## 3 Results
### Spray Drift Potential  
_Spray configuration_ had a significant effect on ln(DPV) [F(4, 341) = 8.961, \(p\) = 4.312 \(\times\) 10\({}^{-5}\)]. Figure 6 shows the mean DPV per spray configuration and the effect of spray configuration on ln (DPV). The ln(DPV) of the reference broadcast configuration XR11004 did not significantly differ from those of the bed spray configurations, although considerable differences in DPV and drift reductions were present. Configuration XR11004 had a DPV of 19, whereas XR8002, XR8004, AI8004 and AIUB8504 resulted in DPV's of 38, 15, 9, and 6, respectively and therefore in drift reductions of \(-\)97%, 24%, 55%, 70% compared to the reference broadcast application. As a general statement, the principle of the drift test bench is based on the evaluation of spray deposition on a narrow section under the spray boom, in this experimental set-up on the center of a bed. The spray drift potential of the bed spray configurations is therefore overestimated because, unlike broadcast applications, bed spray applications consist of 'full spray zones' and 'no spray zones'. Due to the width and position of the drift test bench in the experiments, only the 'full spray zone' was considered, and thus the lower spray drift potential in 'no spray zones' is not taken into account. Keeping this in mind, configuration XR8002 drastically increased the spray drift potential  
Figure 6: Drift Potential Value (DPV) of the different spray configurations (mean \(\pm\) standard deviation of the mean). Different letters denote significant differences between spray configurations on ln(DPV) (post hoc Tukey test, \(p\) < 0.05). compared to the reference. This can be explained by a combined effect of a higher boom height (0.6 m) and especially a finer droplet size. All else being equal, smaller nozzle sizes generally result in smaller droplet size spectra, and therefore droplets which are more prone to drift [37]. At 300 kPa spray pressure, nozzle XR8002 produced finer droplets with lower velocity than the reference nozzle XR11004 (VMD = 260 \(\upmu\)m vs. 300 \(\upmu\)m), as reported in [20], making them more prone to drift and explaining the increased DPV. In contrast, at 300 kPa spray pressure, air inclusion nozzles produced very coarse (VMD ranging from 443 \(\upmu\)m to 460 \(\upmu\)m) and therefore less driftable droplets [20]. The configurations using air inclusion nozzles thus resulted in the best drift reductions compared to the reference configuration, despite the higher boom height. These findings are in accordance with the drift test bench experiments performed by [21; 38]. Similar results were found in spray drift field tests [39; 40]. As for deposition measurement, _Air support setting_ (F(2, 362) = 14.246, \(p=0.683\)) had no significant effect on ln(DPV), possibly due to the relatively low air velocity as discussed above. Furthermore, the absence of vegetation during the drift test bench measurements might limit the use of these measurements in determining the effect of air support on spray drift potential, as typically an intercepting crop is needed to evaluate the use of air support. Various previous studies showed that air assistance reduced spray drift. For example, angling the air curtain can reduce drift of flat-fan nozzles over stubble by 60% [41]. Depending on the nozzle type [30], an additional drift reduction of 45 to 90% was obtained at 2 to 3 m from the last nozzle using air assistance in potato crops. A significant effect of air support on the total amount of spray drift for Hardi ISO F 110 02, F 110 03, and LD 110 02 nozzles by increasing droplet velocities [40] but contrasting results were also found [28]. More drift was produced with an air-assisted sprayer compared to a standard sprayer, although air-assistance resulted in higher biological efficacy on Brussel sprouts, despite being a difficult to spray crop. The authors thus concluded that air assistance can exacerbate drift unless the parameters such as air velocity and boom height are optimized.