Pneumatic defoliation - Equipment and machinery (part 2)
The equipment carrier
Depending on the manufacturer, one or more equipment carrier variants can be employed. In practice, the best solution has been flexible equipment carriers that can easily be laterally adapted to the foliage canopy and elevated to the top of the trees. it is also advantageous if the arm can be swivelled by 180° to avoid unnecessary turning manoeuvres by the tractor.
Discs and nozzles
The number and size of the discs will determine the working area, i.e. the width of canopy that can be worked. If the discs are arranged in pairs and separately, they can each be swung out independently and thus better adapted to the canopy. Each disc has one or two nozzles to regulate the outgoing airflow and thus determine how hard the air stream hits the leaves.
The effect of physics
Cold air is heavier and denser than warm air, meaning that lighter, warm air will rise faster. When cold air is accelerated it will have more mass than warm air and can thus better penetrate the canopy. Cold air also becomes more quickly saturated with water as it cannot absorb as much moisture as warm air. This in turn means that the penetration of cold air through the foliage is further increased when combined with high humidity. Theoretically, the efficiency of defoliation will increase in damp and cool conditions, which may lead to damage. The normal operating pressure for defoliation operations lies between 0.4 and 0.8 bar: this operating pressure should be adjusted both to the conditions in the apple orchard and to the environmental conditions, as should the driving speed and possibly the nozzle opening. All these parameters should ultimately lead to sufficient exposure of the apples and thus to improved colouring.
Power requirements and diesel consumption
The power required to drive pneumatic defoliators depends upon the installed compressor. Normally at least 70 to 80 hp of tractor power is needed to defoliate the apple trees on just one side. Diesel consumption, on the other hand, varies between 8 and 9 litres of fuel per hour, depending on the operating pressure. This results in a total diesel consumption of some 50 litres per defoliation pass and hectare.
Source: Südtiroler Beratungsring (South Tyrol Advisory Ring): Christian Dallemulle
Image: fruit-tec.com – REDpulse Duo