Non-invasive monitoring of soil water dynamics in mixed cropping systems: A case-study in Ratchaburi province, Thailand

in Vadose Zone Journal (2013)

Agriculture on shallow or steep soils in the humid tropics often leads to low resource use efficiency. Contour hedgerow intercropping systems have been proposed to reduce run-off and control soil erosion ... [more ▼]

Agriculture on shallow or steep soils in the humid tropics often leads to low resource use efficiency. Contour hedgerow intercropping systems have been proposed to reduce run-off and control soil erosion. However, competition for water and nutrients between crops and associated hedgerows may reduce the overall performance of contour hedgerow systems. Electrical resistivity tomography (ERT) is a valuable technique used to assess the distribution and dynamics of soil moisture noninvasively. In this study, we demonstrated its potential to measure soil water depletion in the field in distinct cropping patterns in Ratchaburi province, Thailand. The measurements showed that the soils of our experimental plots were very heterogeneous both along the slope as with depth. This observation highlighted some constraints of the ERT method for soil moisture monitoring in the field, such as the difficulty of defining a relationship between electrical conductivity and soil moisture in very heterogeneous soils. Nevertheless, spatial analysis of the data revealed contrasting water depletion patterns under monocropping and intercropping systems. In this way, ERT provides access to information about the vadose zone moisture dynamics that would be unavailable with classical soil moisture measurements. [less ▲]

Non-invasive monitoring of mixed cropping systems. A case-study in Ratchaburi province, Thailand

Poster (2012, July)

Parameterizing a Dynamic Architectural Model of the Root System of Spring Barley from Minirhizotron Data

in Vadose Zone Journal (2012)

The development of models describing water and nutrient fluxes to and through 3-D spatially resolved root structures in soils brings along the need to predict or describe the root architecture and root ... [more ▼]

The development of models describing water and nutrient fluxes to and through 3-D spatially resolved root structures in soils brings along the need to predict or describe the root architecture and root growth in detail. However, detailed data to calibrate and validate such architecture and growth models is typically not available. Here, we investigate the sensitivity of the root architecture model RootTyp (Pagès et al., 2004) to changes in its model parameters and reconstructed the root system architecture of barley growing in an undisturbed lysimeter using minirhizotron images at four different depths. Root arrival curves from a series of minirhizotron images were used to parameterize RootTyp using a range of realistic architectures. We adjusted a simple architecture to the data, which contained only long primary roots starting from the seed. This simple model unfortunately could not reproduce the observed increase of root density with depth. The model was subsequently improved by allowing root branching and elongation to be horizon-dependent and by making reiteration of root tips possible. Reiteration is an alternative form of branching, where secondary roots can become as long and thick as primary roots. Our results show that minirhizotron data do not contain enough information to warrant identification of the parameters governing these processes, as the additional parameters act similarly on data characteristics as the initial ones. Therefore, different experimental techniques should be combined to constrain the model parameters better in the future. [less ▲]

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)

The dynamic interplay between roots and soil moisture

in Geophysical Research Abstracts (2010, May)

Using electrical resistivity tomography (ERT) to image the topology of soil properties relevant to solute transport characteristics of soils

Poster (2010)

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 ▲]

Electrical resistivyt tomography as tool to image preferential flow pathways in soils

Conference (2009)