Comparison of Electromagnetic Induction and Direct Sensing of Soil Electrical Conductivity

Apparent profile soil electrical conductivity (ECₐ) can be an indirect indicator of a number of soil physical and chemical properties. Commercially available ECₐ sensors can be used to efficiently and inexpensively develop the spatially dense data sets desirable for describing within-field spatial soil variability in precision agriculture. The objective of this research was to compare ECₐ measurements from a noncontact, electromagnetic induction–based sensor (Geonics EM38)¹ ¹Mention of trade names or commercial products is solely for the purpose of providing specific information and does not imply recommendation or endorsement by the USDA or the Univ. of Illinois. to those obtained with a coulter-based sensor (Veris 3100) and to relate ECₐ data to soil physical properties. Data were collected on two fields in Illinois (Argiudoll and Endoaquoll soils) and two in Missouri (Aqualfs). At 12 to 21 sampling sites in each field, 120-cm-deep soil cores were obtained for soil property determination. Depth response curves for each ECₐ sensor were derived or obtained from the literature. Within a single field and measurement date, EM38 data and Veris deep (0–100 cm depth) data were most highly correlated (r = 0.74–0.88). Differences between ECₐ sensors were more pronounced on the more layered Missouri soils due to differences in depth-weighted response curves. Correlations of ECₐ with response curve–weighted clay content and cation exchange capacity were generally highest and most persistent across all fields and ECₐ data types. Significant correlations were also seen with organic C on the Missouri fields and with silt content. Significant correlations of ECₐ with soil moisture, sand content, or paste EC were observed only about 10% of the time. Data obtained with both types of ECₐ sensors were similar and exhibited similar relationships to soil physical and chemical properties.