How To Test Electrical Conductivity (EC) Of Soil

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Testing soil electrical conductivity can be done by preparing a soil sample and inserting a conductivity probe that is connected to a conductivity meter. The probes measure the conductance or resistance of the soil solution indicating its ability to transmit an electric current, displaying the value on the conductivity meter.

Agriculture is a booming industry, and one major attribute to yielding good crops is soil dynamics. To measure soil quality, electrical conductivity (EC) is one major factor, providing growers with valuable indications concerning plant growth and the concentration of dissolved salts and ions (nutrients) within the soil.

In this article, we will look into the importance of electrical conductivity in soil and how you can test it for growing the best crops. 

The Importance Of Electrical Conductivity And Optimal EC Levels

Electrical conductivity (EC) is an important parameter to determine the soil’s ability to support your plant’s growth and levels of dissolved salts and nutrients. In addition, EC provides a reliable reflection of activity levels for significant ecological microorganisms. 

When the soluble salt content (EC value) in the soil gets too high that it exceeds allowable thresholds, reverse osmosis pressure may occur which can result in water leaving the root system. This results in the plant’s root ends browning and drying up. High EC levels can also enhance the possibility of cotton rot fungus disease causing root rots.

On the other hand, if the soil has a low EC value, there will not be enough effective nutrients in the plant, resulting in poor growth. 

Factors Influencing EC in Soil

  • Soil texture (particle size distribution of sand, silt, and clay)
  • Organic matter content
  • Salinity levels (concentration of dissolved salts)
  • Composition of clay minerals (e.g., montmorillonite, kaolinite)
  • Moisture content (water holding capacity and drainage)
  • Temperature
  • Soil compaction and porosity
  • Presence of ions and electrolytes
  • Soil pH
  • Microbial activity
  • Fertilizer and amendment applications

The Relationship Between EC & TDS

Electrical conductivity and total dissolved solids (TDS) are closely related parameters used to measure the concentration of dissolved ions in water or other solutions, like soil. As mentioned, EC is a measure of the ability of a solution to conduct an electrical current, which is directly proportional to the concentration of dissolved ions. Total dissolved solids (TDS) refers to the total concentration of dissolved inorganic and organic substances present in the solution. Generally, a higher TDS value corresponds to a higher EC value, as more dissolved ions contribute to increased electrical conductivity. However, the specific relationship between EC and TDS can vary depending on the composition and nature of the dissolved solids present in the solution.

The units of measure for EC are deciSiemens per meter (dS/m), milliSiemens per centimeter (mS/cm), or micromhos per centimeter (μmhos/cm). 1dS/m = 640ppm TDS is a commonly employed conversion factor although it may vary depending on the types of dissolved salts involved.

4 Ways For Measuring Electricity Conductivity In Soil

To test the EC of soil, there are different ways to obtain results.

1. Laboratory Analysis

Laboratory analysis offers unbeatable accuracy for those looking for it. By using specialized conductivity meters in laboratory facilities, soil samples sent there for assessment will come back with very accurate results. However, this testing method may be time-consuming and more expensive than alternative methods.

2. Soluble Salt Test Strips

Soluble salt test strips are paper strips, used to test EC when immersed in soil. They work by changing color according to the soil solution’s EC value. By comparing the hue on the strip against a provided color chart, you can determine quickly how much is too much as far as EC goes. 

While soluble salt test strips are quick and easy to use, they are not as accurate or reliable as an EC meter. 

3. Electrical Resistivity Imaging (ERI)

Electrical Resistivity Imaging (ERI) is a geophysical technique used to measure the electrical conductivity of soil. It involves injecting an electrical current into the ground through electrodes and measuring the voltage differences at other electrode locations.

By analyzing the resistance patterns, ERI can map the subsurface distribution of electrical conductivity, which is influenced by factors like soil moisture, texture, and salinity. This non-invasive method provides valuable insights into soil properties and heterogeneity.

4. EC Meters

To measure the EC value of soil, handheld meters are most popular because of their high accuracy and ease of use, and as they provide real-time and remote monitoring. EC meters are designed with small portable EC probes that when inserted into the soil will display the reading values on a digital screen.

The Atlas Scientific EC-KIT-0.1 is an advanced device that provides you with accurate conductivity readings to ensure your soil remains healthy and productive.

Some outstanding features of the Atlas Scientific EC-KIT-0.1 include:

  • Ideal for measuring water from 0.07µs to 50,000µs in conductivity range
  • For high-purity water applications
  • This probe has high accuracy and industrial characteristics
  • It can be fully submerged in fresh or saltwater up to the SMA connector indefinitely
  • The Conductivity Probe K 0.1 is NSF/ANSI 51 compliant

If you need to extend the cable over 100 meters without loss of signal – extending a probe cable can easily be done with our SMA Extension Cables.

