• TABLE OF CONTENTS
HIDE
 Copyright
 Title Page
 Table of Contents
 Purpose of this manual
 Soil pH and its uses
 pH electrodes
 Reference electrode
 pH meter
 Electricity conductivity and its...
 EC probe and meter
 Laboratory procedures
 Assistance from the extension soil...
 Literature
 Appendix
 Acknowledgements






Group Title: Florida Cooperative Extension Service circular 1081
Title: Soil pH and electrical conductivity
CITATION PAGE IMAGE ZOOMABLE PAGE TEXT
Full Citation
STANDARD VIEW MARC VIEW
Permanent Link: http://ufdc.ufl.edu/UF00049202/00001
 Material Information
Title: Soil pH and electrical conductivity a county extension soil laboratory manual
Series Title: Circular
Physical Description: 11 p. : ill. ; 28 cm.
Language: English
Creator: Hanlon, Edward A ( Edward Aloysius ), 1946-
Bartos, James Michael, 1964-
Publisher: University of Florida, Institute of Food and Agricultural Sciences, Florida Cooperative Extension Service
Place of Publication: Gainesville Fla
Publication Date: 1993
 Subjects
Subject: Soils -- Testing -- Laboratory manuals   ( lcsh )
Genre: government publication (state, provincial, terriorial, dependent)   ( marcgt )
bibliography   ( marcgt )
non-fiction   ( marcgt )
 Notes
Bibliography: Includes bibliographical references (p. 11).
Statement of Responsibility: E.A. Hanlon and J.M. Bartos.
General Note: Title from cover.
General Note: "April 1993."
Funding: Florida Historical Agriculture and Rural Life
 Record Information
Bibliographic ID: UF00049202
Volume ID: VID00001
Source Institution: Marston Science Library, George A. Smathers Libraries, University of Florida
Holding Location: Florida Agricultural Experiment Station, Florida Cooperative Extension Service, Florida Department of Agriculture and Consumer Services, and the Engineering and Industrial Experiment Station; Institute for Food and Agricultural Services (IFAS), University of Florida
Rights Management: All rights reserved, Board of Trustees of the University of Florida
Resource Identifier: oclc - 28530021

Table of Contents
    Copyright
        Copyright
    Title Page
        Page i
        Page ii
    Table of Contents
        Page iii
    Purpose of this manual
        Page 1
    Soil pH and its uses
        Page 1
        Page 2
        Page 3
    pH electrodes
        Page 4
    Reference electrode
        Page 4
    pH meter
        Page 5
    Electricity conductivity and its uses
        Page 5
    EC probe and meter
        Page 6
    Laboratory procedures
        Page 6
        Soil scooping technique
            Page 6
        Estimation of soil texture
            Page 7
        Soil pH (2:1 V/V)
            Page 7
        Electrical conductivity
            Page 8
        pH meter
            Page 8
            Page 9
        Electricity conductivity meter
            Page 10
    Assistance from the extension soil testing laboratory
        Page 10
    Literature
        Page 11
    Appendix
        Page 11
    Acknowledgements
        Page 11
        Page 12
Full Text





HISTORIC NOTE


The publications in this collection do
not reflect current scientific knowledge
or recommendations. These texts
represent the historic publishing
record of the Institute for Food and
Agricultural Sciences and should be
used only to trace the historic work of
the Institute and its staff. Current IFAS
research may be found on the
Electronic Data Information Source
(EDIS)

site maintained by the Florida
Cooperative Extension Service.






Copyright 2005, Board of Trustees, University
of Florida




/o/

loApril 1993
April 1993


Circular 1081


SOIL pH AND ELECTRICAL CONDUCTIVITY:
A County Extension Soil Laboratory Manual



E. A. Hanlon and J. M. Bartos


















University of Florida
Institute of Food and Agricultural Sciences
Florida Cooperative Extension Service
John T. Woeste, Dean


R~iVEcRS!TY OF FLORIDA LIBRARIES










































C)a
SUM- a
,L]WIt












TABLE OF CONTENTS


Title

Purpose of this manual ..........


Soil pH and its uses .


. . . . . . . . . . . . . . .. 1


pH electrodes .....................

Reference electrode .................

pH m eter .........................

Electrical conductivity and its uses .......

EC probe and meter .................

Laboratory procedures ...............

I. Soil scooping technique ...

II. Estimation of soil texture ..

III. Soil pH (2:1 V/V) .......


IV. Electrical conductivity ...............

V. pH meter ........................

VI. Electrical conductivity meter ...........

Assistance from the Extension Soil Testing Laboratory ...

Literature ....................................

A ppendix ....................................

Acknowledgements .............................

List of Figures


1. pH electrode


. . . . . . . . . . . 4


2. Calom el electrode .................................................... 4


Page

. 1


.............

.............

. . . .

. . . .. .

.............
















SOIL pH AND ELECTRICAL CONDUCTIVITY:
A County Extension Soil Laboratory Manual

E.A. Hanlon and J.M. Bartos


PURPOSE

This manual has been designed as a reference
source for county extension laboratories offering soil
pH and/or electrical conductivity tests to their clients.
This manual, if followed, will assist county faculty in
assuring that these laboratory measurements are done
correctly with high quality assurance.

SOIL pH AND ITS USES

Soil pH measurement is useful because it is a
predictor of various chemical activities within the soil.
As such, it is also a useful tool in making
management decisions concerning the type of plants
suitable for a location, the possible need to modify
soil pH (either up or down), and a rough indicator of
the plant availability of nutrients in the soil.

Aluminum

Aluminum in the soil can adversely affect plants
if aluminum occurs in certain forms and its activity is
elevated sufficiently. As the activity of aluminum
increases, the soil becomes more acidic and soil pH
decreases. If the pH is low enough and aluminum is
present in sufficient quantity, plants may be stunted or
lost due to aluminum toxicity. In most Florida sandy
soils, there is danger of aluminum toxicity when soil
pH is below 5.0.


The occurrence of aluminum toxicity (at acidic
pHs) decreases somewhat as one travels from the
Florida panhandle and down the peninsula. The
reason for this apparent change is found in changes in
the soil constituents. Aluminum levels tend to
decrease and the aluminum is found in different
minerals in the soil as one travels south in Florida.

Organic soils have low total aluminum. Low soil
pH in these soils does not pose a threat from
aluminum toxicity in Florida.

Nitrogen Fixing Microbes

Legume plants have a helpful relationship with
selected soil microbes. These microbes convert
nitrogen gas from the atmosphere to forms useful to
the plant for growth and improved yield. In turn, the
microbes are supplied nutrients and carbohydrates
from the plant. This mutual, beneficial existence is
termed symbiosis. Agronomic examples of this
symbiotic relationship are alfalfa, peanut, and
soybean.

Soil pH directly affects the activity of these
microbes. Research, conducted in the absence of
aluminum toxicity, has shown that once the soil pH
has decreased to 4.7 or lower, the ability of the
microbes to convert nitrogen is greatly reduced. If
aluminum is present, then both the microbial
symbiotic activity and the normal metabolism of the
plant are adversely affected.


* Associate Professor, Soil and Water Science Department, Institute of Food and Agricultural Sciences (IFAS), Extension Soil Management
Specialist and Director of the University of Florida, Extension Soil Testing Laboratory; and Coordinator of Research Activities of the University
of Florida, Extension Soil Testing Laboratory, University of Florida, Gainesville FL 32611.
















SOIL pH AND ELECTRICAL CONDUCTIVITY:
A County Extension Soil Laboratory Manual

E.A. Hanlon and J.M. Bartos


PURPOSE

This manual has been designed as a reference
source for county extension laboratories offering soil
pH and/or electrical conductivity tests to their clients.
This manual, if followed, will assist county faculty in
assuring that these laboratory measurements are done
correctly with high quality assurance.

SOIL pH AND ITS USES

Soil pH measurement is useful because it is a
predictor of various chemical activities within the soil.
As such, it is also a useful tool in making
management decisions concerning the type of plants
suitable for a location, the possible need to modify
soil pH (either up or down), and a rough indicator of
the plant availability of nutrients in the soil.

Aluminum

Aluminum in the soil can adversely affect plants
if aluminum occurs in certain forms and its activity is
elevated sufficiently. As the activity of aluminum
increases, the soil becomes more acidic and soil pH
decreases. If the pH is low enough and aluminum is
present in sufficient quantity, plants may be stunted or
lost due to aluminum toxicity. In most Florida sandy
soils, there is danger of aluminum toxicity when soil
pH is below 5.0.


The occurrence of aluminum toxicity (at acidic
pHs) decreases somewhat as one travels from the
Florida panhandle and down the peninsula. The
reason for this apparent change is found in changes in
the soil constituents. Aluminum levels tend to
decrease and the aluminum is found in different
minerals in the soil as one travels south in Florida.

