Agriculture Reference
In-Depth Information
TABLE 1:
Vertical distribution of monitoring units across the vadose zone of the organic
and conventional farms.
Farm
Probe
Depth to monitoring unit center (m)
Depth to
water table
(m)
Organic
FTDR
0.2
0.4
0.9
1.9
2.9
4.9
7.8
10
12.8
15
VSP
0.2
0.4
1.3
2.3
3.3
5.3
8.3
10.5
13.3
Conven-
tional
FTDR
0.2
0.4
0.7
1.7
2.7
5.7
9.6
14.6
19.6
26
VSP
0.2
0.4
1
2
3
6
10
15
20
14.2.2 MONITORING SETUP
Two representative greenhouses, organic and conventional, that special-
ize in growing vegetables, such as cherry tomatoes, peppers and zucchini,
were selected and instrumented with VMSs (Fig. 1). Technical descriptions
of VMS structure, performance and installation procedures have been pre-
viously presented in other publications (Rimon et al., 2007; Dahan et al.,
2008, 2009; Rimon et al., 2011a). To avoid overloading this manuscript
with technical information, only a brief description will be presented here.
The VMS is composed of a flexible sleeve installed in uncased slanted
(35) boreholes hosting multiple monitoring units at various depths. Each
monitoring unit has a flexible time domain reflectometry sensor (FTDR),
for continuous measurements of sediment water content, and vadose zone
sampling ports (VSP) for frequent collection of pore-water samples from
the entire unsaturated zone. Slanted installation ensures that each moni-
toring unit faces an undisturbed sediment column that extends from land
surface to the probe depth. In the borehole, the flexible sleeve is filled with
high-density solidifying material to ensure sleeve expansion for proper at-
tachment of the monitoring units to the borehole's irregular walls, sealing
its entire void and preventing potential crosscontamination by preferential
flow along the borehole. Each VMS included nine monitoring units dis-
tributed vertically and laterally along the entire vadose zone cross section
(Table 1). Installation orientation was aligned with the growing rows. The
representativeness of measurements made by the VMS, with respect to
