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Exploring variable air flow rate as a function of leaf area index for optimal spray deposition in trellised vineyards



In 3D crops, excessive fan airflow speed may reduce deposition and increase spray losses due to canopy compression. To solve this problem, variable fan airflow rate as a function of canopy characteristics is a key in the context of a sustainable crop protection technology. The effects on spray canopy deposition of different air volume rates (low, medium, and high) generated by a 700 mm diameter axial fan, combined with 4 and 8 km h-1 forward speed, were assessed in a vineyard at an early and late growth stage. The objective was to identify the fan airflow setting (m3 h-1) which maximizes canopy spray deposition (% of applied) with the final aim to determine the relationship between leaf area index (LAI) and optimal fan airflow rate. The results confirmed that an excessive airflow rate significantly decreases spray deposits. When the forward speed increased from 4 to 8 km h-1, the airflow rate had to be increased from low to medium to maximize canopy spray deposition. The results showed the importance of total air volume applied per hectare (m3 ha-1) as a parameter to maximize the spray deposits, irrespective of forward speed. Finally, the relationship between the LAI (adim.), accounting for crop characteristics and canopy density, and the total air volume applied (m3 ha-1) to maximize the canopy spray deposition was identified.
Aspects of Applied Biology 147, 2022
International Advances in Pesticide Application
Exploring variable air ow rate as a function of leaf area index for
optimal spray deposition in trellised vineyards
1Department of Agricultural, Forest and Food Sciences (DiSAFA), University of Turin
(UNITO), Turin, Italy
2CAFFINI S.p.a., Palù, Italy
3Flanders Research Institute for Agriculture, Fisheries and Food (ILVO), Merelbeke, Belgium
4Agricultural University of Athens (AUA), Athens, Greece
Corresponding Author Email:
In 3D crops, excessive fan airow speed may reduce deposition and increase spray losses
due to canopy compression. To solve this problem, variable fan airow rate as a function
of canopy characteristics is a key in the context of a sustainable crop protection technology.
The eects on spray canopy deposition of dierent air volume rates (low, medium, and high)
generated by a 700 mm diameter axial fan, combined with 4 and 8 km h-1 forward speed,
were assessed in a vineyard at an early and late growth stage. The objective was to identify
the fan airow setting (m3 h-1) which maximizes canopy spray deposition (% of applied)
with the nal aim to determine the relationship between leaf area index (LAI) and optimal
fan airow rate. The results conrmed that an excessive airow rate signicantly decreases
spray deposits. When the forward speed increased from 4 to 8 km h-1, the airow rate had to
be increased from low to medium to maximize canopy spray deposition. The results showed
the importance of total air volume applied per hectare (m3 ha-1) as a parameter to maximize
the spray deposits, irrespective of forward speed. Finally, the relationship between the LAI
(adim.), accounting for crop characteristics and canopy density, and the total air volume
applied (m3 ha-1) to maximize the canopy spray deposition was identied.
Key words: Precision agriculture, variable airow rate, electrically driven axial fan, spray
canopy deposit, airblast sprayer
The adjustment of the air jet (fan airow rate, velocity and, if possible, direction) in vineyard
sprayers in function of the canopy morphology (size, leaf density and row distance) can avoid
areas with under- or over-application of plant protection products (PPP) and can reduce losses
due to spray drift. Vines of the same variety can strongly vary in shape, size, and foliage density
within the same parcel and among plots. A precise and continuous air jet adjustment according to
the crop characteristics within the vineyard is thus key for an ecient and sustainable pesticide
application. In general, the fan airow aims to carry the PPP droplets onto the target and move the
foliage in order to improve the deposition on the internal part of the canopy and on the underside
of the leaves. Nevertheless, it is well known for 3D crops that an excessive air support may reduce
deposition, owing to canopy compression, and increase spray losses (Hislop, 1991; Balsari &
Marucco, 2004). For example, Pergher (2005) reported that a reduction of the air ow rate from
10.6 to 6.3 m3 s-1 increased mean foliar deposits by 25–30% in a vineyard. Therefore, the possibility
to vary fan airow as a function of canopy characteristics, especially density, is key in the context
of a sustainable crop protection technology.
Current technical solutions generally foresee the use of mechanically driven fans with dierent
revolution speed using a gearbox and/or lowering the Power Take O (PTO) of the tractor. Another
solution consists of reducing the fan air suction section by a diaphragm. In recent years, more
advanced sprayers with adjustable fan settings, which are able to vary continuously and in real
time the airow characteristics, have been developed. These sprayers are either equipped with
several axial fans mounted in dierent positions on the sprayer or can change the width of the fan
air outlet channel and/or the blades pitch, etc. (García-Ramos et al., 2012; Endalew et al., 2010;
Hołownicki et al., 2017; Salcedo et al., 2021). However, for all these solutions, the possibility to
vary airow settings continuously and automatically along the rows is limited.