Organic soils have low total aluminum. Low soil
pH in these soils does not pose a threat from
aluminum toxicity in Florida.

Nitrogen Fixing Microbes

Legume plants have a helpful relationship with
selected soil microbes. These microbes convert
nitrogen gas from the atmosphere to forms useful to
the plant for growth and improved yield. In turn, the
microbes are supplied nutrients and carbohydrates
from the plant. This mutual, beneficial existence is
termed symbiosis. Agronomic examples of this
symbiotic relationship are alfalfa, peanut, and
soybean.

Soil pH directly affects the activity of these
microbes. Research, conducted in the absence of
aluminum toxicity, has shown that once the soil pH
has decreased to 4.7 or lower, the ability of the
microbes to convert nitrogen is greatly reduced. If
aluminum is present, then both the microbial
symbiotic activity and the normal metabolism of the
plant are adversely affected.


* Associate Professor, Soil and Water Science Department, Institute of Food and Agricultural Sciences (IFAS), Extension Soil Management
Specialist and Director of the University of Florida, Extension Soil Testing Laboratory; and Coordinator of Research Activities of the University
of Florida, Extension Soil Testing Laboratory, University of Florida, Gainesville FL 32611.







Soil pH and Electrical Conductivity


Solubility of Plant Nutrients

Soil pH directly affects the solubility of many of
the nutrients in the soil needed for proper plant
growth and development. These chemical reactions
are complex and have often been generalized with
charts that oversimplify chemical conditions in specific
soils. One should be careful in using these pH-
nutrient charts when dealing with soils in Florida.
They may be misleading.

As soil pH decreases, nutrients, such as
phosphorus, usually decrease in plant availability
because of precipitate reactions with iron and
aluminum. However, plants can affect their micro-
environment and are often found to grow well over a
range of soil pH. This range of successful growth is
often as great as 1 to 2 pH units. In general, many
plants will do well in a soil pH range of 5.5 to 7.5.
Specific plants, such as azalea or pine seedlings,
actually require low soil pH. Such plants are often
iron inefficient, meaning that they require low soil pH
to aid in the uptake of iron from the soil.

As soil pH increases above 6.5, manganese, a
micronutrient, may become limiting to plant growth.
Phosphorus and micronutrients such as copper and
zinc also decrease in their plant availability at high
pH. Soils composed of limestone (such as those in
the Dade County area) have a high native soil pH of
about 8.3. Plants grow in these high pH soils, but
nutrient deficiencies are common.


Optimum pH Ranges for Plants

As stated above, most plants do well over a range
of soil pH values. This point bears repeating because
the best management of soil pH is often to do
nothing. Because many plants directly modify the
chemical environment around their roots, nutrient
limitations are not found, plant production is not
adversely affected, and visual stress symptoms are not
observed.

The University of Florida, IFAS, Extension Soil
Testing Laboratory (ESTL) uses the IFAS
Standardized Fertilization Recommendation System.
This system contains all of the IFAS approved
fertilizer and liming recommendations (Hanlon et al.,
1990). Specific pH values are cited in this system as
target pHs. A target pH is a soil pH, within the
optimum pH range, that is used for the calculation of
lime rates. A target pH is usually selected such that
the adverse effects of aluminum toxicity are avoided,
and so that nutrient availability for that crop will be
adequate. A target pH is not the only pH at which
the crop will do well.


Table 1. Lime requirement to reach a target pH of 6.0 or 6.5 for selected soils with soil pH = 5.7.

Lime Requirement
Sample Soil pH Target pH = 6.0 Target pH = 6.5
lb lb lb lb
acre 1,000 sq ft acre 1,000 sq ft
Alachua 5.7 1000 23.0 2600 59.7
Columbia 5.7 500 11.5 1000 23.0
Jackson 5.7 600 13.8 1500 34.4
Jackson 5.7 800 18.4 2100 48.2
Okaloosa 5.7 600 13.8 1500 34.4
Polk 5.7 600 13.8 1500 34.4
Polk 5.7 800 18.4 2100 48.2
Putnam 5.7 600 13.8 1500 34.4


Page 2







Soil pH and Electrical Conductivity


Liming of Soils

If the soil pH is greater than 0.2 units below the
target pH, the ESTL will complete an additional test,
the Adams-Evans Buffer. This test has been
specifically designed for the sandy soils found in the
southern United States. Furthermore, current lime
recommendations have been calibrated for Florida
conditions using both the soil pH and the Adams-
Evans Buffer.

Soil pH is a measure of the active acidity, that
portion of the hydrogen ions that is active in the soil
solution. Soil pH does not measure the reserve
acidity. Reserve acidity is that portion of hydrogen
and other acid-contributing ions that are sorbed on
soil particles. Usually, the reserve acidity is much
greater than the active acidity. The Adams-Evans test
is designed to measure this reserve acidity. Together,
the target pH, the soil pH, and the Adams-Evans test
can be used to determine the amount of lime
required to adjust the soil pH from its current reading
to the target pH.

To see the effect of reserve acidity on lime
recommendations, the data in Table 1 have been
compiled. Soil samples from the indicated counties
were all selected to have the same soil pH of 5.7.
However, the amount of lime in pounds/acre or
pounds per 1,000 sq ft to raise the soil pH to a target
pH of 6.0 (columns 3 and 4) or to a target pH of 6.5
(columns 5 and 6) varies widely.

Unfortunately, the Adams-Evans test is rather
complex and contains chemicals that must be handled
and disposed of as hazardous waste. For this reason,
county Extension laboratories should not offer the
Adams-Evans test. However, local knowledge of the
county and its soils can help considerably with local
lime recommendations. It is recommended that
liming recommendations made at the county
laboratory be verified by submitting a small
percentage (e.g., 5%) of soil samples to the ESTL.
Comparison of the local recommendations with those
from the ESTL will allow county extension faculty to
calibrate their recommendations.


Acidifying Soil

In some situations, it may be desirable to acidify
the soil, that is, to lower soil pH. If the high soil pH
is a natural condition, there is little that can be done
to lower soil pH permanently. Treatment with sulfur
will lower the pH for a few weeks, but the pH will
eventually increase.

In landscaping, it is often better to select plants
which are adapted to the natural soil pH range, rather
than to use plants which will need constant soil pH
maintenance and usually look unhealthy even after
this extra effort.

In situations where the high soil pH condition was
created by human activity, for instance overliming, it
is often feasible to lower the soil pH with one or two
applications of sulfur. In such cases, the amount of
overliming is relatively small, say 1 ton/acre (46
lb/1000 sq ft) and can be treated successfully. In
naturally occurring, high pH soils, the effective lime
equivalent will usually be over 100 tons/acre.

Unfortunately, there is no soil test available to
assist in determining the amounts of sulfur (S) needed
to reduce soil pH. If plants are actively growing,
agricultural sulfur treatment should be restricted to a
maximum of 300 lb S/acre (7 lb S/1,000 sq ft).
Damage may still occur at this rate if the S is allowed
to remain in contact with the foliage.

Multiple treatments during the growing season
should be done with caution; that is, allowing enough
time (usually about 1 month) for the previous S
treatment to react with the soil. Sulfur added to the
soil must undergo oxidation by soil microbes resulting
in the production of hydrogen ions and sulfate. Since
microbial action controls the effectiveness of the
treatment, warm moist soil conditions are preferable
to dry or cool conditions. Treatment of the soil with
gypsum, which is calcium sulfate, will not change soil
pH because gypsum does not contribute any acidity to
the soil. It is a pH-neutral salt.


Page 3







Soil pH and Electrical Conductivity


pH ELECTRODES

Figure 1 represents a drawing of the pH
electrode, often called a glass electrode. The
electrode and its reference electrode (Figure 2) may
be combined into a single combination electrode.
However, for ease of understanding, this discussion
will deal with separate electrodes. All electrode parts
are similar, whether they are used as two separate
electrodes or as a single combination electrode.


Figure 1 pH Electrode

The glass ball at the end of the pH electrode is
composed of a special glass which has specific surface
properties. The ball should not be touched nor
allowed to dry out. Inspection of this part should
include insuring that the ball has not been cracked,
that it is full of solution, and that there is a thin wire
extending into the upper portion of the ball within the
electrode.

If the electrode has been inverted, the ball may
not contain any solution. Gently tapping the
electrode side with one's fingers while holding it
vertical with the ball down is usually enough to
displace the entrapped air with solution.

Most manufacturers include instructions for
maintaining (rejuvenating) the electrode if the ball
has been allowed to dry out. Rejuvenation often calls
for strong acids which present a personal safety
hazard. County faculty may wish to replace electrodes
rather than attempting rejuvenation.

