Image analysis of water sensitive paper as a tool for the evaluation of spray distribution of orchard sprayers

Transcription

1 Aspects of Applied Biology 57, 2000 Pesticide Application Image analysis of water sensitive paper as a tool for the evaluation of spray distribution of orchard sprayers By A DE MOOR, J LANGENAKENS and E. VEREECKE Agricultural Research Centre Gent (CLO), Department of Mechanisation, Labour, Buildings, Animal Welfare and Environmental Protection (DvL), Van Gansberghelaan 115, B-9820 Merelbeke, Belgium and P JAEKEN Department of Ecology Royal Research Station of Gorsem, Brede Akker 3, B-3800 St. Truiden, Belgium P LOOTENS and P VANDECASTEELE Agricultural Research Centre- Gent (CLO), Department of Plant Physiology and Ecophysiology, Van Gansberghelaan 109,B-9820 Merelbeke, Belgium Summary Several tests were performed on commercially used orchard sprayers with different types of air discharge systems (conventional, cross flow, directional spouts). The measurements were conducted in a hangar on an apple orchard planted in containers. Pure tab water and water with minerals (Mg, Mn, Zn) were sprayed. Water sensitive paper and blotting paper were put in and around the trees to evaluate the distribution in the canopy by image analysis and/or chemical analysis. The distribution is characterised by a large variability which is partially caused by the random effects of the tree itself. By means of a large number of replicates and correct statistical methods the measurements can be interpreted, but the link between this three dimensional distribution and the adjustment of the sprayer that caused it is very hard to find. Therefore vertical poles, on which water sensitive paper was stuck, were used to further develop an adjustment procedure by means of image analysis. It is possible to determine the spot density, spot size, the histogram of spot sizes and distance between spots. As orchard sprayers are always equipped with air-assistance, it is very important to take the optimisation of the air pattern into account. Therefore the air pattern was also measured. This method of calibration and adjustment of orchard sprayers eliminates human error, maintains a quality standard and provides us with an easy, fast, automated and accurate analysis of the spray quality. Key words: air-assistance, orchard sprayer, spray distribution, spray deposit, image analysis, water sensitive paper

2 Introduction Spray coverage is influenced by many factors including driving speed, droplet size, canopy geometry and density, climatic conditions and basic sprayer performance (Praat, Mankletow, Suckling & Maber, 1996). A correct adjustment of the sprayer improves the accuracy and the efficiency and results in a more uniform and targeted spray deposit which helps to prevent inadequate pest control, induction of resistance, economical loss of product, time and labour and environmental pollution (Praat, Mankletow, Suckling & Maber, 1996). The sprayer can be adjusted by directing the air deflectors or adjustable air spouts, by switching off nozzle pairs or by the use of correct nozzle type or fan speed. Although several procedures have already been proposed to improve the orchard sprayer calibration, no satisfaction was yet found and in practical conditions this topic does not receive the attention it requires (Gracia, Planas & Bosch, 1996; Gil, Badiola, Armengol & Bernat, 1996, Holownicki, Doruchowski, Godyn, & Swiechiowski, 1996; Pergher & Gubiani, 1996; Pergher & Gubiani, 1997). Therefore we try to establish a practical method to calibrate orchard sprayers that is simple, fast, objective and reliable. For the evaluation of biological efficiency, it might be crucial to determine the distribution of the spray liquid within the canopy. For this purpose analytical methods, which determine the amount of captured tracer in a quantitative way, are expected to be the most reliable. Nevertheless, coefficients of variation (CV) range between 40-80, the variability within individual trees and between individual leaves is even twice as large (Praat, Mankletow, Suckling & Maber, 1996). This is all partially due to the random effect of the tree itself. Deposits from directly exposed leaves are much higher than those from both partially or badly exposed leaves (Perger & Gubiani, 1995; Perger Gubiano & Tonetto, 1997). Statistical techniques are being developed to interpret these variable data. The same problem appears in case water sensitive papers are positioned in the canopy (Salyani & Fox, 1999). Nevertheless the techniques used to obtain reliable and objective data out of the digital images of these papers are very useful in the development of adjustment procedures (Salyani & Fox, 1994). To explain the relationship between the distribution pattern and the sprayer settings vertical poles are used. In this case problems of variance, due to the randomness of the tree or coverage by leaves do not interfere. By image analysis of WSP, attached to the vertical poles, we can evaluate the distribution of the aerosol, a mixture of sprayed droplets and air. The obtained spray pattern is generated by, on the one hand liquid which is distributed by the nozzles and influenced by their size, type, angle, pressure and liquid characteristics. On the other hand the air pattern that can be altered by the fan properties (position of blades, capacity, size, location and speed). Therefore not only the liquid distribution, but also the air pattern was measured at three different distances away from the outlet. Materials and methods The sprayers Six commercial air-assisted sprayers with different types of air discharge systems (conventional, cross flow, directional spouts) are used with fixed settings to study the adjustment procedure (Fig. 1-6). Sprayers equipped with axial as well as centrifugal fans are used. Two types were equipped with two fans. Settings were kept at 540 rpm and fan setting 1 for all measurements.

