MANAGING AGRICULTURAL WATER QUALITY IN FIELDS AND WATERSHEDS: NEW PRACTICES AND TECHNOLOGIES
Location: Agroecosystems Management Research Unit
Title: The use of soil electrical conductivity to investigate soil homogeneity in Story County, Iowa, USA
Submitted to: Soil Horizons
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: June 25, 2012
Publication Date: September 4, 2012
Citation: Brevik, E., Fenton, T., Jaynes, D.B. 2012. The use of soil electrical conductivity to investigate soil homogeneity in Story County, Iowa, USA. Soil Horizons. 53:5. DOI:10.2136/sh12-04-0013.
Interpretive Summary: Land use planning, application of precision agriculture techniques, and siting conservation practices require detailed soil information. Conducting detailed soil mapping surveys can be tedious and expensive but an emerging method for obtaining this information more rapidly and inexpensively is by measuring the apparent electrical conductivity (EC) of the soil which varies with soil type. This research evaluated the accuracy of EC surveys for differentiating soil map units across a field having soils formed in an old glacial lake bed. As a consequence, these soils exhibit only slight variations in their properties. We found that the EC survey was not able to differentiate among soil map units formed in this environment and thus caution should be used before universally applying this technique for soil mapping. These findings will benefit scientists and soil surveyors about the limitations in using EC surveys.
Precision agriculture, environmental applications, and land use planning needs have led to calls for more detailed soil maps. A remote sensing technique that can differentiate soils with a high degree of accuracy would be ideal for soil survey purposes. One technique that has shown promise in Iowa is electrical conductivity (ECa) measured by the Geonics® EM-38. Electrical conductivity readings obtained with this technique result from a combination of the soils’ water content, clay content, soluble salt content, and temperature. One way ECa techniques have been evaluated as soil survey tools involves grid mapping a field, doing an ECa survey of that field, and comparing the maps obtained using each method. Good results have been obtained in this way for several fields in central Iowa that contain soils that are fairly variable over relatively short distances. A field with lacustrine-derived soils that exhibit only slight variations in soil properties across the field was chosen for this study. This led to highly uniform ECa readings and an inability to differentiate between soil map units using the ECa data. However, this was also valuable information as it confirmed the uniform nature of the soils in the field, a critical criterion for a precision agriculture study being conducted in that field.