Can we use Electrical Resistivity Tomography to measure root zone moisture dynamics in fields with multiple crops?

in 2012 Scientific program (2012, December 07)

Evaluating experimental design of ERT for soil moisture monitoring in contour hedgerow intercropping systems

in Vadose Zone Journal (2012)

Links between root length density profiles and models of the root system architecture

in Vadose Zone Journal (2012)

Three-Dimensional Electrical Resistivity Tomography to Monitor Root Zone Water Dynamics

in Vadose Zone Journal (2011), 10(1), 412-424

Knowledge of soil moisture dynamics and its spatial variability is essential to improve our understanding of root water uptake and soil moisture redistribution at the local scale and the field scale. We ... [more ▼]

Knowledge of soil moisture dynamics and its spatial variability is essential to improve our understanding of root water uptake and soil moisture redistribution at the local scale and the field scale. We investigated the potential and limitations of electrical resistivity tomography (ERT) to measure three-dimensional soil moisture changes and variability in a large, undisturbed, cropped soil column and examined the interactions between soil and root system. Our analysis sustained the value of ERT as a tool to monitor and quantify water contents and water content changes in the soil, as long as the root biomass does not influence the observed resistivity. This is shown using a global water mass balance and a local validation using time domain reflectometry (TDR) probes. The observed soil moisture variability was rather high compared to values reported in the literature for bare soil. The measured water depletion rate, being the result of combined effects of root water uptake and soil water redistribution, was compared with the evaporative demand and root length densities. We observed a gradual downward movement of the maximum water depletion rate combined with periods of redistribution when there was less transpiration. Finally, the maximum root length density was observed at −70 cm depth, pointing out that root architecture can strongly depend on soil characteristics and states. [less ▲]

Sensitivity and resolution of ERT for soil moisture monitoring in contour hedgerow intercropping systems: a methodological analysis

Scientific conference (2011)

Non-invasive monitoring of water and solute fluxes in a cropped soil

Doctoral thesis (2010)

Although the influence of root water uptake on solute transport is commonly recognized as important, it has barely been studied throughout the literature. However, plants take up a big amount of the ... [more ▼]

Although the influence of root water uptake on solute transport is commonly recognized as important, it has barely been studied throughout the literature. However, plants take up a big amount of the infiltrating water and therefore they influence water flow patterns in the soil and concurrently solute transport processes. For this reason, experiments are required to investigate the relationship between plant root water uptake and flow field variability. Within this PhD project, we tried to elucidate the role of root water uptake on soil moisture distribution and solute transport in two undisturbed soil columns. During three consecutive experimental phases, the soil hydraulic and solute transport characteristics were investigated and the influence of growing barley on water content and tracer movement were studied. Soil water concentration and moisture content in the lysimeters were monitored non-invasively using 3-D electrical resistivity tomography (ERT). ERT is a valuable technique to monitor processes in the unsaturated zone. It is suitable to quantify solute concentration or soil moisture content at the decimeter scale in different soils and under varying conditions. In combination with TDR and effluent measurements, different aspects of the solute transport process and manifestations of preferential flow can be investigated. Steady-state step tracer experiments are very suitable for this purpose. Soil moisture measurements with ERT were conducted as well, but an horizon-specific in-situ calibration of the ERT-measurements for water content was a prerequisite for success. We observed that the solute transport in our silty lysimeters was considerably more heterogeneous than in the loamy-sand soil studied by Koestel (2008; 2009a; 2009b). We observed a clear preferential flow path in one of the lysimeters and found that soil layering had a big influence on the leaching process. The measured water depletion rate, being the result of combined effects of root water uptake and soil water redistribution during the barley experiment without irrigation, was compared with the evaporative demand and root length densities. We could observe a gradual downward movement of the maximum water depletion rate together with periods of redistribution when there was less transpiration. However, we were unable to make the distinction between soil water fluxes and root water uptake, since modeling of the soil water flow field using the time series of water content was not satisfying. We observed root growth at rhizotube surfaces and noted an increasing number of roots with depth. Since the minirhizotron measurements were only conducted at four depths and thus represent a small volume of the entire root zone, we estimated a root architecture model for the barley plants using RootTyp. We were able to set up a simple model, but to obtain better results, the effect of soil constraints and the process of re-iteration should be included. Many aspects of water flow and solute transport in the root zone need to be further investigated. The need for high-quality soil moisture data and simultaneous root architecture data remains. ERT is a promising technique to fill part of this gap, however some issues need to be solved before it can be used without difficulties. Next to measurements, the effort to improve our soil water flow models must be continued in order to improve the estimation of soil water fluxes. Only in this way, we will be able to measure root water uptake at the lysimeter and field scale. This is a necessary step towards a better understanding of the interactions in the soil-plant continuum. [less ▲]