3 Calibration of the nozzles All spraying tests were done with several different types of nozzles (Table 1). The nozzles were calibrated at an equal volume of 0.50 l min (± 7%). Forward speed was kept constant at 6 kmh. Table 1. Different types of nozzles used during the experiments. Flow rates (l/min) for the used pressures (bar). Nozzle Type Pressure Flow rate (bar) (l min ) TeeJet Conejet TXAVK-04 green Hollow cone nozzle Teejet Conejet TXAVK-06 red Hollow cone nozzle Albuz ATR lila Hollow cone nozzle Albuz ATR brown Hollow cone nozzle Teejet XR green Flat fan nozzle Table 2. Sprayers used and the flow rate (m³h ) of the fan Sprayer Fan Type Flow rate (m³s ) Hardi Condor V Axial Hardi CondorJet Axial Bamps Duoprop Axial Bamps Turblow axial Hardi Tango Centrifugal Douven Delta Centrifugal ±11000 Experimental set-up Preliminary tests The aim was to evaluate the randomness of measurements with trees and to compare analytical methods with image analysing techniques. Measurements were conducted in a hangar on a container-orchard. Trees of approximately 3 m height were planted in containers and brought in a hangar. The distance within the row was 1.25 m and between the rows 3.5 m. The measurements were conducted during spring and early summer. Two sided water sensitive and filter papers were attached to the branches, as if they were leaves. For this reason the tree was divided into several sections (Fig. 7). In each available section of in total five trees an artificial collector was placed. Spraying was done with a tank mix with minerals or with pure tab water. By chemical determination of the amount of minerals captured by the filter paper the percentage of spray recovered by the canopy is determined. By image analysis of the water sensitive paper spot size, covered area and distance between spots were evaluated. The droplet spread varies with physical properties such as surface tension, direction (angle) and energy of impact on the cards. By division of the spot diameter by the spread factor, it would be possible to determine the diameter and volume of the original droplet that splashed on the paper. This means that all

4 droplets are considered to have the same physical properties and to hit the water sensitive paper under equal conditions, which is usually not the case within a canopy. To develop the adjustment procedure only the covered area was considered, as it is directly influenced, by the settings of the sprayer. Droplet size on the contrary is not only hard to determine with this technique, but primarily determined by the nozzle and not by the adjustment of the sprayer in general. Experimental set-up Vertical distribution measurements A second experiment was conducted without the presence of the trees, but under similar conditions. Vertical poles of 4 m height on which ribbons of water sensitive paper were attached, were positioned at the level of the centre of the trees, 60 cm more to the front and 60 cm more to the back (Fig. 7). After spraying with pure tab water, the stained water sensitive papers were collected, scanned and parameters such as covered area, spot size and distance between droplets were determined by the image analysing system. Back Middle Front Top Middle Bottom SPRAY DIRECTION SPRAY DIRECTION 60 cm Frontview Topview 60 cm Fig. 7. Experimental set-up of trees and poles in the hangar, frontview and topview. Experimental set-up Air discharge measurements The total airflow rate of the sprayers was estimated by measurements of the air velocity at the air outlet and multiplied by the surface of the outlet. The air patterns were measured with hot wire anemometers on lines parallel with the sprayer. These lines are located at distances of 1 m, 1.75 m and 3.5 m away from the centre of the fan. The distances along the line are defined by the projection of line in angles of 10, 20 and 30 of the line perpendicular with the fan outlet. All measurements were conducted with the sprayer driven in the first gear and the PTO of the tractor at 540 rpm. The results are shown in the following graphs.

