Abstract
The pulse width modulation (PWM) spray system is the most advanced technology to obtain variable rate spray application without varying the operative sprayer parameters (e.g. spray pressure, nozzle size). According to the precision agriculture principles, PWM is the prime technology that allows to spray the required amount where needed without varying the droplet size spectra which benefits both the uniformity of spray quality and the spray drift reduction. However, some concerns related to the effect of on–off solenoid valves and the alternating on/off action of adjacent nozzles on final uneven spray coverage (SC) have arisen. Further evaluations of PWM systems used for spraying 3D crops under field conditions are welcomed. A tower-shaped airblast sprayer equipped with a PWM was tested in a vineyard. Twelve configurations, combining duty cycles (DC: 30, 50, 70, 100%) and forward speeds (FS: 4, 6, 8 km h−1), were tested. Two methodologies, namely field-standardized and real field conditions, were adopted to evaluate the effect of DC and FS on (1) SC variability (CV%) along both the sprayer travel direction and the vertical spray profile using long water sensitive papers (WSP), and (2) SC uniformity (IU, index value) within the canopy at different depths and heights, respectively. Furthermore, the SC (%) and deposit density (Nst, no stains cm−2), determined using short WSP, were used to evaluate the spray application performances taking into account the spray volumes applied. Under field-controlled conditions, the pulsing of the PWM system affects both the SC variability measured along the sprayer travel direction and along the vertical spray profile. In contrast, under real field conditions, the PWM system does not affect the uniformity of SC measured within the canopy. The relationship between SC and Nst allowed identification of the ranges of 200–250 and 300–370 l ha−1 as the most suitable spray volumes to be applied for insecticide and fungicide plant protection products, respectively.
Highlights
An overview of the most important droplet size and velocity characteristics of the XR 8002 nozzle spraying at 0.4 MPa pressure without solenoid valve and with solenoid valve working at different duty cycles (30%, 50%, 70%, 100%), and measured at 0.5 m under the spray boom is given in Table 2, with:
The Phase Doppler Particle Analyser (PDPA) measurements indicate that the addition of a solenoid valve to the spray system and operated at 100% duty cycle slightly reduced the droplet size of the tested standard flat fan nozzle (Dv0.5 no solenoid valve vs. solenoid valve at 100% Duty cycle (DC) = 250 vs. 228 μm)
(2) In contrast, under real field conditions, the on–off effect of the pulse width modulation (PWM) system does not affect the uniformity of spray coverage measured within canopies at different depths and heights, neither did the adopted forward speed show a significant effect
Summary
The European Green Deal, and the Farm to Fork Strategy, strives to reduce the overall use of agrochemicals by 50% by 2030 (EC, 2020). Only the exact (minimum) amount of product required to achieve the desired biological effect would be released and all product discharged from the sprayer would reach the desired target (Giles & Comino, 1989). Achieving this goal is extremely challenging for agricultural spray applications; pesticide losses, under- and over-application, as well as inadequate coverage and deposition, should be avoided as much as possible to safeguard the environment, food safety and human health
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