While dierent methodologies have been established to determine the optimal spray application
rate depending on the canopy characteristics (Llorens et al., 2010; Garcerà et al., 2017), few data
exist concerning the relationship between airow characteristics and canopy morphology (size
and density). Instruction manuals (TOPPS, 2014), digital tools (Doruchowski et al., 2013), and
devices (Bahlol et al., 2020) that allow to roughly adjust the airow characteristics to the target
have been developed. However, such tools require a manual fan setting which cannot be done for
each specic canopy morphology and, in most cases, the airow adjustment is totally left to the
operator’s skills and experience.
Therefore, within the H2020-OPTIMA project (OPTimised Integrated Pest Management for
precise detection and control of plant diseases in perennial crops and open-eld vegetables,, a cost-eective integrated system, enabling to vary the fan revolution
speed automatically and continuously according to the canopy density, was designed (Grella et
al., 2022). Canopy density values are obtained from one ultrasonic sensor per sprayer side and
are processed through an algorithm in a controller. Based on the output from the algorithm, the
controller communicates the required fan revolution speed to the fan inverter. This algorithm is based
on the relationship between canopy characteristics and fan airow rate and has to be determined
The objective of this experimental work was i) to determine the optimal airow rate to be set
in a trellised vineyard to maximize canopy spray deposit for dierent canopy morphologies and
forward speeds, and ii) to investigate the feasibility of leaf area index (LAI) as a parameter for
dening the optimal fan setting.
Materials and Methods
Test location and vineyard characterization
Field trials were carried out at DiSAFA facilities (Grugliasco, Italy) in an experimental espalier-
trained vineyard (cv: Barbera) at two growth stages, namely early (BBCH 57, inorescences fully
developed; owers separating) and late (BBCH 89, berries ripe for harvest). The vine rows were
62 m long and oriented NW–SE (146° azimuth). Planting distances were 2.8 m between rows and
0.8 m within rows, resulting in a density of 4,464 vines ha-1. The inclined point quadrat technique
(PQT) was applied to accurately characterize the vineyard crop before the trials (Grella et al.,
2019). PQT measurements were taken in the vegetative strip of six vines coincident with those
used for canopy deposition sampling described in the following section (Experimental plot layout
and sampling system). The mean vegetative parameters, namely leaf layers and gaps, were thus
obtained, and leaf area index (LAI) was calculated from Eq. (1) according to Vitali et al. (2013):
LAI = Ly*(Hc/Rd) (1)
where LAI is leaf area index (adim.); Ly is the average number of leaf layers (n°); Hc is the canopy
height (m); Rd is the inter row distance (m).
An overview of the vegetative characteristics of the vines used for experimental sampling is
presented in Table 1. The average number of leaf layers was 0.77 and 2.31, the average of gaps was
60 and 14 %, and LAI was 0.33 and 1.33 (adim.), respectively for the early and late growth stage.
Table 1. Vegetative characteristics of the vines used for sampling at early and late growth stage
stage BBCH Depth (m) Height (m) N° of leaf
layers Gap (%) LAI
Early 57 0.39 1.06 0.82 61 0.35
Early 57 0.31 1.05 0.75 61 0.32
Early 57 0.38 0.89 0.81 58 0.29
Early 57 0.44 1.18 0.79 57 0.37
Early 57 0.38 1.07 0.72 60 0.31
Early 57 0.46 1.20 0.75 63 0.36
Late 89 0.42 1.65 2.13 19 1.25
Late 89 0.50 1.61 2.39 13 1.37
Late 89 0.44 1.55 2.11 18 1.17
Late 89 0.62 1.59 2.25 11 1.28
Late 89 0.42 1.62 2.31 17 1.34
Late 89 0.54 1.66 2.67 6 1.58
Sprayer characteristics and congurations tested in eld trials
A prototype vineyard sprayer, i.e. Smart Synthesis (Cani S.p.a., Palù, Verona, Italy), was
employed. It is a trailed sprayer with a 1,000 L polyethylene tank and an innovative electrically
driven axial fan (KEB automation KG, Barntrup, Germany) (Fig. 1a). The fan, 700 mm in diameter
and consisting of nine blades, sucks in the air from the front of a tower shaped air conveyor. The
latter is equipped with multiple adjustable deectors placed internally at the edge of the air-jet outlet,
thus allowing to direct the airow to precisely match the canopy height. An electric-control varies
the orientation of the whole air conveyor with respect to the central axis of the air-jet discharge
system backwards and forward, thus determining the incidence angle of both airow and spray jets
on the canopy. Furthermore, the sprayer was equipped with a DynaJet® Flex 7140 Pulse Width
Modulation (PWM) system (TeeJet, Spraying Systems Co., Wheaton, Illinois, USA) featured by
eight PWM solenoid valves coupled with a single nozzle holder per sprayer side (Fig. 1b). The
PWM valves can vary the duty cycle of the pulse signals continuously from 30 to 100% to change
the spray outputs but were only used at 100% DC in this study. Further details are provided in
Grella et al. (2021, 2022) and Zwertvaegher et al. (2022).
