TENSIOMETER BASED AUTOMATED IRRIGATION FOR TOMATO UNDER PLASTICULTURE - Management, Performance, and Applications of Micro Irrigation Systems - page 201

comparisons of the effects of irrigation duration and frequency at different thresholds
for vegetables on fi ne textured soils are largely unavailable.
The purpose of this research was to use a tensiometer-controlled, automated irriga-
tion system to compare pulsed irrigation to longer-duration, high-volume irrigations at
different soil water potential (Ψ s ) levels for tomato grown using a plasticulture produc-
tion system in a silt loam soil.
16.2 MATERIALS AND METHODS
This study was conducted during 2009 and 2010 at the University of Kentucky Hor-
ticulture Research Farm in Lexington, KY (lat. 38°3'N, long. 84°30'W). 'Mountain
Fresh' tomato seeds (Seedway, Elizabethtown, PA) were planted into 72 cell green-
house trays filled with soil-less media (Pro-Mix BX; Premier Tech, Riviere-du-Loup,
QC, Canada) on 15 April 2009 and 4 May 2010. Seedlings were grown in the green-
house with temperature set points of 25/20 °C (day/night). Plants were watered daily
as needed and fertilized weekly with a 150 mg·L -1 nitrogen (N) solution (20N-4.4P-
16.6K; Scotts, Marysville, OH). Tomato plants were greenhouse grown using recom-
mended practices for transplant production in Kentucky [6]. Tomato seedlings were
transplanted using a water-wheel planter on 29 May 2009 and 14 June 2010. Plants
were set into 4-5-inch tall raised beds covered with 1-mil embossed black plastic
mulch with a single line of drip irrigation tubing (12-inch emitter spacing, 0.45 gal/
min per 100 ft., Aqua-Traxx; Toro, El Cajon, CA) placed approximately 1 inch below
the soil surface in the center of each bed. Plants were set approximately 4 inches to the
side of drip irrigation lines. Beds were approximately 30-inches across and spaced on
approximately 6.5-ft centers. Transplants were placed in single rows on each bed with
18-inch in-row spacing.
The soil was a Maury silt loam series, mesic Typic Paleudalfs. Soil samples were
collected after bed formation and transplanting. Five samples were taken from each
plot to a depth of 100 cm, in 20-cm segments. The pipette method was used for particle
size analysis [29]. Soil texture was found to be either silt loam or silty clay loam. Sand
and silt content varied from 6.5% to11.0% and 49.6% to73.2%, respectively. Clay
content ranged from 19.3% to 39.3%. Bulk densities of soil under natural conditions
were determined using a core of known volume [11]. A core sampler was pushed into
the soil at depths of 5-15 cm and 25-35 cm. Soil extracted from the sampler was oven
dried and weighed. Bulk density varied from 1.33-1.74 g·cm -3 .
Preplant fertility (19N-8.3P-15.8K; Southern States Cooperative, Richmond, VA)
was applied under the plastic mulch at a rate of 75 lb/acre N. Supplemental fertility
was initiated two weeks after transplanting and was supplied through fi ve fertigation
events alternating between calcium nitrate and ammonium nitrate, applied at a rate of
15 lb/acre N per week. Preventative spray schedules for diseases were followed with
weekly sprays made according to recommendations for fresh market tomato grown
in Kentucky [6]. One application of spiromesifen (Oberon 2SC; Bayer Crop Science,
Research Triangle Park, NC) was made in August 2009 to control two-spotted spider
mite ( Tetranchyus urticae ).
Automated irrigation was managed using paired or single-switching tensiometers