Water and Soil Characterization - pH and Electrical Conductivity (2022)

Created by Monica Z. Bruckner, Montana State University, Bozeman

What Are pH and Electrical Conductivity?

Water and Soil Characterization - pH and Electrical Conductivity (1)

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(Video) EC Measurements Over the Years

Davis Mine was originally used to extract pyrites. The waters of the emerging stream are acidic and rich in iron compounds which are then exploited by various bacteria that produce oxidized iron compounds with the typical orange/brown color. The image of the site was provided by Cristine Barreto, courtesy of the microscope web site.

It is often useful to characterize an environment, such as a body of water, by measuring its pH and electrical conductivity (EC). pH is a measure of the acidity of the water or soil based on its hydrogen ion concentration and is mathematically defined as the negative logarithm of the hydrogen ion concentration, or

pH = -log[H+], where the brackets around the H+ symbolize "concentration"

The pH of a material ranges on a logarithmic scale from 1-14, where pH 1-6 are acidic, pH 7 is neutral, and pH 8-14 are basic. Lower pH corresponds with higher [H+], while higher pH is associated with lower [H+].

Electrical conductivity (EC) is a measurement of the dissolved material in an aqueous solution, which relates to the ability of the material to conduct electrical current through it. EC is measured in units called Seimens per unit area (e.g. mS/cm, or miliSeimens per centimeter), and the higher the dissolved material in a water or soil sample, the higher the EC will be in that material.

How Are pH and Electrical Conductivity Measured?

A meter and probe or litmus paper can be used to measure the pH of a sample. The more accurate, but expensive, of these methods is the meter and probe. pH meters are calibrated using special solutions, or buffers with a known pH value. Calibration protocols can be found in manufacturer's instructions, but a simplified protocol can also be found.

Using litmus or pH paper is the simpler and less expensive way of measuring pH. This method employs special strips of paper that change color based on the pH of a sample solution. The strips come in a variety of resolutions, from simple acid vs. base comparison to a narrow resolution of pH values. These strips of paper can measure the difference 0.2-0.3 pH in a sample. Litmus paper changes color based on whether the sample solution is acidic or basic, turning red or blue, respectively. pH strips indicate a sample's pH by changing color as well; these colors are indicated on the package and vary for different pH ranges and manufacturers.

(Video) Characterization of problem soils based on pH EC ESP SAR #problemsoil #soilreaction #soilph

Electrical conductivity can be measured using a meter and probe as well. The probe consists of two metal electrodes spaced 1 cm apart (thus the unit of measurement is microSeimens or milliSeimens per centimeter). A constant voltage is applied across the electrodes resulting in an electrical current flowing through the aqueous sample. Since the current flowing through the water is proportional to the concentration of dissolved ions in the water, the electrical conductivity can be measured. The higher the dissolved salt/ion concentration, the more conductive the sample and hence the higher the conductivity reading.

How To - Protocols and Concerns for pH and EC Measurements

The following are general protocols for measuring pH and EC. Manufacturer's instructions and guidelines should be followed, if available.

Water and Soil Characterization - pH and Electrical Conductivity (2)

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(Video) Importance and Calculation of PBS, ESP, SAR and RSC

These pH strips can measure pH in a series of ranges by putting sample on a strip and comparing its color change with colors on the box that correspond to a certain pH. The strip on the left measures pH 0-7 and shows results of a strong acid sample; the center strip is pH range 5-10 and shows results of a 6.97 buffer solution sample; the strip on the right measures a broad range (pH 1-14) and shows results of a 10% bleach water solution sample. This image can be enlarged by clicking on it. Photo by Monica Bruckner.

Measuring pH using litmus paper or pH strips:

  1. Place a droplet of sample on the paper - be sure you drop or pour the sample over the paper rather than dipping the paper into the sample, as the latter may contaminate the sample.
  2. Observe color change on the paper. If using litmus paper the paper will turn a red or pink color if the sample is acidic, while a blue paper indicates a basic sample. If using pH strips, colors corresponding to pH values should be listed on the packaging.


