Time-lapse monitoring of root water uptake using electrical resistivity tomography and mise-à-la-masse: a vineyard infiltration experiment

• Published in: Soil Vol. 6; no. 1; pp. 95 - 114
• Main Authors: Mary, Benjamin, Peruzzo, Luca, Boaga, Jacopo, Cenni, Nicola, Schmutz, Myriam, Wu, Yuxin, Hubbard, Susan S., Cassiani, Giorgio
• Format: Journal Article
• Language: English
• Published: Göttingen Copernicus GmbH 06-03-2020; Copernicus Publications
• Subjects: Current distribution; Current injection; Current sources; Electric contacts; Electric currents; Electrical resistivity; Experiments; Grapevines; Imaging techniques; Infiltration; Moisture content; Monitoring; Plant roots; Roots; Soil; Soil water; Soils; Tomography; Uptake; Vineyards; Water content; Water uptake; Wineries & vineyards
• ISSN: 2199-398X; 2199-3971; 2199-398X; 2199-3971
• DOI: 10.5194/soil-6-95-2020

This paper presents a time-lapse application of
electrical methods (electrical resistivity tomography, ERT; and
mise-à-la-masse, MALM) for monitoring plant roots and their activity
(root water uptake) during a controlled infiltration experiment. The use of
non-invasive geophysical monitoring is of increasing interest as these
techniques provide time-lapse imaging of processes that otherwise can only
be measured at few specific spatial locations. The experiment here described was conducted in a vineyard in Bordeaux (France) and was focused on the
behaviour of two neighbouring grapevines. The joint application of ERT and
MALM has several advantages. While ERT in time-lapse mode is sensitive to
changes in soil electrical resistivity and thus to the factors controlling
it (mainly soil water content, in this context), MALM uses DC current
injected into a tree stem to image where the plant root system is in effective
electrical contact with the soil at locations that are likely to be the same
where root water uptake (RWU) takes place. Thus, ERT and MALM provide
complementary information about the root structure and activity. The
experiment shows that the region of likely electrical current sources
produced by MALM does not change significantly during the infiltration time
in spite of the strong changes of electrical resistivity caused by changes
in soil water content. Ultimately, the interpretation of the current source
distribution strengthened the hypothesis of using current as a proxy for
root detection. This fact, together with the evidence that current injection
in the soil and in the stem produces totally different voltage patterns,
corroborates the idea that this application of MALM highlights the active
root density in the soil. When considering the electrical resistivity
changes (as measured by ERT) inside the stationary volume of active roots
delineated by MALM, the overall tendency is towards a resistivity increase
during irrigation time, which can be linked to a decrease in soil water
content caused by root water uptake. On the contrary, when considering the
soil volume outside the MALM-derived root water uptake region, the
electrical resistivity tends to decrease as an effect of soil water content
increase caused by the infiltration. The use of a simplified infiltration
model confirms at least qualitatively this behaviour. The monitoring results
are particularly promising, and the method can be applied to a variety of
scales including the laboratory scale where direct evidence of root
structure and root water uptake can help corroborate the approach. Once
fully validated, the joint use of MALM and ERT can be used as a valuable
tool to study the activity of roots under a wide variety of field
conditions.