Electronic Journal of Polish Agricultural Universities (EJPAU) founded by all Polish Agriculture Universities presents original papers and review articles relevant to all aspects of agricultural sciences. It is target for persons working both in science and industry,regulatory agencies or teaching in agricultural sector. Covered by IFIS Publishing (Food Science and Technology Abstracts), ELSEVIER Science - Food Science and Technology Program, CAS USA (Chemical Abstracts), CABI Publishing UK and ALPSP (Association of Learned and Professional Society Publisher - full membership). Presented in the Master List of Thomson ISI.
Volume 7
Issue 2
Agricultural Engineering
Available Online: http://www.ejpau.media.pl/volume7/issue2/engineering/art-03.html


Waldemar ¦wiechowski, Grzegorz Doruchowski, Ryszard Hołownicki, Artur Godyń



The characteristics of air jet together with travel velocity of the sprayer are crucial factors influencing the penetration of air in the tree canopy. The objective of the study was to determine the volume of air penetrating into the canopy of apple trees, produced by three orchard sprayers with different fan types and operated at different travel velocities. Due to different fans, the following discharge systems were available: radial air flow, cross-flow and directed air flow. The sprayers were driven at 4, 6 and 8 km/h along the trees inside which the air velocity was measured in 9 points, placed in 3 vertical layers. The obtained data was processed to get the air volume penetrating the tree canopy and being delivered to the points of measurements. The influence of travel velocity on air penetration in the tree depended on the character of the air jet produced by the sprayer. For high volume/low speed air jets (radial air flow and cross flow) the decrease of travel velocity caused consid

Key words: orchard sprayer, travel velocity, air velocity, air flow, canopy penetration..


An air jet generated by orchard sprayer plays an important role in conveying the spray into the target crop during spraying. There are three types of fans used in orchard sprayers: axial, radial and tangential. Most of the sprayers used in Poland are equipped with axial fans producing a radial air flow of capacity between 20 000 and 40 000 m3 h-1. In order to limit a spray plume produced by traditional axial fan sprayers to the actual size of trees the air ducts such as deflectors are mounted on the fans. The axial and tangential fans produce high capacity air jets with velocity around 30 m s-1 measured in the fan outlet. The air jets generated by radial fans have velocity around 50 m s-1 but their capacity is relatively low which makes them easily dispersed during the movement of sprayer and sometimes less effective in terms of penetration into tree canopies. As reported by Randall [6] the sprayers producing air jets of great volume and low velocity penetrate the tree canopies more effectively than those of lower volumes and higher velocities.

The parameters of air jet together with travel velocity of the sprayer are crucial factors influencing the quality of treatments and the spray emission beyond the target area. Fox [5] reports that during practical applications the off-target emission is considerable and it significantly contributes to environmental pollution. The proper adjustment of air jet parameters affects the resultant trajectory of spray droplets and hence it plays an important role in spray deposition [7].

According to Fox [3] even a slight wind blowing at 2-5 m s-1 can disturb the air flow of the initial velocity 50 m s-1. It has been explained by a 10-fold reduction of air jet velocity at the distance of 3 m from the fan outlet. The measurements carried out in a wind tunnel showed that at the distance of 2.4 m from the outlet of tangential fan the cross wind at velocities 3.0, 4.5 and 6.7 m s-1 deflected the air jet by the angle 15°, 60° and 70° respectively. The air jet is deflected also as the sprayer is driven along the rows of trees [2, 4]. Walklate [10] reported that effectiveness of crop penetration decreased in proportion to the square of travel velocity. However, between sprayer velocities 3.2 and 4.7 km h-1, Derksen and Gray [1] did not find any significant differences in air jet velocity in the trees. Fox [2] observed that reduction of penetration is caused by air jet deflection, dispersion of air stream in the ambient air and absorption of energy of the air by the tree foliage. When the sprayer operating velocity decreased from 6.4 to 3.6 km h-1, the air velocity measured in the tree decreased by 10-15%.

As reported by Travis [9] deflection of the air jet during spray treatments in orchards reduces the spray deposition on the trees and worsens the spray distribution within the canopies. However, Fox [3] and Walklate [11] showed that the travel-wind induced bending of the air jet reduced the wind drift and increased the total deposition of spray on the trees, but at the expense of penetration ability and uniformity.

