.29 7.82 3.87 9.14

18 3.55 7.34 7.42 4.36 7.44 4.38 4.29 5.10 5.46 4.27 5.46 4.18 4.25 5.66 5.12 5.70 9.28 7.46 3.57 9.32

19 3.45 7.11 7.42 4.32 6.95 4.31 4.26 5.05 5.44 4.21 5.41 4.26 4.21 5.55 5.11 5.58 9.36 7.61 3.56 9.25

20 3.69 7.23 7.34 4.46 7.33 4.46 4.44 5.27 5.52 4.47 5.51 4.47 4.44 5.72 5.40 5.75 8.93 7.50 3.97 8.93

21 3.59 7.53 7.60 4.59 7.50 4.50 4.35 4.99 5.50 4.29 5.25 4.39 4.29 5.59 5.20 5.60 9.45 7.53 3.73 9.20

22 3.49 7.51 7.53 4.35 7.57 4.26 4.23 5.09 5.39 4.31 5.40 4.25 4.23 5.56 5.04 5.56 9.40 7.55 3.48 9.42

23 3.66 7.50 7.57 4.46 7.40 4.50 4.42 5.22 5.54 4.37 5.53 4.45 4.46 5.70 5.35 5.75 9.49 7.65 3.93 9.53

24 3.24 7.33 7.35 4.22 7.33 4.18 4.13 4.90 5.10 4.20 4.93 4.30 4.19 5.22 4.90 5.28 9.32 7.23 3.56 8.91

25 3.66 7.45 7.48 4.27 7.46 4.25 4.25 5.09 5.35 4.23 5.36 4.25 4.24 5.51 5.08 5.50 9.20 7.47 3.65 9.24

26 3.67 6.74 6.96 4.46 6.80 4.27 4.28 5.06 5.33 4.40 5.55 4.53 4.42 5.65 5.18 5.59 9.28 7.62 3.68 9.09

27 3.54 7.35 7.31 4.30 7.36 4.26 4.36 5.06 5.38 4.25 5.40 4.38 4.27 5.49 5.11 5.58 9.16 7.34 3.66 9.22

28 3.65 7.20 7.15 4.25 7.20 4.30 4.30 5.05 5.30 5.00 5.55 4.25 5.00 5.50 5.05 5.50 8.80 7.20 3.75 8.70

29 3.63 7.49 7.46 4.31 7.42 4.23 4.26 5.09 5.33 4.25 5.34 4.29 4.24 5.50 5.06 5.51 9.52 7.51 3.73 9.47

30 3.61 7.57 7.61 4.41 7.57 4.34 4.36 5.19 5.46 4.58 5.45 4.37 4.58 5.62 5.13 5.61 9.44 7.65 3.74 9.46

31 3.58 7.31 7.46 4.35 7.37 4.31 4.30 5.13 5.39 4.30 5.39 4.31 4.33 5.56 5.14 5.59 9.25 7.47 3.71 9.29

32 3.58 7.58 7.53 4.30 7.57 4.27 4.24 5.06 5.38 4.50 5.38 4.24 4.47 5.52 5.04 5.51 9.31 7.53 3.55 9.31

33 3.51 7.47 7.44 4.53 7.48 4.26 4.27 5.07 5.38 4.25 5.42 4.30 4.22 5.52 5.08 5.54 9.26 7.45 3.95 9.28

34 3.56 7.26 7.32 4.38 7.26 4.24 4.29 5.02 5.26 4.21 5.26 4.36 4.24 5.45 5.07 5.43 9.14 7.49 4.69 9.10

35 3.62 7.48 7.48 4.29 7.52 4.33 4.30 5.12 5.43 4.29 5.41 4.29 4.29 5.55 5.16 5.59 9.22 7.57 3.64 9.24

36 3.82 7.41 7.47 4.58 7.45 4.53 4.39 5.08 5.37 4.63 5.36 4.40 4.55 5.53 5.11 5.84 9.29 7.56 3.75 9.29

37 3.51 7.45 7.47 4.23 7.46 4.21 4.20 5.04 5.39 4.37 5.35 4.23 4.36 5.47 5.02 5.52 9.21 7.47 3.50 9.19

38 3.60 7.60 7.60 4.20 7.60 4.20 4.40 5.10 5.40 4.50 5.40 4.40 4.50 5.50 5.10 5.50 9.30 7.60 3.80 9.30

39 3.55 7.39 7.39 4.21 7.44 4.23 4.26 5.05 5.29 4.21 5.28 4.17 4.13 5.44 5.02 5.42 9.11 7.36 3.52 9.17

40 3.56 7.58 7.52 4.35 7.58 4.29 4.28 5.08 5.42 4.27 5.43 4.29 4.25 5.54 5.08 5.54 9.27 7.52 3.72 9.29

41 3.51 7.52 7.53 4.30 7.53 4.29 4.26 5.03 5.38 4.53 5.38 4.23 4.53 5.55 5.04 5.56 9.30 7.54 3.52 9.32

42 3.64 7.41 7.52 4.45 7.42 4.30 4.27 5.04 5.35 4.23 5.34 4.35 4.24 5.48 5.09 5.53 9.42 7.59 4.25 9.35

43 3.40 7.60 7.70 4.30 7.60 4.20 4.10 5.00 5.30 4.40 5.30 4.10 4.40 5.50 5.00 5.50 9.70 7.60 3.60 9.70

44 3.54 7.34 7.43 4.20 7.35 4.21 4.20 5.00 5.30 4.19 5.29 4.21 4.12 5.42 5.02 5.34 9.28 7.42 3.33 9.27

45 3.72 6.37 6.61 4.73 6.40 4.67 4.22 4.79 5.20 4.28 5.17 4.34 4.21 5.28 5.08 5.37 9.20 7.59 3.69 9.40

46 3.69 5.18 7.58 4.61 6.84 5.05 4.37 4.76 5.70 4.65 5.48 4.37 4.63 5.12 5.18 5.61 9.28 7.57 3.79 9.26

47 3.69 7.64 7.57 4.51 7.58 4.45 4.35 5.20 5.60 4.36 5.62 4.30 4.39 5.73 5.22 5.69 9.26 7.62 3.81 9.30

48 3.63 7.55 7.55 4.49 7.55 4.39 4.37 5.13 5.47 4.32 5.44 4.37 4.30 5.55 5.14 5.56 9.29 7.58 4.04 9.29

