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

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). Next to that, time domain reflectometry (TDR) probes, tensiometers and temperature probes were installed to measure local soil water contents, matrix potentials and electrical conductivities. Also the outflow volume and the electrical conductivity of the effluent were registered. 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, since the water content is kept constant during tracer movement. 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.