Estimation of the spatial variability of root water uptake of maize and sorghum at the field scale by electrical resistivity tomography

Abstract

Saving water for crop production is an old, but ongoing, challenge which requires a better understanding of the in situ functioning of root systems. In particular, this requires a better quantification and understanding of the spatial and temporal variability of the root water uptake at the field scale. Electrical Resistivity Tomography (ERT) is a nondestructive soil imaging technique, related to water content, which could help in spatializing active zones of water uptake. In this article, we evaluate ERT as an alternative method for quantifying and spatializing root water uptake at the field scale. To this aim, an experimental field study with maize and sorghum submitted to different water supply levels (Fully, Moderately or Poorly Irrigated treatments-FI, MI, PI zones) was conducted for 3 months with concomitant conventional, local, water balance measurements and 2D ERT imaging. ERT images showed an heterogeneous depletion of soil water by the crops, particularly, in the MI and PI zones with patches of high/low electrical resistivity (and thus water content) variations. This heterogeneity was greatest in the MI zone and points to spatial variations in rooting pattern and/or root efficiency. The 5-days difference in electrical resistivity could be quantitatively related to root uptake in the surface layer (down to 60 cm) but the relationship depends on the mean soil water content. At greater soil depth, in the water stressed zones, the water extraction front progressing downwards could not be assessed with the ERT surface setting used in this study. As a conclusion, ERT can be a useful, unique, technique for monitoring and estimating field water uptake by plant roots and its variability if combined water content measurements are available for in situ calibration and if the sensitivity/resolution of the technique is improved for estimation over the whole root zone.

Methods to estimate changes in soil water for phenotyping root activity in the field

“…ERT has been used to study the variation of soil electrical conductivity in the root zone (Srayeddin and Doussan 2009;Furman et al 2013). ERT is well suited for use in electrically resistive environments such as dry soil, provided good electrical contact can be achieved between electrodes and soil.…”

Nonstationarity of the electrical resistivity and soil moisture relationship in a heterogeneous soil system: a case study

“…Similar observations of root zone drying, highlighted by an increase in ER, were shown in Mediterranean contexts by Al Hagrey (2007) and Nijland et al (2010) on soils planted with cork oaks or covered by seminatural vegetation of evergreen shrubs and trees. However, only Srayeddin and Doussan (2009) have quantified and mapped root water uptake of maize and sorghum in field conditions using time-lapse ERT. Recently, Garré et al (2012) tested the ability of different ERT electrode arrays to detect soil moisture dynamics in a monocropping and an intercropping system.…”

The Use of Electromagnetic Induction to Monitor Changes in Soil Moisture Profiles beneath Different Wheat Genotypes

“…Soil s is also a function of the pore fluid electrical conductivity and temperature (Corwin and Lesch, 2005). Electrical resistivity tomography has been used to study the variation of soil electrical conductivity in the root zone (Srayeddin and Doussan, 2009;Furman et al, 2013). It is best suited for use in electrically resistive environments such as dry soil.…”