Soil electrical conductivity: a precision farming tool

Farmers are increasingly focused on precision agriculture. This includes collecting more detailed information about the spatial characteristics of their farming operations. These specific characteristics include the soil composition, as this has a large influence on crop growth. One of the easiest and cheapest ways to define soil properties is to measure the soil electrical conductivity, which provides much more measurements in a shorter amount of time than traditional soil sampling.

What is soil electrical conductivity?

Electrical conductivity (EC) is the ability of any material to conduct an electrical current. Soil is an electrical conductor; its EC is a measure of how fast the current flows through the soil. The speed, or conductivity, depends on the amount of moisture that is held by soil particles. The moister the soil, the higher the conductivity. Sand therefore has a low conductivity, silts a medium conductivity and clays have a high conductivity. Electrical conductivity thus correlates strongly to soil particle size and texture. Also, the soil EC responds to the amount of salt in the soil.

What do differences in soil EC tell the farmer?

It is important for a farmer to know the soil texture of the fields, as it has a major impact on productivity. Soil texture influences for instance the water-holding capacity, cation exchange capacity, drainage, top soil depth, and nitrogen use efficiency.
As said, the differences in soil EC are caused by the soil composition, so for instance the amount of sand, clay, or organic matter in that part of the field. Knowing the soil composition at every part of the field helps the farmer to apply the right amount of seeds, irrigation, and fertilizers to their field. In other words, this enables the farmer to practice precision agriculture, rather than treating the whole field as if the field has a uniform composition and thus requires the same treatment.

Commercial example

An example of a commercially available soil EC measuring apparatus is the Veris Soil EC Mapping System (manufactured by Veris Technologies in Kansas, US). The machine has units with disks attached to a toolbar, which act as electrodes. Soil EC readings are recorded every second, at two different depths. A GPS receiver is attached to the machine to record the exact location at which the recordings are taken. The data recorded are compiled and can then be transformed to a graphical representation of the soil electrical conductivity of the field. Soil properties are relatively constant, so a single soil EC map of a field is sufficient for years.

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