The air movement in the tree canopy appears as a pulse. Recording the velocity of such short pulse requires the use of anemometers with a short response time [8]. For mapping of the air movement in the tree several anemometers are usually used. Their layout depends on the size, shape and density of the canopy. According to Svensson [8] one of the characteristics of the air velocity pulse is the maximum velocity. It could be regarded as an expression for how well the air jet was able to penetrate the canopy, namely penetration effectiveness. However the instantaneous maximum often exhibits great variation and is sensitive to random influence, and therefore should be used with care. The measured air velocity integrated over time of the sprayer pass expresses the flow of air through a position, thus indicating how much of the available flow has penetrated the canopy. Because the air contains the spray droplets, air flow volume during a pass is one of the factors influencing the deposition resu lt.

The objective of this study was to determine the volume of air penetrating into the canopy of apple trees during use of orchard sprayers with different fan types and for different travel velocities of sprayers.


The experiment was carried out in semi-dwarf apple orchard in full-leaf stage. The trees of average height 3.0 m and width 1.6 m were spaced 4.0 × 2.5 m.

The following sprayers with different air discharge systems were used in the experiment (fig. 1):
– axial fan sprayer – radial air flow (32 m s-1; 43 m3 h-1),
– tangential fan sprayer – cross flow of air (26 m s-1; 34 m3 h-1),
– radial fan sprayer with adjustable air spouts – directed air flow (44 m s-1; 12 m3 h-1).

Fig. 1. Sprayers used in the experiment: A – axial fan sprayer; B – tangential fan sprayer; C – radial fan sprayer with adjustable air spouts

Each sprayer with shut nozzles and fan operating at the speed so it produced the air flow at the parameters given above was driven along the row of trees at travel velocities 4, 6 and 8 km h-1. Each sprayer pass at a given velocity was repeated 5 times. In the row of relatively homogeneous trees one of them was selected in random to locate 9 hot film anemometers (TSI Inc.) in its canopy, as shown on figure 2. In the layout of anemometers three canopy layers were distinguished: LAYER 1 – outer, the closest to the sprayer; LAYER 2 – central; LAYER 3 – outer, the farthest from the sprayer. The anemometers were connected to AAC-2 logger recording simultaneously all the measurements of velocity of air passing through the canopy (fig. 2 ). Data were recorded at the frequency 250 Hz and interpreted by the computer software numerically or graphically (fig. 3).

Fig. 2. Layout of hot film anemometers in the tree canopy


Fig. 3. The graph of air velocity

The graphs of the air velocity measured in each of 9 sensor locations were analyzed for identification of initial/terminal times of the measurements that were to be used in the calculation of air volumes passing the locations of the tree canopy. For each measurement (graph) the initial and terminal time was identified separately. The initial time was set at the moment from which the velocity showed a rapid and continuous increase above the level of noise signal and the terminal time then the air velocity dropped to this level and stabilised (fig. 3).

Based on the results of the air velocity measurements the volume of the air flow for each sensor location was calculated according to the formula:


Q – volume of air flowing through the location of the anemometer, m3
P – surface area of the anemometer sensor, m2 to – initial time of the measurement, s
tk – terminal time of the measurement, s
V – air velocity, m s-1

The integer in the equation (1) was estimated according to the formula:


Vi – spot individual velocity, m s-1
n – number of Vi values during measurement interval (tk – to)


For each of three vertical canopy layers (layer 1 – the closest to the sprayer, layer 2 – central, layer 3 – the opposite side of the canopy) the average air flow was calculated out of data from three measuring points (fig. 2). The results were presented graphically on linear charts that allow to follow the air flow changes across the canopy for different travel velocities, separately for each sprayer type (fig. 4A, B and C).

Fig. 4. Air volume delivered into the tree canopy during applications at three travel velocities:
A – radial flow sprayer; B – cross-flow sprayer; C – directed air jet sprayer

In case of radial flow sprayer the air volume clearly tended to decrease as the distance from the sprayer increased. No such clear tendency was observed for the two other sprayers (fig. 4B, C). Instead they delivered more air to the centre of the canopy than to the outer zones. In the centre of the canopy, where the foliage was much poorer the sensors were exposed to the turbulent movement of air acting from different directions and being recorded as a long signal. Even if the air velocity in the centre of the tree was slow the length of the signal affected the magnitude of integer of velocity by time, expressing the air flow. Different situation took place in case of high volume air jet from the radial flow sprayer (axial fan). It maintained the energy when passing through the outer foliage and acted on the anemometers in the layer 1 with relatively high velocity and than kept losing the energy on its travel across the canopy. This resulted in decrease of air volume at layers 2 and 3.