5 30 20 SPRAYER 10 FAN cm cm 350 cm -30 Fig.. 8. General overview (topview) of the measuring situation Results The Hardi Condor V is characterised by an air plume that flares out to the upper side of the machine. The highest velocity (22-24 ms ) is found in the centre of the cloud and is situated at 60 cm height and 10. At 1m from the centre of the fan, the plume has become very large and less powerful in the centre (146 ms ). This centre is now found at 0, but still at the same height. At 3.5 m from the sprayer, the air velocity is negligible (80 ms ). This sprayer thus generates an enormous cloud that should be limited as much as possible by the use of deflector plates. As the strong centre is situated at 60 cm the spray cloud does not sufficiently reach the top of the trees and therefore this type is more useful in low orchards. The conventional type blows from the underside of the tree to the higher parts and does usually reach more the underside of the leaves. For the Hardi Condor Jet, a very strong centre (38-40 ms ) is situated at approximately the same height as the centre of the fan. The higher air outlets are characterised by a much lower air velocity that is still higher than for the conventional Hardi Condor V. The pattern is thus more or less elongated with a peak in the lower part. The cloud does not fan out that much and is limited in height. At 1.75 m this same elongated pattern is recognised. This also means that, while the conventional type blows from bottom to top, the cross flow type blows more horizontally, and thus reaches relatively more upper sides of leaves. The plume is not fanned out, but on the contrary very marked out. At further distance (3.5 m) the pattern can not be recognised any more and velocities fall back to 10 ms. The air pattern of the Bamps Duoprop is fanciful and the pattern is influenced by the rotating direction of the fan, which means an up worth air movement at the right side and a

6 down worth one at the left side. A peak in air velocity of ms is measured at 180 cm height between the two fans. At further distance from the machine, the pattern is slightly recognisable but at 1.75 m the air velocity falls back 102 ms, which is rather low. At 3.5 m, 10 ms is still measured. Two centres are found in the air pattern of the Bamps Turblow. The first one is found at approximately the same height as the centre of the lower fan. The second peak in the cloud was found at 320 cm height. The centre of the second fan is found at 284 cm height. As the fans are positioned in opposite directions on a central support the centres are localised symmetrically to the centre of the sprayer. As they both blow towards the central axe, the plume of the lower and higher fan mix in the zone between the two fans. At one metre the air pattern already reaches a height that is too high for a classic apple orchard. Moreover, the aerosol fans out and an enormous cloud is generated. The mixture drifts away in several directions at 3.5 m (80 ms ). The Hardi Tango is equipped with five directional spouts that can be detected in the pattern. The maximal air velocity at 1m from the centre is higher for the lower spouts (28-30 ms ) which are close to the fan, than for the spouts that are mounted higher (22-24 ms and 146 ms ). Also in the pattern at 1.75 m, this pattern is recognised. The tree lower spouts generate one long peak (146 ms ). The two higher mounted spouts generate peaks with approximately equal air speeds. The air pattern is straight on and not angled relatively to the sprayer. At a distance of 3.5 m a long and small spray cloud with maximal air velocity of 80 ms is found. The air cloud does not reach more than 2.5 m, typical for sprayers design for vineyard spraying. The air distribution of the Douven Delta is characterised by an elongated, narrow air cloud, in which the individual outlets are not recognisable. The pattern is very homogenous over the entire height. The highest velocity (24-26 ms ) is measured at 140 cm, approximately at the middle of the sprayer. The further from the sprayer the higher this peak is situated. In general the direction of the spray cloud is backward (0 ). At 1.75 m the air pattern is similar and still very homogenous. This pattern can also be recognised at 3.5 m, but the air velocity is lower (6-8 ms ). Conclusion Preliminary tests indicated that it is very hard to adjust a sprayer by means of measurements in which trees are involved. Chemical analysis of filter paper as well as image analysis of WSP are suitable techniques to determine the amount of sprayed liquid, but the tree itself, characterised by it s own randomness, disturbs the spray pattern and the final result. The leaves also may cover others and thus interfere. A substantial variation in distribution pattern between different replicates exists and the link between the measured pattern and the spray setting can only partially be declared. The vertical spray pattern obtained by image analysis of the water sensitive paper on the poles, is very similar to the air patterns. The (coloured) data set of vertical spray patterns will be shown at the AAB meeting. The results of the air velocity measurement are given in fig. 1 6 (cde). This very clear relationship confirms that the air discharge system and the fan characteristics influence the obtained pattern strongly and that the adjustment of the sprayers should be based on knowledge of the air pattern. The most remarkable findings were that the Hardi Condor V generates air plumes which fans out and has very powerful centre. The cross flow type, Hardi Condor Jet, is still characterised by this peak, but the cloud is directed by the air outlets and this gives a more homogenous distribution. The types with two fans show two

