Electrical impedance imaging of the root zone

P. Newilla, D. Karadagli?b, F. Podda, B.D. Grievea, M. Staerklec, J. Leipnerc, C.

Screpantic, T.A. Yorka

aSchool of Electrical & Electronic Engineering, University of Manchester, Oxford Road, Manchester M13 9PL, UK

bSchool of Engineering and Built Environment, Glasgow Caledonian University, Glasgow

cBiological Sciences, Syngenta Crop Protection Muenchwilen AG, Switzerland

Abstract

Exploration of electrical impedance measurements for imaging water transport in and around the roots of plants is described. The scientific aim is to use the images to inform phenotyping in crop breeding programmes. The present work considers preliminary measurements on a laboratory scale rhizotron fitted with 60 capacitively- coupled contactless conductivity (C4D) electrodes in a rectangular array. This reduces electrochemical effects by including an insulating layer on the surface of the electrodes. The resistance of the bulk material is deduced from spectroscopic considerations. Electrical impedance is measured between pairs of electrodes to build up a two- dimensional map. A modified electrical model of the electrodes is proposed which includes the resistive and reactive components of both the insulating layer and the bulk material. Using soil as the bulk material the effect of water content, compaction and temperature are explored. Moisture has the strongest influence particularly under dry conditions. Impedance measurements decrease by a factor of 1000 as soil moisture is increased from 5% to 30%. Compaction, up to a pressure of 0.21 kg/cm2, changes the impedance by up to 20%, under dry conditions. Measurements show a temperature sensitivity of about 2% / °C. Preliminary growth tests show changes in impedance as a root system develops and are compared to a control test with no plant.

Keywords: capacitively-coupled contactless conductivity; ERT; root zone monitoring