Roots are movers of water in the soil. One method of movement is through
hydraulic lift, which occurs when plants extract water from a moist subsoil
and release it into a dry topsoil. Detection of hydraulic lift has been
hampered by the lack of instruments sensitive enough to measure the small
amount of water moved. Recently, the dual-probe heat-pulse (DPHP) technique
has been used to monitor with fine spatial resolution the soil water content
in root-zones. The objective of this research was to determine if water is
released by hydraulic lift, using the DPHP technique. Sunflower
(Helianthus annuus L.) was grown in a column (38 cm
height; 25 cm diam.; bulk density = 1.45
Mg/m3) packed with a Haynie very fine sandy loam
(coarse-silty, mixed, calcareous, mesic Mollic Udifluvents; FAO-Eutric
Fluvisols) with its roots divided between a top dry layer and a lower wet
layer. Eight DPHP sensors installed in the soil column were used to monitor
soil water content. During 24 measurement days, hydraulic lift was evident
only when the plant was wilted. This occurred when the lower ‘wet’
layer had been allowed to dry and then it was re-watered. At this time, the
roots in the upper dry layer released water, increasing the soil water content
in the centre of the root mass by 0.019
m3/m3 (increase from 0.121
m3/m3 to 0.140
m3/m3). The soil-water
increase was similar to other values reported in the literature and show it to
be small.
A Dual-Probe Heat-Pulse Sensor with Rigid Probes for Improved Soil Water Content Measurement
