Agriculture Reference
In-Depth Information
7.1 INTRODUCTION
Subsurface drip irrigation (SDI) systems are preferably used over alternative systems
for crop production in several parts of the world because the large initial SDI system
costs can be offset by crop profits. If the longevity of the SDI systems can be increased
through properly designed and maintained systems, these systems could be economi-
cally justified for a great diversity of row crops. In some regions, SDI systems have
been used for lower
value commodity crop production such as in Kansas for irrigating
corn and West Texas to irrigate cotton [8, 13, 14]. Cotton producers have replaced
furrow irrigation systems with SDI systems to spread limited water resources for the
declining aquifers of West Texas and also to remain profitable.
The use of SDI systems in row crops may also be infl uenced by the initial cost of
the system. The cost of an SDI system will depend on the drip-line spacing or the row
confi guration [8]. The cost percentages by irrigation components for a 1.02 m drip-
line spacing are approximately: pump and fi lters 14%, drip-line 38%, PVC pipe 25%,
installation 15%, and fertilizer injectors and accessories 8% [11]. The drip-line repre-
sents the greatest cost of the system and its longevity can greatly impact the system's
annual amortized cost. Economic comparisons of SDI systems and center pivot sprin-
kler irrigation systems (CP) for corn production in Kansas have indicated that SDI
systems must last at least 10 to 15 years to approach economic competitiveness with
CP systems [15]. Successful maintenance programs can help prevent emitter clogging
and increase the longevity of the system. The longevity of subsurface drip irrigation
(SDI) systems is a key factor in the profi tability of these systems when used for lower
‐
‐
value commodity crops (typically the fi ber and grain crops). The system management
and maintenance protocols, as well as the source water quality, can greatly impact the
longevity of these systems. Enciso et al. [10] evaluated 10 subsurface drip irrigation
systems in 2008 and 8 additional systems in 2009 that had been in operation between 6
and 20 years. System uniformity was evaluated by the uniformity parameters, emitter
discharge variation, qvar, and the lower quartile distribution uniformity of emitter dis-
charge, DUlq. Pressure measurements along the drip-line also were used to determine
if qvar was primarily explained by friction losses. Two
thirds of the evaluated SDI
systems had qvar less than 20% and DUlq greater than 80, which would be accept-
able, and one
‐
third of the systems had qvar less than 10% and DUlq greater than 90,
which would be good to excellent uniformity. There was very little correlation in sys-
tem uniformity and system life with the oldest system (20 years) having the greatest
uniformity. Uniformity problems on nearly two
‐
thirds of the systems appeared to have
been exacerbated by incorrect operating pressure (both too low and too high) with the
six best performing systems operating between 65% and 100% of the manufacturer's
specifi ed nominal operating pressure. Water hardness and total dissolved salts were the
major water quality concerns. Poor maintenance (e.g., no or infrequent chlorination;
inadequate fi ltration system back fl ushing) appeared to reduce uniformity in between
one
‐
half of the systems. The producer's lack of installation records and
operator's guides likely negatively impacted system uniformity through these poor
management and maintenance procedures. The use of both qvar and DUlq to evaluate
performance of SDI systems appeared to enhance the determination of the primary
‐
third and one
‐
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