Using the electrically driven axial fan, dierent fan revolution speeds were set to test the eect
of fan airow rate (m3 h-1) on canopy deposition at the two growth stages. Three levels of airow
rate (low, medium, and high) were arbitrarily selected for tests. The fan revolution speeds at each
level varied according to the growth stage (as the canopy density increased) from 400 to 1,000
rev min-1 for the early growth stage, and from 700 to 1,750 rev min-1 for the late growth stage
(Table 2). The electric axial fan ensured the desired fan revolution speed, irrespective of the PTO
revolution speed, throughout the trials. In addition, two sprayer forward speeds (4 and 8 km h-1)
were combined with selected fan settings, at both growth stages, to test their eect on the canopy
deposition and possible interactions with airow rate (Table 2).
Fig. 1. Prototype vineyard sprayer equipped with electrically driven fan and PWM spray system during eld
trials at a) early (lateral sprayer view) and b) late (back sprayer view) growth stages.
Table 2. Overview of electrically driven axial fan settings tested in eld trials at early and late
growth stage in combination with two forward speeds for their eect on canopy deposition
Forward speed
(km h-1)
Fan speed
(rev min-1)
Airow rate
(m3 h-1)
Total air volume
applied (m3 ha-1)
Early 4.0 Low 400 4,728 4,225
Early 4.0 Medium 700 8,378 7,488
Early 4.0 High 1,000 11,876 10,614
Early 8.0 Low 400 4,728 2,113
Early 8.0 Medium 700 8,378 3,744
Early 8.0 High 1,000 11,876 5,307
Late 4.0 Low 700 8,378 7,488
Late 4.0 Medium 1,300 15,398 13,762
Late 4.0 High 1,750 20,663 18,468
Late 8.0 Low 700 8,378 3,744
Late 8.0 Medium 1,300 15,398 6,881
Late 8.0 High 1,750 20,663 9,234
The sprayer was equipped with eight standard at fan nozzles XR 80 02 VS (TeeJet, Spraying
Systems Co., Wheaton, Illinois USA) per sprayer side. All trials were carried out at a xed working
pressure of 0.40 MPa and 100% PWM duty cycle, providing an individual nozzle ow rate of 0.91
L min− 1. Based on a preliminary check of the vertical spray prole, only four and six nozzles per
sprayer side were activated at the early and late growth stage, respectively. Irrespective of growth
stage, the bottom nozzle was turned o on both sides while at the top three and one nozzles were
turned o at early and late growth stage, respectively. Resulting spray volumes were 390 and 195
L ha-1 at early growth stage and 585 and 293 L ha-1 at late growth stage for 4 and 8 km h-1 forward
speed, respectively.
In all cases the internal air deectors were adequately adjusted to match the canopy height and to
minimize spray losses over the canopy. The air conveyor was placed orthogonal to the rows (90°
relative to the central axis of the air-jet discharge system) in all trials.
Experimental plot layout and sampling system
The trials were performed by spraying the two outermost vineyard rows, with a total area of 347
m2 (62.0 m × 5.6 m) (Fig. 2a). Canopy spray deposition measurements were performed at three
locations along the sprayed rows, corresponding to three vine canopies per sprayed row. In total,
measurements were taken from six vines, as shown in Fig. 2a. At the early growth stage, spray
deposition was assessed at four sampling positions, i.e. at two heights (1 and 2) and two depths (A
and C) (Fig. 2b), while at the late growth stage nine sampling positions were assessed, i.e. three
heights (1, 2, and 3) and three depths (A, B, and C) (Fig. 2c). To assess the deposition, round lter
papers (120 mm diameter and 90 g m-2 extra rapid, Gruppo Cordenons S.p.A., Milan, Italy) were
clipped to vertical masts at each sampling position. Each collector represented a total exposed
surface area of 226 cm2. At the end of each spray application, samples were left to dry for 10 min,
placed into individual bags and sealed. To prevent tracer photo-degradation, the samples were
collected in closed dark boxes. Each test was repeated three times.