49 3.60 7.49 7.40 4.45 7.49 4.27 4.21 5.02 5.36 4.41 5.39 4.21 4.41 5.58 5.01 5.50 9.30 7.38 3.81 9.37

50 3.51 7.42 7.48 4.33 7.44 4.27 4.40 4.97 5.30 4.48 5.32 4.26 4.50 5.49 5.01 5.48 9.28 7.49 3.54 9.28

51 4.04 7.64 7.62 4.60 7.67 4.53 4.51 5.30 5.55 4.41 5.54 4.51 4.40 5.68 5.28 5.68 9.34 7.62 4.31 9.32

52 3.61 7.60 7.58 4.31 7.61 4.31 4.30 5.13 5.46 4.26 5.51 4.31 4.27 5.58 5.13 5.60 9.28 7.60 3.68 9.28

53 3.60 7.18 7.27 5.34 7.38 4.54 4.42 5.20 5.40 4.44 5.36 4.47 4.31 4.45 5.16 5.47 8.96 7.42 5.22 8.95

318 KALRA: JOURNAL OF AOAC INTERNATIONAL VOL. 78, No.2, 1995

Table 4. Collaborative study results for pH measurements of saline-sodie soilsa

Lab. 2 3 4 5 6 7 8 9

Sample

10 11 12 13 14 15 16 17 18 19 20

1 7.47 7.59 4.98 4.35 7.67 5.95 5.50 4.90 7.76 6.17 9.36 5.94 9.47 4.28 6.10 4.12 5.48 4.34 5.60 5.64

2 7.66 7.46 4.81 4.26 7.80 5.75 5.44 4.78 7.68 5.89 9.75 5.79 9.71 4.41 5.92 3.96 5.40 4.23 5.40 5.42

3 7.45 7.40 4.60 4.15 7.60 5.70 5.15 4.60 7.60 5.80 9.25 5.65 9.15 3.70 5.80 3.70 5.20 4.10 5.35 5.35

4 7.52 7.63 4.87 4.11 7.76 5.80 5.64 4.70 7.79 6.02 9.76 5.66 9.80 4.23 5.89 4.12 5.49 4.07 5.46 5.36

5 7.56 7.57 5.16 4.46 7.76 5.76 5.54 4.70 7.79 5.96 9.27 5.74 9.20 4.04 5.90 3.93 5.40 4.23 5.37 5.38

6 7.33 7.40 4.54 4.11 7.45 5.55 5.16 4.51 7.47 5.76 9.47 5.64 9.48 3.89 5.75 3.91 5.23 4.17 5.27 5.23

7 7.54 7.57 4.84 4.31 7.78 5.80 5.39 4.81 7.79 6.00 9.46 5.82 9.46 4.21 6.00 4.05 5.37 4.31 5.56 5.56

8 7.42 7.61 5.02 4.16 7.58 5.98 5.70 4.88 7.64 6.20 9.47 5.99 9.52 4.32 5.94 4.05 5.52 4.31 5.21 5.19

9 7.65 7.67 4.84 4.20 7.63 5.82 5.42 5.05 7.79 6.08 9.65 5.90 9.78 5.30 6.17 4.09 5.13 4.20 5.20 5.30

10 7.31 7.47 4.87 4.33 7.48 5.81 5.38 4.79 7.56 6.01 9.21 7.07 9.36 4.31 5.78 4.04 5.26 4.31 5.48 5.51

11 7.14 7.48 4.52 4.27 7.31 5.61 5.16 4.41 7.17 6.45 9.34 5.51 9.26 4.16 5.67 3.90 5.24 4.15 5.01 5.12

12 7.47 7.70 4.66 4.25 7.62 5.65 5.41 4.67 7.68 5.87 9.62 5.64 9.61 3.99 5.87 3.97 5.39 4.27 5.45 5.49

13 7.49 7.58 4.90 4.34 7.65 5.79 5.44 4.82 7.90 6.00 9.49 5.79 9.39 4.06 6.16 4.03 5.47 4.37 5.60 5.60

14 7.54 7.57 4.95 4.44 7.70 5.81 5.53 4.85 7.75 5.99 9.52 5.87 9.59 4.68 6.61 4.17 5.58 4.44 5.68 5.65

15 7.66 7.59 4.90 4.43 7.62 5.88 5.36 4.75 7.43 5.90 9.16 5.80 9.20 4.06 5.86 3.92 5.32 4.29 5.45 5.53

16 7.56 7.65 4.95 4.49 7.66 5.91 5.65 4.90 7.82 6.14 9.64 6.11 9.63 4.24 6.00 4.20 5.55 4.50 5.62 5.65

17 7.35 7.49 5.22 4.53 7.82 5.92 5.72 5.02 7.79 6.27 9.44 6.48 9.32 6.27 6.50 5.54 5.60 4.61 5.68 5.75

18 7.38 7.43 4.85 4.28 7.58 5.87 5.45 4.85 7.61 6.11 9.52 6.10 9.64 4.14 6.11 4.02 5.45 4.30 5.56 5.55

19 7.62 7.68 4.61 4.21 7.33 5.64 5.13 4.39 7.45 5.75 9.98 5.59 9.82 4.22 5.68 3.67 5.08 4.17 4.97 4.99

20 7.33 7.37 4.69 4.31 7.47 5.73 5.33 4.74 7.51 5.92 9.12 5.92 9.21 4.43 5.95 4.03 5.49 4.40 5.54 5.52

21 7.38 7.35 5.92 4.55 7.28 5.95 5.42 5.35 4.59 7.59 9.48 5.98 9.57 5.14 5.91 4.08 5.38 4.24 5.39 5.35

22 7.78 7.59 4.62 4.29 7.72 5.78 5.42 4.75 7.77 5.99 9.67 5.78 9.63 4.00 5.95 3.95 5.43 4.26 5.50 5.52

23 7.85 7.51 5.04 4.42 7.56 5.92 5.44 4.89 7.59 6.18 9.53 5.92 9.50 4.38 5.86 4.13 5.43 4.34 5.58 5.60

24 7.45 7.52 4.35 4.16 7.48 5.66 5.60 4.31 7.54 5.98 9.69 5.76 9.71 4.33 5.84 3.88 5.13 4.14 5.25 5.28

26 6.70 6.71 4.31 4.22 6.77 5.32 5.12 4.23 6.77 5.36 9.09 5.23 9.10 3.53 5.34 3.75 5.27 4.06 4.95 4.87

