Submitted to: Agronomy Journal
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/7/2002
Publication Date: 5/1/2003
Citation: SUDDUTH, K.A., KITCHEN, N.R., BOLLERO, G.A., BULLOCK, D.G. COMPARISON OF ELECTROMAGNETIC INDUCTION AND DIRECT SENSING OF SOIL ELECTRICAL CONDUCTIVITY. AGRONOMY JOURNAL. 2003. V. 95. P. 472-482. Interpretive Summary: Soil apparent electrical conductivity (EC) is influenced by a number of factors, including soil moisture, clay content, and salinity. Because of this, spatial measurements of conductivity can, when properly calibrated, provide indicators of a number of soil parameters important in site- specific crop management, or precision agriculture. Two types of EC sensors usable in precision agriculture are commercially available. The Geonics EM38 is a non-contact sensor which measures EC to a depth of approximately 1.5 m through the principle of electromagnetic induction. The Veris 3100, a newer product, uses coulters in contact with the soil to provide two simultaneous EC measurements to depths of approximately 0.3 m and 1.0 m. We obtained EC measurements in crop production fields in Missouri and Illinois using both these instruments, and found that they gave similar, but not identical results. Differences between the sensors were more pronounced on the Missouri claypan soil fields due to the existence of highly contrasting soil layers. The two soil properties most strongly related to EC were clay content and cation exchange capacity (CEC). The results of this research will benefit users of EC instruments, giving them a better understanding of the advantages and limitations of each type. The results will also benefit scientists and extension personnel, who may need to understand the differences between the instruments for research or demonstration purposes.
Technical Abstract: Apparent profile soil electrical conductivity (ECa) can provide an indirect indicator of a number of soil physical properties. Commercially available ECa sensors can be used to efficiently and inexpensively develop the dense datasets desirable for describing within-field spatial soil variability in precision agriculture. The objective of this research was to compare ECa measurements from a non-contact, electromagnetic induction-based sensor (Geonics EM38) 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). Within each field, 120-cm deep soil cores were obtained for soil property determination at between 12 and 21 sampling sites. 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 0cm depth) data were most highly correlated (r = 0.74 to 0.88). Difference 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 CEC 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 properties.