The biggest differences between travel velocities in terms of air volume penetrating into the tree canopy were obtained for the radial flow sprayer (fig. 4A). A reduction of travel velocity by 50% (from 8 to 4 km h-1) caused nearly a triple increase of air volume. For the cross-flow sprayer the same reduction of travel velocity resulted in a double increase of air volume. As expected, these results clearly showed that during a slower driving and hence a longer time of air jet penetration into the trees a higher volume of air convening spray droplets is passing through the canopy. It means that more spray is delivered into the tree canopy which may result in producing a higher spray deposition on leaves and branches. For the directed air jet sprayer the differences in air volume recorded in the tree canopy at different travel velocities were smaller, probably because of considerably lower air volume produced by this sprayer compared to the other sprayers which must have resulted in lower penetration effectiveness [6].


The influence of travel velocity on apple tree penetration expressed by air volume delivered to different locations in the canopy depended on the parameters of the air jet produced by the sprayer. For high volume/low speed air jet the decrease of travel velocity caused considerable increase of air volume penetrating the tree while for low volume/high speed air jet no significant differences were observed. In the earlier case the penetrating air volume was in general relatively high and tended to decrease in the consecutive vertical layers of the tree while in the latter case the air volume stayed at the low and constant level across the canopy.


  1. Derksen R. C., Gray K. L., 1995. Deposition and air speed patterns of air-carrier apple orchard sprayers. Transaction of the ASAE 38 (1), 5-11.

  2. Fox R. D., Reichard D. L., Brazee R. L., Hall F. R., 1984. Penetration of apple tree canopy by orchard sprayer air jets. Ohio Agricultural Research and Development Center. Research Circular 283 p. 22-25.

  3. Fox R. D., Reichard D. L., Brazee R. L., 1985. A model study of the effect of wind on air sprayers jets. Transaction of the ASAE 28 (1), 83-88.

  4. Fox R. D., Reichard D. L., Brazee R. L., 1987. Travel and wind affect jet sprayers. American Nurseyman 165 (1), 100-102.

  5. Fox R. D., Reichard D. L., Brazee R. L., Hall F. R., 1990. Downwind residue from air spraying of a dwarf apple orchard. Transactions of the ASAE 33 (4), 1104-1108.

  6. Randall J. M., 1971. The relationships between air volume and pressure on spray distribution in fruit trees. J. Arg. Eng. Res. 16(1), 1-31.

  7. Schmidt K., Koch H., 1995. Adjustment of air blast sprayers and distribution of pesticide deposition in orchards. Nachrichtenblatt Deutschen Pflanzenschutzdienst 47 (7), 161-167.

  8. Svensson S. A., 2001. Air jet influence on application results in orchards. Mat. Konf. “Racjonalna Technika Ochrony Ro¶lin”, p. 122-134.

  9. Travis J. W., Skroch W. A., Sutton T. B., 1987. Effect of canopy density on pesticide deposition and distribution in apple trees. Plant Disease 71 (7), 613-615.

  10. Walklate P. J., Weiner K. L., 1993. Engineering models of air assistance orchard sprayers. ISHS International Symp. Engineering as a Tool to Reduce Pesticide Consumption and Operator Hazards in Horticulture. Ulvik – Norway, 8-13 VIII 1993, 1-8.

  11. Walklate P. J., Richardson G. M., Cross J. V., 1996. Measurements of the effect of air volumetric flow rate and sprayer speed on drift and leaf deposit distribution from an air-assisted sprayer in an apple orchard. Proceedings of Agricultural Engineering Research, AgEng96, Paper 96A-131, 9 p. Madrid, Spain.

Waldemar ¦wiechowski, Grzegorz Doruchowski, Ryszard Hołownicki, Artur Godyń
Research Institute of Pomology and Floriculture
18 Pomologiczna Street, 96-100 Skierniewice, Poland
phone (+48 46) 833 20 21 w. 281
e-mail: wswiecho@insad.pl

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