27 7.48 7.50 4.67 4.23 7.74 5.80 5.44 4.65 7.70 5.94 9.26 5.70 9.22 3.92 5.95 3.90 5.36 4.20 5.47 5.14

28 7.30 7.00 4.70 4.10 7.05 5.50 5.20 4.70 7.30 5.70 8.20 6.00 8.65 4.30 5.70 4.00 5.25 4.25 5.45 5.50

29 7.60 7.60 4.70 4.02 7.74 5.61 5.45 4.72 7.77 5.92 9.73 5.81 9.70 4.45 5.90 4.01 5.45 4.36 5.48 5.47

30 7.60 7.60 4.78 4.54 7.78 5.78 5.55 4.76 7.77 5.92 9.55 5.81 9.57 4.15 5.91 4.03 5.49 4.55 5.50 5.49

31 7.30 7.52 4.79 4.26 7.41 5.63 5.43 4.61 7.39 5.95 9.43 5.69 9.41 4.35 5.78 4.03 5.39 4.19 5.38 5.40

32 7.53 7.55 4.80 4.62 7.82 5.78 5.50 4.78 7.74 6.03 9.56 5.76 9.51 4.40 5.99 4.04 5.42 4.53 5.55 5.52

33 7.33 7.35 5.54 4.40 7.60 5.63 5.25 4.60 7.54 5.92 9.31 5.80 9.29 5.23 5.92 4.05 5.32 4.25 5.45 5.41

34 7.38 7.50 5.93 4.59 7.50 6.16 5.14 4.67 7.48 6.56 9.03 6.48 9.08 3.99 6.08 4.20 5.35 4.19 5.67 5.42

35 7.65 7.61 5.05 4.33 7.90 5.86 5.40 4.78 7.89 6.07 9.51 6.02 9.54 4.53 6.07 4.05 5.58 4.35 5.72 5.74

36 7.63 7.66 5.03 4.68 7.60 5.81 5.65 4.82 7.61 6.02 9.65 5.95 9.69 4.24 6.07 4.23 5.51 4.63 5.47 5.51

37 7.54 7.53 4.57 4.61 7.75 5.80 5.34 4.78 7.66 5.96 9.45 5.81 9.42 3.88 5.97 3.88 5.34 4.66 5.46 5.42

38 7.50 7.50 4.70 4.50 7.70 5.80 5.40 4.70 7.80 6.00 9.50 5.80 9.50 3.90 6.00 3.90 5.30 4.50 5.50 5.50

39 7.64 7.60 4.74 4.24 7.73 5.71 5.41 4.79 7.76 5.97 9.60 5.69 9.64 4.04 5.94 4.00 5.45 4.29 5.54 5.55

40 7.51 7.51 4.75 4.32 7.70 5.85 5.41 4.86 7.70 6.08 9.49 5.85 9.49 4.12 6.08 3.95 5.40 4.39 5.57 5.59

41 7.61 7.61 4.76 4.63 7.77 5.83 5.39 4.76 7.80 6.00 9.60 5.82 9.65 3.97 6.04 3.96 5.33 4.63 5.46 5.50

42 7.62 7.66 4.89 4.36 7.76 5.87 5.58 4.78 7.79 6.04 9.60 5.91 9.63 4.09 6.01 4.05 5.46 4.31 5.57 5.60

43 7.70 7.70 4.70 4.50 7.80 5.70 5.30 4.70 7.90 6.00 9.90 5.70 10.00 4.10 5.90 3.90 5.30 4.60 5.50 5.50

44 7.45 7.42 4.58 4.16 7.59 5.61 5.29 4.56 7.58 5.78 9.29 5.64 9.39 3.92 5.85 3.88 5.31 4.17 5.36 5.40

45 6.98 7.67 5.09 4.41 6.94 5.93 5.86 4.91 7.90 6.13 9.89 5.98 10.02 4.35 5.72 4.16 5.38 4.29 5.67 5.53

46 7.31 7.56 4.92 4.74 7.79 5.87 5.43 4.82 8.15 6.03 9.64 5.89 9.75 4.07 5.95 4.07 5.42 4.73 5.60 5.63

47 7.55 7.65 4.97 4.41 7.85 6.07 5.69 5.06 7.87 6.30 9.43 6.09 9.46 5.04 6.11 4.26 5.63 4.45 5.72 5.68

48 7.47 7.50 4.83 4.30 7.60 5.73 5.43 4.77 7.59 5.88 9.31 5.78 9.38 4.45 5.78 3.78 5.16 4.05 5.35 5.33

49 7.59 7.59 4.78 4.63 7.72 5.79 5.39 4.74 7.72 6.00 9.52 5.80 9.52 4.02 5.99 3.98 5.40 4.61 5.46 5.49

51 7.72 7.67 5.25 4.49 7.85 5.92 5.51 4.79 7.83 6.04 9.61 6.23 9.44 4.81 6.15 4.11 5.49 4.24 5.57 5.54

52 7.68 7.74 4.88 4.30 7.90 5.84 5.46 4.85 7.90 6.10 9.71 5.93 9.64 4.04 6.10 4.01 5.46 4.30 5.60 5.57

53 7.64 7.58 5.84 4.50 7.61 6.12 6.16 4.91 7.54 5.98 9.10 5.83 9.24 5.43 5.91 4.83 6.02 4.59 5.82 5.64

• Results not provided by Laboratories 25 and 50.

KALRA: JOURNAL OF AOAC INTERNATIONAL VOL. 78, No.2, 1995 319

Table 5. Collaborative study results for pH measurements of organic soils

Sample

Lab. 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40

6.51 6.34 8.13 6.80 7.66 7.27 5.54 7.61 7.02 7.87 5.49 7.05 6.66 8.09 7.55 6.81 7.23 7.88 6.40 7.57

2 6.03 6.00 8.10 6.60 7.50 7.11 5.12 7.56 6.91 7.84 5.18 6.93 6.64 8.19 7.41 6.67 7.13 7.83 6.16 7.40

3 6.20 6.05 8.00 6.15 7.50 7.10 4.85 7.50 6.90 7.75 4.90 6.85 6.60 8.05 7.40 6.55 7.05 7.80 6.05 7.40

4 5.91 5.97 7.97 6.06 7.41 6.97 4.90 7.43 6.83 7.74 4.91 6.81 6.54 7.99 7.34 6.58 6.99 7.72 5.89 7.29