Inspection of the electrode wire should not reveal
any loose connections or breaks in the insulation.
There are no serviceable parts on the pH electrode.


REFERENCE ELECTRODE

The reference electrode, also known as a calomel
electrode, is shown in Figure 2. The electrode
contains a fibrous or ceramic chip which allows the
internal solution to slowly flow out from the body of
the electrode into the external solution of the sample
which is being measured. This leaking results in a
completed electrical circuit. Inspection should include
checking that the chip is in place and is relatively
clean of debris from past use. Often the chip will be
white or light gray in color, indicating that it is still
functioning. If the chip is a different (darker) color,
the electrode may not function properly. Use of a
small amount of abrasion may restore the chip, but
too much abrasion may damage the electrode.

Lastly, the barrel of the electrode often contains
a filler port near the top of the electrode. Most
manufacturers recommend that the covering be
removed from this port so that pressures do not
develop within the operating electrode. The solution,
often a concentrated solution of potassium chloride
(see specifications for your specific electrode), should
be kept within 1 inch of the filler port. This level is
sufficient to insure that the internal solution level is
higher than the sample solution being analyzed: This
difference permits flow out from the electrode
through the chip.

A relatively new type of electrode is constructed
with an internal fluid which is a gel. This type of
electrode does not contain a filler port because it can
not be serviced by the user.


Fiu. -"i
-FocT r


.entsfC Ar


- SILvE.tiLEe!iR~E.
- ICe LcunoM LEM.L





- CERAIWcCIIP


Figure 2 Calomel Electrode


Sow-unoL


Page 4







Soil pH and Electrical Conductivity


pH ELECTRODES

Figure 1 represents a drawing of the pH
electrode, often called a glass electrode. The
electrode and its reference electrode (Figure 2) may
be combined into a single combination electrode.
However, for ease of understanding, this discussion
will deal with separate electrodes. All electrode parts
are similar, whether they are used as two separate
electrodes or as a single combination electrode.


Figure 1 pH Electrode

The glass ball at the end of the pH electrode is
composed of a special glass which has specific surface
properties. The ball should not be touched nor
allowed to dry out. Inspection of this part should
include insuring that the ball has not been cracked,
that it is full of solution, and that there is a thin wire
extending into the upper portion of the ball within the
electrode.

If the electrode has been inverted, the ball may
not contain any solution. Gently tapping the
electrode side with one's fingers while holding it
vertical with the ball down is usually enough to
displace the entrapped air with solution.

Most manufacturers include instructions for
maintaining (rejuvenating) the electrode if the ball
has been allowed to dry out. Rejuvenation often calls
for strong acids which present a personal safety
hazard. County faculty may wish to replace electrodes
rather than attempting rejuvenation.

Inspection of the electrode wire should not reveal
any loose connections or breaks in the insulation.
There are no serviceable parts on the pH electrode.


REFERENCE ELECTRODE

The reference electrode, also known as a calomel
electrode, is shown in Figure 2. The electrode
contains a fibrous or ceramic chip which allows the
internal solution to slowly flow out from the body of
the electrode into the external solution of the sample
which is being measured. This leaking results in a
completed electrical circuit. Inspection should include
checking that the chip is in place and is relatively
clean of debris from past use. Often the chip will be
white or light gray in color, indicating that it is still
functioning. If the chip is a different (darker) color,
the electrode may not function properly. Use of a
small amount of abrasion may restore the chip, but
too much abrasion may damage the electrode.

Lastly, the barrel of the electrode often contains
a filler port near the top of the electrode. Most
manufacturers recommend that the covering be
removed from this port so that pressures do not
develop within the operating electrode. The solution,
often a concentrated solution of potassium chloride
(see specifications for your specific electrode), should
be kept within 1 inch of the filler port. This level is
sufficient to insure that the internal solution level is
higher than the sample solution being analyzed: This
difference permits flow out from the electrode
through the chip.

A relatively new type of electrode is constructed
with an internal fluid which is a gel. This type of
electrode does not contain a filler port because it can
not be serviced by the user.


Fiu. -"i
-FocT r


.entsfC Ar


- SILvE.tiLEe!iR~E.
- ICe LcunoM LEM.L





- CERAIWcCIIP


Figure 2 Calomel Electrode


Sow-unoL


Page 4








Soil pH and Electrical Conductivity


pH METER

The pH meter is a sensitive electronic device,
often designed with printed circuits making it quite
reliable. However, improper handling (bumps, hot
dash-board storage, or solution spills) can damage the
meter. The meter is designed to measure changes of
millivolts between the reference and pH electrodes.
To understand the sensitivity needed to measure
millivolts, human neck pains are often induced by 7 to
20 millivolts.

Most problems associated with reading pH usually
originate with faulty electrodes. Additionally, if the
meter contains batteries, they should be checked
before each use. Low or inadequate power supply
will result in inaccurate pH readings.

In any case, unless the instrument completely
fails, it will always give a pH reading whether it is
functioning correctly or not! It is the responsibility of
the operator to detect problems and to report
accurate pH results.

ELECTRICAL CONDUCTIVITY AND ITS USES

The Electrical Conductivity (EC) of a solution is
a measure of the ability of the solution to conduct
electricity. The EC is reported in either millimhos
per centimeter or the equivalent deciSiemens per
meter. When ions (salts) are present, the EC of the
solution increases. If no salts are present, then the
EC is low indicating that the solution does not
conduct electricity well.

The EC indicates the presence or absence of salts,
but does not indicate which salts might be present.
For example, the EC of a soil sample might be
considered relatively high. No indication from the EC
test is available to determine if this condition was
from irrigation with salty water or if the field had
been recently fertilized and the elevated EC is from
the soluble fertilizer salts. To determine the source
of the salts in a sample, further chemical tests must
be performed.

Soluble Salts vs. EC

Prior to 1989, the ESTL reported Soluble Salts
values. Soluble salts is an older term and is derived
from EC measurements. Unfortunately, there are a
number of assumptions which have to be made before
soluble salts can be calculated. Conversion factors
(EC to soluble salts) were different across the United


States, ranging from 600 to 700. Florida used a
conversion factor of 700.

These assumptions, and their introduced errors,
are avoided by reporting the actual EC measurement.
The EC can also be directly used in the body of
literature which is continuously growing concerning
plant productivity under the effects of salinity. The
older term soluble salts should be avoided by county
Extension laboratories.

Interpretation of Electrical Conductivity of
Irrigation Water

Frequent use of irrigation water will directly
influence the salts in the soil profile. Salts are
influenced by factors such as rainfall content and
timing, internal soil drainage, and irrigation practices.
Usually, rainfall contains low amounts of salts and
acts to dilute salts that are present in the soil. If the
rainfall is of sufficient volume or duration, and the
soil has internal drainage, the added rainfall is enough
to leach salts from the soil. During drying conditions,
water is lost from the soil due to evaporation, and
salts are effectively concentrated. If irrigation water
contains appreciable salts, then intensive management
is required to produce healthy plants. Therefore, EC
measurement of the irrigation water source is an
excellent management decision. Table 2 has been
developed to assist in making a decision to use a
water source.


Table 2. Classification
conductivity.


of irrigation water by electrical


Class of Water Specific Conductance
dS/m
Excellent <0.25
Good 0.25 to 0.75
Permissible 0.76 to 2.00
Doubtful 2.00 to 3.00
Unsuitable >3.00


Interpretation of Electrical Conductivity of
Soils

In actuality, the interpretation of EC of a soil or
media must be made considering the plants) to be
grown. The EC of the soil has little direct
detrimental effect on sandy mineral soils or on media.
However, EC directly affects plants growing in the
soil or media. The impact of EC on plants is also
directly affected by water management.


Page 5








Soil pH and Electrical Conductivity


pH METER

The pH meter is a sensitive electronic device,
often designed with printed circuits making it quite
reliable. However, improper handling (bumps, hot
dash-board storage, or solution spills) can damage the
meter. The meter is designed to measure changes of
millivolts between the reference and pH electrodes.
To understand the sensitivity needed to measure
millivolts, human neck pains are often induced by 7 to
20 millivolts.

Most problems associated with reading pH usually
originate with faulty electrodes. Additionally, if the
meter contains batteries, they should be checked
before each use. Low or inadequate power supply
will result in inaccurate pH readings.

In any case, unless the instrument completely
fails, it will always give a pH reading whether it is
functioning correctly or not! It is the responsibility of
the operator to detect problems and to report
accurate pH results.

ELECTRICAL CONDUCTIVITY AND ITS USES

The Electrical Conductivity (EC) of a solution is
a measure of the ability of the solution to conduct
electricity. The EC is reported in either millimhos
per centimeter or the equivalent deciSiemens per
meter. When ions (salts) are present, the EC of the
solution increases. If no salts are present, then the
EC is low indicating that the solution does not
conduct electricity well.

