Have you ever wondered why electricians stake metal poles into the ground while working? Yes, your garden soil has electrical properties. However, does this apply to the potting soil of your potted plants?
Potting soil can conduct electricity. This applies also to outdoor soil. However, the increased presence of water, dissolved mineral salts, organic matter, clay, silt, and fine particles in potting soil increases the electrical conductivity (EC) of the soil. The point of measuring electrical conductivity is to have an indirect measure of soil health and plant growth.
You’re probably not gonna be using potting soil for any electrical projects anytime soon but the electrical conductivity of soil actually has some important implications for gardening, agriculture, and soil health. Measuring soil electrical conductivity can help you plot out where you’re gonna put that rose bed in the future!
Table of Contents
- 1 Is Potting Soil Electrically Conductive?
- 2 Why is Soil Electrically Conductive?
- 3 Why is Electrical Conductivity (EC) Important?
- 4 Optimal Electrical Conductivity of Soil
- 5 Effect High and Low Electrical Conductivity Levels in Soil
- 6 How To Measure Electrical Conductivity
- 7 The Electrical Conductivity of Potting Soil
- 8 How To Adjust Electrical Conductivity
- 9 Electrical Conductivity in Hydroponics
- 10 Summary of Potting Soil Conduct Electricity
- 11 Sources
Potting soil is electrically conductive that depending on the composition. Higher levels of organic matter, mineral salts, water, small soil particles, and higher clay content increases electrical conductivity (EC).
Potting soil comes in varying compositions made for different plants which affect their electrical conductivity. Generally, soilless potting soil is less conductive due to the lack of clay or silt.
The electrical conductivity of potting soil is a shared trait with regular soil. Soil itself is electrically conductive since it is full of ions (charge-carrying atoms or molecules which are consumed by plants) that can conduct electricity. This is why electrical engineers hook some electrical currents to the earth to “ground” them, dispersing any excess electrical current.
Soil is a mixture of dissolved minerals salts, water, and organic matter. Due to this, the soil is full of charge-carrying ions (cations and anions) that can conduct an electrical current.
The dissolved mineral salts include cations (positively charged ions) and anions (negatively charged ions). Cations in soil include Ammonium (NH4+), Calcium ion (Ca2+), Potassium ion (K+), Sodium ion (Na+), and Magnesium ion (Mg2+). Anions in soil include Sulfate (SO4 2-), Chlorine ion (Cl-), Nitrate (NO3-), and Bicarbonate (HCO3-).
Depending on the composition, hydration, clay content, mineral, and ion content, soil can either be good or poor conductors. The material composition of the soil is key in determining its electrical conductivity which means soil can either be a good conductor or a poor conductor/decent insulator (dielectric).
The presence of water, dissolved mineral salts, fine clay, and organic matter make the soil more conductive. The reduction of these materials and the addition of non-conductive materials such as carbonate rocks and sand (silica) make the soil less conductive.
Soil electrical conductivity is an indirect indicator of soil health and its effect on plant growth. Extremely low electrical conductivity means the soil does not have enough nutrients. Extremely high electrical conductivity means that there are excess nutrients in the soil, causing nutrient burn and other issues.
Maintaining an optimal electrical conductivity level is as important to soil growth as it is to hydroponics. The same principles apply that the electrical conductivity level indicates how “healthy” the growing medium is for the plants. Maintaining an optimal electrical conductivity level is the difference between starving your plants or overfeeding them with nutrients.
The optimal electrical conductivity of soil is 100-400 mS/m (milliSiemens per meter) depending on the plant grown.
The electrical conductivity of the soil should be kept within 100-400 mS/m since this is the “Goldilocks range” for fertile soil and is beneficial for most plant growth. A lack or excess may lead to plant health degradation either by lack or excess of nutrients, respectively. In fact, the high amount of dissolved mineral salts could make it more difficult for plants to absorb water and nutrients due to osmotic pressure.
The lower range is more appropriate for plants that do not have high nutritional requirements such as cacti and succulents. The higher range is more appropriate for most plants that require moderate to high nutrients such as herbs and trees, respectively.
Dangerously high electrical conductivity levels (>1600 mS/m) cause sodicity, increased erosion, sodium poisoning, and decreased water absorption. Worryingly low electrical conductivity levels (<100 mS/m) can deprive plants of essential nutrients and are generally less water retentive.
High electrical conductivity levels in soil exhibit white, powdery, and dry topsoils. It burns your plants with nutrients but deprives them of water. Low electrical conductivity levels in soil do not look any different from normal soil but their lack of dissolved mineral salts shows when plant growth is stunted.
The electrical conductivity pertains to the salinity of the soil which refers to the dissolved mineral salts. High electrical conductivity levels can be a bad indicator since this is often related to “sodicity” which means that there is a higher proportion of sodium ions compared to other ions.
Sodicity caused by high electrical conductivity levels causes the sodium ions to break the plasticity of clay, making them easier to break apart and dry up. This has the effect of making the soil less water retentive and less resistant to erosion, creating dry cracks on the surface.
Sodic soil is measured at >400 mS/m and with a sodium absorption ratio of >15. Though determining the sodium absorption ratio is difficult to determine without specialized equipment and knowledge, sodic soil can be clearly seen by its milky color, dry texture, and easy dispersion of clay particles.