5 6.18 6.22 7.94 6.37 7.43 6.99 5.18 7.41 6.82 7.76 5.18 6.75 6.53 7.99 7.35 6.47 7.01 7.75 6.24 7.36

6 5.78 5.69 7.30 6.62 7.14 7.07 4.80 7.06 6.95 7.48 4.91 6.57 6.52 7.52 7.39 6.92 6.99 7.54 6.13 7.27

7 6.30 6.17 8.21 6.32 7.56 7.18 5.12 7.54 6.89 7.81 5.02 6.90 6.58 8.12 7.41 6.59 7.13 7.80 6.01 7.38

8 6.13 5.96 8.06 6.47 7.48 7.28 5.19 7.50 7.11 7.91 5.16 6.72 6.63 8.08 7.49 6.97 7.26 7.83 6.31 7.42

9 5.60 5.50 7.60 5.80 7.30 6.50 4.30 7.10 6.60 7.60 4.80 6.30 6.30 7.90 7.20 6.40 6.60 7.40 6.00 7.10

10 6.23 6.14 7.97 6.45 7.23 7.22 5.16 7.44 6.92 7.72 5.26 6.69 6.57 7.85 7.38 6.68 7.12 7.59 6.49 7.36

11 5.24 5.25 7.10 6.60 6.37 6.75 4.63 6.55 6.76 6.93 4.43 5.64 6.60 6.54 6.88 6.66 6.50 6.64 5.22 6.67

12 6.26 6.19 8.18 6.35 7.54 7.19 5.18 7.56 6.99 7.72 5.16 6.97 6.63 8.39 7.43 6.58 7.08 7.81 6.12 7.39

13 5.82 5.59 7.57 5.79 7.32 6.85 4.54 7.30 6.67 7.52 4.54 6.63 6.45 7.63 7.28 6.49 6.81 7.53 5.62 7.25

14 6.45 6.25 8.34 6.33 7.68 7.32 5.25 7.63 7.07 7.88 5.28 7.03 6.76 8.25 7.56 6.74 7.16 7.88 6.31 7.54

15 6.38 6.23 8.20 6.40 7.61 7.25 5.25 7.60 6.97 7.95 5.29 6.80 6.70 8.18 7.48 6.62 7.16 7.96 6.64 7.50

16 6.39 6.17 8.11 6.37 7.64 7.28 5.18 7.58 7.08 7.90 5.17 6.95 6.76 8.10 7.54 6.84 7.24 7.91 6.20 7.56

17 6.54 6.26 7.93 6.44 7.56 7.06 5.17 7.36 6.99 7.76 5.46 6.96 6.68 7.95 7.49 6.77 7.07 7.64 6.30 7.46

18 6.37 6.14 7.87 6.29 7.51 7.08 5.09 7.54 6.86 7.73 5.06 6.99 6.67 8.06 7.41 6.61 7.08 7.73 6.16 7.39

19 5.48 5.44 7.41 6.35 7.33 7.00 5.51 7.28 6.82 7.61 4.49 6.52 6.41 7.55 7.34 6.74 6.86 7.67 5.81 7.28

20 6.14 6.07 8.05 6.28 7.49 7.10 4.96 7.49 6.88 7.77 4.96 6.85 6.56 8.06 7.39 6.63 7.06 7.76 6.02 7.38

21 5.70 5.87 5.97 6.12 7.27 7.14 5.30 7.02 6.78 7.59 5.43 6.35 6.41 7.30 7.32 6.89 7.07 7.44 7.12 7.25

22 6.32 6.14 8.35 6.42 7.59 7.21 5.14 7.52 7.01 7.92 5.12 6.96 6.63 8.36 7.38 6.63 7.10 7.79 6.14 7.38

23 5.99 6.02 7.44 6.55 7.33 7.18 5.32 7.34 6.94 7.82 5.32 6.78 6.67 7.99 7.48 6.87 7.24 7.88 6.35 7.39

24 5.69 5.61 7.60 5.76 7.22 6.86 4.52 7.22 6.67 7.52 4.55 6.58 6.39 7.69 7.11 6.44 6.86 7.54 5.85 7.17

25 6.15 6.00 8.08 6.20 7.54 7.17 4.98 7.53 6.89 7.74 4.96 6.88 6.59 8.04 7.41 6.59 7.06 7.77 6.04 7.38

26 5.18 5.08 6.96 5.70 6.66 6.33 4.84 6.77 6.35 7.12 4.09 5.86 5.75 7.12 6.81 6.23 6.52 6.95 5.64 6.70

27 6.30 6.06 8.06 6.23 7.45 7.07 5.10 7.52 6.85 7.75 5.08 6.84 6.57 8.03 7.38 6.54 7.02 7.74 6.02 7.33

28 6.20 6.05 7.60 6.15 7.15 6.90 5.15 7.15 6.70 7.40 5.10 6.70 6.40 7.70 7.10 6.45 6.80 7.40 6.10 7.10

29 5.78 6.56 7.80 5.85 7.40 6.89 4.60 7.44 6.72 7.77 4.60 6.70 6.46 7.98 7.34 6.42 6.86 7.69 5.75 7.34

30 6.29 6.12 8.18 6.35 7.53 7.16 5.09 7.51 6.95 7.94 5.12 6.90 6.61 8.20 7.42 6.62 7.15 7.97 6.14 7.40

31 6.02 5.85 7.88 6.08 7.38 7.00 5.06 7.49 6.86 7.71 5.05 6.81 6.63 7.94 7.42 6.71 7.05 7.70 6.08 7.35

32 6.21 6.04 8.09 6.31 7.52 7.09 5.00 7.51 6.89 7.90 5.05 6.88 6.60 8.12 7.40 6.62 7.11 7.85 6.09 7.41

33 6.02 6.00 7.99 6.22 7.46 7.12 4.87 7.46 6.96 7.76 4.93 6.87 6.64 8.05 7.42 6.72 7.11 7.76 6.06 7.40

34 6.15 5.99 8.01 6.30 7.46 7.07 5.10 7.49 7.77 5.15 7.03 7.04 6.76 8.07 7.36 6.84 7.09 7.74 6.18 7.35

35 6.23 6.09 8.20 6.30 7.56 7.19 5.08 7.58 6.97 7.91 5.12 6.88 6.65 8.22 7.45 6.69 7.16 7.85 6.18 7.44