The EC indicates the presence or absence of salts,
but does not indicate which salts might be present.
For example, the EC of a soil sample might be
considered relatively high. No indication from the EC
test is available to determine if this condition was
from irrigation with salty water or if the field had
been recently fertilized and the elevated EC is from
the soluble fertilizer salts. To determine the source
of the salts in a sample, further chemical tests must
be performed.

Soluble Salts vs. EC

Prior to 1989, the ESTL reported Soluble Salts
values. Soluble salts is an older term and is derived
from EC measurements. Unfortunately, there are a
number of assumptions which have to be made before
soluble salts can be calculated. Conversion factors
(EC to soluble salts) were different across the United


States, ranging from 600 to 700. Florida used a
conversion factor of 700.

These assumptions, and their introduced errors,
are avoided by reporting the actual EC measurement.
The EC can also be directly used in the body of
literature which is continuously growing concerning
plant productivity under the effects of salinity. The
older term soluble salts should be avoided by county
Extension laboratories.

Interpretation of Electrical Conductivity of
Irrigation Water

Frequent use of irrigation water will directly
influence the salts in the soil profile. Salts are
influenced by factors such as rainfall content and
timing, internal soil drainage, and irrigation practices.
Usually, rainfall contains low amounts of salts and
acts to dilute salts that are present in the soil. If the
rainfall is of sufficient volume or duration, and the
soil has internal drainage, the added rainfall is enough
to leach salts from the soil. During drying conditions,
water is lost from the soil due to evaporation, and
salts are effectively concentrated. If irrigation water
contains appreciable salts, then intensive management
is required to produce healthy plants. Therefore, EC
measurement of the irrigation water source is an
excellent management decision. Table 2 has been
developed to assist in making a decision to use a
water source.


Table 2. Classification
conductivity.


of irrigation water by electrical


Class of Water Specific Conductance
dS/m
Excellent <0.25
Good 0.25 to 0.75
Permissible 0.76 to 2.00
Doubtful 2.00 to 3.00
Unsuitable >3.00


Interpretation of Electrical Conductivity of
Soils

In actuality, the interpretation of EC of a soil or
media must be made considering the plants) to be
grown. The EC of the soil has little direct
detrimental effect on sandy mineral soils or on media.
However, EC directly affects plants growing in the
soil or media. The impact of EC on plants is also
directly affected by water management.


Page 5







Soil pH and Electrical Conductivity


Salt Index Use and Calculation

As EC increases, more attention to water
management is needed to prevent salinity from
adversely affecting plants. The Extension Soil Testing
Laboratory uses a 2:1 solution:soil ratio with which to
determine EC. Many states use a saturated paste
extract. This saturated paste method is more time
consuming than the 2:1 extraction, and results in
inadequate amounts of solution in Florida's sandy
soils. The conversion from the 2:1 extraction result
to the saturated paste result, termed salt index, is easy
and accurate.

EC (salt index) = EC (2:1) x 8.

In general, when the soil EC (2:1, water:soil)
exceeds 0.25 dS/m (or 0.25 x 8 = 2.0 dS/m salt index),
many plants experience stress due to salts. Other
plants (e.g., bermudagrass) are quite tolerant to salts.
Due to this species-dependent effect of EC, a listing
of the effects of increasing EC on selected plants has
been compiled (Hanlon et al., 1993).

EC PROBE AND METER

There are a wide variety of EC probes and meters
marketed. Those instruments using probes that are
placed in the soil or media in situ (directly in the soil
without taking a sample) are not considered in the
following discussion. Since EC is a measurement of
the conductivity of the soil solution, the measurement
should be made under a controlled mixture of
solution to soil (2:1). These conditions usually do not
exist when direct reading instruments are used.

Electrical Conductivity Probe

The probe consists of a tube, usually of plastic,
into which electrodes have been installed. Two
common electrode arrangements are: 1) two plates; or
2) a rod located concentrically in a ring. In either
case, the electrodes are held a specific distance apart.
The gap between the electrodes is filled with the
water sample or filtered solution from a soil sample,
either by filling a reservoir or by placing the probe in
the solution.

When the probe is immersed in the solution, ions
contained in the solution will permit electrical flow
from one electrode to another. If a large number of
ions are present (salty conditions), then the EC of the
sample will be higher than a sample with low number
of ions (low salts).


Some older instruments require that a mixture of
soil and solution be packed into the electrode
receptacle. While readings from these older
instruments may be adequate, accurate results are
harder to obtain because readings are affected by the
sample packing method.

Inspection of the probe should include insuring
that the probe is clean and free of debris, and that all
electrical connections are in place. Some probes may
experience a buildup of corrosion on the electrodes
with time. Indication of corrosion, if not directly
visible, is indicated by the constant need to reset the
instrument because of drifting, often in one direction
as corrosion progresses.

Electrical Conductivity Meter

Meters for EC are extremely reliable. Meters
from the 1950s which use a "cat's eye" tube are still in
use. Newer meters using digital displays are often
susceptible to failure of one or more segments of the
digital display, usually related to corrosion within the
instrument.

As with failures associated with pH meters, EC
meters will always provide an EC, unless the problem
results in total instrument failure. It falls upon the
operator to insure that the reported EC is an accurate
measurement of the conductivity of the sample.

LABORATORY PROCEDURES

The following procedures are used at the ESTL
and are based on good laboratory procedures with
sufficient quality control measures to insure that pH
and EC readings are accurate and reliable. While
equipment may vary among County Extension
Laboratories, procedures should be developed that
directly parallel those used by the ESTL.

I. Soil Scooping Technique

The ESTL uses a scoop (that is, a volume
measurement) for both pH and EC determinations.
The scoop is a plastic and metal device which may be
obtained from a commercial manufacturer (e.g.,
Custom Laboratories, Orange City, FL). Alternately,
the scoop may be constructed from locally available
materials, such as measuring spoons or coffee scoops.
The intent is to use a consistent volume of soil and
water.


Page 6







Soil pH and Electrical Conductivity


Salt Index Use and Calculation

As EC increases, more attention to water
management is needed to prevent salinity from
adversely affecting plants. The Extension Soil Testing
Laboratory uses a 2:1 solution:soil ratio with which to
determine EC. Many states use a saturated paste
extract. This saturated paste method is more time
consuming than the 2:1 extraction, and results in
inadequate amounts of solution in Florida's sandy
soils. The conversion from the 2:1 extraction result
to the saturated paste result, termed salt index, is easy
and accurate.

EC (salt index) = EC (2:1) x 8.

In general, when the soil EC (2:1, water:soil)
exceeds 0.25 dS/m (or 0.25 x 8 = 2.0 dS/m salt index),
many plants experience stress due to salts. Other
plants (e.g., bermudagrass) are quite tolerant to salts.
Due to this species-dependent effect of EC, a listing
of the effects of increasing EC on selected plants has
been compiled (Hanlon et al., 1993).

EC PROBE AND METER

There are a wide variety of EC probes and meters
marketed. Those instruments using probes that are
placed in the soil or media in situ (directly in the soil
without taking a sample) are not considered in the
following discussion. Since EC is a measurement of
the conductivity of the soil solution, the measurement
should be made under a controlled mixture of
solution to soil (2:1). These conditions usually do not
exist when direct reading instruments are used.

Electrical Conductivity Probe

The probe consists of a tube, usually of plastic,
into which electrodes have been installed. Two
common electrode arrangements are: 1) two plates; or
2) a rod located concentrically in a ring. In either
case, the electrodes are held a specific distance apart.
The gap between the electrodes is filled with the
water sample or filtered solution from a soil sample,
either by filling a reservoir or by placing the probe in
the solution.

When the probe is immersed in the solution, ions
contained in the solution will permit electrical flow
from one electrode to another. If a large number of
ions are present (salty conditions), then the EC of the
sample will be higher than a sample with low number
of ions (low salts).


Some older instruments require that a mixture of
soil and solution be packed into the electrode
receptacle. While readings from these older
instruments may be adequate, accurate results are
harder to obtain because readings are affected by the
sample packing method.

Inspection of the probe should include insuring
that the probe is clean and free of debris, and that all
electrical connections are in place. Some probes may
experience a buildup of corrosion on the electrodes
with time. Indication of corrosion, if not directly
visible, is indicated by the constant need to reset the
instrument because of drifting, often in one direction
as corrosion progresses.

Electrical Conductivity Meter

Meters for EC are extremely reliable. Meters
from the 1950s which use a "cat's eye" tube are still in
use. Newer meters using digital displays are often
susceptible to failure of one or more segments of the
digital display, usually related to corrosion within the
instrument.