Fig. 2. Schematics of a) trial layout for the measurement of canopy deposition (aerial view) and related
sampling strategy at early b) and c) late growth stages; canopy depths A, B, and C, and canopy heights 1,
2, and 3.
Sprayed mixture and laboratory analysis
To measure the collector spray deposits, E-102 Tartrazine yellow dye tracer was added to the
sprayer tank at a target concentration of about 10 g L−1. Before and after each spray application, the
tank mixture was sampled directly from the nozzles to determine the precise tracer concentration
of each repetition.
The collectors were washed with deionized water to extract the tracer. The Tartrazine concentration
was determined by measuring the absorbance of the washing solution with a spectrophotometer
UV-1600PC (VWR, Radnor, PA, USA) set to 427 nm wavelength for peak absorption of the dye
and comparing it to the calibration curve obtained in the laboratory prior to the analysis. In all
cases, three absorbance measurements were taken from each sample.
The deposit on each collector (Di), expressed per unit area in μL cm−2, was calculated from Eq.
(2) as follows:
where Di is the spray deposit on a single collector (μL cm−2); psmpl is the absorbance value of the
sample (adim.); pblk is the absorbance of the blanks (adim.); Vdil is the volume of the deionized
water used to extract tracer deposit from the collector (μL); pspray is the absorbance value of the
spray mixture concentration applied during testing and sampled at the nozzle outlet (adim.); Acol
is the projected area of the collector exposed to the spray (cm2).
For a broad comparison of data, the spray deposit values (μL cm-2) were transformed to be expressed
as % of applied volume.
Di = ((psmpl - pblk) * Vdil) / (pspray * Acol) (2)
Data processing and statistical analysis
All statistical analyses were performed using IBM SPSS Statistics (Version 27) predictive
analytics software for Windows®. To investigate at what sprayer setting combinations the highest
spray depositions were obtained, a three-way ANOVA was performed with growth stage (early
vs late), airow rate (low vs medium vs high) and forward speed (4 vs 8 km h-1) as independent
variables and canopy deposition (% of applied volume) as dependent variable. The interactions
among independent variables were also investigated. To investigate the dierences among spray
deposition obtained at dierent airow settings, the means were compared using a Duncan post-
hoc test for multiple comparison (P < 0.05). The fan settings able to maximize the canopy spray
deposits at dierent forward speeds at late and early growth stage were then objectively identied.
A one-way ANOVA was carried out to investigate the eect of forward speed (4 vs 8 km h-1) on
spray canopy deposit obtained just from the fan settings able to maximize the canopy deposition.
Results and Discussion
The three-way ANOVA (Table 3) indicates that growth stage exerted a statistical inuence on
the canopy deposition (% of applied volume) irrespective of fan airow setting and forward speed
Table 3. Results of the three-way ANOVA for the canopy deposition (% of applied volume)
Sources DF P > (F) Signicance a
Main eects
Growth stage (GS) 1 3.24E-22 ***
Fan airow setting (ARF) b21.39E-07 ***
Forward speed (FWS) 10.393 NS
GS × AFR 20.969 NS
GS × FWS 1 0.447 NS
AFR × FWS 2 1.01E-04 ***
GS × AFR × FWS 2 0.576 NS
a Statistical signicance level: NS P > 0.05; * P < 0.05; ** P < 0.01; *** P < 0.001,
b Fan airow rate corresponds to Low, Medium and High levels.
Average canopy depositions expressed as % of applied volume were 38.5% . 25.5% for early
and late growth stages, respectively. The huge increase in canopy density along the growing
season resulted in a decrease in average deposition, as the inner parts of the row are much more
dicult to reach. In addition, airow setting signicantly aected canopy deposition (Table 3), as
it varied the airow rate (m3 h-1) (Table 2). The higher the fan airow rate, the lower the canopy
deposition irrespective of growth stage (33.4% low, 32.5% medium and 25.9% high). A signicant
interaction was found between air ow setting and forward speed, meaning that eect of forward
speed depended on air ow setting (as can be seen in Fig 3). Fig. 3 displays the average canopy
spray deposition obtained for dierent air ow setting forward speeds and growth stages. At 4
km h-1, the adoption of a low fan speed (400 and 700 rev min-1 at early and late growth stages,
respectively) allowed to obtain a signicant increase in spray deposition compared to the other
fan speeds. At 8 km h-1, the highest spray depositions were obtained with the medium fan speed
(1,000 and 1,300 rev min-1 at early and late growth stages, respectively). The medium fan speed
resulted in a signicantly higher deposition than the low and high fan speed at the early growth
stage, but at the late growth stage only the dierence with the high fan speed was signicant. The
results are in line with those found by other authors reporting a decrease in canopy deposition due
to an excessive airow rate generated by axial fan sprayer (Pergher, 2005; Balsari & Marucco,
2004). However, at 8 km h-1 the low fan speed probably did not provide enough airow to open
and move the dense (late stage) canopy, resulting in a reduced spray penetration and lower spray
deposition value. When increasing forward speed, the airow rate must be increased in order to
maximize spray deposition at both growth stages.
