SEALNET | Asian Soil Laboratory Network: 3rd meeting. Manila, Philippines, 23 - 27 September 2019. Presenter: Ms.Nilo

1. Soil Electrical Conductivity (SEC)
(soil/water, 1:5)
GLOSOLAN-SOP-EC/01
Gina P. Nilo, Ph.D.
Philippines

2. Brief Background
What is Electrical Conductivity?
• Conductivity (or specific conductance) of an electrolyte solution is a
measure of its ability to conduct electricity.
• Specific conductance is determined using an electrical resistance
(Wheatstone) bridge, commonly referred to as either a conductance
or a conductivity meter. Specific conductance of a solution is the
conductance that is measured at 25°C (77°F) between electrodes 1
cm3 in surface area and placed 1 cm apart.
• Most meters currently measure conductivity directly.
• SI unit for EC is S/m or as dS/m
Source:
1. Rhoades, J.D. (1996). Salinity: Electrical Conductivity and Total Dissolved Solids In D.L. Sparks (Ed.-in-Chief), Soil Science Society of America, Book Series
5. Methods of Soil Analysis Part 3, Chemical Methods. Madison, Wisconsin: Soil Science Society of America, Inc.
2. J.Benton Jones, Jr.(2001) Laboratory Guide For Conducting Soil Test and Plant Analysis, MS 2458:2012 Determination of Specific Electrical Conductivity,
H.F Yeoh, Working Manual for Plant Analysis, Soil and Analytical Services, Manual No.4,

3. Common Procedures/Steps
among SEALNET member
countries

4. Country Particle size (mm)
Bangladesh ≤ 2
Bhutan ≤ 2
Cambodia ≤ 2
China ≤ 2
India - ICRISAT
- ICAR-IISS
≤ 2
≤ 2
Indonesia ≥ 2
Japan ≤ 2
Laos ≤ 2
Malaysia 0.595
Myanmar ≤ 2
Nepal ≤ 2
Pakistan ≤ 2
Philippines ≤ 2
Thailand - Katserat University
- LDD
≤ 2
≤ 2
Vietnam ≤ 2
Soil Particle Size (mm)
Sample Particle
Size:
≤ 2 mm

5. Country Deionized Water or
Distilled Water
pH EC
Bangladesh distilled 5.2 0.02 dS/m
Bhutan slightly acidic - -
Cambodia - 6.5-6.8 2-4 uS/cm
China distilled - ≤ 0.2 mS/m
India - ICRISAT
- ICAR-IISS
distilled
distilled
-
-
-
-
Indonesia - 7.0 < 1.5 dS/m
Japan - - -
Laos distilled 6.5-7.4 < 3 uS/cm
Malaysia - - 0.182 dS/m
Myanmar - 6.56 0.882 mS/cm
Nepal double distilled - -
Pakistan - 6.5-8.5 < 10 uS/cm
Philippines deionized - -
Thailand - Katserat Univ.
- LDD
-
-
-
> 5.6
-
≤ 2.0 uS/cm
Vietnam - - < 0.2 mS/m
Quality of Water
Used
Most labs used
Distilled water
(Type III water)

6. Country Sample
weight (g)
Vol Water
(mL)
EC
(soil/water ratio)
Bangladesh 10 50 1:5
Bhutan 20 50 1:2.5
Cambodia 10 50 1:5
China 20 100 1:5
India - ICRISAT
- ICAR-IISS
20
20
40
40
1:2
1:2
Indonesia 10 50 1:5
Japan 10 50 1:5
Laos 10 50 1:5
Malaysia 10 50 1:5
Myanmar 10 50 1:5
Nepal 25 50 1:2
Pakistan 20 50 1:2.5
Philippines 20 20 1:1
Thailand - Katserat Univ.
- LDD
10
10
50
50
1:5
1:5
Vietnam 20 100 1:5
Soil EC (soil/water ratio)
soil/water: Ratio 1:5
Sample wt. – 10g
Water vol. – 50mL

7. Country Shaking Time
(min.)
Standing Time
(min.)
Bangladesh 30 30
Bhutan 60 -
Cambodia 30 10
China 3 hrs 30
India - ICRISAT
- ICAR-IISS
30 30
60 60
Indonesia 30 30
Japan 60 0
Laos 60 30
Malaysia 60 30
Myanmar 60 30
Nepal 60 30
Pakistan Intermittent
stirring for 10 min
Overnight
Philippines 60 30
Thailand - Katserat Univ.
- LDD
1 30
60 30
Vietnam 30 30
Shaking and Standing Time
Shaking Time – 60 min.
Standing Time– 30 min.