As with failures associated with pH meters, EC
meters will always provide an EC, unless the problem
results in total instrument failure. It falls upon the
operator to insure that the reported EC is an accurate
measurement of the conductivity of the sample.

LABORATORY PROCEDURES

The following procedures are used at the ESTL
and are based on good laboratory procedures with
sufficient quality control measures to insure that pH
and EC readings are accurate and reliable. While
equipment may vary among County Extension
Laboratories, procedures should be developed that
directly parallel those used by the ESTL.

I. Soil Scooping Technique

The ESTL uses a scoop (that is, a volume
measurement) for both pH and EC determinations.
The scoop is a plastic and metal device which may be
obtained from a commercial manufacturer (e.g.,
Custom Laboratories, Orange City, FL). Alternately,
the scoop may be constructed from locally available
materials, such as measuring spoons or coffee scoops.
The intent is to use a consistent volume of soil and
water.


Page 6







Soil pH and Electrical Conductivity


Salt Index Use and Calculation

As EC increases, more attention to water
management is needed to prevent salinity from
adversely affecting plants. The Extension Soil Testing
Laboratory uses a 2:1 solution:soil ratio with which to
determine EC. Many states use a saturated paste
extract. This saturated paste method is more time
consuming than the 2:1 extraction, and results in
inadequate amounts of solution in Florida's sandy
soils. The conversion from the 2:1 extraction result
to the saturated paste result, termed salt index, is easy
and accurate.

EC (salt index) = EC (2:1) x 8.

In general, when the soil EC (2:1, water:soil)
exceeds 0.25 dS/m (or 0.25 x 8 = 2.0 dS/m salt index),
many plants experience stress due to salts. Other
plants (e.g., bermudagrass) are quite tolerant to salts.
Due to this species-dependent effect of EC, a listing
of the effects of increasing EC on selected plants has
been compiled (Hanlon et al., 1993).

EC PROBE AND METER

There are a wide variety of EC probes and meters
marketed. Those instruments using probes that are
placed in the soil or media in situ (directly in the soil
without taking a sample) are not considered in the
following discussion. Since EC is a measurement of
the conductivity of the soil solution, the measurement
should be made under a controlled mixture of
solution to soil (2:1). These conditions usually do not
exist when direct reading instruments are used.

Electrical Conductivity Probe

The probe consists of a tube, usually of plastic,
into which electrodes have been installed. Two
common electrode arrangements are: 1) two plates; or
2) a rod located concentrically in a ring. In either
case, the electrodes are held a specific distance apart.
The gap between the electrodes is filled with the
water sample or filtered solution from a soil sample,
either by filling a reservoir or by placing the probe in
the solution.

When the probe is immersed in the solution, ions
contained in the solution will permit electrical flow
from one electrode to another. If a large number of
ions are present (salty conditions), then the EC of the
sample will be higher than a sample with low number
of ions (low salts).


Some older instruments require that a mixture of
soil and solution be packed into the electrode
receptacle. While readings from these older
instruments may be adequate, accurate results are
harder to obtain because readings are affected by the
sample packing method.

Inspection of the probe should include insuring
that the probe is clean and free of debris, and that all
electrical connections are in place. Some probes may
experience a buildup of corrosion on the electrodes
with time. Indication of corrosion, if not directly
visible, is indicated by the constant need to reset the
instrument because of drifting, often in one direction
as corrosion progresses.

Electrical Conductivity Meter

Meters for EC are extremely reliable. Meters
from the 1950s which use a "cat's eye" tube are still in
use. Newer meters using digital displays are often
susceptible to failure of one or more segments of the
digital display, usually related to corrosion within the
instrument.

As with failures associated with pH meters, EC
meters will always provide an EC, unless the problem
results in total instrument failure. It falls upon the
operator to insure that the reported EC is an accurate
measurement of the conductivity of the sample.

LABORATORY PROCEDURES

The following procedures are used at the ESTL
and are based on good laboratory procedures with
sufficient quality control measures to insure that pH
and EC readings are accurate and reliable. While
equipment may vary among County Extension
Laboratories, procedures should be developed that
directly parallel those used by the ESTL.

I. Soil Scooping Technique

The ESTL uses a scoop (that is, a volume
measurement) for both pH and EC determinations.
The scoop is a plastic and metal device which may be
obtained from a commercial manufacturer (e.g.,
Custom Laboratories, Orange City, FL). Alternately,
the scoop may be constructed from locally available
materials, such as measuring spoons or coffee scoops.
The intent is to use a consistent volume of soil and
water.


Page 6








Soil pH and Electrical Conductivity


Table 3. Soil texture can be determined by the feel of the soil sample.

Textural Name Description
Sand Loose and single-grained with a gritty feeling when moistened. Not sticky and will not form a
ribbon when pressed between the thumb and index finger. Includes fine sand, loamy sand,
and loamy fine sand.
Sandy Loam Contains sufficient silt and clay to give coherence to the moistened soil. Feels gritty and
slightly sticky. Will not form a ribbon. Includes fine sandy loams.
Clay Loam Forms short ribbons less than 3 cm long. Forms a hard, firm aggregate when dry. Includes
sandy clay loams and silty clay loams.
Clay Extremely sticky and plastic when moist. Easily firms ribbons longer than 3 cm. Includes
sandy clays.
Organic/Mineral Term used in place of a textural class Soil Intergrade for soils that contain up to 500 organic
matter by volume.
Organic Term used for soils that are predominately organic but which may contain up to 50%/ mineral
matter by volume.


The soil scooping technique requires practice,
despite its unsophisticated appearance. The
technique depends upon uniform actions by the
technician from sample to sample to produce
consistent packing of soil into the scoop. This
consistency can be directly measured by repeatedly
scooping the same soil and weighing each scoop.
Weights should be uniform within each scoop
(volume) and soil-sample combination. Weights will
vary from soil to soil, especially when there is a
noticeable difference in soil texture.

A. Sample Handling and Preparation

The sample should be air-dried and passed through a
2-mm sieve before scooping.

B. Procedure

1. Dip the scoop into the center of the soil
sample and fill the scoop with a twisting
motion so that extra soil is mounded above
the rim of the scoop. Do not press the
scoop or force the soil against the side of
the container (Jones, 1980).

2. Strike the handle near the scoop three
times with a plastic rod to settle soil
particles.

3. Level the scoop with the plastic rod. Strike
off all excess soil above the rim of the scoop
in a single stroke so that the soil is not
compacted into the scoop.


II. Estimation of Soil Texture

Knowledge of soil texture is useful in the
recommendation of lime. Local soil conditions may
be quite uniform so that little differences may be
found throughout the county. However, such
uniformity is expected to be rare in most counties.
After the soil has been air-dried and sieved, a small
amount of dry soil should be moistened and rubbed
between the forefinger and thumb. An estimation of
the texture is made by comparing the "feel" of the
sample to that of a set of soil samples of known
texture (Table 3).

III. Soil pH (2:1 V/V)

This procedure uses a 20-cc (~ 25 g) soil scoop
and 40 mL of pure water to obtain a 2:1 water-to-soil
ratio. Most problems with this procedure are
associated with the glass or calomel electrodes.
However, sample pH may also be affected by
contaminated water, by microbial activity if samples
are allowed to sit for several hours before
determining pH, or by improper scooping techniques.

A. Standard Solutions

Obtain commercial standard solutions of pH
4.00, 7.00, and 10.00.


Page 7








Soil pH and Electrical Conductivity


Table 3. Soil texture can be determined by the feel of the soil sample.

Textural Name Description
Sand Loose and single-grained with a gritty feeling when moistened. Not sticky and will not form a
ribbon when pressed between the thumb and index finger. Includes fine sand, loamy sand,
and loamy fine sand.
Sandy Loam Contains sufficient silt and clay to give coherence to the moistened soil. Feels gritty and
slightly sticky. Will not form a ribbon. Includes fine sandy loams.
Clay Loam Forms short ribbons less than 3 cm long. Forms a hard, firm aggregate when dry. Includes
sandy clay loams and silty clay loams.
Clay Extremely sticky and plastic when moist. Easily firms ribbons longer than 3 cm. Includes
sandy clays.
Organic/Mineral Term used in place of a textural class Soil Intergrade for soils that contain up to 500 organic
matter by volume.
Organic Term used for soils that are predominately organic but which may contain up to 50%/ mineral
matter by volume.


The soil scooping technique requires practice,
despite its unsophisticated appearance. The
technique depends upon uniform actions by the
technician from sample to sample to produce
consistent packing of soil into the scoop. This
consistency can be directly measured by repeatedly
scooping the same soil and weighing each scoop.
Weights should be uniform within each scoop
(volume) and soil-sample combination. Weights will
vary from soil to soil, especially when there is a
noticeable difference in soil texture.

