Campbell Scientific CS616 and CS625 Water Content Reflectometers - Manual (Page 32)

CS616 and CS625 Water Content Reflectometers
FIGURE 7-2 compares the CS616/CS625 response in the FIGURE 7-1 loam
soil to a higher density sandy clay loam for two different electrical
conductivities. The bulk density for both sandy clay loam soils is 1.6 g cm -3 .
The electrical conductivity at saturation for the sandy clay loam labeled
compacted soil is 0.4 dS m -1 . The compacted soil, high EC had an electrical
conductivity at saturation of 0.75 dS m -1 .
16 18 20 22 24 26 28 30 32 34
0
0.1
0.2
0.3
low EC soil
low EC, compacted soil
high EC, compacted soil
CS616 output period (usec)
Vo
lu
m
etr
ic
W
ate
r
Co
nte
nt
(f
ra
cti
on
al
)
FIGURE 7-2. CS616 and CS625 response for low EC loam with bulk
density 1.4 g cm -3 , a low EC sandy clay loam with bulk density 1.6 g
cm -3 , and a high EC sandy clay loam with bulk density 1.6 g cm -3 .
The compacted soil response shows the effect of compaction and high clay
content. The signal attenuation caused by compaction or high clay content
causes an offset in the response as shown by the near-parallel curves at water
contents above 10%. This is the effect of attenuation by the solid phase.
The effect of increased electrical conductivity for the same soil is shown by the
response curve high EC, compacted soil. Higher electrical conductivity causes
a decrease in the slope of the response curve. This is the effect of attenuation
by the solution phase.
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