MICRO-IRRIGATION SYSTEMS FOR POT-IN-POT ORNAMENTAL NURSERY PRODUCTION - Management, Performance, and Applications of Micro Irrigation Systems - page 305

by the plant and established a set point based on the relationship between maximum
photosynthesis and midday stem water potential [44] to control timing of irrigation.
Both the photosynthesis-based irrigation scheduling system [12] and daily water
replacement irrigation [51] appear to meet water conservation criteria compared to
a timer-based irrigation strategy. The major difference between the photosynthesis-
based irrigation system vs. daily replacement is that the photosynthesis-based system
irrigates based on instantaneous water use, while daily water replacement only ap-
plies irrigation once per day. Therefore, plants irrigated under daily replacement could
experience periods of water stress on days with signifi cant transpirational demand at
the expense of plant growth and water use effi ciency. In contrast, the photosynthesis-
based model was developed to schedule irrigation on-demand whenever container
moisture was reduced to a level where stomata were predicted to begin to close re-
stricting carbon.
21.6 ADVANCED IRRIGATION STRATEGIES TO ENHANCE IRRIGATION
EFFICIENCY
21.6.1 CYCLIC IRRIGATION
Cyclic irrigation is a conservative irrigation strategy for PIP production system where-
by plant's daily water allotment is applied as multiple smaller volume of water at
predetermined intervals instead of a conventional single application [8, 55, 25]. Most
soilless container substrates have a low capacity for retaining nutrients and water, and
large irrigation volume results in significant nutrient loss, particularly nitrates [11].
Cyclic irrigation was found to improve irrigation application efficiency by allowing
time for water to move through the micropore system of container substrate [22] by
around 38% over single water applications [47].
Tayler et al. [46] reported that cyclic irrigation increased plant height and relative
caliper growth of Pinus strobus by over 80% and 35%, respectively, compared with
once-daily irrigation. Nursery studies testing cyclic irrigation on woody ornamentals
have attributed the resulting increase in growth to cumulative reductions in midday
water stress [41] and subsequent maintenance of stomatal conductance rates, therefore
increasing net photosynthesis [50]. In a study conducted using 'Okame' cherry mul-
tiple irrigation cycles resulted in increased stem diameter, shoot dry weight and total
biomass compared to a single irrigation application [40]. A PIP study reported about
25% increase in the trunk diameter of red maple and oak plants [8, 23] receiving three-
cycle irrigation compared to those trees grown with single irrigation.
Cyclic irrigation was found to reduce nutrient leaching by 41% and irrigation run-
off by 30% [11]. A 30% to 89% reduction in nitrate and ammoniacal nitrogen 1each-
ing was observed with cyclic irrigation by allowing effi cient plant nitrogen uptake
compared to a single watering [9, 22] and by decreasing runoff volume [11]. A wire-
less sensor-controlled set-point based cyclic irrigation in PIP was found to reduce
daily water applications to dogwood ( Cornus fl orida 'Cherokee Brave') and red maple
( Acer rubrum 'Autumn Blaze') trees by 63% and 33%, without affecting the growth
of either species and with signifi cant labor savings in daily irrigation management,
which translated into an annual net savings of $5,263 for this operation and a payback