36 6.10 6.01 8.10 6.31 7.53 7.77 4.98 7.50 7.00 7.94 5.14 6.88 6.63 8.16 7.43 6.72 7.16 7.95 6.18 7.41

37 6.28 6.17 8.13 6.33 7.47 7.02 5.02 7.45 6.85 7.79 5.01 6.83 6.62 8.11 7.40 6.57 7.05 7.84 6.10 7.34

38 6.30 6.20 8.20 6.30 7.60 7.20 5.10 7.60 7.00 8.00 5.10 7.00 6.70 8.20 7.40 6.70 7.20 8.00 6.20 7.40

39 6.84 6.31 8.28 6.74 7.60 7.31 5.23 7.56 7.05 7.86 5.23 6.93 6.67 8.20 7.44 6.68 7.14 7.84 6.17 7.43

40 6.29 6.10 8.15 6.27 7.57 7.13 5.01 7.57 6.96 7.81 5.04 6.94 6.64 8.15 7.46 6.62 7.05 7.83 6.10 7.44

41 6.11 5.94 8.06 6.16 7.50 7.06 4.95 7.51 6.83 7.89 4.95 6.85 6.58 8.08 7.40 6.57 7.06 7.89 5.97 7.42

42 6.35 6.08 8.10 6.32 7.67 7.25 4.99 7.64 7.02 7.89 5.05 6.95 6.69 8.09 7.51 6.73 7.20 7.90 6.19 7.49

43 6.20 6.00 8.10 6.20 7.60 7.10 5.10 7.60 6.90 8.10 5.10 6.90 6.50 8.40 7.40 6.50 7.10 8.10 6.00 7.50

44 6.35 6.06 8.14 6.52 7.42 7.17 5.28 7.38 6.91 7.78 5.14 6.70 6.56 8.12 7.37 6.65 7.08 7.79 6.22 7.31

45 6.63 6.38 6.92 6.83 6.93 6.78 5.45 6.84 6.86 7.75 5.24 6.59 6.43 8.23 7.42 6.57 6.90 7.80 6.29 7.41

46 6.25 6.04 8.11 6.51 7.62 7.36 5.08 7.59 6.96 7.95 5.17 6.77 6.61 8.14 7.48 6.65 7.11 7.91 6.07 7.40

47 6.43 6.28 8.22 6.50 7.64 7.21 5.26 7.68 7.09 7.94 5.25 7.06 6.75 8.30 7.56 6.74 7.22 7.93 6.29 7.49

48 6.34 6.20 8.19 6.42 7.56 7.23 5.22 7.53 7.00 7.86 5.24 6.94 6.66 8.20 7.43 6.69 7.11 7.84 6.26 7.41

49 6.38 6.10 8.00 6.38 7.48 7.04 5.10 7.41 6.88 7.82 5.18 6.83 6.52 7.98 7.41 6.59 7.01 7.82 6.10 7.40

50 6.12 6.04 8.17 6.23 7.52 7.09 5.02 7.51 6.91 7.93 5.02 6.87 6.58 8.13 7.38 6.61 7.06 7.93 6.08 7.38

51 6.53 6.36 8.22 6.57 7.66 7.23 5.50 7.64 7.03 7.88 5.53 7.00 6.72 8.24 7.52 6.74 7.20 7.88 6.37 7.49

52 6.40 6.20 8.30 6.37 7.60 7.22 5.19 7.61 6.97 7.88 5.19 6.90 6.62 8.27 7.51 6.74 7.15 7.80 6.26 7.46

53 6.27 6.23 7.92 6.60 7.46 7.14 5.41 7.39 7.02 7.64 5.15 6.88 6.75 7.88 7.45 6.95 7.03 7.64 6.06 7.00

320 KALRA: JOURNAL OF AOAC INTERNATIONAL VOL. 78, NO.2, 1995

All laboratories infonned us that all 80 bags containing test samples were received intact. All 53 laboratories were familiar

with soil-to-liquid suspension methods. Five laboratories indi­cated that they did not have any experience with the saturated paste method.

Most of the participants used a combination electrode, while some used a glass electrode and a calomel reference electrode. Two laboratories reported that it was difficult to obtain a stable reading when using the method for mineral soils (due to lack

of a significant amount of supernatant liquid), while the

method for saline-sodic soils gave stable readings. Ten labora­tories found it necessary to tilt beakers when measuring pH by the method for mineral soils in order to cover the junction of the combination electrode by the supernatant liquid. Increasing

the amount of soil to 20 g and the volume of water or CaCl2 solution to 20 mL would have eliminated that problem.

One laboratory reported that readings from the method for organic soils were less stable than from the methods for mineral and saline-sodic soils. When using the saline-sodic soils

method, most of the collaborators took readings 1 h after pre­paring the saturated paste. One laboratory reported that there was no difference in the readings taken at 1 , 1 . 5, or 2 h after the preparation of saturated paste.

There are no potential hazards in handling reagents, sam­ples, or buffer solutions. None of the participating laboratories provided any comments regarding the safety aspects of the col­laboratively studied methods.

Recommendation

On the basis of the results of this study it is recommended that the methods for measurement of pH of mineral, saline-so­dic, and organic soils be adopted ftrst action.

Acknowledgments

The Associate Referee is grateful to the Soil Science Society of America (SSSA) and the AOAC INTERNATIONAL for the

opportunity to coordinate this study. Thanks are also due to the Canadian Forest Service for its cooperation. I thank the follow­ing individuals for their assistance at different stages of the study, whose help and cooperation have been of vital impor­tance to this collaborative study: AOAC Methods and Safety Committees; Nat B. Dellavalle; Editors of Agronomy News and The Referee; Thomas L. Jensen and Charles L. Focht (Succeed­ing General Referees for Nutrients in Soils); 1. Benton Jones, Jr; Fred Kaisaki; John 1. Mortvedt (Chainnan) and other mem­bers of the SSSA S889 Committee: Joan K. Bartz (also SSSA

liaison to AOAC INTERNATIONAL), Boyd G. Ellis, Ellis G. Knox, Ted R. Peck, and Dean E. Wesley; Daniel H. Mowrey (Committee Statistician); Julie Nonnan and Lucyna Kurtyka (Succeeding Methods Program Coordinators); D.G. Maynard; John Shuya; Sheldon Radford; Joe Crumbaugh; SSSA Re­viewers: SJ. Donohue, Mark A. Flock, Gordon V. Johnson, John L. Kovar, and Dean E. Wesley; Harold C. Thompson, Jr

