Project Description       Back to Freeze Page 

Objective:  To document the effectiveness of freeze protection systems (overhead water application) at protecting a southwest Florida tomato crop.

Experimental Methods:  Four field plots are instrumented to measure the air temperature at points above the ground within the crop canopy and above the crop canopy.  In Field A, a single datalogger (PA) collects temperature measurements from two 25-thermocouple multiplexers.  One multiplexer measures temperatures in the "Rotator System" freeze protection system in the west half of the field while the other multiplexer measures temperatures in the adjacent "Drip System" control plot in the east half of the field. The Field A datalogger also collects ambient air temperature and wind speed at the edge of the field.  In Field B, the second datalogger (PB) has a dedicated 32-thermocouple multiplexer and collects temperature measurements from the "Wobbler System" in the north half of the field.  The third datalogger (PC) also has a 32-thermocouple multiplexer.  This unit measures temperatures in the adjacent "Drip System" control plot in the south half of the field.  Between the two halves of Field B is located a weather station with the fourth datalogger (PD).  This unit collects wind speed, ambient air temperature, rainfall, and (soon) solar radiation and relative humidity.

Horticultural Methods:  Irrigation water is delivered to both halves of Field A and Field B using a combination of a drip fertigation system and a semi-closed seepage irrigation system.  The Rotator and Wobbler systems are used only to deliver water for freeze protection, not irrigation.  The tomato field is set up under a standard 6-row bed configuration with each row set at 9 inches high using plastic mulch on 6-foot spacing.  Field A has a 46' bed width while Field B has a slightly narrower 44' bed width.

Freeze Protection System Characteristics:  Both the Rotator and Wobbler systems deliver approximately 100 gallons per minute per acre.

Rotator System:  The Rotator system delivers a slowly rotating arch of water much like a standard overhead sprinkler system.  The system uses Rotator emitters, model WF18 with nozzle #18 Gold, manufactured by Nelson Irrigation Corporation.  The emitters are spaced in a 38' by 46' grid in a staggered pattern. These emitters deliver 4.02 gpm at 50 psi.  The precipitation rate average is 0.23 in/hr with a maximum of 0.32 in/hr and minimum of 0.09 in/hr.
 
 

Wobbler System:  The Wobbler systems delivers an umbrella of finer water droplets over the crop canopy.  The systems uses #5 miniWobbler emitters manufactured by Senninger Irrigation.  The emitters are spaced in a 17' by 19' grid pattern. They deliver 0.95 gpm at 30 psi.  The distribution pattern is approximately linear in the radial direction from 1 to 21 feet with a maximum precipitation rate of approximately 0.125 in/hr measured 18 inches below the emitter at a radius of 1 foot. This overlapping grid pattern should provide a relatively uniform application rate over the field.
 

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