Measuring pH of a liquid using a pH meter and probe:

  1. Turn on the pH meter and calibrate the probe using two standard solutions (pH 4, 7, and 10 buffers are recommended, dependant on the range you are measuring). Calibration procedures vary by instrument, so following the manufacturer's instructions is highly recommended. BE SURE TO RINSE THE PROBE THOROUGHLY BETWEEN BUFFERS USING DEIONIZED WATER AND CAREFULLY BLOT THE PROBE DRY USING A KIM WIPE. pH meters should be calibrated before each use (before each series of samples, not between each sample itself) or when measuring a large range of pH.
  2. Check calibration by measuring the pH of the standard solutions in measure rather than calibrate mode.
  3. Collect sample water in a glass or plastic container. Collect enough so the probe tip can be submerged in sample; either rinse the probe with deionized water (and blot dry) or with sample before inserting the probe into the collection vessel.
  4. Submerge the probe into the sample and wait until the pH reading on the meter stabilizes. Many meters have automatic temperature correction (ATC), which calculates the pH taking into account temperature, if your meter does not have this feature, you may need to adjust a knob on the meter to correct the pH for temperature. Record the measurement when the pH reading is stable.


Measuring EC of a liquid sample using a meter and probe:

Water and Soil Characterization - pH and Electrical Conductivity (3)

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These three meters and probes can measure pH (left) and electrical conductivity (center and right). The image can be enlarged if you click on it. Photo by Monica Bruckner.

(Video) pH, EC and TDS of water samples

  1. Turn on the EC meter and calibrate the probe using a standard solution of known conductivity (choose a standard close to what you believe the sample is). Calibration procedures vary by instrument, so following the manufacturer's instructions is highly recommended. BE SURE TO RINSE THE PROBE THOROUGHLY BEFORE AND AFTER CALIBRATION USING DEIONIZED WATER AND CAREFULLY BLOT THE PROBE DRY USING A KIM WIPE. EC meters should be calibrated before each use (before each series of samples, not between each sample itself) or when measuring a large range of EC.
  2. Check calibration by measuring the EC of the standard solutions in measure rather than calibrate mode.
  3. Collect sample water in a glass or plastic container. Collect enough so the probe tip can be submerged in sample; either rinse the probe with deionized water (and blot dry) or with sample before inserting the probe into the collection vessel.
  4. Submerge the probe into the sample and wait until the EC reading on the meter stabilizes. Many meters have automatic temperature correction (ATC), which calculates the EC taking into account temperature, if your meter does not have this feature, you may need to adjust a knob on the meter to correct the EC for temperature. Record the measurement when the EC reading is stable.


Measuring soil pH:

Soil pH can be measured using a pH meter (usually mixing the soil sample with water or a salt solution) or by adding a dye to the soil and observing a color change that can be compared with a chart for pH determination. The latter method can be done using a kit that contains the necessary chemicals. For more information on measuring soil pH and why soil pH matters, please visit The NRCS Soil pH website.

(Video) How to Measure Conductivity of the given solution with Conductivity Meter. || RathoreSliet ||

Measuring soil EC:

Soil EC can be measured via electrodes inserted directly into the ground or by extracting soil water using a lysimeter (an instrument that uses suction to extract soil or groundwater from the ground. EC of groundwater can also be measured using a probe inserted into a well (a perforated tube inserted into the ground that can measure water table height) or piezometer (a tube only open at the bottom that measures the water potential at the depth where the opening is located). The electrode method employs a special series of probes, two of which send electrical current through the soil and two of which measure the voltage drop. To measure soil water EC, water is extracted from a lysimeter, well, or piezometer and measured. Alternately, a probe attached to a meter can be lowered into a well or piezometer and the liquid EC can be measured in that manner.