(Chainnan of the Methods Committee on Feeds, Fertilizers and

Agricultural Related Materials); and the following collabora­

tors:

Donna Collins, W.M. Ward Technical Services Laboratory,

Manitoba Environment, Winnipeg, MB, Canada

Clive Dawson, B.c. Ministry of Forests, Research Labora­tory, Victoria, BC, Canada

Brian Douglas, P.E.I. Soil and Feed Testing Laboratory, Charlottetown, PEl, Canada

Brian G. Drought, Soil Science & Agricultural Engineering, Agriculture Canada, Research Station, Summerland, BC, Can­ada

Lloyd Hodgins, Saskatchewan Soil Testing Laboratory, University of Saskatchewan, Saskatoon, SK, Canada

P.M. Kelly, Chemical and Geological Laboratories, Cal­gary, AB, Canada

John Konwicki, Department of Soil Science, Faculty of Ag­riculture and Forestry, University of Alberta, Edmonton, AB,

Canada

Grant Kowalenko, Agriculture Canada, Research Station, Agassiz, BC, Canada

Ian Murchison, Agriculture Canada, Research Station, Brandon, MB, Canada

Anne Neary, Ministry of Environment, Dorset, ON, Canada

Randy Neumann, and John Ashworth, Norwest Laborato­ries, Edmonton, AB, Canada

Rosalind Olive, Soil and Plant Testing Laboratory, Univer­sity of New Brunswick, Hugh John Flemming Forestry Centre, Fredericton, NB, Canada

Liz Pastorek, and Jane Trush, Laboratory Services Branch,

Ministry of Environment, Rexdale, ON, Canada

Terry Peel, Econotech Services Ltd., New Westminster, BC,

Canada

Jo Ramakers, Great Lakes Forestry Centre, Canadian Forest

Service, Sault Ste. Marie, ON, Canada

Vernon Rodd, Nappan Experimental Farm, Nappan, NS, Canada

Rod Schultz, and Gerry Lutwick, Alberta Environment, Lethbridge, AB, Canada

Regis Simard, Agriculture Canada, Research Station, Sainte-Foy, PQ, Canada

Sen Tran, and Pierre Audesse, MAPAQ, Soils Service, Sainte-Foy, PQ, Canada

Donald Trenholm, Newfoundland Forestry Centre, Cana­dian Forest Service, St. John's, NF, Canada

Evelyn Turcotte, Petawawa National Forestry Institute, Ca­nadian Forest Service, Chalk River, ON, Canada

Ann Van Niekerk, Paciftc Forestry Centre, Canadian Forest Service, Victoria, BC, Canada

Joel Villanueva, and P.N. Vijan, Alpha Laboratories, Inc., Don Mills, ON, Canada

Chang Wang, Centre for Land and Biological Resources Research, Central Experimental Farm, Ottawa, ON, Canada

Paul Yeung, Alberta Environmental Centre, Vegreville, AB,

Canada

H.P. Agrawal, Department of Soil Science and Agricultural

Chemistry, Banaras Hindu University, Varanasi, India

R.S. Singh, Central Research Laboratory, Udai Pratap Col­lege, Varanasi, India

Zev Gerstl, Agricultural Research Organization, The Vol­cani Center, Institute of Soils & Water, Bet Dagan, Israel

Earl Allen, Department of Agronomy, Oklahoma State Uni­versity, Stillwater, OK

Vernon W. Case, University of Kentucky, Soil Testing Laboratory, Lexington, KY

Sherry M. Combs, University of Wisconsin, Department of

Soil Science, Madison, WI

Joe Denning, University of Nebraska, Lincoln, NE

SJ. Donohue, Soil Testing Laboratory, VIrginia Tech, Blacksburg, VA

Mark A. Flock, Brookside Farms Laboratory Association,

Inc., New Knoxville, OH

James B. Friedericks, Servi- Tech Laboratory, Hastings, NE

Gary 1. Gascho, Coastal Plain Experiment Station, Univer­sity of Georgia, Department of Agronomy, Tifton, GA

Bryan Hopkins, Agronomy Department, Kansas State Uni­versity, Manhattan, KS

Donald Horneck, Central Analytical Laboratory, Oregon State University, Corvallis, OR

Robert A. Isaac, Agriculture Services Laboratories, Soil, Plant & Water Analyses Laboratory, University of Georgia, Athens, GA

John Kovar, Agronomy Department, Louisiana State Uni­versity, Baton Rouge, LA

Robert O. Miller, Department of Land, Soil, and Water, Uni­versity of California, Davis, CA

Robert Munter, Soil Testing Laboratory, University of Min­nesota, S1. Paul, MN

Mike Neville, Milwaukee Metropolitan Sewerage District, Milwaukee, WI

Charles B. Nolan, Conagra Frozen Foods Analytical Labo­ratory, Batesville, AR

Wayne Pask, Office of Indiana State Chemists, Purdue Uni­versity, West Lafayette, IN

Ted R. Peck and Marilyn Sullivan, University of lllinois, Agronomy Department, Urbana, IL

KALRA: JOURNAL OF AOAC INTERNATIONAL VOL. 78, No. 2, 1995 321

W. Shaw Reid, CU Nutrient Analysis Laboratory, Cornell University, Department of Soil, Crops and Atmosperic Sci­

ences,Ithaca,� Janet Sorrels, Agrico Agronomic Services Laboratory,

Washington Court House, OH M. Ray Tucker, North Carolina Department of Agriculture,

Raleigh,NC Darryl D. Warncke, MSU Soil Testing Laboratory, Michi­

gan State University, East Lansing, MI

Maurice E. Watson, Research Extension Analytical Labora­tory, Ohio State University, Wooster, OH

Larry Wikoff, Minn. Valley Testing Laboratory, Grand Forks,ND

References

(1) McLean, E.O. ( 1982) in Methods of Soil Analysis, Part 2,

Agron. 9, AL. Page, RH. Miller, & D.R. Keeney (Eds), Am. Soc. Agron., Madison, WI, pp. 199-224

(2) Schofield, RK, & Taylor, AW. (1955) Soil Sci. Soc. Am.

Proc. 19, 164-167

(3) Diagnosis and Improvement of Saline and Alkali Soils

( 1954), L.A Richards (Ed.), Agriculture Handbook 60, U.S.

