Agriculture Reference
In-Depth Information
PIP uses an alternative to standard overhead irrigation by using either trickle emit-
ters or spray stakes in each individual container (Fig. 2) alleviating some of the prob-
lems associated with container production for water application, water use and nutrient
runoff [38, 39]. Loss from wind and evaporation is considerably reduced in this type
of micro irrigation system because only the container surface is watered, not the entire
container yard surface [6]. Weatherspoon and Harrell [52] reported that irrigation ap-
plication effi ciencies of overhead sprinklers averaged 13% to 26% over the course of
a year. Typically irrigation application effi ciency is around 90% for PIP. Haydu and
Beeson Jr. [20] reported that microirrigated plants reached market size in signifi cantly
shorter time than those irrigated with conventional overhead systems (28 weeks versus
82 weeks for live oak). However, irrigation practices with PIP production method have
raised concerns over water use effi ciency because of drainage water loss through the
containers is not readily detectable [57]. Nurseries can be a source of pollution that
runoff water can contain pesticides, fertilizers and other chemicals released into sur-
face and ground water. To obtain high water use effi ciency and to automate irrigation
control, it is important to implement various water management strategies.
21.4 MICRO-IRRIGATION MANAGEMENT OPTIONS FOR PIP
Although micro irrigation is the standard method for irrigating trees in PIP, there is
limited research based information on irrigation automation and scheduling. Limited
rooting volume and low water holding capacity of the porous substrate necessitates
irrigation scheduling in PIP to be much more frequent with lower volumes per irriga-
tion event, compared with growing similar species in field soils [5]. There is potential
for increasing irrigation application efficiency through improved irrigation scheduling
[49] by improving water management within a container. Grower-friendly irrigation
strategies to optimize water use efficiency for PIP production that will minimize water
use while maximizing high quality plant growth are presented in the following sec-
tions.
Irrigation scheduling is the method used to determine the amount of water (how
much?) to be applied to a plant and the timing (when to irrigate?) and length (how long
irrigation should last?) of application. Irrigation scheduling has a signifi cant impact on
water use effi ciency. Inadequate irrigation management can result in ineffi cient water
use and excessive irrigation result in nutrient and pesticide leaching into ground water.
Scheduling can be relatively static and arbitrary (timer-driven), substrate moisture-
based, based on environmental models, or plant-based. The goal of an effi cient irriga-
tion program is to supply the crop with enough water to maximize crop growth while
minimizing water waste due to runoff and leaching.
21.4.1 STATIC SCHEDULING
The conventional container production practice is to irrigate once per day by auto-
matic timers or based on growers' experience. Many growers continue to follow fixed
predetermined schedules with quantities of water that often exceed crop needs [10].
With static irrigation, application is not linked directly to plant or substrate moisture
status and thus may result in short drought periods during critical crop stages lead-
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