Electrical conductivity in soils may be a precision farming tool.

Although soil electrical conductivity -- the ability of the soil to conduct an electrical charge -- is still a new concept, researchers at the University of Missouri-Columbia think it can help producers make intelligent management decisions. The scientists have been taking measurements about every 60 feet in test fields to generate electrical conductivity maps of Missouri's claypan soils.

"I think soil electrical conductivity is going to be an extremely important mapping tool," Newell Kitchen, a USDA/ARS soil scientist at MU, told Implement & Tractor. "Think of it as a soil X-ray. It reflects a number back, and that number relates to the amount of electrical conductivity at that particular place in the field."

A recent technique for measuring conductivity is the electromagnetic induction (EM), a non-invasive, non-destructive sampling method that can be done quickly and inexpensively. The Missouri team has been using a 3-foot long commercial available instrument, the EM-38, from Geonics Ltd., ON, Canada. Pulled over a field by an ATV-pulled sensor cart or incorporated into a coulter, the EM-38 induces a magnetic field that varies in strength with depth in the soil (Fig. 1). A receiving coil reads the induced current and produces a number value. The higher the reading, the nearer the claybed to the service (Fig. 2).

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Readings can be affected by salinity, compaction, clay type, soil moisture, temperature, and topsoil depth.

However, maps made at different times of the year show that soil electrical conductivity stays fairly stable and produces useful data that can be correlated with yield maps and other data. Also, various physical and chemical properties of the soil affect its ability to transmit electricity, and some of those soil properties can affect yields, Kitchen explained.

"The resulting information can help producers make management decisions, such as a variable rate nitrogen fertilizer plan (Fig. 3). The maps produced give a detailed picture of the soil's relative variation in electrical conductivity, not what causes the variation but differences in the levels," he said.

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"Soil electrical conductivity data will be very helpful for rooting depth on some soils, and it can show us how water-related properties of the soil and landscape affect grain crop production."