Assessment of aerosol deposition and movement in open field conditions

Overall objective of this study was to evaluate the dispersion of aerosol plumes generated by a truck-mounted ultra low-volume (ULV) applicator and a hand-held thermal fogger under open field conditions.  Experiments were also planned to determine the relative capture efficiencies of various sampling techniques in such applications.  The ULV applicator was used at three travel speeds (8.5, 16.8, 24.8 km/h) and the thermal fogger at two release heights (0.6 and 1.1 m above ground) to investigate the effect of speed or release height on deposition at 6, 12, 24, and 48 m downwind.  High volume air sampler (HVS), low volume air samplers (LVS), spinning cotton ribbon (CR) samplers, polypropylene green plastic cards (GC), acetate cards (AC), and water-sensitive papers (WSP) were used to collect deposits.  The ULV applicator was tested with water and oil sprays while the thermal fogger was tested with the latter tracer only.  Using water- and oil-based tracers, all deposition targets were analyzed by fluorometry.  Results showed decreased tracer deposition with increase in sampling distance.  Overall, travel speed affected deposition at the near sample locations only, but in most sample locations, normalized deposits were comparable at all speeds.  Spray release height did not affect deposition of active samplers but had significant effect on deposition of passive samplers at 6 m location only.  Overall, the higher release height resulted in more deposition in most downwind locations.  There were good correlations between depositions on active and passive samplers. The HVS, CR, GC, and AC samplers were effective in sampling aerosol plume dispersion under open field conditions.  The paper includes relationships among capture efficiencies of various samplers.Keywords: ULV applicator, thermal fogger, deposition samplers, Yellow 131SC dye, Pyranine 10G, fluorometr

Choice of tracers for the evaluation of spray deposits

Tracer substances, used to evaluate spraying effectiveness, ordinarily modify the surface tension of aqueous solutions. This study aimed to establish a method of using tracers to evaluate distribution and amount of spray deposits, adjusted to the surface tension of the spraying solution. The following products were tested: 0.15% Brilliant Blue, 0.15% Saturn Yellow in 0.015% Vixilperse lignosulfonate, and 0.005% sodium fluorescein, and mixtures of Brilliant Blue plus Saturn Yellow and Brilliant Blue plus sodium fluorescein at the same concentrations. Solutions were deposited on citrus leaves and stability was determined by measuring fluorescence and optical density of solutions without drying, dried in the dark and exposed to sunlight for 2, 4 and 8 h. These values were compared to those obtained directly in water. The static surface tension of the tracer solution was determined by weighing droplets formed during a period of 20 to 40 seconds. The Brilliant Blue and Saturn Yellow mixture at 0.15% was stable under all conditions tested. It was not absorbed by the leaves and maintained the same surface tension as that of water, thus permitting concentration adjustment to the same levels used for agrochemical products, and allowing the development of a qualitative method based on visual evaluation of the distribution of the pigment under ultraviolet light and of a quantitative method based on the determination of the amount of the dye deposited in the same solution. Spray deposition could be evaluated at different surface tensions of the spraying solution, simulating the effect of agrochemical formulations

Evaluation of a variable rate controller for aldicarb application around buffer zones in citrus groves

Computers and Electronics in Agriculture, 2007; 56:147–160Advances in precision farming technologies have facilitated controlled application of agrochemicals and documentation procedures to follow environmental regulations. This paper details evaluation of a commercial variable rate (VR) controller for preventing aldicarb applications in the buffer zones around potablewater wells of citrus groves. The controllerwas coupled to two common drive mechanisms, a ground-driven electric clutch-engaged (GDEC) and pulse-width-modulation motor-driven (PWMM). The evaluation involved determination of dynamic performance of the VR application system through quantification of reaction times and rate transition distances and determination of appropriate “look-ahead” times for each of the drive mechanisms. Without a look-ahead (zero) setting, the mean midpoint reaction distances were about 1.8 and 3.6m for the GDEC and PWMM mechanisms, respectively, at 7.0-km/h ground speed. For the GDEC, a look-ahead time of 1 s gave the mean midpoint reaction distances of −0.06 and 0.04m during step-up and step-down of the rate, respectively. For PWMM, the best look-ahead times were 1 and 2 s during step-up and step-down of the rate, respectively.However, since the prototype unit could not accommodate two look-ahead times, the compromise look-ahead time for both step-up and -down was 2 s. Validation in the actual buffer zone showed that, at 95% confidence level, the buffer zone should be increased by 2.5 or 3.3m in commercial applications using GDEC or PWMM systems, respectively

Investigation of laser and ultrasonic ranging sensors for measurements of citrus canopy volume

Applied Engineering in Agriculture 2002, Vol. 18(3): 367–372This study compared ultrasonic and laser measurements of citrus canopy volume with manual measurement methods. Fifteen trees with different canopy heights and volumes were used. Manual and ultrasonic measurements provided dimensions for computing the canopy volume whereas laser measurements gave information that could be used to compute a ‘laser canopy volume index.’ Ultrasonic and laser methods agreed with manual methods (R2 > 0.85, RMSE < 2.15 m3). Laser showed better prediction of canopy volume than the ultrasonic system because of the higher resolution. Ultrasonic or laser sensors can be used for automatic mapping and quantification of the canopy volumes of citrus trees