Forest soils often contain many large coarse fragments making it difficult
to insert probes to measure soil water content. The ability of time domain
reflectometry (TDR) to give reliable measurements of water content in soil
with up to 40% coarse fragments was evaluated at a site in the southern int
erior of British Columbia, Canada. A commercial time domain reflectometer w
as used with 0.3-, 0.5- and 0.75-m-long probes to measure soil water conten
t of the profile and layers within the profile. A probe had a shorting diod
e at the surface and two 3-mm-diameter stainless steel rods inserted vertic
ally, 30 mm apart, as the waveguide. Diverging rods or profile discontinuit
ies resulted in erroneous readings that required a review of the recorded s
ignals and recalculation the travel time. Soil physical and hydrologic soil
properties were determined and the soil calibrated for TDR. An accuracy of
+/-0.02 m(3) m(-3) was obtained with measurement of soil bulk density and
minimizing probe and travel time errors. Variation in water content between
probes reflected the variability in coarse fragment content; however, the
ranking of the probes stayed constant with time and rates of change were si
milar between probes. One standard deviation on the measured change in the
volume of water between measurement days for the 0 to 0.5 m depth was +/-6
mm (n = 20), equivalent to 0.012 m(3) m(-3). Measurements of water content
of the layers had one standard deviation of 0.02 m(3) m(-3).