A. Sample Handling and Preparation

The sample should be air-dried and passed through a
2-mm sieve before scooping.

B. Procedure

1. Dip the scoop into the center of the soil
sample and fill the scoop with a twisting
motion so that extra soil is mounded above
the rim of the scoop. Do not press the
scoop or force the soil against the side of
the container (Jones, 1980).

2. Strike the handle near the scoop three
times with a plastic rod to settle soil
particles.

3. Level the scoop with the plastic rod. Strike
off all excess soil above the rim of the scoop
in a single stroke so that the soil is not
compacted into the scoop.


II. Estimation of Soil Texture

Knowledge of soil texture is useful in the
recommendation of lime. Local soil conditions may
be quite uniform so that little differences may be
found throughout the county. However, such
uniformity is expected to be rare in most counties.
After the soil has been air-dried and sieved, a small
amount of dry soil should be moistened and rubbed
between the forefinger and thumb. An estimation of
the texture is made by comparing the "feel" of the
sample to that of a set of soil samples of known
texture (Table 3).

III. Soil pH (2:1 V/V)

This procedure uses a 20-cc (~ 25 g) soil scoop
and 40 mL of pure water to obtain a 2:1 water-to-soil
ratio. Most problems with this procedure are
associated with the glass or calomel electrodes.
However, sample pH may also be affected by
contaminated water, by microbial activity if samples
are allowed to sit for several hours before
determining pH, or by improper scooping techniques.

A. Standard Solutions

Obtain commercial standard solutions of pH
4.00, 7.00, and 10.00.


Page 7







Soil pH and Electrical Conductivity


B. Sample Handling and Preparation

The soil sample should be air-dried and passed
through a 2-mm sieve. Irrigation water samples
require no preparation.

C. Procedure

1. One scoop (see Soil Scooping Technique) of
soil to a 3-oz plastic cup using a 20-cc (~ 25-
g) scoop.

2. Add 40 mL of pure water to each cup using
an automatic pipette or suitable volumetric
container. Stir with a glass rod and let the
sample stand for 30 min.

3. Standardize the pH meter (see following
section, pH Meter).

4. Stir the sample again immediately before
measuring the soil pH. Do not place the
electrode(s) directly in the sand layer at the
bottom of the container. The electrodes
should be positioned in the solution just
above the sand layer.

5. Record pH to the nearest 0.1 pH unit
(suggested format of XX.X).

IV. Electrical Conductivity

This test, often called "Soluble Salts," requires
that 20 cc (~ 25 g) of soil be mixed with 40 mL of
pure water, resulting in a water:soil ratio of 2:1. The
4-hr equilibration period provides time for some
slowly-soluble constituents to approach solution
equilibrium. Little error results from much longer
equilibration times, but shorter time periods might
introduce inconsistent results for some samples.

A. Standards

A solution of 0.005 N KCl has an electrical
conductivity of 720 1 dS/m (mmho/cm) at 250C.
Use a commercially prepared solution as the
reference solution.

B. Sample Handling and Preparation

The soil sample should be air-dried and passed
through a 2-mm sieve. Irrigation water samples
require no preparation.


C. Procedure

1. Place 20 cc (-25 g) of soil in a plastic 3-oz
cup.

2. Add 40 mL of pure water, stir, and allow to
stand for 4 h.

3. Without stirring the sample, filter the
solution through a Whatman No. 41 (11 cm)
paper and collect the extract in a funnel tube
or other suitable container. The intent is to
remove the soil and other debris from the
solution.

4. Standardize the conductivity meter (see the
following section on the Conductivity Meter).

5. Move the probe up and down in the solution
several times to dislodge any bubbles on the
electrode surfaces. Measure the electrical
conductivity of the extract contained in the
funnel tube.

6. Rinse the interior and exterior of the probe
with pure water between samples. Remove
any excess water from the exterior of the
probe by blotting with a tissue.

7. Record all meter readings as displayed. Note
that some meters use a floating-point display
while others use a reading which depends
upon a switch setting.

V. pH Meter

Instructions for the proper use of a pH meter,
including electrode care and instrument-specific
settings, are given in this subsection. While
instrument settings may vary among meters, daily
operation of pH meters is relatively standard. Most
problems with pH instruments originate within the
electrode(s) or in the electrical connections to the
instrument. Prevention of early electrode
deterioration is best accomplished by following the
information in sections B and C that follow. Use of
only one standard buffer solution is not adequate for
proper calibration. Do not reuse a buffer solution
which has been left out overnight or has been used to
"store" electrode(s). It is advisable to maintain a
supply of a reference soil sample (See Appendix for
more information) to be used as a check sample with
every set of samples. Early detection of problems is
the best method of avoiding inaccurate results.


Page 8







Soil pH and Electrical Conductivity


B. Sample Handling and Preparation

The soil sample should be air-dried and passed
through a 2-mm sieve. Irrigation water samples
require no preparation.

C. Procedure

1. One scoop (see Soil Scooping Technique) of
soil to a 3-oz plastic cup using a 20-cc (~ 25-
g) scoop.

2. Add 40 mL of pure water to each cup using
an automatic pipette or suitable volumetric
container. Stir with a glass rod and let the
sample stand for 30 min.

3. Standardize the pH meter (see following
section, pH Meter).

4. Stir the sample again immediately before
measuring the soil pH. Do not place the
electrode(s) directly in the sand layer at the
bottom of the container. The electrodes
should be positioned in the solution just
above the sand layer.

5. Record pH to the nearest 0.1 pH unit
(suggested format of XX.X).

IV. Electrical Conductivity

This test, often called "Soluble Salts," requires
that 20 cc (~ 25 g) of soil be mixed with 40 mL of
pure water, resulting in a water:soil ratio of 2:1. The
4-hr equilibration period provides time for some
slowly-soluble constituents to approach solution
equilibrium. Little error results from much longer
equilibration times, but shorter time periods might
introduce inconsistent results for some samples.

A. Standards

A solution of 0.005 N KCl has an electrical
conductivity of 720 1 dS/m (mmho/cm) at 250C.
Use a commercially prepared solution as the
reference solution.

B. Sample Handling and Preparation

The soil sample should be air-dried and passed
through a 2-mm sieve. Irrigation water samples
require no preparation.


C. Procedure

1. Place 20 cc (-25 g) of soil in a plastic 3-oz
cup.

2. Add 40 mL of pure water, stir, and allow to
stand for 4 h.

3. Without stirring the sample, filter the
solution through a Whatman No. 41 (11 cm)
paper and collect the extract in a funnel tube
or other suitable container. The intent is to
remove the soil and other debris from the
solution.

4. Standardize the conductivity meter (see the
following section on the Conductivity Meter).

5. Move the probe up and down in the solution
several times to dislodge any bubbles on the
electrode surfaces. Measure the electrical
conductivity of the extract contained in the
funnel tube.

6. Rinse the interior and exterior of the probe
with pure water between samples. Remove
any excess water from the exterior of the
probe by blotting with a tissue.

7. Record all meter readings as displayed. Note
that some meters use a floating-point display
while others use a reading which depends
upon a switch setting.

V. pH Meter

Instructions for the proper use of a pH meter,
including electrode care and instrument-specific
settings, are given in this subsection. While
instrument settings may vary among meters, daily
operation of pH meters is relatively standard. Most
problems with pH instruments originate within the
electrode(s) or in the electrical connections to the
instrument. Prevention of early electrode
deterioration is best accomplished by following the
information in sections B and C that follow. Use of
only one standard buffer solution is not adequate for
proper calibration. Do not reuse a buffer solution
which has been left out overnight or has been used to
"store" electrode(s). It is advisable to maintain a
supply of a reference soil sample (See Appendix for
more information) to be used as a check sample with
every set of samples. Early detection of problems is
the best method of avoiding inaccurate results.


Page 8








Soil pH and Electrical Conductivity


A. Calibration of Electrode(s)

1. Rinse electrode(s) with pure water and
blot dry with a tissue or clean paper towel.

2. Using commercially prepared buffer
solutions of pH 4.00, 7.00, and 10.0, pour
approximately 30 mL into labeled, 3-oz.
plastic cups. Do not reuse buffer solutions
in which electrode(s) have been immersed
for daily storage.

3. Set the meter to operate in the "pH"
mode.

4. Place the electrode(s) into new buffer
solution (pH 7.00) and allow the
electrode(s) to equilibrate. A stable
reading should be obtained within about 30
seconds. Readings which are not stable
after 1 minute indicate that the
electrode(s) may be malfunctioning.

5. Using the "Calibration" (often labelled
"Standard") knob, adjust the pH-meter
display to read 7.00. Do not move (or
press) either the "Temperature" or "Slope"
adjustments at this time.

