MICRO-IRRIGATION SYSTEMS FOR POT-IN-POT ORNAMENTAL NURSERY PRODUCTION - Management, Performance, and Applications of Micro Irrigation Systems - page 306

21.6.2 IRRIGATION TIMING
Most of the plants grown in PIP require irrigation on a daily basis considering low
water holding capacity and high porosity of container substrate. Current best manage-
ment practices in the US on above ground container production recommend single
irrigation to occur during early morning hours to reduce drift and evaporative loss of
water [55]. Beeson [3] reported increased growth of four woody ornamentals when
irrigation was applied during the day in contrast to early morning irrigation. Irriga-
tion during the afternoon hours increased top and root growth of Rhododendron ×
'Hershey's Red' compared to an evening irrigation by reducing substrate heat load and
minimizing water stress during later part of the day [50]. A PIP study conducted using
Cotoneaster dammeri 'Skogholm' showed that plants that were irrigated both during
the afternoon and all day significantly outperformed plants irrigated during predawn
hours [53] showed that plants that were irrigated both during the afternoon and all
day significantly outperformed plants irrigated during predawn hours. However, some
sources [42] recommend, from a water conservation standpoint, daytime as a poor
time to irrigate considering high water loss due to evapotranspiration during the hot-
test ours of the day (10:00 am to 4:00 pm). These studies suggest a lack of information
on optimal irrigation timing under PIP conditions and growers may want to consider
irrigating at times other than early morning to increase growth by minimizing sub-
strate dry down and reducing heat load in the later part of the day.

21.7 CASE STUDY
A PIP study was conducted at the University of Kentucky Horticulture Research Farm
in Lexington, KY (lat. 38º3'N, long. 84°30'W, msl elevation 381 m) to evaluate timing
of cyclic irrigation in redbud ( Cercis canadensis ). Hourly weather data were obtained
from an on-farm weather station and monthly mean air temperature, solar radiation
and cumulative precipitation were reported as August (23 0 C, 624 MJ m -2 , 18 cm), and

September (20 C, 549 MJ m -2 , 3.6 cm). Liners were grown in either 7-gallon or 15

gallon containers filled with 85% pine bark: 15% peat (vol/vol) in PIP systems. Sub-
strate moisture content were continuously monitored using EC5 (Decagon, IL) sensors
inserted into three representative containers per irrigation treatment. Acquisition and
control of water content were carried out using a Campbell CR-1000 data logger. Ir-
rigation was scheduled to replace 100% daily water used for evapotranspiration [51].
The quantity of water determined by the daily water use method was applied in
three equal amounts and applied at the following times: cyclic irrigation starting at (i)
7, 8, and 9 am; (ii) 12, 1, and 2 pm; or (iii) at 5, 6,and 7 pm. A timer and switches in
the control unit regulates the irrigation valve in calculated pulse intervals, for example,
8-12 min and cease operation and reset the system, awaiting the next 'on' signal at
the specifi ed time. Irrigation in each treatment replicate was controlled by a solenoid
valve (The Toro Co., Riverside, CA). Irrigation was delivered with one Tornado ray
jet emitter at ~6 gph (Plastro Irrigation Systems Ltd.) per container. Substrate water
content and crop water use were monitored at a 15 min frequent interval throughout
the season. Main stem diameter (caliper) was measured at 3 feet above the substrate
surface after initial potting and at the end of growing season.

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