Common EC Ranges Of Soil

Different plants and crops have different growing needs, therefore the EC value of the soil varies depending on what you are growing. Here are some ranges for different crops:

  • Most field crops and vegetables: 0 – 4 dS/m
  • Salt-sensitive crops like beans and strawberries: < 1 dS/m
  • Salt tolerant crops like cotton, dates: up to 8 dS/m
  • Soils above the limit of 4 dS/m may face salinity constraints for many crops
  • Very low readings below .2 dS/m could indicate nutrient deficiencies

Soil Sampling Protocol

Before testing the EC of soil, you need to collect a sample that has no contamination that could influence the EC reading. 

Firstly, to maintain consistency in environmental conditions, all soil samples should be collected on the same day of testing.

Soil samples should be collected from different areas around the plant/crop. To get a good idea of the area’s EC level, we recommend taking at least 10 samples per acre from random locations. You should also take soil samples from different depths, specifically targeting depths around the crop roots, since this is where most growth occurs and essential nutrients are absorbed.

If you want to measure the EC of the entire composition of a field’s subsoil, take those 10+ samples and merge them to create a collective sample. This should give you a good representation of the EC in that particular area. 

Measuring Soil Solution Electrical Conductivity

Collecting soil samples is super easy! Utilize a probe for soil sampling at six inches deep (note: root depth may vary with crop type, so verify your particular crop’s depth requirements). There are three main tools capable of taking uniform soil samples with depth:

  • Push probes
  • Hammer probes
  • Bucket augers

Collecting the soil sample:

  1. Take about an ounce or 6 spoons (30 g) for each sample
  2. Put each of the separate samples into plastic bags
  3. After collecting the samples mix them inside a plastic bag properly so that a composite sample can be formed out of them
  4. Once you have acquired representative soil samples, prepare a soil solution by using one of the following:

Soil Slurry (Dilution 1:2)

With this method, add water to your soil sample until it becomes liquid, then make sure that there are higher amounts of water than solid material measured by a ratio that is two units of water to one unit of soil.

Saturated Media Extract (SME) Method

This method involves wetting the soil sample using water depending on its content moisture. This gives a soil solution sample that represents the whole farm.

Soil Solution Sampling and Analysis Technique (SSAT)

The SSAT technique involves the use of a lysimeter tube to extract liquid from the field which directly provides an index for nutritional and saline glory in the soil.

Whichever option you go for, it is essential that you first calibrate your EC meter so that accurate measurements can be made. In soil analysis field, daily calibration is the best practice.

To measure the electrical conductivity of your prepared soil solution, follow these steps:

  1. Dip the EC sensor into the soil solution contained in a beaker
  2. Wait for the EC meter to stabilize before taking any readings
  3. Record three readings from one sample and calculate the average
  4. Rinse the EC sensor after every measurement in running water to avoid contamination between different soil solutions 

Direct Soil EC Testing

An alternative way to test the EC of soil is direct soil EC testing. Some EC meters/probes are specifically designed for that purpose, allowing you to directly measure the conductivity of soil in the field.

Direct soil EC testing:

  1. For accuracy and reliability, calibrate the EC probe before measuring
  2. Create a hole if necessary to insert the electrode into the soil at the desired location
  3. Take note when the reading stabilizes then record measurement accordingly

When you are done testing the EC of the soil, please ensure that the probe is thoroughly rinsed so that there are no abrasive materials that could damage the electrodes inside the probe. 

It is important to note that direct soil EC testing may not be suitable in all areas. This method might become challenging (possibly impossible) if there are stones or hardness in the soil. In such cases, SSAT or soil slurry preparation methods should be used instead.

To have a comprehensive view of your entire farm field, remember to make several measurements across various locations to obtain a representative sampling of the soil’s EC levels. It takes account of such things as temperature and moisture content while taking readings so that those variations don’t affect EC results as they are corrected through automatic temperature compensation features common with most quality conductivity meters and probes.

Interpreting EC Results and Actionable Insights

Measuring electrical conductivity does not mark an endpoint in understanding soil health, but rather acts as the basis for understanding other aspects of plant nutrition requirements and crop growth.

After understanding the EC level, growers can look into the specific macronutrients to fully appreciate plant demands. So, unless you are producing hydroponics crops, maximizing yield often requires a deep investigation of individual nutrients. This allows specific measures targeted at improving the nutrient management plan for crops, providing the best possible combination of necessary ingredients for more robust growth of plants.

Conclusion

EC provides insights into soil health, nutrient availability, and crop productivity. Whether you use handheld EC meters, soluble salt test strips in laboratories, electrical resistivity imaging, or soil moisture sensors, they all provide reliable and representative results.

Should you need any further information regarding how to test the electrical conductivity of soil or our recommendations on suitable EC meters and probes for your testing requirements please feel free to contact our world-class team at Atlas Scientific.

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