6. Place the meter in the "Standby" mode.
Some meters do not have a standby mode.

7. Rinse the electrode(s) into a waste cup
with pure water and blot dry as above.

8. Place the electrode(s) in new buffer
solution (pH 4.00) and allow the
electrode(s) to equilibrate with the buffer
solution.

9. Set the meter to operate in the "pH"
mode.


10. Using the "Temperature" knob (sometimes
labelled "Slope"), adjust the pH-meter
display to read 4.00. Do not readjust the
"Calibration" setting at this time.

11. Repeat Steps 6 through 9 using the pH
10.0 buffer solution. No settings should be
changed as the pH 10.0 buffer is being
read.

12. Repeat Steps 3 through 11 until readings
of 7.00, 4.00, and 10.0 are obtained without
adjusting the instrument. These standards
should be set 0.05.

13. Using a reference soil sample (see
Appendix), read the pH and determine if
the pH reading agrees with the "known"
reading of the reference soil. Use of a
reference soil sample, a soil that can be
analyzed with every sample set, is strongly
recommended. Use of a reference soil is
an excellent quality assurance measure and
verifies that the electrode(s)/meter are
functioning correctly in a soil solution and
not just in standard buffers. The reference
soil sample should be read once about 20
samples. If the reading drifts by more than
0.2, then restandardize the meter.

14. Standardize the instrument according to
the above procedure after every 50
samples. If the instrument has shown drift
of 0.05 pH units or more, reread the last
few samples to verify the accuracy of the
recorded readings.

B. Daily Electrode Storage

1. Place the meter in the "Standby" mode.

2. Wash the electrode(s) with pure water.

3. Immerse the electrode(s) in pH 7.00 buffer
solution.


Page 9







Soil pH and Electrical Conductivity


C. Electrode Servicing

1. If the pH reading drifts, replace the glass
electrode. Wait until the reading from the
new electrode is stable. Usually, new
electrode(s) should be kept in pH 7.00
buffer solution overnight before use.

2. After use, wash the electrode(s) with pure
water.

3. Immerse the electrode(s) in pH 7.00 buffer
solution.

VI. Electrical Conductivity Meter

Conductivity measurements must be made on
solution samples only. The most common problem
with conductivity meters concerns failure of the
electrodes (mounted within the hollow plastic probe)
to make proper contact with the solution. The probe
must be kept clean by adequately flushing the interior
of the probe with pure water. When analyzing a
solution, insure that the solution covers the bottom 3
to 5 cm (1 to 1.5 inches) of the probe. Agitation of
the probe in the unknown and standard solutions is
required to obtain reproducible results. Agitation
insures complete wetting of the internal electrodes by
removing any air bubbles using the solution of
interest.

A. Calibration

1. Turn ON the "Supply" or "Power" switch.

2. Turn OFF the "Temperature Correction"
switch (back panel).

3. Set the "Scale" wafer switch, if any, to read
mmho/cm.

4. Place the conductivity probe into a
standard solution of 0.005 M KC1. Agitate
the probe using an up-and-down movement
to create better solution to probe contact.

5. After agitation, the meter should read 0.72
0.04 mmho/cm (0.72 0.04 dS/m).

6. Agitate the probe again and reread the
standard solution. Both the first and
second readings should be the same value
if the probe is in good contact with the
solution.


7. Wash the probe with pure water on both
inner (inject wash water through the hole
at the top of the probe) and outer surfaces.
Blot the probe dry. Do NOT rub the
outer surface of the probe with the tissue
paper.

8. Read the reference soil sample and verify
that the current reading agrees with the
known value for the reference soil (see
Appendix for suggested acceptable
variation).

9. Occasionally, "EEE" will appear on the
instrument display indicating that the
sample reading exceeds the current scale
setting. Move the "Scale" wafer switch to
the next highest position and reread the
sample. This switch changes the reading
by factors of 10. Note the correct decimal
reading.

10. Record the entire meter reading including
location of the decimal point.

11. Return the "Scale" wafer switch to the
original position before reading the next
sample.

ASSISTANCE FROM THE EXTENSION SOIL
TESTING LABORATORY

The ESTL is available with the following forms
of assistance:

1. A 4-hour In-Service training course is offered by
the Director and Coordinator. This training
course is designed as an on-site aid to all those
county faculty, master gardeners, and other
office personnel that handle or analyze soil and
water samples. Operation of county equipment
is checked using both electronic evaluation as
well as comparison with ESTL equipment on the
same samples.

2. Soil samples used for calibration of local lime
recommendations can be analyzed for soil pH
and Adams-Evans Buffer. This activity should
be scheduled with the Director prior to sending
samples.


Page 10







Soil pH and Electrical Conductivity


C. Electrode Servicing

1. If the pH reading drifts, replace the glass
electrode. Wait until the reading from the
new electrode is stable. Usually, new
electrode(s) should be kept in pH 7.00
buffer solution overnight before use.

2. After use, wash the electrode(s) with pure
water.

3. Immerse the electrode(s) in pH 7.00 buffer
solution.

VI. Electrical Conductivity Meter

Conductivity measurements must be made on
solution samples only. The most common problem
with conductivity meters concerns failure of the
electrodes (mounted within the hollow plastic probe)
to make proper contact with the solution. The probe
must be kept clean by adequately flushing the interior
of the probe with pure water. When analyzing a
solution, insure that the solution covers the bottom 3
to 5 cm (1 to 1.5 inches) of the probe. Agitation of
the probe in the unknown and standard solutions is
required to obtain reproducible results. Agitation
insures complete wetting of the internal electrodes by
removing any air bubbles using the solution of
interest.

A. Calibration

1. Turn ON the "Supply" or "Power" switch.

2. Turn OFF the "Temperature Correction"
switch (back panel).

3. Set the "Scale" wafer switch, if any, to read
mmho/cm.

4. Place the conductivity probe into a
standard solution of 0.005 M KC1. Agitate
the probe using an up-and-down movement
to create better solution to probe contact.

5. After agitation, the meter should read 0.72
0.04 mmho/cm (0.72 0.04 dS/m).

6. Agitate the probe again and reread the
standard solution. Both the first and
second readings should be the same value
if the probe is in good contact with the
solution.


7. Wash the probe with pure water on both
inner (inject wash water through the hole
at the top of the probe) and outer surfaces.
Blot the probe dry. Do NOT rub the
outer surface of the probe with the tissue
paper.

8. Read the reference soil sample and verify
that the current reading agrees with the
known value for the reference soil (see
Appendix for suggested acceptable
variation).

9. Occasionally, "EEE" will appear on the
instrument display indicating that the
sample reading exceeds the current scale
setting. Move the "Scale" wafer switch to
the next highest position and reread the
sample. This switch changes the reading
by factors of 10. Note the correct decimal
reading.

10. Record the entire meter reading including
location of the decimal point.

11. Return the "Scale" wafer switch to the
original position before reading the next
sample.

ASSISTANCE FROM THE EXTENSION SOIL
TESTING LABORATORY

The ESTL is available with the following forms
of assistance:

1. A 4-hour In-Service training course is offered by
the Director and Coordinator. This training
course is designed as an on-site aid to all those
county faculty, master gardeners, and other
office personnel that handle or analyze soil and
water samples. Operation of county equipment
is checked using both electronic evaluation as
well as comparison with ESTL equipment on the
same samples.

2. Soil samples used for calibration of local lime
recommendations can be analyzed for soil pH
and Adams-Evans Buffer. This activity should
be scheduled with the Director prior to sending
samples.


Page 10







Soil pH and Electrical Conductivity


3. Operation of county instrumentation can be
checked at the ESTL. Instrument inspection by
the Coordinator of the ESTL should be done by
appointment.

4. Specific questions from county Extension faculty
regarding pH and EC should be directed to the
Director via IFAS VAX (user identification:
HANLON) or telephone (904 392-1804).

LITERATURE

Hanlon, E.A., G. Kidder, and B.L. McNeal. 1990.
Soil-test interpretations and recommendations. Fla.
Coop. Extn. Ser., IFAS, Univ. of Fla.,
Gainesville, FL. Circular No. 817. 49 pp.

Hanlon, E.A., B.L. McNeal, and G. Kidder. 1993.
Electrical Conductivity Interpretations. Fla. Coop.
Extn. Ser., IFAS, Univ. of Fla., Gainesville, FL.
(In Press).

Jones, Jr., J.B. (ed.). 1980. Handbook on reference
methods for soil testing. Council on Soil Testing
and Plant Analysis, Athens, GA.

APPENDIX

Soil pH Definition

The test for soil pH measures the acidity (pH
less than 7.0) or alkalinity (pH greater than 7.0). If
the pH is equal to 7.0, then it is called neutral. The
pH scale ranges from 1 to 14; however, most soils in
Florida fall between 4 and 8.5. The following
equation defines pH:

Soil pH = -log(H+).

