Estimating Topsoil Water Content of Clay Soils With Data From Time-Lapse Electrical Conductivity Surveys

Abstract

Spatial estimation of soil-water content (θ) at the field, hillslope, or catchment scale is required in numerous applications. Time-lapse electrical resistivity and apparent electrical conductivity (ECa) surveys are recognized as a useful source of information about both spatial variations in θ and spatial differences in soil properties. The objective of this work was to test the hypothesis that the accuracy of the regression relationships between θ and collocated ECa survey data can be improved for any given time if several time-lapse ECa surveys rather than a single ECa survey are used. Vertisol plots under conventional tillage and direct drilling were surveyed for gravimetric θ (θg) in the top 0.3-m layer at 17 times and for topsoil ECa at 13 times in 2008 through 2010. Both dry and wet periods were covered by the surveys. On four occasions, θg and ECa surveys were done on the same day. Only weak correlations (with R < 0.21) were found between ECa and θg measured on the same day. The accuracy of regression predictions of θg substantially improved when data of several ECa surveys, rather than a single survey, were used. Therefore, the knowledge about the temporal variability in soil properties, as captured by the time-lapse ECa data, can improve the estimation of spatial variability in soil properties affecting soil-water content.