How To Measure Electrical Conductivity Of Soil(EC)

What is soil conductivity?

Soil conductivity refers to the ability of soil to conduct current, which is described by measuring the conductivity of soil extract. The unit is MS / M (i.e. 10 μ S / cm). When the measurement result is greater than or equal to 100ms / M (i.e., 1000 μ S / cm), keep three significant digits; When the measurement result is less than 100ms / m, keep it to one decimal place.

Soil conductivity is the sum of anions and cations in soil extract, representing the soil’s salt content. So, determining soil conductivity can directly reflect the content of mixed soil salt.

Types of EC

• ECE, the conductivity of extract of saturated paste of soil sample.
• ECA, bulk soil conductivity (Rhoades, 1990).

ECE is a common method for measuring soil salinity. We can get it by preparing soil extract and measuring it;

ECA refers to the total conductivity of soil samples (bulked), which sensors can measure for a long time, an essential index of soil’s physical and chemical properties. Under certain soil water content conditions, ECE and ECA are positive linear correlations, which specific calibration methods can convert.

In general, the soil conductivity is measured by the conductivity of soil solution (ECE) because it can best reflect the actual concentration of salt ions in the soil at this time. However, due to the complex operation of this method in the process of getting soil solution, some researchers gradually focus on the study of soil bulk conductivity (ECA).

The measurement process of soil bulk conductivity is simple and accurate. Therefore, this method has become one of the most commonly used and reliable methods to detect, analyze and evaluate soil salinization.

Related:

How To Measure Conductivity Of Water

Why measure the electrical conductivity (EC) of soil?

The growth of plants is closely related to sunlight, air, water, and nutrients in the soil. Different plants have different tolerance to soil salinity and nutrient concentration. So how to measure whether there are enough nutrients in the soil?

One of the methods to evaluate soil nutrients is the conductivity method. The conductivity in the soil is proportional to the salt content of the soil. Therefore, we can determine the number of soil nutrients by measuring the soil conductivity to help us analyze fertilization or salinity.

Measurement method of soil conductivity

There are many ways to test soil conductivity: test soil pore water, total or volume conductivity of soil, or prepare soil into the slurry to test soil conductivity.

Soil pore water conductivity:

1)The measurement of soil pore water conductivity requires using a soil solution collector to extract the water from the soil and then using the conductivity meter to test the EC Value of the aqueous solution.

It is also suitable for the sample collection when measuring other components of the pore water around the soil at the plant’s root.

Total conductivity of soil:

2)The total conductivity of soil is measured by inserting a special conductivity electrode directly into the soil. The measured data are the total conductivity of air, water, and soil.

Pros:

It is suitable for field measurement without other equipment.

Note:

It is recommended to use a conical electrode to ensure complete contact between the electrode and the soil sample.

3) Measurement of conductivity by saturated mud method

Mix soil samples with purified water in a certain proportion and measure the conductivity after leaching the salt in the soil.

Step:

A. Set the instrument correctly and calibrate the conductivity electrode.

B. Sampling

• Take soil samples—one sample per 1000 square meters. At least two samples were collected, Even in a small area (the more representative samples, the better test result).
• Avoid extracting samples with apparent abnormalities from the soil.
• Sampling volume: the same amount of soil is collected for each sample.
• Extraction depth: dig out 5cm of topsoil; Herbaceous crops: depth 20-40 cm; Orchard: depth 20 to 60 cm.
• Lay the soil sample on a newspaper and let the soil dry in a cool place or an oven at 40 ° C.
• Crush the dried soil and mix to get a uniform mixture, and remove stones and vegetable residues.
• This mixture of soil samples for analysis.

C. Soil solution preparation and measurement

• Sieve the soil sample (2mm).
• The deionized water is mixed with the soil sample according to the ratio of soil to the water of 1:2.
• Mix well for 30 seconds.
• Wait about 1 hour.
• Filter the soil sample and measure the EC value of the filtrate.

Note:

When extracting the soluble salt in the soil with water, try to completely dissolve the soluble salt and make the insoluble salt and medium soluble salt (calcium carbonate, calcium sulfate, etc.) insoluble or less soluble as much as possible. Therefore, take soil water ratio and oscillation time appropriate.

Common soil-water ratios of 1:2.5, 1:2, and 1:1, or saturated slurry leaching solutions exist. However, for some clay-heavy soils, the smaller water–soil ratio brings more difficulties to the operation; we can increase the proportion of water, such as 1:5, 1:10, or 1:20.

However, this will cause a high total amount of soluble salts (especially in soils with more calcium sulfate and calcium carbonate). Therefore, we should uniformly determine the soil water ratio and extraction time in preparing soil water leaching solution.

Soil Conductometric Meter

We can measure the dielectric constant by transmitting high-frequency electromagnetic waves with Soil Conductometric Meter, then automatically calculate the soil moisture content and conductivity. A High-frequency electromagnetic wave simultaneously measures the capacitance and conductivity characteristics of the measured object. The capacitance characteristic reflects the soil water content, and the conductivity characteristic reflects the soil salt content.
Because the dielectric constant of soil or air in the soil is tiny, while that of water is very large, if the soil moisture content increases, the capacitance part of the soil moisture characteristics also increases accordingly. We can know the moisture directly using the appropriate calibration curve relationship.