Investigation of the Effect Soil particles size on the Currency Time Domain Reflectometry for water content measurement

Document Type: Original Article


1 Department of Water Engineering , University of Kurdistan, Iran.

2 Regional Water Company of Kurdistan, Kurdistan, Iran.


This study carried out on the provided textures at laboratory. The provided textures were infused
inside the PVC cylinder with 30cm height and 25cm diameter. The studied textures were loamy
sand, sandy loam, sandy clay-loam, clay loam and clay. After 24 hours of saturation, the soil water
content of the samples was measured by oven-dry gravimetric and TDR methods. For each textures
at any stage of measurement the determination of moisture and di-electric constant were done at
three capture windows and with three repetitions. In each day the moisture measurement of each
texture was carried out by these two methods until a moisture range was determined. The results of
this research show that: 1- For all soil textures the measured moisture at the capture windows of 20
ns has more accuracy compared to the other capture windows. and TDR device can not measure the
soil water content at capture window of 40 ns. 2- For loamy-sand and sandy-loam textures when the
moisture was less than 20% and also for other textures for total range of measurement, the TDR
device measured the moisture values less than the gravimetric method. This difference is increased
when the soil ranged from light to heavy textures. 3- From the statistical view at probably level of
1% there is not difference between the measured value of moisture by TDR device and gravimetric
method. 4- For the all textures the fitted regression lines have high regression coefficient.


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