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

摘要

Recent advances in apparent soil electrical conductivity (EC _a ) sensor technology have provided the opportunity to rapidly map soil spatial variability for site-specific management. However, characterizing (or identifying the causes of) the EC _a variability has remained difficult, with EC _a and soil property (such as soil water and clay content) relationships showing a wide range of varying strength across fields. In this study, our objective was to characterize the main soil properties that alter EC _a and evaluate the temporal variability of EC _a 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 and non-saline fields, EC _a 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). The experimental linear functions of EC _a versus soil properties changed over time when soil solution concentration (EC _w ) changed considerably. That finding was supported by theory (the dual-pathway EC _a model) showing the relationship between EC _a and soil stable properties (such as clay content) to be governed by the status of the soil transient properties of EC _w and ? _w at the time of the EC _a mapping. The temporal effect of varying soil temperature on EC _a could be significant but was not accounted for due to lack of temperature data. Results collectively suggest that because of the lack of reliability of using empirical EC _a and soil property relationships for predictive purposes over time, on-site calibration of EC _a versus soil properties of interest are needed at each EC _a mapping