we are doing research on the effect the surface soil moisture of the low
mounds on the germination of tree seeds. We are interested in the
moisture conditions in the top 2-3 cm soil layer. The mounds consist of
organic soil (peat), mineral soil (sand, silt) or the mixture.
We have been monitoring the soil moisture by using ThetaProbe
(vertically) with shortened 3-cm rods instead of the normal 6-cm rods.
We compared these two rod lengths in laboratory in peat soil. We
achieved a pretty good linear relationship between the two lengts
(R2=0.98). However, the value we got with 3-cm rods were half of the
values we got with 6-cm rods. We have used the manufactor's calibration,
but we are planning to calibrate the ThetaProbe individually for all the
We would appreciate your opinion of our procedure. Is it ok, what kind
errors we may face, and have some of You used ThetaProbe as we did and
what kind of experiences you have?
We are also interested on other possible methods to measure the surface
soil moisture without disturbing the soil surface. Besides ThetaProbes,
we have Tektronix 1502 and TDR100 available in our institute. We have
heard that we can't use very short rods with TDR. What is the minimum?
Is there any new TDR-probe designs we could use to solve our problem?
Finnish Forest Research Institute
Rovaniemi Research Unit