Frost Protection - UTL Repository

ACTIVE PROTECTION METHODS
same effect on air temperature in the canopy. For example, petroleum wax
heaters used only 60 percent of the energy normally needed to get the same
protection (Schultz, Lider and Parsons, 1968). Modification of temperature
within the inversion layer was more concentrated near the ground – where the
crop is – when burning petroleum wax and coke bricks compared with feedback
chimney burners (Gerber, 1969). Thus, to improve efficiency it is clearly better
to have many small fires than a few big fires.
Mobile heaters
A mobile heater is commercially available as a method for frost protection;
however, scientific evaluations of the machine have not yet been published. The
mobile heater uses four 45-kg propane tanks to supply the fuel for the heater,
which mounts on the back of a tractor (Figure 7.6). The heater uses a centrifugal
fan to blow the heated air horizontally and perpendicular to the tractor direction
as it moves up and down the rows. After starting the heater, the fuel supply is
adjusted to give a temperature of approximately 100 °C where the air vents from
the machine. When operated, the airflow extends to 50 to 75 m either side of the
machine. The tractor is driven up and down rows far enough apart so that the
area of influence overlaps. The manufacturer recommend that the tractor make
one complete cycle through the crop about every 10 minutes, a period allowing
coverage of about 5–7 ha.
In some unpublished experiments, the mobile heater showed little effect on the
minimum temperatures recorded within protected orchards. Since the energy
output from the machine is much less than energy losses from a crop during a
radiation frost night, this was not unexpected. However, whenever the machine
FIGURE 7.6
A mobile heater for frost protection mounted on the back of a tractor
Photo: R.L. Snyder
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