8. Country Calibration Standards Reference Materials
used
Bangladesh 147 & 1413 uS/cm (NIST) CRM & Check sample
Bhutan KCl soln. Check Sample
Cambodia 1413 uS/cm (NIST) -
China KCl soln. Check Sample
India - ICRISAT
- ICAR-IISS
1413 uS/cm KCl soln. Check sample (internal)
1413 uS/cm KCl soln. -
Indonesia 1413 uS/cm KCl soln. Check sample
Japan 140.9 mS/m KCl soln. -
Laos 1413 uS/cm (NIST) Check sample
Malaysia 1413 uS/cm (NIST) Check sample
Myanmar 1410-1430 uS/cm KCl soln. Check sample
Nepal 0.01N KCl Local control sample
Pakistan 1413 uS/cm KCl soln. -
Philippines 147 & 1413 uS/cm (NIST) CRM & Check sample
Thailand - Katserat Univ.
- LDD
1413 uS/cm (NIST) Check sample (internal)
1413 & 12880 uS/cm (NIST) Check sample (internal)
Vietnam 147 & 1413 uS/cm (NIST) CRM & Check Sample
Calibration Standards and
Reference Materials used
Calibration Standard –
147 & 1413 uS/cm (NIST)
Reference Materials –
CRM & Check Sample
Note:
1. Use of prepared KCl solution is optional, however, readily
available NIST standard solution is better for traceability.
2. Check sample – preparation should follow ISO Guide 80

9. Country Quality Control Measures
Bangladesh Duplicate in every 10 samples
Bhutan Calibration of EC meter & internal proficiency testing
Cambodia -
China Blanks, duplicate analysis & PT participation
India - ICRISAT
- ICAR-IISS
Internal standards in set of 50 samples & duplicate analysis
Duplicate in every 10 samples w/ %RSD
Indonesia Duplicate in every 20 samples w/ %RSD & PT participation
Japan Measure in duplicate and calculation of average value
Laos Duplicate w/ % RSD, Control Chart & PT participation
Malaysia Duplicate w/ % RSD, Control Chart & PT participation
Myanmar Duplicate analysis & participation in ring test
Nepal Using of 2 local control samples (check sample)
Pakistan Inter-lab comparison
Philippines Duplicate w/ % RSD, Control Chart & PT participation
Thailand - Katserat Univ.
- LDD
PT participation
Duplicate w/ % RPD, Control Chart & PT participation
Vietnam Duplicate analysis
Quality Control Measures
Duplicate w/ % RSD, Control Chart
& PT participation
Note:
1. QC measures employed will vary with the QC/QA procedures
implemented by the laboratories.

10. Country Report Unit No. of decimals
Bangladesh dS/m 1
Bhutan mS/cm 2
Cambodia uS/m 2
China mS/cm 3 valid digit
India - ICRISAT
- ICAR-IISS
dS/m 2
dS/m 2
Indonesia dS/m 2
Japan mS/cm 2
Laos uS/cm, mS/cm 2
Malaysia mS/cm 2
Myanmar dS/m 2
Nepal mS/cm 2
Pakistan dS/m 2
Philippines mS/cm 2
Thailand - Katserat Univ.
- LDD
dS/m 2
dS/m 2
Vietnam mS/m 2
Report Unit & No. of
decimal
Report Unit – dS/m
No. of decimal - 2
Note:
1 dS/m = 1mS/cm

11. Comparison of Common Steps/Procedures with
International References
Please click this link

12. Factors Affecting Analysis of Soil Electrical Conductivity
1. Sample particle size
2. Laboratory reagent water
3. Reaction Temperature
4. Soil/water ratio
5. Environment

13. Soil EC – Sample Particle Size (≤2 mm)
• Following drying, the soil sample is crushed, either by hand or by using a
mechanical device and then passed through a 10-mesh (2-mm)screen
(Anonymous, 1994a).
• Sieving through a 10-mesh (2-mm) screen removes stones and other
extraneous substances, yielding a uniform sample that can be easily
handled in the laboratory and stored indefinitely.
• Particle size reduction can have an effect on some elemental
determinations, as discussed by Kahn (1979) for the determination of
Cu, Fe, and Zn and by Houba et al. (1993) for equilibrium extraction
reagent procedures.