In words, soil pH is equal to the negative
logarithm of the hydrogen ion activity. Activity is
related to concentration and activity is usually
somewhat less than concentration in soil systems.
From a horticultural or agronomic viewpoint, plant
roots are "experiencing" the activity, not the
concentration, effects of the hydrogen ion.


Reference Soil Sample

A reference soil sample is a sample which is
analyzed each time pH and/or EC are analyzed. The
source of the sample should be such that sufficient
volumes can be taken for use by the county
laboratory. A sample of 3 to 5 pounds of air dried
soil can be used for several months by most county
laboratories.

The sample should be completely air dried and
then sieved to pass a 2-mm screen. The sample
should be thoroughly mixed and stored in a dry
location. A working subsample may be kept in the
laboratory conveniently in a cylindrical cardboard
container (e.g., used for ice cream). When the
subsample has been used to the point where the
remainder occupies less than about 1/3 of the
container, it should be refilled from the main sample.

The subsample should be mixed before each use
by inverting the container several times. Mixing
prevents separation of the finer particles from the
coarser particles.

The subsample results should be recorded at
least once per use. The ESTL runs one reference
soil sample for every 20 soil samples. If drift greater
than 0.2 pH units or 0.05 dS/m is noted, then the
instrument should be recalibrated and/or repairs made
before continuing with unknown samples. If
recalibration corrects the problem, several previously
analyzed samples should be re-read to confirm the
observed values. It is the intent of this procedure to
provide high quality pH and EC readings by verifying
that the instruments are reproducing the reference
soil sample values correctly.

ACKNOWLEDGEMENTS

The authors would like to thank J.M. DeVore,
Senior Laboratory Technician, and J.S. Gonzalez,
Chemist, for their efforts in developing and testing
these procedures.


Page 11







Soil pH and Electrical Conductivity


3. Operation of county instrumentation can be
checked at the ESTL. Instrument inspection by
the Coordinator of the ESTL should be done by
appointment.

4. Specific questions from county Extension faculty
regarding pH and EC should be directed to the
Director via IFAS VAX (user identification:
HANLON) or telephone (904 392-1804).

LITERATURE

Hanlon, E.A., G. Kidder, and B.L. McNeal. 1990.
Soil-test interpretations and recommendations. Fla.
Coop. Extn. Ser., IFAS, Univ. of Fla.,
Gainesville, FL. Circular No. 817. 49 pp.

Hanlon, E.A., B.L. McNeal, and G. Kidder. 1993.
Electrical Conductivity Interpretations. Fla. Coop.
Extn. Ser., IFAS, Univ. of Fla., Gainesville, FL.
(In Press).

Jones, Jr., J.B. (ed.). 1980. Handbook on reference
methods for soil testing. Council on Soil Testing
and Plant Analysis, Athens, GA.

APPENDIX

Soil pH Definition

The test for soil pH measures the acidity (pH
less than 7.0) or alkalinity (pH greater than 7.0). If
the pH is equal to 7.0, then it is called neutral. The
pH scale ranges from 1 to 14; however, most soils in
Florida fall between 4 and 8.5. The following
equation defines pH:

Soil pH = -log(H+).

In words, soil pH is equal to the negative
logarithm of the hydrogen ion activity. Activity is
related to concentration and activity is usually
somewhat less than concentration in soil systems.
From a horticultural or agronomic viewpoint, plant
roots are "experiencing" the activity, not the
concentration, effects of the hydrogen ion.


Reference Soil Sample

A reference soil sample is a sample which is
analyzed each time pH and/or EC are analyzed. The
source of the sample should be such that sufficient
volumes can be taken for use by the county
laboratory. A sample of 3 to 5 pounds of air dried
soil can be used for several months by most county
laboratories.

The sample should be completely air dried and
then sieved to pass a 2-mm screen. The sample
should be thoroughly mixed and stored in a dry
location. A working subsample may be kept in the
laboratory conveniently in a cylindrical cardboard
container (e.g., used for ice cream). When the
subsample has been used to the point where the
remainder occupies less than about 1/3 of the
container, it should be refilled from the main sample.

The subsample should be mixed before each use
by inverting the container several times. Mixing
prevents separation of the finer particles from the
coarser particles.

The subsample results should be recorded at
least once per use. The ESTL runs one reference
soil sample for every 20 soil samples. If drift greater
than 0.2 pH units or 0.05 dS/m is noted, then the
instrument should be recalibrated and/or repairs made
before continuing with unknown samples. If
recalibration corrects the problem, several previously
analyzed samples should be re-read to confirm the
observed values. It is the intent of this procedure to
provide high quality pH and EC readings by verifying
that the instruments are reproducing the reference
soil sample values correctly.

ACKNOWLEDGEMENTS

The authors would like to thank J.M. DeVore,
Senior Laboratory Technician, and J.S. Gonzalez,
Chemist, for their efforts in developing and testing
these procedures.


Page 11







Soil pH and Electrical Conductivity


3. Operation of county instrumentation can be
checked at the ESTL. Instrument inspection by
the Coordinator of the ESTL should be done by
appointment.

4. Specific questions from county Extension faculty
regarding pH and EC should be directed to the
Director via IFAS VAX (user identification:
HANLON) or telephone (904 392-1804).

LITERATURE

Hanlon, E.A., G. Kidder, and B.L. McNeal. 1990.
Soil-test interpretations and recommendations. Fla.
Coop. Extn. Ser., IFAS, Univ. of Fla.,
Gainesville, FL. Circular No. 817. 49 pp.

Hanlon, E.A., B.L. McNeal, and G. Kidder. 1993.
Electrical Conductivity Interpretations. Fla. Coop.
Extn. Ser., IFAS, Univ. of Fla., Gainesville, FL.
(In Press).

Jones, Jr., J.B. (ed.). 1980. Handbook on reference
methods for soil testing. Council on Soil Testing
and Plant Analysis, Athens, GA.

APPENDIX

Soil pH Definition

The test for soil pH measures the acidity (pH
less than 7.0) or alkalinity (pH greater than 7.0). If
the pH is equal to 7.0, then it is called neutral. The
pH scale ranges from 1 to 14; however, most soils in
Florida fall between 4 and 8.5. The following
equation defines pH:

Soil pH = -log(H+).

In words, soil pH is equal to the negative
logarithm of the hydrogen ion activity. Activity is
related to concentration and activity is usually
somewhat less than concentration in soil systems.
From a horticultural or agronomic viewpoint, plant
roots are "experiencing" the activity, not the
concentration, effects of the hydrogen ion.


Reference Soil Sample

A reference soil sample is a sample which is
analyzed each time pH and/or EC are analyzed. The
source of the sample should be such that sufficient
volumes can be taken for use by the county
laboratory. A sample of 3 to 5 pounds of air dried
soil can be used for several months by most county
laboratories.

The sample should be completely air dried and
then sieved to pass a 2-mm screen. The sample
should be thoroughly mixed and stored in a dry
location. A working subsample may be kept in the
laboratory conveniently in a cylindrical cardboard
container (e.g., used for ice cream). When the
subsample has been used to the point where the
remainder occupies less than about 1/3 of the
container, it should be refilled from the main sample.

The subsample should be mixed before each use
by inverting the container several times. Mixing
prevents separation of the finer particles from the
coarser particles.

The subsample results should be recorded at
least once per use. The ESTL runs one reference
soil sample for every 20 soil samples. If drift greater
than 0.2 pH units or 0.05 dS/m is noted, then the
instrument should be recalibrated and/or repairs made
before continuing with unknown samples. If
recalibration corrects the problem, several previously
analyzed samples should be re-read to confirm the
observed values. It is the intent of this procedure to
provide high quality pH and EC readings by verifying
that the instruments are reproducing the reference
soil sample values correctly.

ACKNOWLEDGEMENTS

The authors would like to thank J.M. DeVore,
Senior Laboratory Technician, and J.S. Gonzalez,
Chemist, for their efforts in developing and testing
these procedures.


Page 11















































UNIVERSITY OF

SFLORIDA
The Institute of Food and Agricultural Sciences is an equal opportunity/affirmative action employer authorized to provide
research, educational information and other services only to Individuals and institutions that function without regard to race,
color, sex, age, handicap, or national origin. For information on obtaining other Extension publications, contact your county
Cooperative Extension Service office. Florida Cooperative Extension Service/Institute of Food and Agricultural
Sciences/University of Florida/John T. Woeste, Dean.




University of Florida Home Page
© 2004 - 2010 University of Florida George A. Smathers Libraries.
All rights reserved.

Acceptable Use, Copyright, and Disclaimer Statement
Last updated October 10, 2010 - - mvs