Effects of crops on solute transport in undisturbed soil

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.