14. Standard Sieve Sizes

15. Types of Laboratory Reagent Water
Type/Grade Description
I
(Ultra pure)
• Essentially free from dissolved or colloidal ionic and organic contaminants and suitable
for the most stringent analytical requirements including high-performance liquid
chromatography.
• Production of reagents for molecular biology applications (DNA sequencing, PCR).
Preparation of solutions for electrophoresis and blotting.
II
(deionized)
• Very low in inorganic, organic or colloidal contaminants and suitable for sensitive
analytical purposes, including AAS and the determination of constituents in trace
quantities; should be produced, for example, by multiple distillation , or by deionization
or reverse osmosis followed by distillation.
• Used in buffers, pH solutions and microbiological culture media preparation and for
preparation of reagents for chemical analysis.
III
(Distilled)
• Suitable for most laboratory wet chemistry work and preparation of reagent solutions,
should be produced , for example, by single distillation or by reverse osmosis
• Used for glassware rinsing, filling autoclaves and heating baths and humidifiers.
Source: ISO 3696:1987 – Water for analytical laboratory use – Specification and test methods

16. Different Standards for Laboratory Reagent Water
ISO 3696:1987 Standard
0.001 dS/m 0.005 dS/m0.0001 dS/m

17. Different Standards for Laboratory Reagent Water
0.001 dS/m 0.000025 dS/m0.000056 dS/m

18. Effect of Reaction Temperature
• Electrolytic conductivity (unlike metallic conductivity) increases with temperature
at a rate of approximately 1.9 % per degree Centigrade.
• Since each ion has a different temperature coefficient, for precise work,
conductivity ideally should be determined at 25 °C.
• EC can be measured at other known temperatures and corrected to the 25 °C
reference using appropriate temperature coefficients (usually based on NaCl).
• Most meters measure conductivity directly and can be automatically
compensated at 25 °C.
Source: Rhoades, J.D. (1996). Salinity: Electrical Conductivity and Total Dissolved Solids In D.L. Sparks (Ed.-in-Chief), Soil Science Society
of America, Book Series 5. Methods of Soil Analysis Part 3, Chemical Methods. Madison, Wisconsin: Soil Science Society of America, Inc.,
p. 423

19. Effects of soil/water ratio
• The extraction ratios (1:1, 1:5, etc.) are easier to make than that of saturation,
but they are less well related to field soil water composition and content. More
importantly, salinity and compositional errors from dispersion, hydrolysis,
cation exchange, and mineral dissolution increase as the water/soil ratio
increases (Reitemeier, 1946).
• As a compromise, Sonnevelt and van den Ende (1971) recommended a 1:2 (1
part soil = 2 parts water) volume extract, since it is closer to the saturation
extract ratio but quicker to make.
• The extraction procedure (soil/water ratio) chosen will yield different
interpretative results; therefore, it is important that the interpretation values
chosen are appropriate to the extraction procedure employed (J.Benton Jones,
Jr., 2001).
Conclusion:
The soil/water ratio to be chosen should be widely used and already has established
interpretation values.

20. Environment effects
• Exposure of the saturated soil sample or extracting solution to the
atmosphere may cause changes in conductivity due to loss or gain of
dissolved gasses: CO2 and NH3-N.
• The EC should be measured as soon as the extracts are prepared
because of possible changes in ionic content due to microbial activity
during storage at room temperature. If needed, however, extracts can
be stored for a week under refrigeration (4°C) before measuring
EC.
Source: Estefan, G., R. Sommer and J. Ryan. (2013). Methods of soil, plant, and water analysis. A manual for the West Asia and North
Africa region. 2.Motsara, M. R. and R. N., Roy. (2008). Guide to laboratory establishment for plant nutrient analysis (Vol. 19). Rome: Food
and Agriculture Organization of the United Nations, p. 68

21. Thanks for your attention