Submitted to: Soil Science
Publication Type: Peer reviewed journal
Publication Acceptance Date: 1/10/2012
Publication Date: 5/9/2012
Citation: Gonzalo, M., Vanderlinden, K., Pachepsky, Y.A., Giraldez, J., Espejo, A. 2012. Estimating topsoil water content of clay soils from with data from time-lapse electrical conductivity surveys. Soil Science. 177(6):369-376. Interpretive Summary: Spatial variation in soil water content determines essential variations in plant growth and development conditions. Since intense spatial measurement of soil water content is impractical, soil electrical conductivity (EC) data are used as a proxy. Soil electrical conductivity depends not only on soil water content but also on soil properties, and therefore empirical relationships relating EC and soil water content have relatively low accuracy. Our hypothesis was that pooled results of many electrical conductivity surveys carried out at different weather conditions would reflect the spatial differences in soil properties better than a single survey. If this assumption is correct, then relating soil water measurements to collocated data of several previous EC surveys should result in improved accuracy for regression relationships between soil water content and EC. The hypothesis was tested with data of soil water measurements and EC surveys obtained on clay soils under two management practices in Andalusia, Spain. A wide variety of soil conditions, with different soil water contents, encompassing a dry-wet-dry weather sequence, was covered with the EC surveys. Substantial improvement in accuracy and reliability of soil water content predictions was found when more than one EC survey data were used as predictors. Results of this work will be useful to researchers and producers in the precision agriculture field in that the more accurate regression relationships between soil water contents and EC can provide more accurate conversion of soil EC mapping into the soil water content maps.
Technical Abstract: Spatial estimation of soil water content (') at the field, hillslope, or catchment scale is required in numerous applications. Time-lapse electrical resistivity and electrical conductivity surveys were recognized as the useful source of information about both spatial variations in soil water contents and spatial differences in soil properties. The objective of this work was to test the hypothesis that the accuracy of the regression relationships between soil water content values and collocated electrical conductivity survey data can be improved for any given time if several time-lapse ECa surveys rather than a single EC surveys are used. Vertisol plots under conventional tillage and under diect drilling were surveyed for gravimetric water contents in 0-0.3m layer 17 times and for electrical conductivity of the topsoil 13 times in 2008 through 2010. Both dry and wet periods were covered by surveys. In four occasions surveys were done on the same day. Only weak correlations (with R2 <0.21) were found between electrical conductivity and gravimetric water contents measured on the same day. The accuracy of regression predictions of gravimetric water contents substantially improved when data of several electrical conductivity surveys survey rather than single survey were used.