The electrical conductivity of soil can be measured by penetrating the soil with a soil electrical conductivity tester. Insert the instrument 2 inches (5 cm) or more into the ground and wait for the reading to stabilize to have a final measurement.
The depth of the soil can affect the reading of the electrical conductivity since there are more dissolved mineral salts and water the deeper we go. We can use this to our advantage by only reading the proper soil depth in relation to how deep the roots of our plants grow.
There is also an alternative method which consists of mixing a sample of the soil with a small jar of water. However, the above method is the simplest method available to gardeners. This can be used on potting soil, regular soil, small garden beds, and simple potted plants.
There are more elaborate methods available such as the use of a lysimeter, an instrument that siphons groundwater for testing. These are better suited for larger-scale agricultural operations where planting covers a larger area compared to gardening.
Note: The electrical conductivity of soil can be influenced by the presence of water. For example, dry sand is almost non-conductive with an electrical conductivity of 3-6 mS/m. By adding water to the sand, the wet sand’s electrical conductivity jumps up to 100 mS/m.
The composition of the potting soil can have a significant impact on its electrical conductivity. Potting soil that contains actual soil such as silt or clay has increased electrical conductivity. Potting soil without soil may have lower electrical conductivity unless the composition offsets the lack of soil.
This is why it’s important to determine whether potting soil is soilless. That’s not to say that soilless mixes are not electrically conductive but they might be less so compared to potting soil with clay or silt.
Potting soil with this type of composition is better suited to plants that require a moderate or high amount of water and nutrients. The higher electric conductivity (EC) means that there is an increased amount of dissolved mineral salts in the soil. Some of these mineral salts include phosphorus, nitrogen, and potassium, among others which are plant nutrients.
Potting soil with this type of composition is well-suited for plants that do not require that much water or nutrients such as succulents. The lower electric conductivity means that there is a decreased amount of mineral salts in the soil which means that there may be fewer nutrients available.
Adjusting the electrical conductivity of the soil means the addition or reduction of water, organic matter, mineral salts, or clay. Adjustment is necessary when the electrical conductivity is too high or too low to prevent the negative effects of either and to return the soil’s electrical conductivity to optimal levels.
Adjusting for potting soil is easier since we already know their composition based on their product information. Soils found in gardens are more difficult to adjust due to their volume and undetermined composition.
Increasing the electrical conductivity entails adding more clay, organic matter, and water to the composition. Adding fertilizer is a sure-fire method of increasing the electrical conductivity of the soil due to the enhanced nutrient levels added. These methods increase the level of anions and cations in the soil, making it more electrically conductive.
Decreasing the electrical conductivity entails adding more insulating materials such as fine sand and large rocks. Periodically watering and draining the soil can carry away the dissolved mineral salts from the soil as drain water. Finally, allowing the nutrients of the soil to be naturally absorbed by the plants without any periodic fertilization can decrease the electrical conductivity of the soil.
Outdoor garden soil electrical conductivity can be adjusted by adding or reducing the organic matter, water, mineral salts, and clay present in the soil.
Increasing the electrical conductivity entails adding more clay, organic matter, and water to the soil and mixing thoroughly. Adding fertilizer will significantly increase the electrical conductivity of the soil due to the enhanced presence of dissolved mineral salts that serve as nutrients for the plants.
Decreasing the electrical conductivity of garden soil is more difficult. We can definitely change the composition by adding more insulating materials such as large rocks or fine sand, however, the larger volume occupied by garden soil makes adjustment presents a greater hassle.
Another method of reducing electrical conductivity is by making sure that water is effectively drained and dried. A proper drainage system makes sure that excess mineral salts escape the soil.
While electrical conductivity is an indirect method of determining water and dissolved mineral salts in the soil, the same is a direct method in hydroponics. The optimal electrical conductivity level for hydroponics is 0.5-2 mS/cm.
In hydroponics, the sole growing medium used for hydration and nutrition is water alone. Water serves as nutrient storage, delivery, and uptake in hydroponics. As such, the nutrient reservoir (the water containing the dissolved nutrients) is meticulously monitored to make sure that the plant is nourished but not subject to nutrient burn.
Here we see a cross-section between the two disciplines on basic principles. The nutrients plants absorb are ions and these ions are either cations or anions which facilitate the electrical conductivity of the growing medium. As such, the electrical conductivity of the growing medium gives us a fair understanding of how healthy it is for the plants.
Potting soil, much like regular soil, can be a good or poor electrical conductor, depending on the composition and hydration of the soil. As a rule of thumb, increased levels of hydration, organic matter, dissolved mineral salts, clay, and silt will make the potting soil more electrically conductive.
The Electrical Conductivity (EC) of soil may not have much usefulness in electrical garden projects, however, they serve as indirect indicators of soil health and, by extension, plant growth. It gives an idea of the level of dissolved mineral salts and water in the soil.
Electrical Conductivity may be adjusted by adding or reducing the conductive materials present in the soil. For potting soil, it can be argued that a soilless composition is less electrically conductive due to the lack of clay and silt.
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