Fig. 3. Average canopy deposition (% of applied volume) for the dierent fan speed setting (low, medium,
high) at 4 and 8 km h-1 forward speed and at early and late growth stage. The bars show the mean ± standard
error of the mean. Dierent letters on the bars denote signicant dierences within forward speed and growth
stage (Duncan’s post hoc test, P < 0.05).
Focusing solely on the fan settings able to maximize the canopy deposition, the one-way ANOVA
underlines that there is no signicant eect of forward speed (4 vs 8 km h-1) on canopy deposition
[F(1, 1) = 0.697, P = 0.406]. This is because an adequate level of air volume per ground area (m3
ha-1) was maintained through changes in fan revolution speed setting. Indeed, at early growth stage,
increasing forward speed from 4 to 8 km h-1 did not signicantly aect spray deposition because
the fan speed was increased from low (400 rev min-1) to medium (700 rev min-1) resulting in similar
amounts of total air volume applied, i.e. 4,225 vs 3,744 m3 ha-1 (Table 2). Similar results were found
at the late growth stage with highest spray deposition values for total air volumes applied of 7,488
m3 ha-1 (4 km h-1 and low fan speed - 700 rev min-1) and 6,881 m3 ha-1 (8 km h-1 and medium fan
speed – 1,300 rev min-1) (Table 2). It indicates that within each growth stage, canopy spray deposition
can be maximized by applying an adequate total air volume per ground area (m3 ha-1) through the
correct combination of fan revolution speed and forward speed. Total air volume applied was thus
demonstrated to be the main factor to take into account to maximize the canopy spray deposition.
Based on this nding, a linear t model was obtained to describe the relationship between the LAI
(Table 1) and the corresponding optimal air volume applied (m3 ha-1) to maximize canopy spray
deposition (Fig. 4). The model thus provides values for the total air volume to be applied at the
dierent growth stages. A threshold LAI value of 2.5 (represented by the red line perpendicular on
the x axis in Fig. 5) was set because in modern commercial trellised vineyards leaf layers is kept
below 2.5 through adequate canopy management techniques, such as shoot trimming, positioning,
and tying (Intrieri & Poni, 1995). As an example, a LAI value of 2.45 can be achieved by a trellised
vineyard with “extreme” features, i.e. 2.2 m inter-row distance, vegetative strip of 1.8 m width,
canopy depth of 0.8 m and mean leaf layer equal 3.0. Based on the linear model, the corresponding
optimal value for the total air volume would be 10,735 m3 ha-1. At 4 km h-1 forward speed, this
corresponds with a fan speed setting of about 1,000 rev min-1, or slightly higher (Table 2). At 8 km
h-1 forward speed, fan settings higher than those tested in this experiment (1,750 rev min-1) would
be needed.
Fig. 4. Linear t model describing the relationships between the Leaf Area Index (LAI, adim.) and the total
air volume applied (m3 ha-1) based on experimental data obtained in the tests at 4 and 8 km h-1 forward speeds.
The red lines represent a maximum threshold LAI value in modern vineyards that denes the maximum
total air volume to be applied (10,735 m3 h-1) in vineyard spray application.
The results obtained from this preliminary, experimental work are the basis for the development of
a smart sprayer equipped with an electrically driven axial fan able to provide an optimized variable
airow rate based on a real-time measurements of canopy characteristics. This study explores the
possibility to use the LAI as a parameter for setting the optimal fan speed (rev min-1) automatically
in order to deliver the desired total air volume applied (m3 ha-1). Further relationships among other
available canopy parameters (i.e. number of leaf layers, % of gaps, tree row volume, and leaf wall
area) and total air volume applied per ground area (m3 ha-1) are under investigation in order to
dene the most useful canopy parameter for selecting the optimal fan setting. Additional trials are
ongoing to evaluate the eect of a wider range of fan revolution and forward speed settings on
canopy spray deposition.
This project has been funded by the European Union’s Horizon 2020 research and innovation
program under grant agreement No 773718 (OPTIMA-project). Special thanks go to KEB ITALIA
S.r.l. for providing technical support, and to Marco Resecco for the help provided during eld
experimental activities.
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Application, pp. 47–54.
