CHARACTERIZATION OF APPARENT SOIL ELECTRICAL CONDUCTIVITY VARIABILITY IN IRRIGATED SANDY AND NON-SALINE FIELDS IN COLORADO

Abstract

Recent advances in apparent soil electrical conductivity (ECa) sensor technology have provided the opportunityto rapidly map soil spatial variability for site-specific management. However, characterizing (or identifying the causes of)the ECa variability has remained difficult, with ECa and soil property (such as soil water and clay content) relationshipsshowing a wide range of varying strength across fields. In this study, our objective was to characterize the main soil propertiesthat alter ECa and evaluate the temporal variability of ECa and soil property relationships using multi-year measurements(1998 to 2003) in three center-pivot irrigated fields in eastern Colorado. Results show that for the irrigated sandy andnon-saline fields, ECa maps may be viewed as surrogate maps for soil water content (.w), clay, cation exchange capacity,and/or organic matter content due to their strong correlations (with correlation coefficients between 0.66 and 0.96). Theexperimental linear functions of ECa versus soil properties changed over time when soil solution concentration (ECw)changed considerably. That finding was supported by theory (the dual-pathway ECa model) showing the relationship betweenECa and soil stable properties (such as clay content) to be governed by the status of the soil transient properties of ECw and.w at the time of the ECa mapping. The temporal effect of varying soil temperature on ECa could be significant but was notaccounted for due to lack of temperature data. Results collectively suggest that because of the lack of reliability of usingempirical ECa and soil property relationships for predictive purposes over time, on-site calibration of ECa versus soilproperties of interest are needed at each ECa mapping.