Results Analysis

pH and EC measurements can vary greatly and are affected by several environmental factors including, climate, local biota (plants and animals), bedrock and surficial geology, as well as human impacts on the land. Common values of pH and EC for particular environments can be found in the literature, such as peer-reviewed journal articles or textbooks. In general, pH readings between 1-6 are considered acidic, 7 is neutral, and 8-14 are basic. Relatively dilute waters, such as distilled water or glacial melt water have low electrical conductivities, ranging from zero to the microSeimen range, whereas temperate streams and lakes, especially those with a significant groundwater contribution, generally have higher electrical conductivities.

Related Links

  • LakeAccess.org Electrical Conductivity Information (link down) - this site provides general information about electrical conductivity, including what it is, what affects EC, and how it is measured.
  • LakeAccess.org pH Information (link down)- this site provides general information about pH, including what it is, what affects pH, and how it is measured.
  • University of Washington pH Protocol - this site, from the University of Washington, provides a protocol for measuring pH.
  • NRCS Soil Taxonomy Measurements - this NRCS website provides information regarding the measurement of soil pH.

Teaching Activities

  • Measuring pH in Liquid Samples and Measuring pH in Soil Samples - these activities, from GLOBE.gov, provide laboratory activities that measure pH in soil and liquid samples, respectively.
  • Waterwatch Teacher Education Resources - this website provides a variety of information and links to further information, including curriculum resources, CD-ROM and on-line resources, Waterwatch manuals, equipment, factsheets, and videos.
  • Changes in Conductivity Teacher's Guide - this PDF teacher's guide, from UIUC, provides a laboratory activity (with background information) involving the measurement of electrical conductivity from freshwater systems. The activity is intended for grades 10-12.
  • Field Methods Laboratory Activities - this resource, from the University of Texas at Dallas, provides a series of laboratory activities/protocols that involve measuring various parameters such as water temperature, pH, EC, dissolved oxygen, and turbidity.

FAQs

What is the relationship between soil pH and electrical conductivity? ›

According to Bruckner (2012), lower soil pH indicates larger number of hydrogen ions in the soil. Hydrogen ions can appear in varying amount in the soil environment which can affect the level of electrical conductivity. Higher amount of hydrogen ions in the soil will show a higher rate of electrical conductivity.

How is electrical conductivity measured in soil samples? ›

This is the traditional way to measure EC. It is measured by taking a soil sample, making a saturated paste of soil and deionized water, extracting the water, and then measuring the EC of the extracted solution. Published EC values reported in the literature are almost always saturation extract EC.

Why Different soils have different soil EC and pH? ›

pH and EC measurements can vary greatly and are affected by several environmental factors including, climate, local biota (plants and animals), bedrock and surficial geology, as well as human impacts on the land.

How will you determine the electrical conductivity in soil water suspension? ›

The electrical conductivity indicates the amount of soluble (salt) ions in soil. The determination of electrical conductivity (EC) is made with a conductivity cell by measuring the electrical resistance of a 1:5 soil:water suspension. Conductivity meter and cell. Shaking bottles.

What is the ideal electrical conductivity of soil? ›

The optimal EC value for plant growth is usually between 0.8-1.8, and should not exceed 2.5.

What affects electrical conductivity of water? ›

Conductivity in water is affected by the presence of inorganic dissolved solids such as chloride, nitrate, sulfate, and phosphate anions (ions that carry a negative charge) or sodium, magnesium, calcium, iron, and aluminum cations (ions that carry a positive charge).

How do you measure pH and EC in soil? ›

Take the meter readings

Measure pH: Remove the electrode cap from the pH meter and switch on. Dip the electrode 1-2 cm into the solution and stir. Wait for the display to stabilise, then record the reading in the record sheet. Rinse the electrode in distilled water between each sample.

