Agriculture Reference
In-Depth Information
FIGURE 1
Measuring pressure and emitter discharge in a subsurface drip irrigation system.
7.2.2 EVALUATION OF MICRO IRRIGATION SYSTEM
One method to evaluate clogging problems is to perform an evaluation of the irrigation
system. It is recommended to measure emitter discharge and pressure at 18 selected
locations within a single zone to detect problems (Fig. 1).
Enciso et al. [9] recommends to pick six drip-lines, evenly spaced across the width
of the zone for sampling. Along each of the six drip-lines, three measurements should
be made, near the inlet and distal ends (approximately 8-9 m from ends) and near the
center of the drip-line length. The measurements can be made by placing a container
under selected emitters as shown in Fig. 1. In case of subsurface drip irrigation the
measurements can be made by carefully excavating the soil by hand, trying to avoid
damaging the drip-line, to a depth below the emitter to allow small water collection
containers. Water dripping from each sampled emitter can be collected for a period of
time as measured by a stop watch. Collection errors can be further reduced by collect-
ing and averaging two or three water collection samples for each of the 18 selected
emitters. Emitter discharge is calculated as the average sample catch volume divided
by sample time. The emitter discharge collected at different locations should be com-
pared against the design fl ow rate. The drip-line pressure at each sampling location can
be determined using a glycerin-fi lled pressure gage (±1.5% of full scale, 0 to 207 kPa).
A syringe, connected to the pressure gage with plastic tubing, can be used to pierce the
drip-line, providing a nonleaking interference fi t. After using the syringe to measure
the drip-line pressure, a small plastic plug (also known as goof plug: to provide an
interference fi t) can be inserted into the hole of the drip-line as a permanent repair of
the leak. Sadler et al. [20] reported the excavation process itself can affect the emitter
discharge with increases of as much as 4% due to removal of overburden on some soil
types. However, these differences in emitter discharge are still small and the emitter
discharges are being compared against each other (i.e., all sampled emitters are being
excavated) so the effect is less important.
The Lower Quartile Distribution Uniformity is calculated using Eq. (1).
q
⎡⎤
lq
DU
=
100
⎢⎥
⎣⎦
(1)
lq
 
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