Dept of Agriculture, Washington, DC, p. 84

(4) Robbins, c.w., & Wiegand, c.L. ( 1990) in Agricultural Sa­

linity, Assessment, and Management, KK Tanji (Ed.), ASCE

Manuals and Reports No. 7 1, Am. Soc. Civil Eng., New

York, NY, pp. 201-219

(5) Kalra, Y.P., & Maynard, D.G. (1991) Methods Manualfor

Forest Soil and Plant Analysis, Forestry Canada, Northwest

Region, Northern Forestry Centre, Edmonton, AB, Canada,

Inf. Rep. NOR-X-319

(6) Guidelines for Collaborative Study Procedure to Validate

Characteristics of a Method of Analysis, (1989) 1. Assoc. Off.

Anal. Chem. 72, 694--704

(7) Handbookfor AOAC members (1989), AOAC, Arlington, VA

(8) Youden, W.J., & Steiner, E.H. ( 1975) Statistical Manual of

the AOAC, AOAC, Arlington, VA

(9) Pleijsier, L.K ( 1986) The Laboratory Methods and Data Ex­

change Programme, Interim Report on the Exchange Round

86-1, International Soil Reference and Information Centre,

Wageningen, The Netherlands

Reprinted from the Journal of AOAC International Vol. 78, No. 2, 1995

322 K-\LRA: jOl!RNAL OF AOAC I:--'IERNATIONAL VOL. 78. No. 2. 1 995

Appendix: Descriptions of Soils Used in the Collaborative Study for pH Measurementsa

Halii Series

Clnssification: Clayey, fefitic, isothennic Typic Gibbsihumox. Location: Island of Kauai, Hawaii, University of Hawaii

Wailua Experiment Station, Wailua, Kauai, edge of experimen­tal maize field. approximately 270 m northwest of Station of­fice and approximately 35 m east of dirt road along western portion of ridge: latitude 22°04' 17''N, longitude 1 59°24'03"W.

Vegetation: Grassy area adjacent to experimental maize field; Kaimi clover (Desmodium canum), Hilograss (Paspalum

conjugatum), Dallisgrass (Paspalum dilatatum), and rattail­grass (Sporobolus africanus).

Climate: Mean annual rainfall, 2500 mm, mean annual tem-perature. 20°e.

Parent material: Residuum from melilite nepheline basalt Physiography: Gently sloping upland ridge. Relief Convex side slope of ridge. Slope: 3%. Permeability: Moderately rapid. Drainage: Well drained. Moisture: Moist. Descnbed by: H. Ikawa. Collected by: H. Ikawa, lR. Gordines, and K. Kagihara. Date sampled: March 19, 1981. Remarks: Colors are for moist soil. Textures are "apparent

field textures." Ap----O-35 cm; dark brown (7.5YR 3/2) gravelly silty clay

loam; moderage very fine and fme subangular blocky struc­ture; friable, sticky, plastic, many very fme roots; many very fine pores; lower portion of horizon has many iron concretions, mostly ranging in size 1-2 mm., some as large as I cm; few rock fragments, mostly 2-3 cm. occasionally 5-10 cm; very strongly acid (pH 5.0); abrupt smooth boundary.

Houghton Series

The Houghton series is a member of the euic, mesic family of Typic Medisaprists. The soil formes chiefly in herbaceous organic deposits more than 5 1 in. thick. The surface 0-12 in. layer is dominated by black highly decomposed organic mate­rial, subsurface 12-35 in. layer is dark reddish brown and black highly decomposed organic material and the bottom layer is dark reddish brown highly decomposed organic material. The soil is about neutral throughout.

Type location: Clinton County, Ml; 100 ft west of farm lane at comer where lane turns north; SEV4, SWV4, SWV4, Sec. 1 1, Bath Township; on Michigan State University muck farm.

Typifying pedon: Houghton muck-<:ultivated. (Colors are for moist soils unless otherwise stated.)

Oal-D-9"-Black (7.5YR 210) broken face and rubbed sapric material; about 5% fiber, a trace rubbed; weak coarse

subangular blocky structure: neutral (pH 7.0 in KC1); abrupt smooth boundary.

0a2-9- 1 3"-Black (7.5YR 2/0) broken face very dark brown (7.5YR 212) rubbed sapric material; about 5% fiber, a trace rubbed; weak medium granular structure; neutral (pH 7.0 in KC1); abrupt smooth boundary.

0a3-1 3-24" -Dark reddish brown (5YR 3/2) broken face dark reddish brown (5YR 212) rubbed sapric material; about 15% fiber, less than 5% rubbed; massive, breaking to thick platy fragments; neutral (pH 7.0 in KCl); abrupt smooth boundary.

Oa4-24-32"-Black (5YR 211 ) broken face and rubbed sapric material; about 10% fiber. a trace rubbed; massive; few woody fragments; neutral (pH 7.0 in KC1); clear wavy bound­

ary. OaS-32-48" -Dark reddish brown (5YR 212) broken face

black (5YR 211) rubbed sapric material about 20% fiber, less than 10% rubbed; massive, breaking to thick platy fragments; neutral (pH 7.0 in KC1); abrupt smooth boundary.

Houston

Soil type: Houston Black clay, 1-3% slopes. Classification: Udic Pellusterts, fine montmorillonitic, thennic. Location: Bell County, TX; ca 2 miles south of Temple, in

native pasture in south part of the Blackland Research Center. In microbasin.

Date sampled: June 3, 1977, sampled in core hole 30 in. in diameter. Sampled by Robert N. Ramsey.

Physiography: Gently sloping upland. The soil formed in Taylor Marl of the Upper Cretaceous period.

Sample numbers: National Soil Survey Laboratory (NSSL) Tex-77-U27-2-1 -2-3-4.

Pedon description: All 0-36 cm, very dark gray ( 1 OYR 3/1) clay, black ( l OYR 211 ) moist; moderate fme subangular and angular blocky structure; extremely hard, very firm; common fine roots; few fragments of snail shells; calcareous, moder­ately alkaline; clear wavy. NSSL-Tex-77-027-2- 1 boundary.

Laurentides

Location: Laurentides Provincial Park, latitude 47°16'00" N, longitude 7 1 °9'20" W.

