Agriculture Reference
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functioned to turn on irrigation while the other turned it off. In the single-tensiometer
treatment, irrigation solenoids were turned on and off by one switch. A single-tensi-
ometer treatment was chosen to determine if a simpler automated system with one
measurement point could be comparable to a two-tensiometer setup. Tensiometers
were placed approximately 8 inches from the tomato plants and 4-inches from the
edge of the raised beds, at a depth of 8-inches from the upper surface of the bed. On/
off set points for the four, two-tensiometer treatments were as follows: on/off −30/-10,
−30/-25, −45/-10, −45/-40 kPa. The single-tensiometer treatment was set at −35 kPa
in 2009 and −40 kPa in 2010. These set points were based on previously reported
thresholds [8, 39]. Irrigation treatments were implemented on 17 June 2009 and 27
June 2010 after plants were established. The frequency and duration of the automated
and manual irrigation events were recorded with data loggers (Hobo U9 State Data
Logger; Onset, Cape Cod, MA). Water usage for the season was calculated by multi-
plying the frequency and duration of irrigation events by the fl ow rate of drip irrigation
tubing at a constant pressure (10 psi). There were four replications of irrigation treat-
ments. Treatment plots consisted of 20 plants (measurements were taken on 16 plants
in the center of each plot) arranged in a completely randomized design for a total of
20 experimental plots. Previous research indicated that growing conditions in the plots
used for this trial were uniform and a blocking design was not required.
In the 2009 growing season, two soil moisture probes (EC-5; Decagon Devices,
Pullman, WA) per plot were placed at 6 and 12-inch depths into the raised beds in
the same relative location to the tomato plants as tensiometers. Data loggers were
unavailable for soil moisture data collection in 2010. On 3 July 2009, an access hole
adjacent to the plant bed was dug and probes were inserted into undisturbed soils in
the plant bed under the plastic. Probes were inserted in a parallel orientation with
the soil surface at depths of 6 and 12 inches. Probes were connected to data loggers
(Em 50; Decagon Devices) and soil volumetric water content (VWC) recorded hourly
throughout the season.
Tomatoes were harvested fi ve times each year. In 2009 harvests were conducted
from 4 Aug. to 8 Sept. In 2010 fruit were harvested from 16 Aug. to 13 Sept. Plants
were harvested approximately weekly. Fruit were graded according to U.S. Depart-
ment of Agriculture standards for fresh market tomatoes [37].
Predawn and midday leaf water potential (Ψ
L
) and leaf relative water content
(RWC) measurements were initiated on 7 and 14 July 2009 and 2010, respectively.
Measurements of leaf RWC and Ψ
L
were conducted during the same time period on
the same days throughout the study. Measurements were taken biweekly in 2009 and
weekly in 2010. Plant Ψ
L
was measured using a pressure chamber (Model 615; PMS
Instrument Company, Albany, OR) using two recently matured, fully expanded leaves
from plants near the center of each plot [27]. Leaf RWC, was conducted according to
the method of Barrs and Weatherley [3], was determined on samples of fi ve, recently
matured, fully expanded leaves obtained from plants near the center of each plot. Upon
removal from plants, leaves for Ψ
L
and RWC were immediately placed in sealed poly-
ethylene bags, packed in a cooler with ice and measured within 30 min of sampling.
Weather data were obtained from an on-farm weather station that recorded envi-
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