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EC mapping surveys field’s clay pan

Researchers are finding new tools to better assess clay pan for producers seeking the best root zone preparations.

“Whether it’s no-till or conventional tillage systems, that clay pan will limit root growth and water-holding capabilities. Understanding how the depth of the clay pan changes across a field can be important if you want to prescribe variable rate or zone management,” says Jason Warren, soil and water conservation specialist, Oklahoma State University, Stillwater.

Most U.S. counties offer soil surveys, affording producers valuable profile information, but they have limitations. Electrical conductivity, or EC, mapping takes those surveys to a new level, by providing a more detailed assessment of clay pan depth.

Key Points

• Electrical conductivity mapping pinpoints compacted soil layer.

• EC can be instrumental in measuring erosion losses.

• Fifteen years of research shows EC to be an accurate tool.


“Generally, these surveys are pretty good at providing a description of the soils found in the field, and they will tell you the general depth to the clay pan, but the usefulness of electrical conductivity mapping is it increases the resolution of that map,” Warren says.

The USDA Agricultural Research Service’s Cropping Systems and Water Quality Research Unit in Columbia, Mo., has been using the EC technology on USDA and producer fields across Missouri for more than 15 years. They looked at using the technology to estimate the topsoil depths above the clay pan and map the variations within each field. The soil depths showed where the soil was disappearing fastest and gave a better understanding of the soil variations throughout the field.

“Some places you have almost no topsoil left because of erosion, and when that takes place, you change the landscape and lose productivity to where it’s much less than other areas,” says Newell Kitchen, a research soil scientist at the unit. Kitchen has been associated with the project since it began.

“Because of the erosion of the topsoil, there is a variability of the productivity in the field, and EC mapping of the soil gives a better understanding of the productivity of the soil.”

Although the scientists didn’t create specific zones based on soil fertility, they were able to create productivity zones based on soil depths in the field.

The clay pan held a clue to soil water availability, a key in understanding productivity. Clay pan water is much less available to plants compared to available water in the topsoil, and the researchers used the technology to find not only the depth of the clay pan, but also the density, clay percentage and water content, which provided a close look at water availability throughout the field.

“If we get a few soil samples across the field and bring them back to the lab to get moisture content readings, they relate back to the map and allow us to look at water across the field,” says Ken Sudduth, a research agricultural engineer at the unit.

“We can get some idea of what the clay pan is, and it gives us an idea of what the rooting environment is.”

Taken together, the data present a detailed soil profile, with depths relating to water erosion, as well as soil productivity and yield variations, and water availability relating to soil depth and the clay pan. The profile maps can lead to better land management practices and help producers decide whether to keep it in crop rotation or find new uses for it, especially if the topsoil is relatively thin.

Fields losing topsoil can be addressed with EC mapping because it shows where erosion is greatest, allowing producers to specifically address those problem areas. No-till is one method often promoted for preserving the topsoil.

Brazil writes from Clermont, Fla.

This article published in the October, 2010 edition of THE FARMER-STOCKMAN.

All rights reserved. Copyright Farm Progress Cos. 2010.