How do you convert pH to conductivity? ›

How to Use Calculated pH from Conductivity to Validate ... - YouTube

Why do we measure electrical conductivity of soil? ›

Soil electrical conductivity (EC) is a measure of the amount of salts in soil (salinity of soil). It is an excellent indicator of nutrient availability and loss, soil texture, and available water capacity.

Why do we measure EC and pH? ›

Testing for pH and electrical conductivity (EC) is essential to success in agricultural production systems. Together, the two are easily measured and can provide vital information on the growing media, hydroponic substrates and other crop inputs being used.

What factors affect the electrical conductivity of the soil? ›

Several important factors that affect the EC value of the soil include temperature, amount of fertilizers, salinity, moisture level, irrigation and types of soil. For the case of temperature [11], as the water temperature in the paddy field increases, the soil EC increases and vice versa.

What increases soil conductivity? ›

Adding organic matter, such as manure and compost, increases EC by adding cations and anions and improving the water-holding capacity. In some cases, a combination of irrigation and drainage is necessary to lower salt concentration and EC. An EC water (ECw) ≤ 0.75 dS/m is considered good for irrigation water.

How does electrical conductivity affect plant growth? ›

In general, higher EC hinders nutrient uptake by increasing the osmotic pressure of the nutrient solution, wastes nutrients, and the increases discharged of nutrients into the environment, resulting in environmental pollution. Lower EC may severely affect plant health and yield [2, 9].

What is the procedure for electrical conductivity? ›

Conductivity is measured as microSiemens per cm (μS/ cm). This is the same unit as a micromho, mho. To convert the electrical conductivity of a water sample (μS/cm) into the approximate concentration of the total dissolved solids (ppm) in the sample, you must multiply the conductivity (μS/cm) by a conversion factor.

How do you measure EC in water? ›

EC water conductivity test equipment can be used in the field to take direct measurements of water. The probe that is inserted into the water sample applies a voltage between electrodes. The drop in voltage measures the resistance of water, which is converted to conductivity.

What is the electrical conductivity of water? ›

High quality deionized water has a conductivity of about 0.05 μS/cm at 25 °C, typical drinking water is in the range of 200–800 μS/cm, while sea water is about 50 mS/cm (or 50,000 μS/cm).

What is pH level of soil? ›

Most soils have pH values between 3.5 and 10. In higher rainfall areas the natural pH of soils typically ranges from 5 to 7, while in drier areas the range is 6.5 to 9. Soils can be classified according to their pH value: 6.5 to 7.5—neutral.

Does conductivity affect pH? ›

Conductivity means the amount of electricity a substance of unit mass and area allows passing through it however, there is no relation between pH and conductivity, as pH is related to the number of hydrogen ions per molecule of an acid/base and conductivity depends on free electrons.

Why is electrical conductivity important in water? ›

The reason that the conductivity of water is important is because it can tell you how much dissolved substances, chemicals, and minerals are present in the water. Higher amounts of these impurities will lead to a higher conductivity.

What happens if conductivity of water increases? ›

Ions increase the water's ability to conduct electricity. Common ions in water that conduct electrical current include sodium, chloride, calcium, and magnesium. Because dissolved salts and other inorganic chemicals conduct electrical current, conductivity increases as salinity increases.

How can we remove conductivity from water? ›

To reduce conductivity, we have to remove the DS (Dissolved solids) by Ion exchanger or RO (Reverse Osmosis) or Distillation.

What is the difference between pH and conductivity? ›

pH is the measurement of a specific ion (i.e. hydrogen), whereas electrical conductivity is a non-specific measurement of the concentration of ions within a sample. Electrical conductivity is measured by conductance between two or four electrodes using amperometric or potentiometric methods.

How is conductivity of water calculated? ›

For water for agricultural and irrigation purpose the values for EC and TDS are related to each other and can be converted with an accuracy of about 10% using the following equation: TDS (mg/l) = 640 x EC (ds/m or mmho/cm).