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Conventional air-assisted sprayers with hydraulic nozzles generate large radial spray plumes which produce significant off-target losses and can consume high power (20–30 kW). Also, it is not uncommon to see these machines treating dwarf orchards, where the spray losses at the full leaf stage may be over 80% of applied spray volume. Significant reductions in spray losses can be obtained with targeted and wind-oriented airflow adjustment. The objectives of the presented studies were to develop an energy saving variable air assistance (VAA) system with continuous real-time adjustment of air volume and with spraying systems mounted on both sides of the sprayer. The system is based on a double axial fan system which allows for remote adjustment of air volume. The nominal air output was 20,000 m³ h⁻¹, for use in typical dwarf and semi-dwarf orchards, and this was designed to be obtained with 10 kW power consumption. The system used variable speed impellers with fixed blades which showed greater suitability than a method with adjustable pitch blades working at constant speed because it provided a wider range of air volumes (±35%). The air volumes produced could be continuously adjusted to obtain airflow profiles, on both sides of the sprayer that were almost symmetrical. The results obtained in tests appear to meet the objectives and, therefore, the VAA system can be considered as a suitable prototype platform for variable rate technology and future intelligent orchard sprayers.
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Rational application of pesticides by properly adjusting the amount of product to the actual needs and specific conditions for application is a key factor for sustainable plant protection. However, current plant protection product (PPP) labels registered for citrus in EU are usually expressed as concentration (%; rate/hl) and/or as the maximum dose of product per unit of ground surface, without taking into account those conditions. In this work, the fundamentals of a support tool, called CitrusVol, developed to recommend mix volume rates in PPP applications in citrus orchards using airblast sprayers, are presented. This tool takes into consideration crop characteristics (geometry, leaf area density), pests, and product and application efficiency, and it is based on scientific data obtained previously regarding the minimum deposit required to achieve maximum efficacy, efficiency of airblast sprayers in citrus orchards, and characterization of the crop. The use of this tool in several commercial orchards allowed a reduction of the volume rate and the PPPs used in comparison with the commonly used by farmers of between 11% and 74%, with an average of 31%, without affecting the efficacy. CitrusVol is freely available on a website and in an app for smartphones.
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p style="text-align: justify;"> Aim : Measurement of leaf area in grapevine has always been a critical point in researches focused on irrigation management, training systems, source-sink interrelationships and efficiency of spray application to canopies. In this work, we propose the use of ultrasonic sensors as a fast and accurate tool for the estimation of large portions of leaf canopy area. Methods and results : Through outputs of ultrasonic sensors installed on a tractor moving along vineyard rows, we calculated an ultrasonic-based leaf density index that we correlated with three measurements or estimates of canopy area: I) direct measurement of the area of a canopy portion (LAØ), assessed by summing the areas of all the leaves, where each single-leaf area was assessed by regressing the leaf diameter (the maximum width perpendicular to the main rip) against the related leaf area calculated on the basis of a relation between the leaf diameter and the leaf area, previously assessed through an area meter on a 20-leaf sample; II) the point quadrat output (LApq); and III) the canopy leaf area index (LAI) obtained through LAI-2000 (Li-Cor) technology. The measurements were assessed on six cultivars in three replicate rows (8-12 plants per cultivar per row) in a vineyard trained to a vertical trellis system. Conclusion : When we correlated the three independent control parameters with each other, we obtained highly significant correlations between LApq and LAØ, but less significant correlations between these two and LAI-2000 outputs. Also, the correlations between ultrasonic outputsoutputs and LAØ and LApq were significant, with R2 ranging between 0.84 and 0.85. On the contrary, no significant correlation was found between ultrasonic outputs and LAI-2000 outputs. These results were obtained by averaging all the values belonging to each replicated cultivar (10.5 m along the row, i.e., twelve contiguous vines); on the contrary, when the analysis was done over a shorter distance (3.5 m, i.e., four contiguous vines), the reliability of the ultrasonic-based method decreased. Significance and impact of the study : These results point to the ultrasonic technology as a powerful tool to estimate large-scale leaf canopy area, with potential applications in precision farming. At the moment, however, the limitation of this approach is the requirement of reference values for leaf area (e.g., assessed by point quadrat) to obtain absolute and not only relative outputs. With this application we can quantify, in a few hours, the canopy of a whole vineyard, in order to analyze different vegetation zones or to follow canopy development.</p
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The flow of air generated by a new design of air assisted sprayer equipped with two axial fans of reversed rotation was analyzed. For this goal, a 3D sonic anemometer has been used (accuracy: 1.5%; measurement range: 0 to 45 m/s). The study was divided into a static test and a dynamic test. During the static test, the air velocity in the working vicinity of the sprayer was measured considering the following machine configurations: (1) one activated fan regulated at three air flows (machine working as a traditional sprayer); (2) two activated fans regulated at three air flows for each fan. In the static test 72 measurement points were considered. The location of the measurement points was as follow: left and right sides of the sprayer; three sections of measurement (A, B and C); three measurement distances from the shaft of the machine (1.5 m, 2.5 m and 3.5 m); and four measurement heights (1 m, 2 m, 3 m and 4 m). The static test results have shown significant differences in the module and the vertical angle of the air velocity vector in function of the regulations of the sprayer. In the dynamic test, the air velocity was measured at 2.5 m from the axis of the sprayer considering four measurement heights (1 m, 2 m, 3 m and 4 m). In this test, the sprayer regulations were: one or two activated fans; one air flow for each fan; forward speed of 2.8 km/h. The use of one fan (back) or two fans (back and front) produced significant differences on the duration of the presence of wind in the measurement point and on the direction of the air velocity vector. The module of the air velocity vector was not affected by the number of activated fans.
