|Sudduth, Kenneth - Ken|
Submitted to: Computers and Electronics in Agriculture
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/22/2003
Publication Date: 3/15/2005
Citation: Sudduth, K.A., Kitchen, N.R., Wiebold, W.J., Batchelor, W.D., Bollero, G.A., Bullock, D.G., Clay, D.E., Palm, H.L., Pierce, F.J., Schuler, R.T. 2005. Relating apparent electrical conductivity to soil properties across the north-central USA. Computers and Electronics in Agriculture. 46:263-283. 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. In this project, two EC sensors used commercially in precision agriculture were evaluated. 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 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 six north-central states using both these instruments and found that they gave similar, but not identical results. Differences between the sensors were greater on fields with more layered soils, such as the Missouri claypan soil fields. The two soil properties most strongly related to EC were clay content and cation exchange capacity (CEC). We found that it may be possible to develop calibrations for clay and CEC that would apply across a wide range of soils and climatic conditions. The results of this research will benefit users of EC instruments, giving them a better understanding of the advantages and limitations of each instrument 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 be used as an indirect indicator of a number of soil physical and chemical properties. Commercially available ECa sensors can efficiently and inexpensively develop the spatially dense datasets desirable for describing within-field spatial soil variability in precision agriculture. The objective of this research was to relate ECa data to measured soil properties across a wide range of soil types, management practices, and climatic conditions. Data were collected with a non-contact, electromagnetic induction-based ECa sensor (Geonics EM38) and a coulter-based sensor (Veris 3100) on twelve fields in six states of the north-central United States. At 12 to 20 sampling sites in each field, 120 cm deep soil cores were obtained and used for soil property determination. Within individual fields, EM38 data and Veris 3100 deep (0-100 cm depth) data were most highly correlated. Differences between ECa sensors were more pronounced on more layered soils, such as the claypan soils of the Missouri fields, due to differences in depth-weighted sensor response curves. Correlations of ECa with clay content and CEC were generally highest and most persistent across all fields and ECa data types. Other soil properties (soil moisture, silt, sand, organic C and paste EC) were strongly related to ECa in some study fields but not in others. Regressions estimating clay and CEC as a function of ECa across all study fields were reasonably accurate (r2 >= 0.55). Thus, it may be feasible to develop relationships between ECa and clay and CEC that are applicable across a wide range of soil and climatic conditions.