What is water pH level? ›

In its purest form, water has a pH of 7, which is at the exact center of the pH scale. Particles in the water can change the pH of the water, and most water for use has a pH of somewhere between 6.5 and 8.5. There are some important things to understand about the pH scale and how it relates to water.

What are the uses of measuring electrical property of soil? ›

The applications of the methods included studying soil water retention, compaction, and soil morphology; mapping soil spatial variability within fields, catenas, or landscapes; locating genetic horizons, compacted or disturbed layers, hydrocarbon pollutants, stones, and groundwater tables in soil profiles; and ...

What is the name of the instrument used to measure conductivity? ›

An electrical conductivity meter (EC meter) measures the electrical conductivity in a solution. It has multiple applications in research and engineering, with common usage in hydroponics, aquaculture, aquaponics, and freshwater systems to monitor the amount of nutrients, salts or impurities in the water.

How do you raise and lower EC in water? ›

To reduce the EC value, clean water is added to the water tank. To increase the EC value, nutrients are added to the water tank. If the EC value of water rises during time, it is a sign that plants are unable to use nutrients in water. This may be due to the wrong nutrients or wrong pH value of the water.

What is the EC of acidic soil? ›

pH < 8.5. EC > 4.0 m. mhos/cm. ESP < 15.

How do you reduce EC? ›

In soil, the logic is the same - dilution is key to lowering your EC. Simply add pH-balanced water; in the case of growing in pots or containers, water until fully saturated and then allow to drain. You would then measure the EC of the run-off.

What are the factors that affects the conductivity of solution? ›

There are three main factors that affect the conductivity of a solution: the concentrations of ions, the type of ions, and the temperature of the solution.
...
Testing Conductivity
  • The concentration of dissolved ions. ...
  • The types of ions in solution. ...
  • Temperature.
29 Jan 2018

Is soil a good conductor of electricity? ›

Soils are electric current conductors, being usually clay soils, with finer particles and with greater points of contact between them, higher conductors when compared to sandy soils, with coarser particles and therefore with smaller points of contact between them.

Is Wet soil more conductive than dry soil? ›

Therefore, a dry soil will have lower conductivity or soil EC than a wet soil. Porosity – Porosity can impact the conduction of electrical current in the soil by providing more space for water. Therefore, higher soil porosity increases the potential of conducting electricity when wet.

When the soil becomes less acidic does the pH increase or decrease? ›

The pH scale goes from 0 to 14 with pH 7 as the neutral point. As the amount of hydrogen ions in the soil increases the soil pH decreases thus becoming more acidic. From pH 7 to 0 the soil is increasingly more acidic and from pH 7 to 14 the soil is increasingly more alkaline or basic.

What does low soil EC mean? ›

Too low EC levels indicate low available nutrients, and too high EC levels indicate an excess of nutrients. Low EC's are often found in sandy soils with low organic matter levels, whereas high EC levels are usually found in soils with high clay content.

Is High EC good for plants? ›

High electrical conductivity (EC) in the growing medium makes it harder for roots to take up nutrients and water–it is like trying to grow plants in sea water and can result in “salt burn” (damage to sensitive root tips) and toxicity symptoms in foliage (Figure 1).

What is the principle of conductivity? ›

Conductivity is the ability of a material to conduct electric current. The principle by which instruments measure conductivity is simple—two plates are placed in the sample, a potential is applied across the plates (normally a sine wave voltage), and the current that passes through the solution is measured.

What are the uses of electrical conductivity measurements? ›

Electrical conductivity measurement is applied to the production process for both quality control and quality assurance. Specifically, it is used to determine how well a material can conduct an electrical current.

What is EC in water quality? ›

Electrical conductivity (EC) is a measurement of water's ability to conduct electricity. EC is related to water temperature and the total concentration, mobility, valence and relative concentration of ions. Generally speaking, higher EC means more electrolytes in the water.