Comparison of Heterogeneous Transport Processes Observed with Electrical Resistivity Tomography in Two Soils

in Vadose zone journal (2010), 9(2), 336-349

Preferential flow in soils can manifest itself in several ways. To illustrate this, we analyzed solute transport during a step tracer experiment in two soils expected to differ in their governing ... [more ▼]

Preferential flow in soils can manifest itself in several ways. To illustrate this, we analyzed solute transport during a step tracer experiment in two soils expected to differ in their governing transport processes: a loamy sand and a silty soil. By combining electrical resistivity tomography (ERT), time domain reflectometry, and effluent measurements, we observed different preferential flow phenomena. The transport process was characterized using voxel- and column-scale effective convective–dispersive equation (CDE) parameters, local velocities, and leaching surfaces. At the column scale, transport in the loamy sand was dominated by a homogenous convective–dispersive transport behavior, but at the scale of the voxel, preferential transport was observed. Transport in the silty soil was considerably more heterogeneous. Preferential flow was identified using ERT, voxel- and column-scale effective CDE parameters, local velocities, and leaching surfaces. In these soils, a clear influence of soil layering on solute transport was observed. [less ▲]

Comparison of transport in lysimeters with undisturbed loamy sand and silty soil using non-invasive imaging with electrical resistivity tomography

Conference (2009, September)

Comparison of transport in lysimeters with undisturbed loamy sand and silty soil using non invasive imaging with electrical resistivity tomography.

in Geophysical Research Abstracts (2009, April 23)

Effects of crops on solute transport in undisturbed soil

Poster (2009)

Models predicting movement of surface applied chemicals incorporate knowledge on the water velocity field and moisture content distribution. Although the influence of root water uptake on solute transport ... [more ▼]

Models predicting movement of surface applied chemicals incorporate knowledge on the water velocity field and moisture content distribution. Although the influence of root water uptake on solute transport is commonly recognized as important, it has been studied sparsely. Yet, plants may take up a large part of the infiltrating water, thereby influencing the water flow pattern in the soil and concurrently solute transport processes. For this reason, experiments are required to investigate the relationship between plant root water uptake and flow field variability. The role of root water uptake on solute transport will be elucidated in two undisturbed soil columns. During three consecutive experiments, the influence of growing barley on tracer movement through a silty soil in two lysimeters will be followed. At the first stage, an inert tracer is put on the two bare lysimeters and leached with constant irrigation. As steady-state flow can be assumed, it is possible to follow the tracer movement in the column by ERT and to identify regions of preferential flow and solute transport parameters. During the second experiment, the tracer will be applied to mature barley grown in the lysimeters. Combining the information about the water content obtained with TDR with the relation between water content, soil solution salinity and bulk electrical conductivity, the soil solution salinity distribution can be derived from images of bulk electrical conductivity obtained with ERT. Root growth will be monitored using a minirhizotron. By comparing the transport parameters obtained after these two experiments, the effect of root water on the transport process can be quantified. When the columns are washed out and the barley is harvested, the third phase will be carried out under the same steady state flow conditions as in the first experiment to investigate the effect of dead roots on soil structure. [less ▲]