Altitude: 700 m M.S.L. Landform: Rolling morainal. Slope: Upper slope, 5%. Drainage: Well drained. Vegetation: Abies balsamea L., Betula papyri/era Marsh,

Picea glauca Voss, Picea mariana BSP, Dryopteris spinulosa,

and Oxalis Montana. Climate: Precipitation, 1 39 cm (47 cm from snowfall).

KALRA: JOU�'1AL OF AOAC I:'oITERNATIONAL VOL. 78. NO. 2. 1 995 313

Parent material: Glacial till. loamy sand. Classification: Orthic ferro-humic podzol (Canadian). Hu­

mic cryothod (American ).

Laurentides: Ae (A2)' 0-5 cm Gray (7 .5YR 5/0 m). light gray (7 .5YR 7/0 d) loamy sand: single grain to weak fine subangular: firm in place. friable when removed: few fine and medium roots: abrupt, wavy to irregular boundary: 3-1 3 cm thick: pH 3.9.

Laurentides LFH: 8-0 cm Black ( I 0YR 211 m), very dark grayish-brown ( lOYR 3/1 d), semi-decomposed to well-de­composed organic matter: fibrous to fine granular: abundant fine and medium roots; abrupt, smooth boundary, 5-15 cm thick; pH 3.6.

Malbis Series

Sample number. S76AL-003-1-( l -4).

Representative profile: Malbis fine sandy loam.

Classification: Plinthic Paleudults: tine-loamy, siliceous, thermic.

Location: Gulf Coast Substation, Baldwin County, AL.

Use of vegetation: Presently used as winter pasture.

Parent rock or regolith: Medium textured Coastal Plain sediments.

Geomorphology, region: Lower Coastal Plain, MLRA- 133.

Position: Upland.

Elevation: About 150 ft.

Drainage and penneability: Well drained and moderately permeable to ca 55 in. Moderately slowly permeable below.

Water table and duration: Water table at 55 in. when de-scribed.

Slope: Less than 1 %.

Effective rooting depth: About 50 in.

Sampled by: B.E llajek, R.L. Guthrie, D.E. Lewis. and L.E Ratliff.

Date sampled: December 17, 1976.

Described by: R.L. Guthrie and D.E. Lewis.

B21t-7-27 in.; yellowish brown ( 1 OYR 5/6) loam; weak medium subangular blocky structure; friable; few fine roots; thin patchy clay films on faces of peds; 5% medium ironstone concre­tions; strongly acid; clear wavy boundary. (S76AL-003-1-2).

Myaaka

Taxonomic class: Sandy, siliceous, hyperthermic Aeric Haplaquods.

Location: Pardee County, FL; on a Range Cattle Experi­ment Station, on an ARC pasture 74, 1400 ft north of drainage canal and 100 west of Hwy 663, NEV4, NWV4, Sec. 33, T. 35; R 24 E.

Vegetation and use: Slash pine and saw palmetto. Used as pasture.

Drainage and penneability: Poorly drained. Permeability is rapid in the surface layer and substratum and moderate or mod­erately rapid in the subsoil.

Parent material: Marine deposits of sandy materials.

Samples collected and profile described by: John M. Rob­bins, Jr, Richard D. Ford. SCS. and Tom Hallmark, IFAS. April 6, 1978.

Horizon: A I .

Depth: 0--8 cm (0--3 in.). Description: Very dark gray ( lOYR 311 crushed) fine sand;

uncrushed colors have a salt and pepper appearance; weak fine crumbs structure: very friable: matted with many fine and me­dium roots: strongly acid: clear smooth boundary.

Peck 90-9: Flanagan SiCL that is classified as a fine, mont­morillonitic, mesic Aquic Argiudoll that has a water pH of 6 . 1 was circulated as soil No. 90-9 in the Fall 1990 Split Soil Sam­ple Study, as soil No. 91-4 in the Spring 199 1 , and as soil No. 91-7 in the Fall 1991 study. This soil came from a field that was never limed and had not been fertilized with phosphorus or potassium for 4 years but was fertilized with nitrogen as the field has grown corn since 1982.

Peck 90-10: Drummer SiCL that is classified as a fine silty, mixed, mesic, Typic Haplaquoll that has a water pH of 5.9 was circulated as soil No. 90-10 in the Fall 1990 Split Soil Sample Study, as soil No. 91-5 in the Spring 199 1 , and as soil No. 91-10 in the Fall 1991 study. This soil came from a research plot grass border area that has not been fertilized or limed for at least 10 years.

Peck 90-11: Harpster SiCL that is classified as a fine silty, mixed, mesic, Typic Calciaquoll that has a water pH of 7.8 was circulated as soil No. 90- 1 1 in the Fall 1990 Split Soil Sample Study, as soil No. 91 - 1 in the Spring 199 1 , and as soil No. 9 1-8 in the Fall 199 1 study. This soil came from the same field as the Flanagan SiCL previously described.

Peck 90-12: Cisne SiL that is classified as a fine, montrnoril­lonitic, mesil Typic Albaqualf that has a water pH of 4.9 was circulated as soil No. 90-12 in the Fall 1990 Split Soil Sample Study, as soil No. 91-3 in the Spring 199 1 , and as soil No. 9 1 - 1 1 in the Fall 199 1 study.

Saline soil (EC = 4.50 mS/cm)

ice U.S. Department of Agriculture-Soil Conservation Serv-

NSSL identification No. : 89PO 1 10. Soil survey No.: S88-ID-029-012-A. Location: 227-15; 280'E and 1200' S of NW corner of sec-

tion 15. Classification: Fine silty, mixed, frigid Typic Natrixeralf. Physiography: Flood plain. Slope Characteristics: 00 1 % south west facing undulating. Elevation: 1502 m MSL.

Hydraulic conductivity: Moderately low. Drainage class: Well drained. Erosion: Slight. Parent material: Alluvium material. Described by: Michael Cook. Date sampled: August 1988.

324 K>.LRA: JOURNAL OF AOAC b'TERNATlONAL VOL. 78. NO. 2. 1 995

Notes: Vegetation-greasewood.

A I-4-5 cm: dark brown ( l OYR 3/3) loam; pale brown

( lOYR 6/3) dry; strong very tine platy structure: soft. very fri­

able. slightly sticky, slightly plastic: common very fine roots:

common very fine vesicular pores: 890941 ; slightly efferves­

cent: abrupt smooth boundary.

" Provided by F. Kaisaki. except for Peck 90-9. 90- 10. 90- 1 1 . and 90- 1 2 samples.

/) Details received from TR. Peck.