What does low electrical conductivity in water mean? ›

Conductivity Change Can Indicate Pollution

A sudden increase or decrease in conductivity in a body of water can indicate pollution. Agricultural runoff or a sewage leak will increase conductivity due to the additional chloride, phosphate and nitrate ions 1.

What increases electrical conductivity in soil? ›

Soils that have a higher content of smaller soil particles (higher content of clay) conduct more electrical current than do soils that have a higher content of larger silt and sand particles (lower content of clay).

What affects soil electrical conductivity? ›

Several important factors that affect the EC value of the soil include temperature, amount of fertilizers, salinity, moisture level, irrigation and types of soil. For the case of temperature [11], as the water temperature in the paddy field increases, the soil EC increases and vice versa.

What is the difference between pH and conductivity? ›

pH is the measurement of a specific ion (i.e. hydrogen), whereas electrical conductivity is a non-specific measurement of the concentration of ions within a sample. Electrical conductivity is measured by conductance between two or four electrodes using amperometric or potentiometric methods.

How do you convert pH to conductivity? ›

How to Use Calculated pH from Conductivity to Validate ... - YouTube

How do you measure pH and EC in soil? ›

Take the meter readings

Measure pH: Remove the electrode cap from the pH meter and switch on. Dip the electrode 1-2 cm into the solution and stir. Wait for the display to stabilise, then record the reading in the record sheet. Rinse the electrode in distilled water between each sample.

What is pH level of soil? ›

Most soils have pH values between 3.5 and 10. In higher rainfall areas the natural pH of soils typically ranges from 5 to 7, while in drier areas the range is 6.5 to 9. Soils can be classified according to their pH value: 6.5 to 7.5—neutral.

What is the electrical conductivity of water? ›

High quality deionized water has a conductivity of about 0.05 μS/cm at 25 °C, typical drinking water is in the range of 200–800 μS/cm, while sea water is about 50 mS/cm (or 50,000 μS/cm).

How does electrical conductivity affect plant growth? ›

In general, higher EC hinders nutrient uptake by increasing the osmotic pressure of the nutrient solution, wastes nutrients, and the increases discharged of nutrients into the environment, resulting in environmental pollution. Lower EC may severely affect plant health and yield [2, 9].

What is meant by electrical conductivity? ›

Conductivity is the measure of the ease at which an electric charge or heat can pass through a material. A conductor is a material which gives very little resistance to the flow of an electric current or thermal energy. Materials are classified as metals, semiconductors, and insulators.

Can electricity change the pH of water? ›

In addition to adding an acid or a base to water, the pH can be changed by electrolysis. In this chemistry science fair project, you will use a 9-volt (V) battery to cause the electrolysis of water. You will track the changes in the pH values over time. Water can be decomposed by passing an electric current through it.

What is water pH level? ›

In its purest form, water has a pH of 7, which is at the exact center of the pH scale. Particles in the water can change the pH of the water, and most water for use has a pH of somewhere between 6.5 and 8.5. There are some important things to understand about the pH scale and how it relates to water.

How does temperature affect conductivity of water? ›

A decrease in the viscosity of water increases the mobility of ions in water. As such, an increase in temperature thus increases conductivity 11. Conductivity increases approximately 2-3% per 1°C increase in temperature, though in pure water it will increase approximately 5% per 1°C 11.

How is conductivity of water calculated? ›

For water for agricultural and irrigation purpose the values for EC and TDS are related to each other and can be converted with an accuracy of about 10% using the following equation: TDS (mg/l) = 640 x EC (ds/m or mmho/cm).

What are the units of conductivity? ›

The unit of measurement for conductivity is expressed in either microSiemens (uS/cm) or micromhos (umho/cm) which is the reciprocal of the unit of resistance, the ohm. The prefix "micro" means that it is measured in millionths of a mho. MicroSiemens and micromhos are equivalent units.

Is water a good conductor of electricity? ›

Water and electricity don't mix, right? Well actually, pure water is an excellent insulator and does not conduct electricity.

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