The airblast sprayers are equipped with a fan generating an air stream that helps the sprayed droplets to reach out and penetrate the tree canopy. Recently an automatic air regulation system has been developed and integrated in an airblast sprayer equipped with a conventional axial fan (900 mm diameter). This system, thanks to a wireless connection between a dedicated tablet and sprayers actuators, allows to remotely control the blade pitch and the air-outlet section, varying the characteristics of airflow generated by the fan. Therefore, the present work aims to characterize the different air streams derived from the combination of two fan outlet section widths (110 and 150 mm) and three blade pitches (20°, 25° and 30°). For each combination, the three components of air velocity (m s−1) were measured, taking as reference the plane following the theoretical trajectory of the main current leaving the fan. In this plane, velocities were measured at 1.0, 3.0, 5.0 and 10.0 m from the outlet section on both sides of the sprayer. At each distance, the velocities from 0.25 to 4.00 m in height were recorded. This same procedure was repeated in two planes parallel to the reference plane, 0.30 m behind and after respectively. Additionally, the velocities in the fan outlet section were also measured to obtain the airflow rate. In general, the outlet section and the blade pitch had a significant effect on the velocity components. An outlet section of 110 mm meant a smaller airflow rate and a higher initial velocity, while with 150 mm the airflow rate reduced and the initial velocity decreased. Velocities could be bigger by enhancing the blade pitch. The turbulence intensity was similar at 1.0 m distance in all cases.
Efficient chemical application is a critical operation during specialty crop production that requires constant sprayer calibrations as well as pertinent adjustments to avoid off target spray losses. However, lack of rapid and in-field assessment tools limit the opportunities for frequent adjustments of orchard sprayer attributes. To overcome such limitations, our team has developed a smart spray analytical system (SSAS). Using SSAS, this study evaluated two commercial orchard sprayers, S1 (Powerblast 400, Rears Manufacturing Co., Eugene, OR, USA) and S2 (Turbo-Mist S30P300NSHD, Slimline Manufacturing Ltd., Penticton, BC, Canada), for their air-assist velocity and spray delivery patterns. Air-assist velocity patterns were studied in controlled conditions along two major planes: along the sprayer air-outlet (P1) and parallel to an imaginary tree row wall (P2), representing specific distances from the sprayer to tree row middles. SSAS data aided in generating several 2-D contour plots of the air-assist velocities along both the planes and for both sides of selected sprayers. Spray delivery patterns were generated along the typical locations of tree row wall and were based on pertinent air-assist velocity patterns. Results suggested that the magnitude of air-assist velocities was higher on the right side for sprayer S1 and on left side for sprayer S2. Such differences could be attributed to the design of fans, blades, rotation, air-inlet and outlet. There existed a consistent shift in air-assist along P2 plane and hence the spray delivery pattern shift on either side of both the sprayers. The uniformity in air-assist velocities decreased with the increasing distance from sprayer outlet. Average symmetries of 82.02 ± 12.81 (standard deviation) % and 44.27 ± 11.44% were observed in air-assist patterns for sprayer S1 and S2 along the plane P1, respectively. Similarly, average symmetries of 87.67 ± 0.53% and 74.03 ± 1.56% were observed in spray delivery patterns for sprayer S1 and S2, respectively. Overall, SSAS was consistent in quantification of the air-assist velocities (standard error ≤ 0.45 m s⁻¹) and spray delivery patterns (standard error ≤ 0.07 ml cm⁻²) of commercial orchard sprayers and can be used at manufacturing stage for building consistent units as well as in the orchard settings for adjusting sprayer attributes to achieve targeted delivery on to the crop canopies.
