Differences in EM-38 readings taken above crop residues versus readings taken with instrument-ground contact
2003
Brevik, E.C. | Fenton, T.E. | Lazari, A.
Soil apparent electrical conductivity (EC) as measured by electromagnetic induction (EM) using the Geonics' EM-38 has shown promise as a soil survey tool in Iowa and other parts of the American Midwest. Surveys made with the EM-38 often take place in the fall after harvest or in the spring prior to planting. Because of this, and because use of conservation tillage and other techniques that leave crop residues on the soil surface is prevalent in many parts of the United States, it is common for fields to have crop residues covering the soil surface when EM surveys are conducted. These residues might alter the soil EC values obtained with the EM-38. To test this possibility, soil EC was determined at two sites with three different types of residue cover (corn (Zea mays L.), soybeans (Glycine max L.), and durum wheat (Triticum turgidum L.)). The residue cover at each site was then brushed aside, and the soil EC was determined with bare ground exposed to the EM-38. On average, soil EC readings were 0.2mS/m higher when the EM-38 was exposed to bare ground, and 68% of the bare ground readings were higher than the corresponding readings through crop residues. However, the 0.2mS/m average difference is not significant when compared to the natural variation found in soil EC readings within any given soil series. Therefore, the results of this study indicate that soil EC values obtained with the EM-38 through crop residues are valid representations of the actual soil EC value.
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