Field assessment of a pulse width modulation (PWM) spray system applying different spray volumes: duty cycle and forward speed effects on vines spray coverage

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.

Preliminary Evaluation of a Blast Sprayer Controlled by Pulse-Width-Modulated Nozzles

“…In this regard, the authors in [25] identified several concerns related to the effects of on-off solenoid valves and the alternating on-off action of adjacent nozzles on uneven spray coverage, specifically the effects of the PWM duty cycle and sprayer forward speed on the variability of spray coverage under standardized and actual field conditions for an espalier-trained vineyard. They used water-sensitive paper to register coverage variability along the sprayer track, the canopy height and the canopy depth.…”

Effect of the Airblast Settings on the Vertical Spray Profile: Implementation on an On-Line Decision Aid for Citrus Treatments

“…Studies of PPP spray mass balance have reported high spray losses during application [1][2][3][4][5][6][7]. Furthermore, huge variations of spray distribution on the canopies have been observed, because pesticide deposition depends on the vegetation [8][9][10][11][12], equipment [9][10][11][12][13][14], operational parameters [15][16][17][18], weather conditions [19] and spray mix properties [20,21]. PPP losses pose risks both to people (operators, bystanders, residents, etc.)…”

“…Sprayer adjustment, sometimes referred to as calibration, is aimed at: (i) adjusting the fan airflow rate and its orientation to the tree canopy to minimize off-target losses [35,36,38,39], (ii) balancing the distribution of spray volume between the right and left side of the airblast sprayer [40], (iii) selecting the proper number of active nozzles and setting their orientation to produce a spray vertical profile that matches the targeted canopy as closely as possible [9,36], and (iv) applying the most appropriate spray volume [18,[41][42][43][44][45].…”

Effect of Image Segmentation Thresholding on Droplet Size Measurement

“…Nowadays, in the field of pesticide application, the correct use of Plant Protection Products (PPPs) is the most common and powerful tool for crop pest control, and, for this reason, it is necessary to satisfy the growing demand for agricultural productivity in a more sustainable way [1][2][3][4][5][6][7][8][9][10]. According to the European Directive 2009/128/EC [11] for spray application, the handling of PPPs is considered an important aspect to avoid undesirable effects on the population and the environment, because, when pesticides are applied to crops, part of the spray may not reach the target, causing serious economic and environmental problems [12][13][14][15].…”