BACKGROUND Drift is one of the most important issues to consider for realising sustainable pesticide sprays. This study proposes an alternative indirect methodology for comparative measurements of Drift Reduction Potential (DRP) generated by airblast sprayers, aimed at overcoming practical inconveniences and drawbacks of standardized ISO22866:2005. A test bench in the absence of target crop and wind was employed to measure Drift Potential Values (DPV). A variation to the proposed method that introduced a crop between sprayer and test bench device was considered to study the canopy effect (absence/presence) and to validate the method. In parallel, direct spray drift measurements (ISO22866) were performed to obtain the Drift Value (DV). Representative vineyard airblast sprayer was tested in four configurations (combination of two fan airflow rates and two nozzle types), under the three methods (direct and indirect) and were classified according to achieved drift reduction percentages (ISO22369‐1:2013) and compared. RESULTS Indirect methods discriminated DPV from different nozzles (conventional, air induction) and fan airflow rate (High, Low) combinations. Indirect methods also showed that despite crop influence on drift amount, target absence has a negligible effect when used specifically for DRP determination/classification. In fact, identical DRP final classifications were achieved for the two methodology tested. Alternatively, all tested configurations resulted in lower DR values following the ISO22866 field method, which caused different final classifications due to the high dependence of results on external factors. CONCLUSIONS The alternative test bench methodology, characterized by the absence of target crop and calm of wind, was considered feasible for comparative measurements of airblast sprayers DRP. This article is protected by copyright. All rights reserved.
Despite technological progress in pesticide application equipment, chemical crop protection continues to contribute to environmental pollution. Water is at risk of contamination with pesticides from point and diffuse sources and could be reduced to a great extent with a better sprayer design. The sprayer manufacturers and pesticide applicators need to take more responsibility for the prevention of water pollution and therefore they have to make environmentally responsible decisions at different stages, from designing to servicing sprayers. The objective of the presented work was to develop an interactive application that would support decisions made by sprayer manufacturers during the production process, and by pesticide applicators when selecting and operating the sprayers. The EOS (Environmentally Optimised Sprayer) is an application evaluating the risk mitigation potential of sprayers based on their technological features, within five risk areas, representing sources of pollution: (i) Inside Contamination; (ii) Outside Contamination; (iii) Filling; (iv) Spray Loss & Drift; (v) Remnants. The evaluator completes the EOS questionnaire by checking for the technical solutions identified in the evaluated sprayer and the result reflects the sprayer quality in terms of potential environmental risk mitigation. The EOS tool also proved its awareness raising facility and educative value when used during training activities and university courses.
The current trend in modelling flow phenomena within trees such as in orchards follows the assumption of the space occupied by the trees as a porous and horizontally homogeneous medium to avoid the flow details associated with the individual plants. This being sufficient at a larger field or regional scale much has to be done at a plant scale to analyse the flow details within the plant and its elements especially for sensitive agricultural operations such as spraying. This article presents an integrated 3D computational fluid dynamics (CFD) model of airflow from a two-fan air-assisted cross-flow orchard sprayer through non-leafed orchard pear trees of 3m average height. In this model the effect of the solid part of the canopy on airflow was modelled by directly introducing the actual 3D architecture of the canopy into the CFD model. The effect of small canopy parts, such as very short and thin branches and flowers that were not incorporated in the geometrical model, on airflow was simulated by introducing source-sink terms in the Reynolds averaged Navier–Stokes (RANS) momentum and k–ɛ turbulence equations in a sub-domain created around the branches. This model was implemented in a CFD code of ANSYS-CFX-11.0 (ANSYS, Inc., Canonsburg, PA, USA). In this work it was possible to link the real 3D architecture of pear canopy into a CFD code of CFX. The model was able to capture the local effects of the canopy and its parts on wind and sprayer airflow directly by inserting the tree structure into the model which gave realistic results. The model showed that within the injection region of the sprayer there was an average reduction of the jet velocity by 1ms−1 for a distance of 2.3m from the sprayer outlet due to the presence of leafless pear canopy. This reduction was variable at different vertical positions due to the difference in the canopy density. Maximal effect of the canopy was observed in the middle height of the trees between 0.25m and 2.5m which is the denser region with a bunch of several branches. The maximum velocity difference observed between these two positions was 1.35ms−1 at 1.75m height. Thus, regions of high and low air velocity zones of the sprayer due to the variable branch density of the pear tree were predicted. The effects of wind speed and direction on the air jet from the sprayer were investigated using the model. For a cross- (direction of 90°) wind speed of 5ms−1 there was about 2ms−1 reduction in the sprayer jet velocity at the jet centre and 0.5m horizontal shift of the jet centre towards the wind direction. Generally there was a decrease in the jet velocity with increasing cross-wind and decreasing wind direction with respect to the jet direction.