7 centres in their pattern. Their air velocity fields are lower (20 ms ) for these two machines and the cloud doesn t carry very far. At 1.75 m the velocity has already fallen back to 10 ms Types with directional air spouts and centrifugal fans deliver at 1.75 m around 12 ms over the entire height of the pattern. They deliver a relatively homogenous distribution with relatively high velocities at the imaginary centre of a tree. This is due to the centrifugal fans that are used in types. For all machines the air velocity falls back to a maximum of about 10 ms at 3.5 m. To optimise the operational adjustment the vertical spray pattern obtained by image analysis of WSP on rigid poles is a very useful, easy and quick tool that can be linked to the air pattern. Acknowledgements The authors would like to thank the Belgian Ministry of Small Enterprise and Agriculture, DG VI, Administration Research and Development for financial support. The following companies supplied equipment for the experiments: BAB Bamps (Belgium), Douven BV (Netherlands), Hardi International (Denmark). We also would like to acknowledge ing. Marc Pieters for the technical assistance during air velocity measurements. References Gil E, Badiola J., Armengol E, Bernat C Design and verification of a moving equipment for orchard and vineyard sprayer calibration. Agricultural Engineering Conference, Madrid, 96A41. Gracia F, Planas S, Bosch M Comparison of two measurement methods of the vertical distribution of sprayers for fruit crops. Agricultural engineering Conference, Madrid. Holownicki R, Doruchowski G, Godyn A, Swiechiowski W Spray deposit within apple tree canopy as affected by the air-jet direction. Agricultural Engineering Conference, Madrid. Kaul, P, Smidt K, Koch H Distribution quality of orchard sprayers. European Plant Protection Organisation Bulletin 13, 4: Pergher G, Gubiani R The effect of spray application rate and airflow rate on foliar deposition in a hedgerow vineyard. Journal of Agricultural Engineering Research 61: Pergher G, Gubiani R Methods for the assessment of vertical spray distributions from air-assisted sprayers: a comparative study. Agricultural Engineering Conference, Madrid, 96 A27. Pergher G, Gubiani R A comparison of methods for assessing vertical spray distributions from air assisted sprayers. Bulletin OEPP/EPPO 27: Pergher G, Gubiani R, Tonetto G Foliar Deposition and Pesticide losses from three air-assisted sprayers in a hedgerow vineyard. Crop protection 16(1): Praat JP, Manktelow D, Suckling DM, Maber J Can application technology help to manage pesticide resistance? NZPPS paper, Canadian Application Technology. Salyani M, Fox RD Performance of image analysis for assessment of simulated spray droplet distribution. Transactions of the ASAE 37(4):

8 Salyani M, Fox RD Evaluation of spray quality by oil- and water-sensitive papers. Transactions of the ASAE 42(1):

9 Fig. 1a. Hardi Condor V Fig. 2a. Hardi Condor Jet Fig. 3a. Bamps Duoprop Fig. 4a. Bamps Turblow Fig. 5a. Hardi Tango Fig. 6a. Douven Delta conventional type with axial fan cross flow type with axial fan and deflector plates cross flow type with 2 axial fans conventional type with 2 opposite axial fans directional air spouts and centrifugal fan directional air spouts and centrifugal fan